Re: Drafted to helo a friend who designs audio amps
A couple of comments: Do the amps compare OK on static measurements? If OK presumably he is fighting a transient problem. How do they compare with narrow transients? Do the catch-all Hafler test that I mentioned. It is one thing for parts to meet specifications, but the parts might exceed the specs and cause problems. Bertho ? ?
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From: [email protected] <[email protected]> On Behalf Of wn4isx via groups.io
Sent: 8 December, 2024 10:29
To: [email protected]
Subject: Re: [electronics101] Drafted to help a friend who designs audio amps? He came up with the preamp, tone, volume, balance, power amp designs 35 years ago. He's been forced to make minor component value changes as semiconductors came and went. The design is somewhat minimalist, the most innovative is his active bias scheme. I've never seen anything like it anywhere and trust me, while I am not an audiophile I do keep up with "State of the Art" designs as a hobby. I'm at a loss to understand how using one batch of transistors produces great sound, and yet another batch of the same transistors produces "muddy" sound. I have some nice audio programs, including some FFT with different display modes. Tomorrow we hit the amps, a good one and 'bad' one, with every trick in my inventory. I've borrowed a high end analog to digital converter that is flat +/- 2dB from DC to 1MHz. I'm hoping pink noise bursts show something. Jimmy started out as an architect but started his audio business because 'modern designs make me want to barf.' He hates parking lots that are laid out decoratively with all curves, tall bushes etc. He moved to England, was licensed and was increasingly depressed over the new buildings in London.? "Nuke the city and start over." As children we'd play and combine our Lincoln Log sets (my father marked all of mine with a T his with a J_ and Jimmy build amazing tunnels for my Lionel electric trains. He built a model of Windsor Castle from sugar cubes in the 9th grade, won a design award. He is self taught but knows his semiconductor design tech better then any real engineer I know. He is the only person I know who will tackle an failed switchmode power supply and has an almost 100% success rate for reliable repair. The few he gave up on he pointed out design flaws.
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Re: Drafted to helo a friend who designs audio amps
On Saturday 07 December 2024 01:37:06 pm wn4isx via groups.io wrote: I once used a 2N???? as an electronic variable capacitor by using the collector base and reverse biasing, so I know transistor junction capacitance varies with applied voltage. I wonder if the audio can modulate the variable capactance of the junction [pretty certain it does] and "Does it have any effect?"
Any diode will do that, and a transistor junction is basically a diode... I remember reading how rectifiers could be used as varactors to tune circuits. -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin
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Re: Drafted to helo a friend who designs audio amps
On Saturday 07 December 2024 08:08:20 am wn4isx via groups.io wrote: I've been dragooned to help a friend I've known since the second grade. Jimmy designs and builds ultra high end audio systems, he builds everything up to the speakers. How do you define high end? Recently he's ran into some odd problems where "identical" transistors behave differently in high end audio. He purchases directly from the manufacturer so the chances of counterfeits is pretty low. But "identical" parts usually aren't. The amount of variation is really somehting to see, sometimes. It's been a life time [1968~1973] since I designed any serious audio amps. I realized my talents lay elsewhere and it was a better value to > trade money for decent amps then spend nearly unlimited hours to obtain similar results. I have a stero receiver and equalizer in the other room that have been sitting there for 3-4 years and I haven't yet gotten around to hooking them up. Got a small amp based on a couple of LM386 chips and a Radio Shack "headphone amplifier'" board that I picked up at some hamfes years ago. Got some LM380 chips that pomise a bit more in the way of output power but I have yet to get around to doiing anything with them yet. That would pretty much cover the extent of my efforts in that area... Note: I do not consider myself an audiophile, I damaged my hearing riding a motorcycle for 35 years and had tinnitus as a young child. It used to be that word had some positive connotations, but lately it more often than not translates to "audiophools" with people claiming absurd things and paying ridiculous money for such things as $1000 power cords. I ain't going there. In my case it was too much sound intensity during my work with pro audio gear and doing sound ffor a number bands. At first it was one hearing aid, for the left ear which was worse than the right one. Then it was a pair of them, as insurance would cover. The latest set is even better, they're rechargable and also have bluetooth connecton to my phone, which has come in handy on a number of occasions. Sooo, I'm refamiliarizing myself with the issues of high end audio design, theory and reality.
No amplifier is perfect, they all have artifacts. One thing that is very different today from way back when is moderate priced USB audio I/O 'cards' allow meaningful FFT analysis that actually matches reality, within limits. I haven't even looked at going there yet. I downloaded this book to start with....
Bob Metzler - Audio Measurement Handbook
An interesting read, so far. I'm about 89 pages into it at the moment. I'm reminded of some of he gear I worked with at one pro sound outfit that I worked for at one point. A "White Sound Analyzer" in particular comes to mind. I'm also reminded of an HP audio osccillator that's in the other room that needs a little TLC. And for projects, I bought some modules from Banggood a while back, basically an LM3915 chip and some LEDs. It was convenient to have a pre-made board for these. Unfortunately whoever they used to supply those chps didn't bother to connect two of the pins at one end of the 18-pin package, so the first two LEDs never lit up, until I sourced some chips from another supplier. They gave me a partial refund for that, but it left a bad taste in my mouth and I'm rather reluctant to order from china at all at this point. While copyrighted it appears in quiet a few respectable locations, I'm guessing the author has waived copyright issues. Or he just wants it out there. I've found one heck of a lot of books online, and have been adding to the pile on my server at times. Rod Elliot of ESP audio has quite a few articles on design and measurement of distortion.
Uses a sound card to measure distortion
Perhaps I'll follow some of those links when I ge done with reading that book... Perhaps the single most useful trick shown by Mr. Elliot is his "distortion adder." It allows sanity checks, which, when dealing with audio distortion is necessary. It is way too easy ending up chasing your tail like a puppy or kitten. Heh. That's why I gave up on amplifier design in 1973. A quasi-comp Sansui AU-555A sounded much better then my best efforts at about 1/2
the cost in material and 1/gazillionth the wasted time. I could have collected sodapop bottle along the highway, turned them in for the
deposit and been time ahead. I'd reached a point where I'd lost confidence in my ability to measure differences in slight design variations.
One important issue, I've been playing with several USB sound cards for several years and realizee "The 5V power rail in most USB systems simply suck!" Modify your USB cable and add your own 5V power supply. I went with a LM7805 with the standard design with an added 1uF tantalum (I hate and distrust tantalums but they have the best filtering capacity for size and a 100uF and 1000uF on the 5V out. I'm not convinced the added capacitors were worthwhile but the PCB I used had the pads for them so I decided to toss them in. Those caps around those regulator chips are important. [Be certain to tie your 5V power supply V-/ground to PC USB V-/ground! I spent an hour late one night wondering "Why doesn't this damn thing work!"]
The residual noise floor was just under 10dB lower with the external supply versus the laptop USB 5V power.
You mileage will vary because every maker of USB almost certainly has different noise issues.. I bought a powered hub some time back, but now it has some issues and needs to be replaced. I suspect Jimmy is running into the hard wall of physics, where each device is inherently different even if made at the same time. This is something I have no idea how to verify.
They don't call it the bleeding edge of technology for nothing.
Oh, and don't bother trying to test the modulator in your SSB/AM/FM ham rig, they all suck. I'm not even gonna go there... -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin
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Re: Drafted to helo a friend who designs audio amps
He came up with the preamp, tone, volume, balance, power amp designs 35 years ago. He's been forced to make minor component value changes as semiconductors came and went.
?
The design is somewhat minimalist, the most innovative is his active bias scheme. I've never seen anything like it anywhere and trust me, while I am not an audiophile I do keep up with "State of the Art" designs as a hobby.
?
I'm at a loss to understand how using one batch of transistors produces great sound, and yet another batch of the same transistors produces "muddy" sound.
?
I have some nice audio programs, including some FFT with different display modes. Tomorrow we hit the amps, a good one and 'bad' one, with every trick in my inventory. I've borrowed a high end analog to digital converter that is flat +/- 2dB from DC to 1MHz. I'm hoping pink noise bursts show something.
?
Jimmy started out as an architect but started his audio business because 'modern designs make me want to barf.' He hates parking lots that are laid out decoratively with all curves, tall bushes etc. He moved to England, was licensed and was increasingly depressed over the new buildings in London.?
"Nuke the city and start over."
?
As children we'd play and combine our Lincoln Log sets (my father marked all of mine with a T his with a J_ and Jimmy build amazing tunnels for my Lionel electric trains. He built a model of Windsor Castle from sugar cubes in the 9th grade, won a design award.
?
He is self taught but knows his semiconductor design tech better then any real engineer I know.
He is the only person I know who will tackle an failed switchmode power supply and has an almost 100% success rate for reliable repair. The few he gave up on he pointed out design flaws.
?
?
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Re: Drafted to helo a friend who designs audio amps
Think harmonic distortion. With an FFT analyser you might see it (or not??? I think I got a glimpse of it¡) It might happen at 250kHz, but will extend far into the MHz, and AUDIO spectrum! Those with the ears to detect it, WILL HEAR IT! From my very limited experience with these high end audio equipment, you should look at the circuitry from a radio perspective. Harmonic distortion spreading far¡ (It¡¯s my best guess, anyway) ? Nuno T. ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Epignathus
Sent: 07 December 2024 21:00
To: [email protected]
Subject: Re: [electronics101] Drafted to help a friend who designs audio amps
Importance: Low? Years ago, I purchased new an Adcom GFA-545 which also sounded terrible. One channel was oscillating at around a megahertz, which bleed into the other channel too. The manufacturer ¡°stopped at nothing¡± to fix it, so I added a zero to counter the pole in the right-half-plane after the input differential pair in both the left and right channels, which reduced the high end bandwidth to about 100 kHz, and stopped the instability. There is no logical reason to have the -3 dB response extend to 250 kHz, especially when it leads to an unstable amplifier. -Doug, W6DSR ? From: [email protected] [mailto:[email protected]] On Behalf Of wn4isx via groups.io
Sent: Saturday, December 7, 2024 11:49
To: [email protected]
Subject: Re: [electronics101] Drafted to helo a friend who designs audio amps ? Jimmy designs complete home theater systems, video switching, audio switching, audio tone/volume/balance, he provides a loop for special effects like 3D decoders, and power amplifiers, "regular" stereo and subwoofer. The last two orders of Freescale (Motorola) act funny. He orders premium units, each one comes with it's own spec sheet. The specs are within norms for his previous but the power amps sound odd, hollow, sort of like left/right mixing giving sort of L-R. Even when he only drives one channel, or both channels in mono. The mid range, ~1kHz to ~4kHz is "wonky." He's my age and has been considering retiring, this might decide for him. ? But he enjoys his work. He is one of the few people I'd even consider going to this level of trouble. ? I warned him we are up against physics that neither of us understand nor have the training to understand. ? He has enough older stock to complete his current orders and isn't taking additional orders until/unless we can solve the problem. ? Oddly they work fine for sub-woofer amps and low level preamps. ? Somewhere I have a file devoted to snake oil smoke and mirrors. My favorite is a set of adaptors that allow the output of a AF power amp to a NEMA 15-R with matching NEMA 15-P to wires for the speaker so you can use a standard AC extension cord. ? The insanity was so intense I didn't believe it was real, so I ordered a set. They occupy a place of shame on my radio room wall. ? I love the "hand made porcelain speaker cable lifters." They hold the speaker cables off the floor, God knows dust mites might cause distortion. ? Although I think RCA connectors and 3.5mm connectors are both abominations and crimes against nature and man. -- Nuno T.
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Re: Drafted to helo a friend who designs audio amps
There is a never ending, intense, perhaps psychotic, argument over "Can humans detect phase differences [or phase distortion.] and it shows up in the amplifier wars...
?
This paper takes hard core look at the question...
https://www.researchgate.net/publication/286939870_Sensitivity_of_Human_Hearing_to_Changes_in_Phase_Spectrum
?
The paper presents data showing "Yes human can detect phase difference" but the data appears to suggest "Not in the real world."
Very few of us ever experience an anechoic chamber. I suspect multiple reflections in most real world scenarios swamp phase issues.
Earphones are clearly different. But the recording and mixing probably destroy any phase relationship to the original.
?
Consider how many albums are created as a series of over dubs, sometimes over a period of months.
?
Good Vibrations might win the most complicated production and mix down process.
https://en.wikipedia.org/wiki/Good_Vibrations
You might be interested by the production details...and ask yourself "What was the original phase relationship between the various instruments."
?
My HP laptop has two microphones and it's interesting to launch an audio vectorscope program. Slight movement of either the laptop or a person speaking totally change the display in unexpected ways.
?
I've played with ultrasonic emitters and receivers since I was 14 and built my first oscilloscope. I'd built an ultrasonic down converter from an article in Popular Electronics and used the same type transducer as a emitter in a 'beacon.'
?
When I built the scope I bought another ultrasonic receiver, scrapped the down converter and built two pre amps, fed one to the vertical the other to the horizontal for an XY display. It was interesting to see how little movement was required to produce wildly rotating XY displays.
?
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Re: Drafted to helo a friend who designs audio amps
My plan is to compare old good devices with new wonky devices and see if there are any determinable differences.
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Re: Drafted to helo a friend who designs audio amps
The matching (testing) amp needn't be perfect - just good enough
to compare devices. That's the point.
Donald.
On 12/7/24 16:20, wn4isx via groups.io
wrote:
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On Sat, Dec 7, 2024 at 04:04 PM, Donald H Locker wrote:
sockets
Sockets tend to be a bad idea for transistors in high
performance audio systems. Even with gold plated transistor
leads and sockets, they are a severe failure point.
?
If we can figure out what parameters are effecting the amps,
we can probably match pairs.
?
Frankly if anyone but Jimmy called me with this problem, I'd
say they were crazy,
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Re: Drafted to helo a friend who designs audio amps
On Sat, Dec 7, 2024 at 04:04 PM, Donald H Locker wrote:
sockets
Sockets tend to be a bad idea for transistors in high performance audio systems. Even with gold plated transistor leads and sockets, they are a severe failure point.
?
If we can figure out what parameters are effecting the amps, we can probably match pairs.
?
Frankly if anyone but Jimmy called me with this problem, I'd say they were crazy,
?
?
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Re: Drafted to helo a friend who designs audio amps
I think as I remember at the time, all the rage was about phase. An amplifier could brag about having little to no phase shift over the passband of 20 to 20,000 Hz. That higher bandwidth helped keep the phase constant over the bandwidth ¨C just a guess¡ ?
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From: [email protected] [mailto:[email protected]] On Behalf Of wn4isx via groups.io
Sent: Saturday, December 7, 2024 13:07
To: [email protected]
Subject: Re: [electronics101] Drafted to help a friend who designs audio amps ? On Sat, Dec 7, 2024 at 03:59 PM, Epignathus wrote: -3 dB response extend to 250 kHz
What moron decided an AF amp needed that frequency response!? That's not asking for trouble, that's begging for it.
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Re: Drafted to helo a friend who designs audio amps
On Sat, Dec 7, 2024 at 03:59 PM, Epignathus wrote:
-3 dB response extend to 250 kHz
What moron decided an AF amp needed that frequency response!?
That's not asking for trouble, that's begging for it.
?
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Re: Drafted to helo a friend who designs audio amps
No idea if this is practical. How many devices in the
amplification chain need to be matched or are critical spec-wise?
If there are a small number, he could build a "matching amp" with
sockets specifically for devices to be matched. Swapping
individual devices and tagging matched pairs/groups as they are
identified would build a stock of usable devices. It might also
allow him to better identify the characteristics important to
achieve matching.
Donald.
On 12/7/24 14:49, wn4isx via groups.io
wrote:
Jimmy
designs complete home theater systems, video switching,
audio switching, audio tone/volume/balance, he provides a
loop for special effects like 3D decoders, and power
amplifiers, "regular" stereo and subwoofer.
The
last two orders of Freescale (Motorola) act funny. He orders
premium units, each one comes with it's own spec sheet. The
specs are within norms for his previous but the power amps
sound odd, hollow, sort of like left/right mixing giving
sort of L-R. Even when he only drives one channel, or both
channels in mono.
The
mid range, ~1kHz to ~4kHz is "wonky."
He's
my age and has been considering retiring, this might decide
for him.
[snip]
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Re: Drafted to helo a friend who designs audio amps
Years ago, I purchased new an Adcom GFA-545 which also sounded terrible. One channel was oscillating at around a megahertz, which bleed into the other channel too. The manufacturer ¡°stopped at nothing¡± to fix it, so I added a zero to counter the pole in the right-half-plane after the input differential pair in both the left and right channels, which reduced the high end bandwidth to about 100 kHz, and stopped the instability. There is no logical reason to have the -3 dB response extend to 250 kHz, especially when it leads to an unstable amplifier. -Doug, W6DSR ?
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From: [email protected] [mailto:[email protected]] On Behalf Of wn4isx via groups.io
Sent: Saturday, December 7, 2024 11:49
To: [email protected]
Subject: Re: [electronics101] Drafted to helo a friend who designs audio amps ? Jimmy designs complete home theater systems, video switching, audio switching, audio tone/volume/balance, he provides a loop for special effects like 3D decoders, and power amplifiers, "regular" stereo and subwoofer. The last two orders of Freescale (Motorola) act funny. He orders premium units, each one comes with it's own spec sheet. The specs are within norms for his previous but the power amps sound odd, hollow, sort of like left/right mixing giving sort of L-R. Even when he only drives one channel, or both channels in mono. The mid range, ~1kHz to ~4kHz is "wonky." He's my age and has been considering retiring, this might decide for him. ? But he enjoys his work. He is one of the few people I'd even consider going to this level of trouble. ? I warned him we are up against physics that neither of us understand nor have the training to understand. ? He has enough older stock to complete his current orders and isn't taking additional orders until/unless we can solve the problem. ? Oddly they work fine for sub-woofer amps and low level preamps. ? Somewhere I have a file devoted to snake oil smoke and mirrors. My favorite is a set of adaptors that allow the output of a AF power amp to a NEMA 15-R with matching NEMA 15-P to wires for the speaker so you can use a standard AC extension cord. ? The insanity was so intense I didn't believe it was real, so I ordered a set. They occupy a place of shame on my radio room wall. ? I love the "hand made porcelain speaker cable lifters." They hold the speaker cables off the floor, God knows dust mites might cause distortion. ? Although I think RCA connectors and 3.5mm connectors are both abominations and crimes against nature and man.
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Re: Drafted to helo a friend who designs audio amps
Jimmy designs complete home theater systems, video switching, audio switching, audio tone/volume/balance, he provides a loop for special effects like 3D decoders, and power amplifiers, "regular" stereo and subwoofer.
The last two orders of Freescale (Motorola) act funny. He orders premium units, each one comes with it's own spec sheet. The specs are within norms for his previous but the power amps sound odd, hollow, sort of like left/right mixing giving sort of L-R. Even when he only drives one channel, or both channels in mono.
The mid range, ~1kHz to ~4kHz is "wonky."
He's my age and has been considering retiring, this might decide for him.
?
But he enjoys his work. He is one of the few people I'd even consider going to this level of trouble.
?
I warned him we are up against physics that neither of us understand nor have the training to understand.
?
He has enough older stock to complete his current orders and isn't taking additional orders until/unless we can solve the problem.
?
Oddly they work fine for sub-woofer amps and low level preamps.
?
Somewhere I have a file devoted to snake oil smoke and mirrors. My favorite is a set of adaptors that allow the output of a AF power amp to a NEMA 15-R with matching NEMA 15-P to wires for the speaker so you can use a standard AC extension cord.
?
The insanity was so intense I didn't believe it was real, so I ordered a set. They occupy a place of shame on my radio room wall.
?
I love the "hand made porcelain speaker cable lifters." They hold the speaker cables off the floor, God knows dust mites might cause distortion.
?
Although I think RCA connectors and 3.5mm connectors are both abominations and crimes against nature and man.
|
Re: Drafted to helo a friend who designs audio amps
I second your view! ? Lots of snake oil and smoke around. Those who do know, keep their mouths shut, and their bank accounts are getting bigger ? Nuno t. ?
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From: [email protected] [mailto:[email protected]] On Behalf Of wn4isx via groups.io
Sent: 07 December 2024 18:37
To: [email protected]
Subject: Re: [electronics101] Drafted to helo a friend who designs audio amps ? The problem my friend is almost certainly facing is the parameter(s) that are driving him nuts aren't standard and aren't specified. I'm sure a process engineer could provide us with a wealth of information but just try and talk to one. They are guarded closer then Roman Vestal Virgins. Hfe at different collector currents, well away from the standard tests levels Ft at different current collector currents Actual switching speed at different collector currents I'm trying to figure a practical way of measuring the collector base, base emitter, and collector emitter junction capacitance under different voltages. I once used a 2N???? as an electronic variable capacitor by using the collector base and reverse biasing, so I know transistor junction capacitance varies with applied voltage. I wonder if the audio can modulate the variable capactance of the junction [pretty certain it does] and "Does it have any effect?" I'm so far over my head I might drown. And a lot of audiophile "Standard of belief" is snake oil and smoke. The idea a special power cable can improve an AC mains powered amp is silly, consider how many feet of house wiring is between the amp and breaker box, how long the cables from the home to the step down transformer, how many miles of wire between "your' transformer and the substation and how many miles of wire between substation and power plant, add to that the interconnectivity of the various national sub-grids.... ? Double blind tests are the only subjective tests I accept. Others are entitled to their own beliefs. -- Nuno T.
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Re: Drafted to helo a friend who designs audio amps
The problem my friend is almost certainly facing is the parameter(s) that are driving him nuts aren't standard and aren't specified. I'm sure a process engineer could provide us with a wealth of information but just try and talk to one. They are guarded closer then Roman Vestal Virgins.
?
I'm going to check
Hfe at different collector currents, well away from the standard tests levels
Ft at different current collector currents
Actual switching speed at different collector currents
I'm trying to figure a practical way of measuring the collector base, base emitter, and collector emitter junction capacitance under different voltages.
?
I once used a 2N???? as an electronic variable capacitor by using the collector base and reverse biasing, so I know transistor junction capacitance varies with applied voltage. I wonder if the audio can modulate the variable capactance of the junction [pretty certain it does] and "Does it have any effect?"
?
I'm so far over my head I might drown.
?
And a lot of audiophile "Standard of belief" is snake oil and smoke.
The idea a special power cable can improve an AC mains powered amp is silly, consider how many feet of house wiring is between the amp and breaker box, how long the cables from the home to the step down transformer, how many miles of wire between "your' transformer and the substation and how many miles of wire between substation and power plant, add to that the interconnectivity of the various national sub-grids....
? Double blind tests are the only subjective tests I accept. Others are entitled to their own beliefs.
?
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Re: Drafted to helo a friend who designs audio amps
As others have said, high end audio goes into the realm of non-book theory. What actually happens is not what you¡¯re thought at school. It resembles radio behaviour. All sorts of weird stuff going on everywhere. The smaller the amount of parts, the easier it gets. Add more parts, you get a big headache! I¡¯ve been told that even the direction a wire is connected can make a difference. One reason so many audiophiles like valve amps, is because of the amount of noise generated (lack of, I¡¯ve been told) I¡¯m not an audiophile, my hearing is also affected (army service), but the electronics of amps have been under my scope. Definitely more difficult than microwaves¡ I dealt with different parts specs, by testing a great number of the same batch. Eventually I got a few that were matched. ? Nuno T. ? ?
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From: [email protected] [mailto:[email protected]] On Behalf Of wn4isx via groups.io
Sent: 07 December 2024 13:08
To: [email protected]
Subject: [electronics101] Drafted to helo a friend who designs audio amps ? I've been dragooned to help a friend I've known since the second grade. Jimmy designs and builds ultra high end audio systems, he builds everything up to the speakers. ? Recently he's ran into some odd problems where "identical" transistors behave differently in high end audio. He purchases directly from the manufacturer so the chances of counterfeits is pretty low. ? It's been a life time [1968~1973] since I designed any serious audio amps. I realized my talents lay elsewhere and it was a better value to trade money for decent amps then spend nearly unlimited hours to obtain similar results. ? Note: I do not consider myself an audiophile, I damaged my hearing riding a motorcycle for 35 years and had tinnitus as a young child. ? Sooo, I'm refamiliarizing myself with the issues of high end audio design, theory and reality. ? No amplifier is perfect, they all have artifacts. One thing that is very different today from way back when is moderate priced USB audio I/O 'cards' allow meaningful FFT analysis that actually matches reality, within limits. ? I downloaded this book to start with.... ? Bob Metzler - Audio Measurement Handbook https://convexoptimization.com/TOOLS/Metzler.pdf ? While copyrighted it appears in quiet a few respectable locations, I'm guessing the author has waived copyright issues. ? Rod Elliot of ESP audio has quite a few articles on design and measurement of distortion. ? https://sound-au.com/articles/distortion.htm ? https://sound-au.com/articles/intermodulation.htm#ref ? https://sound-au.com/articles/intermodulation.htm ? https://sound-au.com/project52.htm ? Uses a sound card to measure distortion https://sound-au.com/project232.htm ? Perhaps the single most useful trick shown by Mr. Elliot is his "distortion adder." It allows sanity checks, which, when dealing with audio distortion is necessary. It is way too easy ending up chasing your tail like a puppy or kitten. ? That's why I gave up on amplifier design in 1973. A quasi-comp Sansui AU-555A sounded much better then my best efforts at about 1/2 the cost in material and 1/gazillionth the wasted time. I could have collected sodapop bottle along the highway, turned them in for the deposit and been time ahead. I'd reached a point where I'd lost confidence in my ability to measure differences in slight design variations. ? ? One important issue, I've been playing with several USB sound cards for several years and realizee "The 5V power rail in most USB systems simply suck!" Modify your USB cable and add your own 5V power supply. I went with a LM7805 with the standard design with an added 1uF tantalum (I hate and distrust tantalums but they have the best filtering capacity for size and a 100uF and 1000uF on the 5V out. I'm not convinced the added capacitors were worthwhile but the PCB I used had the pads for them so I decided to toss them in. ? [Be certain to tie your 5V power supply V-/ground to PC USB V-/ground! I spent an hour late one night wondering "Why doesn't this damn thing work!"] ? The residual noise floor was just under 10dB lower with the external supply versus the laptop USB 5V power. ? You mileage will vary because every maker of USB almost certainly has different noise issues.. ? I suspect Jimmy is running into the hard wall of physics, where each device is inherently different even if made at the same time. This is something I have no idea how to verify. ? They don't call it the bleeding edge of technology for nothing. ? Oh, and don't bother trying to test the modulator in your SSB/AM/FM ham rig, they all suck. -- Nuno T.
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Re: Isolated Power Supplies
'Galvanic' isolation means no common electrical connection, intrinsic means no common electrical connection with a specified safety factor, if unspecified, it would generally mean isolated up to the AC Mains voltage, 120V in the US, 240V most other places.
One of my lab power supplies claims an intrinsic isolation of "up to 1,000V AC or DC." [Yea I take that claim with a large block of salt.]
?
'Galvanic' doesn't include any safety factor. It might be safe to 10,000V or only 10V.
Intrinsic depends on insulation and creepage distance, the distance electricity might leak across. Buy a cheap switch mode power supply at a thrift store and crack the case,?
Trace out the AC inlet, see the isolation zone and then the DC out.
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Re: Drafted to helo a friend who designs audio amps
I like it, use a super fast, low noise opamp to do the summing and monitor the output.
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By chance did an amp with ungodly high TIM happen to be a Crown DC-300? [What an overrated POS]
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I worked part time in college at an odd specialty electronic shop that did all sorts of custom electronics, everything from stepping relay PBXs to exotic high end audio. We sold an early Haffler integrated ?100?W amp to a biker bar. It was only time in my life when a boss ordered me "Carry your pistol and be prepared to use it." There were 5 of us armed to the teeth.
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It was one of the most frightening jobs I was ever on.
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School got too busy the next semester (trying to carry two majors, EE and physical anthropology was somewhat demanding time wise.....] so I lost track of any follow up. [The bar was still there last June when we drove past.]
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I've often how long the amp lasted before it was stolen, blown up or had beer poured in it.?
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It felt [it was!] like a major sacrilege against everything good in the universe to put such a good amp in such a dive with the best JBL speakers of the time.
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That was the first and last biker bar we did and I still get the shakes.
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Now Johnny Angels was a very different bar...being 22 and naive I had no idea there were gay bars....
They wanted a very fancy disco system. I'd have had to design a light sequencer using a Motorola 6800. [I hated programming, still do.] We passed on that gig.
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Much much later, when I worked at the university we were taking a break from setting up a major production in Lexington's classiest hotel, went to the cafeteria and a very pretty young lady got way too close to me? with some really odd body language.
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A coworker cut her off, "Lady he can't afford you."
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That was the moment I realized she was a working girl.....
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I had to hotwire our work van when we were in Dayton because the supervisor lost the keys. Theory became practice. The van was pre steering wheel lock. My coworkers gave me the oddest look when I said, "Oh no big deal, let me get under the dash." 30 seconds later the engine was running and then I got the really odd looks.
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I always thought it funny when TV/Movies made hot wiring out to be quantum mechanics. I learned how in a junkyard owned by a great uncle at 8. I hotwired an old junker and drove it about 200 feet right into a 100 year old oak tree. My father only laughed. Mom wasn't all that amused and muttered something about her only son is going to end up in prison.? [Not yet]
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Hey you try to steer, work the gas peddle, brake and a clutch you can barely press with short legs and your older sister screaming "We are gonna die!" as loud as she could. Once I got moving I couldn't stop ... well not under control.
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The oddest parts of my work life weren't technical.
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Oh damn, just remembered this device....
Sound Impairment Monitor - The Answer?
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The ESP SIM (Sound Impairment Monitor)
Though this one only monitors the long tailed pair...not sure how accurate it would? be.
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The first unit is based on the Baxandall Subtractive Test Set and appeared in a ?mid 1960s? Wireless world. I should have mine, built it in EE to prove a point. Probably need better opamps, LM301A aren't exactly state of the art.
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I'll try to locate the Wireless World where it appeared. might take a week or so.
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Sorry for the mixed fonts.
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Found my SIM" it! God it is primitive, I used that funny ?Dymo? embossed plastic ribbon label maker. They don't hold up well after 50 years. Now to rebuild it and make new labels! [and a new power supply, zeners don't cut it!]
[I saved each and every piece of test equipment I made in EE then later at various jobs.]?
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I did a quick search and found this paper by David Haffler, he's doing the test very different then I expected.4
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And here is a reprint of the Baxandall audio test scheme.?
This works, it will show the minute differences between units of the same model.
I'd loved to have had a PC based FFT system back then.
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I'm betting if we can find a way to measure the subtle non linearities in Hfe in the transistors, we'll find the problem, then he gets to figure out how to design to minimize those variables. I'll borrow a tektronix curve tracer Monday.
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Now, what to bill him....
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Found a few low voltage isolated buck converters on Amazon, 12/24vdc in, 12/5vdc out. While I could make those work, the cost is high. I need something that is able to deliver 12vdc, at least 100w.
Best solution I have found is:
Orion-Tr 12/12-9 (110 W)
Orion-Tr 12/24-5 (120 W)
Both offer 200v 'galvanic' isolation (vs intrinsic?) and should work.
Cost is higher at $64 ea, with needed qty of 4. Ultimately the outputs will be connected to individual LFP cells that are already connected 4s. Basically Top charging. Haven't been able to use 'traditional' LFP batteries as I would be pulling ~180A short burst intermittently. Basically is 2nd Battery used only for starting an engine.
Current solution is using 12vdc to 120vdc converter, and feeding to an isolated smps that is rated for DC on AC inputs. Repeat 4 times. Lots of underhood space used.
While above is very doable, a 500w inverter feeding power supply then LFP single cell chargers through isolation transformers should work as well. Or find isolated versions of the LFP cell chargers.
Anyone have suggestions on isolated converters, or isolated single cell LFP charger? My searches at Amazon, Digikey, Mouser, Allied have been kind of dismal.
And in case you are wondering: Yes, this abomination would comprise several loads switched by latching relays.
~SD
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Bertho
Epignathus