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Alctron MA-1 Schematic question

Dan KE6PO All Messages By This Member #37179 I've recently seen the schematic for the Alctron MA-1. However, there are a couple of features that aren't clear and I hope to get some help from the group. ? On the input side, after XLR1, there are two items labeled S1 and S2. They look like switches. S1 could be a mute switch. S2 looks like it connects XLR1-3 to either R1 or R2, perhaps to compensate for mic Zin.? ? The other question I have is: where is power applied? Alctron's literature says it "operates on 48V, but does not pass phantom power to the mic." OK, but where is the power applied?? ? Dan
kennjava All Messages By This Member #37184 S1 would allow you to disconnect the input at pin 2 (dont know why anyone would want that...), S2 selects an input impedance (~3150 ohms or 150 ohms).? The MA1 preamp is powered by +48v phantom from the following mic preamp it's plugged into. Phantom is not passed through to the MA1's input.
Dan KE6PO All Messages By This Member #37202 Sorry, forgot to include the schematic.?
Dan KE6PO All Messages By This Member #37204 S1 & S2 is understandable, but the power issue still escapes me. The only point at which V+ power can reach the circuit is from XLR2. But I don't see how power gets distributed. If V+ is present on pin 2 or 3, it will only feed the drain of Q3 or Q2. Assuming that there is sufficient Vin generated by the microphone to trigger the gates of Q1 & Q4, there is no V+ on the drains of Q1 & Q4 to feed through to the gates of Q2 or Q3.? ? Clearly, I am missing something about FET functionality.? Can I get a clue?
Jerry Lee Marcel All Messages By This Member #37206 开云体育 Le 12/02/2025 à 03:34, Dan KE6PO via groups.io a écrit?: S1 & S2 is understandable, but the power issue still escapes me. The only point at which V+ power can reach the circuit is from XLR2. But I don't see how power gets distributed. If V+ is present on pin 2 or 3, it will only feed the drain of Q3 or Q2. Assuming that there is sufficient Vin generated by the microphone to trigger the gates of Q1 & Q4, there is no V+ on the drains of Q1 & Q4 to feed through to the gates of Q2 or Q3.? ? Clearly, I am missing something about FET functionality.? Can I get a clue? There is conduction between drain and source in a properly biased FET. From pin2, current flows through Q3, then Q4, then R6 and R7, back to pin1.
Goran Finnberg All Messages By This Member #37222 The schematic is in error. XLR1 Pin 3 goes to XLR 2 Pin 2. XLR1 Pin 2 goes to XLR 2 Pin 3. This implies that we get a polarity shift. Very bad design indeed. Is this really the original schematic or a fake copy. ......... Best regards, Goran Finnberg The Mastering Room AB Goteborg Sweden E-mail: mastering@... Learn from the mistakes of others, you can never live long enough to make them all yourself.??? -?? John Luther (\__/) (='.'=) (")_(") Pyret, Ranglet, Aron, VovVov, Nero, Smurfen & Pussin:RIP
Jerry Lee Marcel All Messages By This Member #37223 开云体育 Isn't the cascode an inverter? Le 13/02/2025 à 11:37, Goran Finnberg via groups.io a écrit?: toggle quoted message Show quoted text The schematic is in error. XLR1 Pin 3 goes to XLR 2 Pin 2. XLR1 Pin 2 goes to XLR 2 Pin 3. This implies that we get a polarity shift. Very bad design indeed. Is this really the original schematic or a fake copy. ......... Best regards, Goran Finnberg The Mastering Room AB Goteborg Sweden E-mail: mastering@... Learn from the mistakes of others, you can never live long enough to make them all yourself.??? -?? John Luther (\__/) (='.'=) (")_(") Pyret, Ranglet, Aron, VovVov, Nero, Smurfen & Pussin:RIP
Jerry Lee Marcel All Messages By This Member #37224 开云体育 The MA1 circuit is a blatant rip-off of the Triton Fethead version 2, which is marginally less bad than the version 1. Le 13/02/2025 à 12:06, Jerry Lee Marcel via groups.io a écrit?: toggle quoted message Show quoted text Isn't the cascode an inverter? Le 13/02/2025 à 11:37, Goran Finnberg via groups.io a écrit?: The schematic is in error. XLR1 Pin 3 goes to XLR 2 Pin 2. XLR1 Pin 2 goes to XLR 2 Pin 3. This implies that we get a polarity shift. Very bad design indeed. Is this really the original schematic or a fake copy. ......... Best regards, Goran Finnberg The Mastering Room AB Goteborg Sweden E-mail: mastering@... Learn from the mistakes of others, you can never live long enough to make them all yourself.??? -?? John Luther (\__/) (='.'=) (")_(") Pyret, Ranglet, Aron, VovVov, Nero, Smurfen & Pussin:RIP
Dan KE6PO All Messages By This Member #37256 Edited On Thu, Feb 13, 2025 at 02:37 AM, Goran Finnberg wrote: Is this really the original schematic or a fake copy. Unknown. This is one I found from multiple net sources, but the origin was not stated.? However, the circuit seemed suspicious, which led to my question. The FET info makes better sense now, yet the design purpose is only inferred. I am trying to solve a practical problem here... For example:? ? Given a dynamic (moving coil) microphone like the Shure SM58, To be used with a Ham Radio like the Yaesu 900, The radio includes some signal processing/compression for the mic input, 48V Phantom power in not supplied per se, but 5VDC is available on the mic connector, The radio assumes a balanced mic input and has a 600ohms Zin, The SM58 has a Zout of 300ohms, According to the SM58 wiring diagram, the mic cartridge uses a transformer interface to the XLR connector. So, is a preamp needed in such an application and, if so, what kind of preamp? Any help here is appreciated. TIA, Dan?
Jerry Lee Marcel All Messages By This Member #37259 开云体育 An in-line preamp such as the Alctron or FETHEAD is certainly NOT suitable, if only because they need 48V phantom power. Why do you think you need a preamp? Have you tried connecting directly the SM58 to the input? It should work. Now, maybe if it works but has not enough "juice", you may have to add a preamp, but you would not need much gain. The SM58 delivers about 2mV at normal speech level at a distance of about 2ft, so with close talk, it should be OK for the required 7mV for full excitation. Le 24/02/2025 à 06:38, Dan KE6PO via groups.io a écrit?: toggle quoted message Show quoted text [Edited Message Follows] On Thu, Feb 13, 2025 at 02:37 AM, Goran Finnberg wrote: Is this really the original schematic or a fake copy. Unknown. This is one I found from multiple net sources, but the origin was not stated.? However, the circuit seemed suspicious, which led to my question. The FET info makes better sense now, yet the design purpose is only inferred. I am trying to solve a practical problem here... For example:? ? Given a dynamic (moving coil) microphone like the Shure SM58, To be used with a Ham Radio like the Yaesu 900, The radio includes some signal processing/compression for the mic input, 48V Phantom power in not supplied per se, but 5VDC is available on the mic connector, The radio assumes a balanced mic input and has a 600ohms Zin, The SM58 has a Zout of 300ohms, According to the SM58 wiring diagram, the mic cartridge uses a transformer interface to the XLR connector. So, is a preamp needed in such an application and, if so, what kind of preamp? Any help here is appreciated. TIA, Dan?
Goran Finnberg All Messages By This Member #37260 I wrote:? >Is this really the original schematic or a fake copy. Original poster Dan answered:? >Unknown. This is one I found from multiple net sources, but the origin was not stated.? That schematic needs then to be seen as a fake copy imo due to the fact that real? manufacturers schematic always afaik or as I have seen in practice has the manufacturers? name / logo somewhere and other pertinent information put there that there should be? no need to think that this is not the real deal. Original poster Dan asked:? >So, is a preamp needed in such an application and, if so, what kind of preamp? >To be used with a Ham Radio like the Yaesu 900 Nothing that you put in your email works at all with Yaesu 900. You need this to be used with the Yaesu 900: https://www.amazon.com/MH-31A8J-Handheld-Microphone-FT-817ND-FT-897DM/dp/B0D9NT2CJ3 ---------- Best regards, Goran Finnberg The Mastering Room AB Goteborg Sweden E-mail: mastering@... Learn from the mistakes of others, you can never live long enough to make them all yourself.??? -?? John Luther (\__/) (='.'=) (")_(") Pyret, Ranglet, Aron, VovVov, Nero, Smurfen & Pussin:RIP
Richards All Messages By This Member #37262 Edited So, is a preamp needed in such an application and, if so, what kind of preamp? _________________________________________________________ NO. You should not require a pre amp for the SM58 and your transceiver. A pre amp is likely to overload the input state on the transceiver - inline pre amps typically provide between 20 and 30 dB gain, which is not required for this application. The SM58 has a medium-hot output level (open signal voltage on the product data sheet) and it should drive the rig well enough without assistance. Do not worry about matching impedance - that is rarely needed on modern circuits (google this and you will learn a lot!) Also, avoid - do not use - the 5v BIAS (not phantom) bias voltage intended to power FET type computer gaming headset microphones and the like. You will likely have an unbalanced connection, so the bias voltage does not become or act or even seem like phantom voltage which only works as a phantom on a balanced cable/input. I say unbalanced, because pins 4 and 5 carry mic signals, without a third pin to ground. The schematic indicates one is signal and the other is shield, although I rather doubt that is the case as the cable has 8 internal twisted pair conductors, and none are shielded per se. The FT900 has a front panel 8-pin modular, RJ45 network type connector - you need to be careful how you wire that . It should expect a dynamic cartridge per spec sheet - see link below. I believe it uses the standard Yaesu Hand Microphones MH-31A8J hand mic, which has a dynamic cartridge. Your Yaesu user manual should have pin out charts for all connectors, which will guide you in building a suitable cable / connector. Otherwise, vendors on eBay.com and elsewhere sell suitable cable adapters to mate the XLR on the SM58 with the 8-pin modular, RJ45 connector on the rig. You will also have to pay attention to the PTT connections, as the microphone on-off switch (if present) will only disconnect the mic from the rig - it will not activate the transmitter as a PTT switch - at least not without substantial re-wiring! K8JHR Schematic for your mic can be found here:
Arjay1949 All Messages By This Member #37274 Well, the posted Alctron MA-1 schematic certainly has at least one error! The idents of Q3 and Q4 are reversed.? As Jerry has surmised, the cascode amplifier inverts the signal. I can confirm that the signal present at the drain of Q2 is connected to pin 3 on the MA.1 pcb, and in the inverse polarity of the signal present on pin 2 of the input. So the polarity of the signal is reversed by the device.... which is presuambly why the output connections are reversed?
Dan KE6PO All Messages By This Member #37290 Edited James, Many thanks! You have address virtually all of my concerns. :)? I bought the SM58 because it was recommended in order to improve sound quality. The MH-31 mic that came with the radio is ok, but nothing to brag about. Now I can create a cable for the SM58 and see how it works. Thanks again. Dan KE6PO
Dan KE6PO All Messages By This Member #37291 Goran, ? Thanks, but I have the stock MH-31 mic that came with the radio. I am just not impressed with the voice quality it produces. Since ham radio is very much about experimentation, this is another experiment intended to improve my signal readability. So, before hooking up anything, research, research, research. You and Richards have helped immensely. Now for the next step... making a cable for XLR to RJ45, with a PTT floor switch. ? Dan KE6PO

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