Photo of the circuit didn't make it to email, but the link works, thanks.
When it comes to tearing down the capsule, I've found that gently peeling away the outer skin from the front edge works pretty well. The actual capsule is held in there by some kind of thick adhesive which breaks apart easily, so it's not very difficult.
Thanks,
-Scott
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On 6/26/24 00:20, sergio_logic via groups.io wrote:
I think I've figured it out: pre-CORE it was probably a topology like the one from the Audio-Technica patent <>(which would be later than DPA doing this).
Why do I say this? I've found old manuals <>, years before 2017 (when CORE was introduced), listing the output impedance as 30-40 ohms (JFET topologies have output impedances of 1000 ohms or more).
So this was at least an emitter follower even then, and 33K makes sense as a value for R1!
In this topology, VDS is "regulated" by the VBE of Q1, which means that for large input SPL generating e.g. ~2V pk-pk at Q1 base, it will still vary by 40-50mV.
In what I suspect is the CORE topology, VDS is regulated by feedback from the error amplifier and under the same input conditions will vary by 4-5mV, extending the linear range and improving the max SPL at 1% THD spec.
Are you in the USA? ?I'd be happy to mail that capsule to you for
further inspection.
Thanks for the kind offer, I live in Europe and I've already ordered one from the UK a couple of days ago, listed on eBay as defective with "thin tinny sound" for the equivalent of $38, shipping included. I don't know if it's CORE or pre-CORE, I guess I'll find out when I do the teardown.
Like I said, I own a 4080 CORE bought new from Thomann a couple of years ago, but I won't go past measuring the U(I) curve in my investigations on that one.
--
---- Scott Helmke ---- scott@... ---- (734) 604-9340 ----
"I have ceased distinguishing between the religious and the secular,
for everything is holy" - Joe Henry
