How to fix the Audio Research D-110 modules

Have zero offset

I just repaired a d-52, the same as a d-100 with lower voltage main rails and fewer output transistors. Essentially the same otherwise. I have no dc offset on either channel, zero. I attribute this to using 1% resistors in the feed back loop to the opamp circuit (1.6M ohm). I did replace all the carbon comp resistors as they were well off their values. All the moduals were ok, just one channel drivers and outputs bad. Required a complete tear down to do this. These run quite warm, so I drilled some vent holes in the top/bottom covers where the transistor tunnels are to allow air to circulate up through the tunnel.
 
Hate to necro-post, but I did take some time to melt apart the stupid epoxy. I know some said they couldn't read part numbers, and I'm not positive if this will even help in any way - but I found the following parts (NOT a complete list - some were damaged too much to read, upon removal) inside an AM-1 module from a D-110B:

-2x 2N6515 (TO-92) - Mfg. logo Motorola
-2x 2N6518 (TO-92) - Mfg. logo Motorola
-1x 16-pin IC holder
-1x 16-pin 316B104 chip (Mfg. logo AB - assumed AeroBase?) - potentially resistor network - many appear to be approx. 100 ohm - damaged so I can't test all.
-1x 2N2222A transistor (TO-18) - Unknown mfg.
-3x TO-18, unreadable
-1x film cap?, unreadable
-2x through-hole resistors, burned unreadable, about (typical/average) 1/4w resistor size

Not really much help, but hopefully it is useful to SOMEONE. If nothing else, maybe it'll save you roasting this thing apart, or fill in the missing blanks, if you do.
 
Also, sorry to necro-post (twice), but can anyone verify the G/D/S positions of the JFET's in the AM-1 modules? I just want to be sure, if possible, as they are not clearly marked and I just went with what I felt was correct based on the rest of the circuit - but it'd be better to have a confirmation from someone more knowledgeable, as well. Thanks for any help you can provide!
 
I have also seen many wierd configurations of (old) jfets in old circuits.
You can even flip the source and drain on some, without malfunction only a change of linearity. You can lookup the schematics for Johns Curls Blowtorch to see this.

But in the end it works best if you just use them with the source heading to 0 Volt through a degenerating resistor.
 
Well, I got an answer AND learned something. I actually haven't had much experience with JFETs yet, this is the first time I've assembled something calling for the use of them. Thank you! Also, not to nit-pick your schematics, I greatly appreciate them, but I believe you forgot the "interconnected line" indicator on the side of R9 not connected to the cap.
 
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... but I believe you forgot the "interconnected line" indicator on the side of R9 not connected to the cap.

Yes, you are right - sorry about that.
An image to clear out any misunderstandings:
 

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Probably another novice question, but I have about 2v DC offset on the channel I built the new AM-1 for - how exactly would I go about trying to eliminate this? I see the +/- offset here, but I don't particularly understand how those work in this circuit, to be perfectly honest.

You should check the opamp in the offset circuit. Also check the supply voltages.
 
They are in fact not! Or rather, they are, but upon looking at the point they reach the op-amp, the -15v rail drops from -14.x after the resistor, to -8.6V. The 15v rail stays intact. After pulling the op-amp, the voltage seems fine. This leads me to believe the op-amp is bad. Is there any suitable more common (and/or less expensive) op-amp than the LM308N that I can use? Even if not permanently, at least for testing, that you know of offhand? Thanks again!
 
Well, now I'm a bit lost. Without the op-amps in (The TL071's or the LM308), it's getting -14.x and 14.x volts; with them in it's getting -8.5 and 14.x volts. It is fine on either side up to R27/R28, then immediately after it drops down to -8.5v, only with the op-amps in though. Any suggestions here? There does not appear to be anything else (besides the op-amps) after R27/R28, aside two transistors that appear to handle voltage to the cards in question. I have pulled them to test and even without them I get -8.5v.
 
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Well, bit of an update. It seems that the amp works fine with the original modules (The one of each I have that functions), on either channel. When I install these modules, the -15v rail gets much closer to what it SHOULD be at; I'm assuming the modules must be installed for those rails to function normally.

I'd love to find an original set of AM-1 and AM-2, the replacements I built from this design seem not to have functioned as expected (but I know that's a bit of a unicorn I'm asking for there). I double-checked with the company to be sure they didn't have any (I expected as much) and I figured it was even worth a shot to ask what they're comprised of originally/any documentation or schematics. I got this back:

The problem is that there is not really any reliable documentation for those modules. Those were designed by the man who started the company and he left no real schematics or documentation for them behind when he passed away many years ago. That is the reason we can no longer produce them and we have no plans on reverse engineering them at this time. I'm sorry we cannot help any further with this.

Just figured I'd share that with you and any future visitors here. I'm gonna tinker with these modules and see what I might have done wrong. I found a few things I was uncertain of when building, so I may have goofed that. I'll try to post any question on ambiguity in diagram as I come by them. Thanks again for even taking the time to make this thread!