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Author Topic: AD20-PS-2 hack  (Read 7938 times)

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Offline Nick's Picks

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AD20-PS-2 hack
« on: March 06, 2007, 10:37:34 AM »
Hey all...

I've got a set of these fine products from Denecke...and I've removed the boards out of each case, as well as the jacks.
I'm going to be combining them together, powering them off the same source (9v all the way) and seeing if I can mount them in a UA5ish style case (that I happen to have on hand) or in a project box of its own.

Anyone ever soup up the analog stage of the ad20?
I'll post some good pics soon and perhaps someone can suggest replacing some parts.
:)
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Offline Digital Quality

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Re: AD20-PS-2 hack
« Reply #1 on: March 06, 2007, 11:59:19 AM »
I took a look inside once - I remember some TI opamps in there and it looked like a discreet stage with a big current mirror. I didn't really trace the signal path but that seemed weird considering there isn't any analog output. I guess that must mean the discreets form an input stage (like maybe with a fixed 15dB gain) and the amps feed the AD.

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Offline Nick's Picks

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Re: AD20-PS-2 hack
« Reply #2 on: March 06, 2007, 02:33:12 PM »
some pics...






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Offline Nick's Picks

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Re: AD20-PS-2 hack
« Reply #3 on: March 06, 2007, 03:01:51 PM »
 :hmmm:




the ad20 board is about the same footprint as the ps2.
so...I'm thinking of building an insulated layer and then machining a new metal
cover complete w/all the I/O.  I can make the stupid mini a real coax female.

I can see how I need to wire the outputs of the ps2 into the inputs on that 15pin on the ad20 board.  so, no problem bridging the gap between them.
I'm going to keep the power supplies separete.  If I combine them I'll probably fry it or add noise at the very least, so this will be fine. 
now...what to replace on the analog section of the ad20....it would be cool if I could flavor this up a bit.
« Last Edit: March 06, 2007, 03:06:13 PM by Nick's Picks »
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Offline Digital Quality

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Re: AD20-PS-2 hack
« Reply #4 on: March 06, 2007, 04:07:50 PM »
Those TI opamps would be pretty easy pickins. Still not sure what those bjt devices are doing - sourcing some current for something.
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Offline junonato

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Re: AD20-PS-2 hack
« Reply #5 on: March 06, 2007, 04:52:27 PM »
good work!  let me know how it works out!  i'de love to have a combined ad20(mod) and ps2 as one unit!
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Offline poorlyconditioned

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Re: AD20-PS-2 hack
« Reply #6 on: March 06, 2007, 05:01:57 PM »
Quote from: Jam_ON 017 on March 06, 2007, 04:07:50 PM
Those TI opamps would be pretty easy pickins. Still not sure what those bjt devices are doing - sourcing some current for something.

The transistors are the front end, and, I believe, providing all the gain.

My opinion is that the circuit is not that good.  Yes, the BJTs provide low noise, but the chosen circuit is not that good from a sound quality point of view.  This might be fine for film, but not great for music.

AFAICT there are four transistors per channel.  The transistors are in a differential arrangement, two transistors on each side (for more gain)?  There should be two more transistors per channel for a constant current source, but they are not there.  I would like to know more about this circuit.  Anyone care to trace it?  I *might* even consider replacing it with a high quality opamp front end.  This might make it sound better (at the expense of a bit more noise).

Anyway, plussssssssssT for getting in there and messing around!

  Richard
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Mics: Sennheiser MKE2002 (dummy head), Studio Projects C4, AT825 (unmodded), AT822 franken mic (x2), AT853(hc,c,sc,o), Senn. MKE2, Senn MKE40, Shure MX183/5, CA Cards, homebrew Panasonic and Transsound capsules.
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Offline Church-Audio

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Re: AD20-PS-2 hack
« Reply #7 on: March 06, 2007, 05:02:14 PM »
Quote from: Nick's Picks on March 06, 2007, 03:01:51 PM
:hmmm:




the ad20 board is about the same footprint as the ps2.
so...I'm thinking of building an insulated layer and then machining a new metal
cover complete w/all the I/O.  I can make the stupid mini a real coax female.

I can see how I need to wire the outputs of the ps2 into the inputs on that 15pin on the ad20 board.  so, no problem bridging the gap between them.
I'm going to keep the power supplies separete.  If I combine them I'll probably fry it or add noise at the very least, so this will be fine. 
now...what to replace on the analog section of the ad20....it would be cool if I could flavor this up a bit.

I would replace all the caps ( in the audio path ) that are disc or electrolytic with Mylar.... I would replace all non metal film resistors with metal film 1%. What are the two 8 pin chips in the front end there? if they are ne5532 replace them with OPA2227PA. I
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Offline Digital Quality

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Re: AD20-PS-2 hack
« Reply #8 on: March 06, 2007, 05:15:17 PM »
Does OPA2227PA work with a single supply?
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Offline Church-Audio

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Re: AD20-PS-2 hack
« Reply #9 on: March 06, 2007, 05:20:45 PM »
Quote from: Jam_ON 017 on March 06, 2007, 05:15:17 PM
Does OPA2227PA work with a single supply?

What is the chip thats in there now? the opa2227pa does not work with a single supply. Is this a single supply? I did not know that.
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Offline Digital Quality

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Re: AD20-PS-2 hack
« Reply #10 on: March 06, 2007, 05:27:30 PM »
I don't know for sure but I imagine that it is as it runs off a 9v alkaline cell.
« Last Edit: March 06, 2007, 05:29:13 PM by Jam_ON 017 »
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Re: AD20-PS-2 hack
« Reply #11 on: March 06, 2007, 05:30:55 PM »
Quote from: Jam_ON 017 on March 06, 2007, 05:27:30 PM
I don't know for sure but I imagine that it is as it runs off a 9v alkaline cell.

My preamps run from a single 9 volt but they are not a single supply. I would really assume that this thing does not run from a single rail because its digital.. There has to be a rail splitter in there somewhere if so. Then the OPA2227PA would be the way to go.. Then we can take a look at the transistors and see what we can do there.
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Offline Digital Quality

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Re: AD20-PS-2 hack
« Reply #12 on: March 06, 2007, 05:36:54 PM »
Hmm - so what's the benefit of running dual supply for a portable? You still have to have all the bypass caps. That's interesting.
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Offline Nick's Picks

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Re: AD20-PS-2 hack
« Reply #13 on: March 06, 2007, 05:38:13 PM »
runs off of either 9v DC in put or 9v battery.
i'll get down to the bench to check out the chips and report back...after dinner.
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Offline Church-Audio

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Re: AD20-PS-2 hack
« Reply #14 on: March 06, 2007, 05:38:36 PM »
Quote from: Jam_ON 017 on March 06, 2007, 05:36:54 PM
Hmm - so what's the benefit of running dual supply for a portable? You still have to have all the bypass caps. That's interesting.

The benefit is increased headroom. Lower noise.
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