Author Topic: AD20-PS-2 hack (Read 7934 times)

Nick's Picks · « **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.

Digital Quality · « **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.

Nick's Picks · « **Reply #2 on:** March 06, 2007, 02:33:12 PM »

some pics...

Nick's Picks · « **Reply #3 on:** March 06, 2007, 03:01:51 PM »

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.

Digital Quality · « **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.

junonato · « **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!

poorlyconditioned · « **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

Church-Audio · « **Reply #7 on:** March 06, 2007, 05:02:14 PM »

Quote from: Nick's Picks on March 06, 2007, 03:01:51 PM

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

Digital Quality · « **Reply #8 on:** March 06, 2007, 05:15:17 PM »

Does OPA2227PA work with a single supply?

Church-Audio · « **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.

Digital Quality · « **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.

Church-Audio · « **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.

Digital Quality · « **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.

Nick's Picks · « **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.

Church-Audio · « **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.

Church-Audio · « **Reply #15 on:** March 06, 2007, 05:40:21 PM »

Quote from: Nick's Picks 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.

If its a dual supply and I am pretty sure it is. There will be + on pin #8 and - on pin #4 of the ne5532 with repect to ground.

Digital Quality · « **Reply #16 on:** March 06, 2007, 05:47:35 PM »

I'm still betting on single side but I'm sorta cheating because I have a fuzzy memory of looking up this chip.

Couldn't you get the same headrooom/noise figure with a higher input voltage vs dual sided?

Church-Audio · « **Reply #17 on:** March 06, 2007, 05:51:32 PM »

Quote from: Jam_ON 017 on March 06, 2007, 05:47:35 PM

I'm still betting on single side but I'm sorta cheating because I have a fuzzy memory of looking up this chip.

Couldn't you get the same headrooom/noise figure with a higher input voltage vs dual sided?

There are a million and one different ways to build a circuit as a general rule with preamps its always better to run a dual supply. When you dont you also increase your chances of noise due to the fact that you dont have the same isolation as you do with you 0 volt ground rail. Because your obtaining part of your signal from the negative rail *tied to audio ground* your also increasing noise. So most good designers would stay away from a single supply for a mic preamp. I am not saying that this is not the case here but I would be surprised with a digital circuit if it was not a dual supply as most of the a/d chips I have ever seen require a dual supply.

Digital Quality · « **Reply #18 on:** March 06, 2007, 05:54:04 PM »

Ahh- ~~CMRR~~ PSRR interesting, thanks.

Kindguy · « **Reply #19 on:** March 09, 2007, 06:34:27 PM »

T+ this is interesting.

oscoastierob · « **Reply #20 on:** April 06, 2007, 04:57:05 PM »

any updates on how this project is going??

Nick's Picks · « **Reply #21 on:** April 06, 2007, 05:45:35 PM »

on the shelf until I get caught up on cable orders.

ArchivalAudio · « **Reply #22 on:** May 01, 2007, 12:34:15 AM »

most of the op amp talk is over my head
but I do know that both the AD-20 and PS 2 can runn off of 7v - 24v DC
though if my memory serves me
the AD-20 is really only 7v to 18v
or may be its the other way around
I used to power my AD-2- and PS-2 off of one single 12v SLA
in order to get the phantom running for longer that a 9v cell

good luck this sounds like a cool project

Nick's Picks · « **Reply #23 on:** May 01, 2007, 06:01:53 AM »

i'm just getting back to it...

Church-Audio · « **Reply #24 on:** May 01, 2007, 10:20:37 AM »

Quote from: Nick's Picks on May 01, 2007, 06:01:53 AM

i'm just getting back to it...

Let me know if you need any help there Nick..

Chris

Nick's Picks · « **Reply #25 on:** May 02, 2007, 07:39:00 AM »

my plan was to take some pictures of the ad20 board, and let you point out what I can attempt to replace in terms of parts on it.

that will help me learn to identify the parts...and get an idea of what good/vs bad is.