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digitalear 29th June 2005 06:32 AM

audiosource amp100 (tda7294) mods
I just cracked open an audiosouce amp100. Some interesting things that would be easy to improve include:

1. power supply caps - existing caps are only 6800uF per rail. With both channels driven, I measured 52 watts into 8 ohm at 1 kHz, but only 42 watts at 20 Hz.

2. op amps - I found 5 - 3 "5532" and 2 "4580". All but one (a 5532) appear to be easily removed from the signal path by bypassing the circuit board that does the input selection and auto-on functionality. The audio inputs an be wired directly to a main board connector that would otherwise be connected to the board being bypassed. I'm not sure, but the remaining 5532 might be used to invert the input audio signal when the amp is configured in bridged mode (I haven't yet traced the circuit).

The transformer is a 53.6V CT 3.2 amp toroid.

Has anyone else modified and audiosource amp100? What changes would you suggest? Are the later amps chips like TDA7293 and TDA7294S sonically superior? Maybe modifying the circuit (hopefully just tieing off some pins) to use the newer parts would make sense.

I've seen factory refurbished units selling for$75-$85

mb 29th June 2005 09:36 AM


Based on my twiddling with my 7294 amp, there are options that can bring it to sing quite sweetly:

- usual power supply optmisation, including soft recovery or schottky rectifiers, bigger / better caps, snubbers
- generous bypass of power supply pins; RC snubbers on power pins
- use of quality (film or BG non-polar) cap for dc block
- lower rail voltage -- brought mine down from 40V to +/- 29V, and it seems happier driving 4R speakers

One of the major upgrades was to *add* a buffer after the volume pot. With just a volume pot w/o buffer, bass and midbass was wooly. With a good buffer, the sound improved a lot. You might think of optimising rather than removing the linestage.

sorenj07 26th September 2007 06:57 PM

I'm interested in grabbing one of these amps as a backup for any downtime when I've got my tube monoblocks on the bench. Does anyone happen to have a schematic of this thing or shots of the inside? Maybe I could squeeze in a tube front-end using a low-profile toroid... :scratch2:

Stormrider 7th October 2007 01:31 PM

I also would be interested in some pictures of the inside. Seems like a decent amp for 100$.

ashok 7th October 2007 02:32 PM

Digitalear ,
Can you post a picture of the insides ?

sorenj07 23rd October 2007 08:10 AM

does anyone else have one of these amps they're willing to strip down for us? :smash:

cronos1 28th September 2008 11:46 PM

I have some photos but I don't know how to post them ?!

Cal Weldon 28th September 2008 11:48 PM

Click the browse button at the bottom of the submit reply window. Approx 100k max.

sorenj07 18th May 2009 02:54 AM

This Thread Ain't Dead Yet! will let you post thumbnail links to basically any photo, give that a try :)

chops 27th August 2011 05:42 AM

Has there been any updates on modding this amp?

I have one stashed away in my closet that I'm going to pull out tomorrow. I'll open it up and take some detailed pics of the innards and post them here.

I'm thinking of "hot-rodding" it and using it as my main amp in my system. Since I already have a sweet Accuphase C-200 preamp, I can bypass not only the volume control, but also the balance and auto input selector features as well as the auto-on feature. Of course, I'll be looking to upgrade any caps in the unit that I can, both in the PS section and in the signal path. After I do all of that, I'll swap it into a new chassis with more room to breath. Besides, I'll need the room for all those new larger caps! :D

If there's any good info on modding this amp, please let me know!

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