How to turn your AudioSource AMP 100 into a real amp. (Paying it forward)

[marstedt]

Thanks for the feedback! Wasn't going to spend more on the adapter than the chip is worth especially if I have many to do. Think I'll try a few options and compare the results if I can.

Thanks for the detailed instructions and explanation, that takes some concerted effort to put together.

[saabracer23]

So am I right in assuming the mouser shopping basket link on the first page is incorrect? I ordered it without looking at it really and I'm tearing into my amp and noticed the there was not a new 12v relay and only one pot was ordered, not both. That's so far, there is probably more missing so I'm making a list. Just thought I'd let you know. Thanks for this though, I'm excited to get it going.

Dan

[bullittstang]

So am I right in assuming the mouser shopping basket link on the first page is incorrect? I ordered it without looking at it really and I'm tearing into my amp and noticed the there was not a new 12v relay and only one pot was ordered, not both. That's so far, there is probably more missing so I'm making a list. Just thought I'd let you know. Thanks for this though, I'm excited to get it going.

Dan

Yes,, you're right the relay is missing, as is one of the pots (the "b") version as well the power supply caps are not in the BOM. Everything else looks to be there.

[saabracer23]

Cool, thank you! Just wanted to make sure that I wasn't loosing my mind. Another question, it says to remover the "rf trap" by removing C100 and C200. I cannot for the life of me find C100 or C200. Any help on where they are located?

Thanks
Dan

[bullittstang]

[QUOTE=saabracer23;n1282028]Cool, thank you! Just wanted to make sure that I wasn't loosing my mind. Another question, it says to remover the "rf trap" by removing C100 and C200. I cannot for the life of me find C100 or C200. Any help on where they are located?/QUOTE]

They are in the front, right-hand side (very close to the edge of the board), right behind the pots. however, not all versions have them. I had one amp that did and one amp that didn't. I think the newer versions have them.

[saabracer23]

Oh okay, thank you for that. I'm almost certain mine does not have them. I scoured that board for quite awhile. So I guess no action needs taken then.

Thanks,
Dan

[gman76]

This might not be the right thread but I bought a Dayton APA100 but based on the photos here, the ref designators are different and components seem to be different. Does anyone have a schematic? I bought it with the intention of modifying it by adding a 2nd set of chip amps (bi-amp), ultimately swapping out the front end and inserting an LR4 2-way active filter. I assumed (maybe wrongly) that someone would have a schematic. Help!

I opened it up and the two power resistors R201/R202 are cookin' hot. (amplifier idle) What the heck. Quickly measured with DMM and they are dropping a lot of volts. Where are they in the circuit?

[tyger23]

Those are power resistors designed to do exactly what you measured... Drop a lot of volts. They're working as designed. In the Pyle amp, I actually changed those out for higher wattage rated resistors, but the ones in the AudioSource were fine. I've not seen the Dayton, but it seems based on the same circuits. Check out my changes to the Pyle and make your best guess . Good luck!

[gman76]

Thanks tyger23. Are these resistors dropping voltage on the V+ and V- rails for the chip amps? If they are used to drop voltage to get the rail voltages within spec, this is a huge waste of power (secondary of xformer voltage is too high). Do you have even a partial schematic?

[tyger23]

Thanks tyger23. Are these resistors dropping voltage on the V+ and V- rails for the chip amps? If they are used to drop voltage to get the rail voltages within spec, this is a huge waste of power (secondary of xformer voltage is too high). Do you have even a partial schematic?

If you look at my thread for the PAMP1000, you'll find the schematics there. It should be virtually identical to the AudioSource or the Dayton, with some minor variances.

Those power resistors are dropping a lot of voltage and (when combined with some zeiner diodes) help to generate the power rails for the signal op-amps only (not the power amps). While not an efficient method of dropping voltage, it is a cheap method. It's much cheaper than using LDO's (which would also require heat sinks).

In the Pyle, they had used 3W resistors, which I felt were a bit under rated for the situation. I believe the resistors are dropping about 2W of power (each), and therefore I prefer them to be rated at 5W. Also, on the Pyle, the resistors were sitting on top of the PCB, which is a big no-no. They need to float above the PCB to get more air flow and dissipate more heat. It looks like your Dayton already has 5W resistors that are floating, so there should be no need to make a change.

[gman76]

Tyger23, thanks again. Things are so much clearer when you can look at a schematic.

I should have expected as much from a hundred dollar amp. Shunt (zener) regulation to power the op-amps? I guess that works but I just may replace these with +/-15V fixed regs. They are going to drop ~20V, I measured +/-35V after the bridge and +/-14.9V at the zeners. In the AMP100, the power resistors are 220 ohm/5W but are dissipating 1.8 watts, as you mention. This might force too much current thru the zener. I just don't like shunt regulation. A bit ridiculous when the regulators only need to support 20mA or so of load current. (5 dual op-amps that drive light loads) A regulator will need to dissipate 20*0.02 or 400mW. I can use a surface mount reg with an exposed pad to dissipate the heat into the board.

And like you showed in the schematic, you increased the gain of the op-amp stage to about 10. I used an iphone to drive the inputs and found that it needed more gain. I'll continue to tinker.

[gman76]

It's been awhile but I'm slowly working on a heavy mod to the APA100, if anyone is interested. I plan to re-purpose much of the hardware and build a 2-way 4th order LR (state variable filter w/ continuously variable freq) bi-amp box. I will use the TDA7294s for the LF drive and add a couple LM1875s to drive my HF drivers. Since there are 8 banana jacks, the plan is to re-wire them. I've already redesigned the rear i/o board and still designing the main board. The block diagram shows the 2 boards being connected via a 12-pin ribbon cable w/ plenty of signals dedicated to GND. Plan to keep the volume and balance (not shown for simplicity). So, 3 more pots will be added - crossover freq, HF level (+/- 6dB), and baffle step comp level. Also added a sub out (2-pole, 150Hz). I borrowed a bit from Rod Elliot's site. For the power supply, I plan to tap off the +/-35V unreg output and create a capacitance multiplier set to +/- 24V to power the LM1875s. From there a simple set of linear regs will output +/-12V using LM317/337.

Edit: Plan to drive a pair of Classix II loudspeakers, Dayton DC160 (8 ohm) and Vifa BC25TG15 (4 ohm).

[mrmky]

I found an Audio Source amp locally which had never even been out of the factory box, brand new for $60. Seeing this thread prompted me to buy it, thinking it would b a good tinker project. When I hooked it up however it sounded so much better than the 3116 I have been using that I am hesitant to change anything. So far the balance and other functions seem to work perfectly. Are the improvements really that substantial? Maybe I'll keep a look out for another one so I can a/b them.

[bullittstang]

My opinion after doing 3 of these and did an A/B on a pair for 2 months. Not a night and day difference but is noticeable and much cleaner, clearer after the mods. Actually the. best part of the mod IMO was the pots, they work better, no pops or static and just do what they are supposed to do better. I don't know if just changing the pots would give you as big of a change, but leaving the old pots on one I immediately ordered the pots after listening to a Modded amp with original pots. The mods are about $45, and IMO you would have an even nicer amp for barely $100 invested. Hard to beat this amp for $100!

[kevinr]

After not listening to this amp for some time I gave it a listen yesterday .
The mods tyger shared definitely make the amp sound a lot better than the stock unit .
I wonder if there is anyway to upgrade the pots even further, or the OEM speaker or RCA terminals for that matter to squeak out some more improvement ?