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

[tyger23]

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

3 o'clock position. When there is no source connected it is totally clean. What I do notice though is if I turn the gain up to full with nothing connected the right speaker cone moves all the way out and back in again when I get right to the end of the rotation. I dont know if this could indicated a bad volume pot? I did cut the shaft, now im wondering if I could have damaged it when I did that... Also I just went over the whole board and checked for shorts and cold solder joints, didnt find anything, now that doesnt mean there is not...after all I definitly am not an expert!

Thanks for the help, it is very much appreciated.

OK - if you're getting cone movement at ANY volume position, then the amp is putting DC voltage out and you've got a major issue (a short or something else). Out of curiosity, did you check the AMP-100 before doing the mods? Was it working fine? I'm worried the actual amp chips might be damaged, but its hard to tell for sure. From this point on, make sure the speakers you're using to test the amp with are cheap throw-away speakers. Once we get the amp sorted, you can move on to your nicer speakers.

You might try disconnecting the cable from the rear panel board that attaches near the volume pots on the main board. This will disconnect the input signals. Then, try your volume knob to see if the cone moves again (USE CHEAP THROW AWAY SPEAKERS, or a multimeter set to measure DCV). If it still happens, the issue is likely on the main board. If not, the issue is likely on the rear panel board.

[Rcstark]

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

Ok. I'll check on that and get back to you. Thanks for the advice.

And yes it was functioning properly before the modification.

[Rcstark]

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

Ok so upon disconnecting the cable I lose the green power led and the speaker cone no longer moves when turning the knob

[tyger23]

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

That tends to indicate to me that whatever is wrong is on the rear panel board. I know there's several revisions of that amplifier out there, so I can't specifically state which one you have. However, in my design (the one pictured on page 1), the cable to the back panel provides power and ground to the preamp circuit and also provides the signals from the inputs into the main board.

I would focus your efforts on the rear panel board. Did you do the rework to remove the autoswitch circuit? Double check that. Otherwise, start looking at the op-amps and make sure they're not reversed or have pins shorted together. When checking for shorts with IC's, look on the top and on the bottom. Sometimes solder will suck up through the hole and create a short on the top side of the board even though you were soldering on the bottom.

[Rcstark]

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

Yes I did keep the auto switching circut. The op-amps have continuity everywhere they should and nothing is shorted together there, also the tabs are pointed toward the rca inputs. Checked and double checked with a meter. Man this is really frustrating haha!

[Rcstark]

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

Small update:

I was able to fix the apparent ground hum, I cleaned up in between the traces on the main board and it looks like I may have let some solder flow to another when shorting between c101 and c102. I can still hear a very slight hum when turned up all the way but nothing like before.

When I use input 1 and let it auto switch, if I pause the music and turn the volume knob to where it would move the speaker cone it only moves very slightly and hums slightly until the switch goes back to input two, then it moves the speaker cone again and I hear a hum again. So looks like one problem fixed or made slightly better? Does the fact it is happening worse on input two suggest anything?

[tyger23]

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

It sounds to me like there's an issue with the second input. It may be a bad op-amp or capacitor associated with Input 2. If input 1 is working well enough for you and the auto-switching is not bothering you, then I'd leave it on input 1 and be done with it.

When on input 2, does the speaker cone move on both the left and the right channels, or just one of the two? Do you have a multimeter? If so, I can point you to some places to check.

[Rcstark]

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

Yeah it does move slightly on input one as we'll but not much I'm assuming that it would be fine to connect a decent speaker to that I care about it? Yes I have a multimeter, I attempted to measure the dc offset (I think that's what you were talking about before?) at the speaker terminals with nothing connected and get .6 mv on the channel in question, when the volume is at full it seems to fluctuate more than with it completely down.

The speaker only moves on the right output. It would be great if you could point me at some things to check. And thanks again for helping, I know it's not really up to you to help out so it's really cool of you to do that!

It might also be worth noting when the speaker moves it actually seems to settle back into position right away.

[tyger23]

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

The speaker only moves on the right output. It would be great if you could point me at some things to check. And thanks again for helping, I know it's not really up to you to help out so it's really cool of you to do that!

That makes things a bit easier to check. Sadly, I don't remember the schematics terribly well, so I'm having to look at my old pictures and notes and guess on a few things.

First, a quick check. Make sure you're not in MONO, or Bridging mode.

If you can measure between C101 and ground and C201 and ground and look for DC voltage when the amp is in the failing condition, that would be helpful. I'm betting C201 will show some DC offset (it shouldn't). However, C104 and C204 (should still have stopped the amplifier from seeing a DC input), so you need to check your rework near those as well. If I remember correctly, those are close to the far edges of the heatsink. Also look for DC voltage on either side of those capacitors (C104, C204). Look for DC voltage on either side of C107 and C207 as well.

[Rcstark]

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

C101 - .7 mV
C201 - 106.4mV

C104 - 2.5mV on the + leg
C204 - 74mV on the + leg
Negative legs show very close to zero

C107 and 207 show very close to zero

[tyger23]

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

Well, you most certainly have an offset on the right channel, but the fact that C204 and C207 are close to zero on the negative legs mean that the DC blocking caps are doing their jobs and the amp should not be putting out DC.

When you said the cone would move all the way out, is it moving in one direction and staying there, or is it "vibrating" like a heavy bass track (i.e. moving in both directions)?

Next, I would try and remove the right channel signal from the cable leading from the back panel. That's the wire in the pin #1 position. Usually, you can remove the wire from the connector mold by:
1. Disconnect the cable from the main board.
2. Find the little white "tabs" on one side of the cable connector.
3. Gently insert an Xacto knife or other sharp object under the tab for the right channel signal.
4. Very gently lift up on the tab, then pull on the cable for the right signal only.

This should remove the right channel signal from the cable connector. Once this is done, re-insert the cable into the motherboard. This way, the left channel will work just fine and the right channel will be disconnected. Measure the DC voltage at C201 again, and then also at the exposed cable for the right channel.

This should tell me where the offset is originating.

[---k---]

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

Glad this thread popped up. I got one of these still sitting in the box never opened. I may have to try this out someday.

[Rcstark]

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

Excellent. What is happening is when I turn the volume from about 7/8ths to full volume the speaker come moves out seemingly all the way then settles back into position again. When I move it back to 7/8ths full I think what happenes is the opposite, it moves in then settled back into position. This is accompanied by a hum thay stays there when the pot is in these last positions. Second input is much worse then the first.


When I get home later today I'll check on what you just suggested and report back. I'm assuming I can just hack up an old rca cable and achieve the same effect instead of disassembling one? Or are you talking about the female connections to the back board?

Thanks.

Ok I read that wrong. I got you now. The cable from the wire harness

[Rcstark]

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

I succeeded in getting the right signal out of the molding...except the crimp on piece decided to stay inside of it. Can I just solder this to the bottom of the board afterwards?

The voltage at c201 reads 0.5mV and at the right signal cable it fluctuates from .4-.8mV.

[Rcstark]

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

Just to be sure, should these measurements be taken with a source plugged in?
Also just double checked and it seems the positive leg of C104 is now about reading -16mV. If there is nothing connected to the rca jacks the measument changes back to a lower voltage.