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

[bullittstang]

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

I have listened to mine for 4-5 hours so far, so I might be a fair assessment.
I don't have any hum, running a cheap 3.5 to RCA cord from my computer (monoprice $2 cord). I tried Auto and Manual switch on the back, tried with speakers in A and B positions and tried with high master volume, low and high on amp and the vice-versa too.
I also tried your most noticeable way which is at a normal playing volume, but with the CD, iTunes and Spotify paused and I still have no hum or hiss. It's as quiet as both my AVR's (Onkyo's, both about 3 years old) and quieter than my homemade Sure chip amp design.
Be glad to try something else, if you want me to, just let me know. Any chance it could be a ground loop issue, 60-Hz hum from the electrical?

[Justinlwtx]

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

It sounds like what was described by someone earlier in the thread. I removed the boards to check for bridges or shorts. I'm also going to scrub the flux off of the board a little better. It's been rainy and humid here, hopefully the rosin soaked up some moisture and is causing it.

[Justinlwtx]

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

Well, verified all joints and scrubbed the boards. Noise is still here. I noticed if I touch the chassis the noise changes. Then noticed that if I wave my hand above the boards I can make it nearly go away in certain positions without touching the chassis.

Does this suggest RF interference, and should I install the RF blocking capacitors?

[bullittstang]

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

...should I install the RF blocking capacitors?

I'm not a professional by any stretch, but I installed those from teh start and have had no hum/hiss or buzz with mine. So I would say to do it.

[Justinlwtx]

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

They're in, no change. Still responding the same to touching and waving above.

I tried grounding the unit, and grounding between components with no change.

[pfrakes]

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

They're in, no change. Still responding the same to touching and waving above.

I tried grounding the unit, and grounding between components with no change.

Since it is so sensitive to magnetic fields yet music does play through the unit, it must be a ground problem related to the circuit board. Unless, of course, you have the amp sitting near or on top of another piece of equipment and the amp is picking up hum from its transformer. Be sure you try moving it away from anything that could be generating a magnetic field.

Next I would carefully inspect each connector going to the circuit board, even if you didn't remove it. Physically move each wire, looking for a break at the point it enters the connector, especially the shield connection on the shielded wires. Also look at the solder side of the board, using a magnifying glass if necessary, looking for hairline cracks around each connector pin.

-Phil

[Justinlwtx]

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

Not near any other equipment. It's in the middle of my workbench connected to speakers and a Raspberry pi/hifiberry dac. Also connected an Airport Express with different interconnect to rule out the source as the issue. I'll pull the boards again and check them over, I haven't found any obvious problems yet.

[pfrakes]

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

You might try unplugging the connector on the main board that comes from the input board. If the hum goes away, then the problem is likely with the input section. If it remains, the problem is on the main board.

[Justinlwtx]

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

I tried that. When you disconnect the input board, the amplifier board turns off. Power signal comes through the input board I'm assuming.

[pfrakes]

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

No, that is not the case. The connector that comes from the input board is a small one, whereas the power coming from the transformer is done so through larger diameter wire.

The power to the transformer itself comes from the power switch, which is unrelated to the input board. So, my guess is that you think the amp is going dead because the noise goes away, but in reality the main board is still powered. If you find that to be true, then concentrate your search for the problem around the input board.

[Justinlwtx]

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

The power indicator light on the power switch turns off as well. It's not red or green like normal standby/on.

[Justinlwtx]

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

Got rid of the majority of the hum. I noticed when I removed the input board from the case it was drastically reduced, then realized the 2 470uf capacitors I installed are just tall enough for their tops to touch the case. I put some vinyl tape across their tops and reinstalled the input board. The hum is nearly gone below 50% volume, but comes in from 50% to full. Again, it goes away completely when I disconnect the source.

[Pete Basel]

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

The relay is a big black rectangle sitting dead in the middle of the unit. There are wires leading from the speaker connectors at the back of the unit to an area on the motherboard very close to this relay. The pots appear to be similar to the ones used in the AMP-100, but without seeing the construction and part number, I can't tell for certain. I'd recommend checking your fuses (one near the AC cord input and two near the big capacitors) and checking all the wires for loose connections.

Also, look at all of your capacitors to see if any are bulging or open. If you can get the main board out, you may want to try and wiggle different caps and other components to see if anything has a cold-solder joint (looks like it's soldered, but when you wiggle it you can see that a crack has developed and the part needs to be re-soldered). Good luck!

[ATTACH=CONFIG]44393[/ATTACH]

I just bought an older one of these, used, that is very similar to yours in the picture
but it has the meters and only a single pair of Sanken output devices. It doesn't
work but nothing is fried inside so that is good. Not hearing the speaker relay
engaging. Fuses are good, have +/- 50V on the output devices. This unit looks
quite old and I think it needs to be recapped. It is probably a leaky cap that is keeping
the output relay from closing.
Nice that they doubled up on output devices.
I'm looking for a schematic to fix this thing.

Output relay and inductors look the same, very similar otherwise.

Output relay is not closing, there is nothing tripped, no DC on the output, nothing,
I think that some of the transistors have become leaky around the DC sense circuit.
Is there a thread on debugging the relay not engaging? It is a very simple circuit
and about all that's left is leakage in one of the sense transistors.

Edit:
Found a rather obscure cap that fixes the relay closing problem, wanted to find the
actual problem before just recapping the whole thing. This is a nice amp wish I had
the one with dual outputs. This circuit board is laid out for another set and the heat
sink is drilled.
Caps are YEC brand - never heard of them, there are quite a few non-polars NPEs.

[bullittstang]

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

I trying to order the parts to upgrade one of these amps I found on CL. However, when I go to Mouser or Digikey, the OPamp LM4562 is either no longer available, or min. order is 200???

Wondering if I can use either the TI NE5532P (digikey #296-1410-5-ND) or OPA2134PA (Mouser #595-OPA2134PA) the OPA2134 was suggested on another forum as a better alternative? I am going to use the same Op Amp in a pre-amp as well, so I need 4 total.

[johngalt47]

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

It turns out that there are newer op amps equivalent to the LM4562 with different part numbers:

http://www.diyaudio.com/forums/chip-amps/107344-lme49720-vs-lm4562.html