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

[driscoll42]

Not to resurrect a dead thread, but the link to the cart on the initial page is broken so I made a new one (this one includes the parts to keep the auto-switching circuit on the rear panel):

Cart: https://www.mouser.com/ProjectManage...sID=b3fee732ee

Project: https://www.mouser.com/ProjectManage...sID=d21c23bae0

Because I'm using a Modi 2 Uber which producses 1.5V RMS, I used R103/203 should be 22.6K (Mouser part number 271-22.6K-RC). From a post Tyger made on 7/8/13 you should change your R103/203 depending :

If your audio source is rated to produce 750mV RMS - 1V RMS (most modern day consumer devices do this), then R103/203 should be 34K. This produces 19.75dB of gain.
If your audio source is rated to produce 1.5V RMS to 2V RMS, then R103/203 should be 22.6K (Mouser part number 271-22.6K-RC). This produces +16.64dB of gain. This is 3dB less than original (about 1/2 the power).
If your audio source is rated to produce >2.5V RMS, then R103/203 should be 15.4K (Mouser part number 271-15.4K-RC). This produces +13.89dB of gain. This is about 6dB less than original (about 1/4 the power).
Source

If I missed anything I'll update this accordingly after I build it.

[lasakro]

Not to resurrect a dead thread

Hey what's wrong with that. I've had two AMP100's for years. Now one with a bad balance pot I found this spectacular thread. I purchased 2 sets of parts but chose to go through Digi-Key since they had everything in stock. Parts will be here tomorrow and I have a nice weekend project ahead of me.

Last week I found a need for another inexpensive 50 WPC amp but AS now has a AMP100VS. One arrive 2 days ago and I don't like the small knobs. I'll rip into that also and see if the circuit is the same.

[AcidWash]

Hey what's wrong with that. I've had two AMP100's for years. Now one with a bad balance pot I found this spectacular thread. I purchased 2 sets of parts but chose to go through Digi-Key since they had everything in stock. Parts will be here tomorrow and I have a nice weekend project ahead of me.

Last week I found a need for another inexpensive 50 WPC amp but AS now has a AMP100VS. One arrive 2 days ago and I don't like the small knobs. I'll rip into that also and see if the circuit is the same.

Did you ever open the 100VS up and check the circuit out? I looked endlessly on PE website for this model, what happened? Did AS go out of business?

[armstead29]

Hello, I have the Audiosource amp 100vs and experiencing volume in balance and dull sounding. Would the Amp 100 mod work with my Amp 100vs.Sure need the help please.

[bullittstang]

open it up and take some high resolution pictures - post them, and I'm sure we can let you know if the same mods will work for your version. At first glance they look very similar, but without the inside pics, can't be 100% sure. I would assume it may be the same topology but uses SMD parts instead of thru-hole, but I could be wrong.

[armstead29]

Sure Will, thanks so much will open and take photos of the inside.

[armstead29]

Sorry, will post photos tomorrow.

[mathiasb]

HI all,

I did the amp upgrade and it appears to work fine in the garage, but whenever I plug it in the living room I get a 120Hz buzz, and quite some RF interference (radio can almost be heard!). I've tried grounding the amp to the other devices, but it doesn't make a difference. Again, it works okay in the garage.

Is there a way to increase the RF filtering of the unit somehow, any tips? Thank you

edit: Other devices in the living room do not have this issue (Rotel amp, Denon AVR, MiniDSP's, Pro-Lite 7.5...)

[bullittstang]

some high-resolution pictures might help. Did you upgrade exactly, or substitute any parts? The supply caps are very close to the top, any chance they are touching the top case cover? also, did you eliminate the RCA switching, or retain inputs as OEM? Did it work fine in this same location prior to the upgrades? If so, then it is something you changed, if not, then it is likely a component lead touching "something", a solder bridge or dry joint.

[mathiasb]

Hey Paul, thank you for the reply. I used the exact parts, eliminating the auto switching function. I've noticed that the buzz I hear is the same buzz that appears when you tilt balance fully left or right, just not as loud - but still there, and noticeable from the listening position with the volume knob around 12.

I always had hum from this amp in this location, hoping the upgrades would help (they most certainly help with other things, but not eliminating this hum!).

I've attached some pictures.

[mathiasb]

Should I see this 20mV ~60Hz ripple on the speaker posts of the unused pair? This shows up on B posts if A speakers are on, and vice versa.

Edit: The second image is the 120Hz hum heard, which is much louder when you tilt balance fully to either channel.

[tyger23]

If you're experiencing RF noise, I recommend looking at step 4 of the second post in my original instructions:

4.Remove the RF immunity trap to help with high-frequency phase by removing C100 and C200. Note that this will make the amp more susceptible to RF noise. If RF noise experienced, replace caps with 220pF ceramic multi-layer caps. [Mouser PN FK28C0G1H221J]

These caps on the op-amp inputs form a low-pass roll off. If you put them back in, it will reduce the RF interference, but it will also start rolling-off the high frequency capability of the amp. Amp design, like life, is full of tradeoffs.

[tyger23]

Should I see this 20mV ~60Hz ripple on the speaker posts of the unused pair? This shows up on B posts if A speakers are on, and vice versa.

Edit: The second image is the 120Hz hum heard, which is much louder when you tilt balance fully to either channel.

The 60hz ripple on the unused pair is not bothersome, as the unused pair becomes physically disconnected when you swap them out. Therefore, the 60Hz ripple is possibly "phantom", being picked up by your scope. It could be indicative of a bad ground, though. That bad ground could be as simple as where you placed your scope probe's ground to having the scope and the amp on a different circuit while taking the measurement.

The 120hz negative spike is more interesting and troubling. I wouldn't expect that, and I don't exactly know where to tell you to look. Where are you probing when you that spike? Maybe try to isolate it by pulling the input board? If it stays/goes away it might help you determine where to look.

[marstedt]

Just FYI, the LM4562 seems like it's back in stock / production.

https://octopart.com/lm4562na%2Fnopb-texas+instruments-24814490

[JRT]

Just FYI, the LM4562 seems like it's back in stock / production.

https://octopart.com/lm4562na%2Fnopb-texas+instruments-24814490

TI's website shows it as active:

https://www.ti.com/product/LM4562