Muffsy Phono Preamp PP-4 question/help

[andrewskaterrr]

Im here to discuss two different topics.

1. I’m hoping that we can have some measurements taken of the Muffsy PP-4.

2. I’m having an issue where mine started popping and making noise, I believe only in the Left channel. It worked for about 2 years without issue, then started doing this after about 6 months of no use.
Im going to do some more testing and check my solder joints etc this week.
- I have the corner filed down for the ground, but my unit is not grounded.
- I had to bypass the amp board with the power cables because they were leaking into the audio chain. So the outlet goes straight to the power board.

I recorded a video so you can hear it.

 

[Thomas_A]

Left channel drop-out was my problem. Seemed to be some bad contact between back panel and RCA grounds. I soldered the RCA lugs together in star ground (see PP3 variant of Muffsy):

Eliminate Hum | Muffsy Phono Kits

www.muffsy.com

 

[andrewskaterrr]

Left channel drop-out was my problem. Seemed to be some bad contact between back panel and RCA grounds. I soldered the RCA lugs together in star ground (see PP3 variant of Muffsy):

Eliminate Hum | Muffsy Phono Kits

www.muffsy.com

So I played around with the ground placement, and even took extra wire and touched it to different parts to make a new bridge. I double checked my screw terminals, and my soldered and scraped off corner, they're good.
What I did find was that I can pull off the ground wire, which makes a steady higher pitched noise, and still hear pops and scratching behind the ground noise going in and out. I think it has to do with something else besides a grounding issue. Do you know of a component that could introduce random noise like that? A cap, transistor, etc?

 

[andrewskaterrr]

Left channel drop-out was my problem. Seemed to be some bad contact between back panel and RCA grounds. I soldered the RCA lugs together in star ground (see PP3 variant of Muffsy):

Eliminate Hum | Muffsy Phono Kits

www.muffsy.com

I just unplugged the TT's RCAs and ground wire, so it's just PP-4 and RCAs out. It still makes noise all by itself. I tried running a cable touching the RCA Out cable to the JBL SDP-55 and touched it around everything, no difference.

 

[Thomas_A]

I just unplugged the TT's RCAs and ground wire, so it's just PP-4 and RCAs out. It still makes noise all by itself. I tried running a cable touching the RCA Out cable to the JBL SDP-55 and touched it around everything, no difference.

I think you should open it and measure at the suggested electric points.

 

[andrewskaterrr]

I think you should open it and measure at the suggested electric points.

I guess I'm stupid because I don't see any suggested electric points. All I've found so far is testing the PSU board on the PP3 and earlier. Unfortunately I don't know enough to figure it out myself. I'm not sure what to look for when looking for audible leakage from electrical measurements, maybe fluctuating voltage? I may have to try resoldering everything, or trashing it and buying a Cambridge.

 

[Thomas_A]

I guess I'm stupid because I don't see any suggested electric points. All I've found so far is testing the PSU board on the PP3 and earlier. Unfortunately I don't know enough to figure it out myself. I'm not sure what to look for when looking for audible leakage from electrical measurements, maybe fluctuating voltage? I may have to try resoldering everything, or trashing it and buying a Cambridge.

Muffsy Phono Preamp Troubleshooting | Muffsy Phono Kits

www.muffsy.com

 

[Thomas_A]

If all ok on PSU, solder the RCA ground lugs togehther. After this I don’t know. Switch the ICs to see if they are faulty?

 

[andrewskaterrr]

If all ok on PSU, solder the RCA ground lugs togehther. After this I don’t know. Switch the ICs to see if they are faulty?

Thanks I’ll try that

 

[andrewskaterrr]

If all ok on PSU, solder the RCA ground lugs togehther. After this I don’t know. Switch the ICs to see if they are faulty?

So I did the tests on that page (PSU and Amp stages), all voltages correct. I then swapped the opamps to see if the left channel opamp was broken, nope, still bad left channel. Also all of my ground testing results in different grounding noise. This almost sounds like a something boiling on and off. That's why I was thinking the issue may have been a capacitor or resistor? Someone on another Pream page told someone that resistors can make these noises. I tested with the top off and on and recorded a video of it. The ground hum is completely different, and the noise is progressively getting worse over time like something is going bad. I measured the 10 resistors in the row for the input impedance switches, and they were correct except for the 3rd which reads 41.6k instead of 82k on both. I'll keep probing other parts.

 

[andrewskaterrr]

 

[mhardy6647]

I'd be looking hard for poor solder joints, especially cold soldered. And especially any point to point.
Been there, done that with DIY phono preamps.

With the patient live, conscious, and responsive , I'd suggest probing the board and any connections by tapping -- use a Tinkertoy (I may be dating myself) -- or a chopstick. Listen to the results of your labors and you may find the culprit(s).

 

[andrewskaterrr]

I'd be looking hard for poor solder joints, especially cold soldered. And especially any point to point.
Been there, done that with DIY phono preamps.

With the patient live, conscious, and responsive , I'd suggest probing the board and any connections by tapping -- use a Tinkertoy (I may be dating myself) -- or a chopstick. Listen to the results of your labors and you may find the culprit(s).

So that's the thing, soldering wise it worked for nearly 2 years, then this started. I just read that the 2 op-amps aren't Left and Right, So I may still have a bad one. I may order a new one to try.

 

[andrewskaterrr]

I just ordered new op-amps to see if they are the issue. Only $18.

https://www.mouser.com/ProductDetail/Texas-Instruments/OPA2134PA?qs=7nS3%252BbEUL6uyT34OzaiM4g%3D%3D

https://www.mouser.com/ProductDetail/Texas-Instruments/LM4562NA-NOPB?qs=QbsRYf82W3Gc2w4DLq%252BZjw%3D%3D

 

[Thomas_A]

So PSU ok. Did you solder all RCA ground lugs together? Original achematics only use two RCA ground lugs.

 

[andrewskaterrr]

So PSU ok. Did you solder all RCA ground lugs together? Original achematics only use two RCA ground lugs.

So I have 2 extra rings, but I'd have to de-solder and re-solder both cables to get them on. I did do testing with just holding a spare wire from the lugs to different parts with no success. I also did continuity testing with my multimeter between various points and had no issues. My solder points all look solid. Besides de-soldering those cables and putting the rings on (which I don't feel like messing with), I'm out of options. So I'm going to wait for the Op-amps to arrive. The noise keeps getting consistently worse the more I have it on, it seems. It's much worse than when I started last week, and months ago when I originally heard it for the first time it was rare, so it seems like something is actively degrading.

 

[Thomas_A]

So I have 2 extra rings, but I'd have to de-solder and re-solder both cables to get them on. I did do testing with just holding a spare wire from the lugs to different parts with no success. I also did continuity testing with my multimeter between various points and had no issues. My solder points all look solid. Besides de-soldering those cables and putting the rings on (which I don't feel like messing with), I'm out of options. So I'm going to wait for the Op-amps to arrive. The noise keeps getting consistently worse the more I have it on, it seems. It's much worse than when I started last week, and months ago when I originally heard it for the first time it was rare, so it seems like something is actively degrading.

Perhaps the opamps then. Caps and resistors should be stable unless there are bad solder joints.

 

[andrewskaterrr]

Well new op-amps didn't fix it. I noticed that If I bring a spare wire close to the Left Input, it will get some ground hum increasing. I tried soldering that wire again and no joy. I tried holding up 2 spare wires to connect all 4 grounds, but no joy, they still all are connected anyways. Removing all the Input/Output cables and running a separate cable out of the Left Output still resulted in the noise (see video). I'm really lost as to what it is. I'm about to give up and just buy a Cambridge.

 

[andrewskaterrr]

**FIXED**
Ok I think I found the issue. This was my last shot at trying to fix it. I started cleaning off the flux between solder joints just to be safe, but also cleaned off the extra solder from where I removed the power lines from the Amp board. I think the extra solder that was covering the hole was causing the issue. It's now clean as can be. It would make sense that it started making noise after I did the bypass. I knew I should've tried cleaning that off sooner but I figured it shouldn't be the issue. Guess I was wrong.
Thanks for trying to help everyone!

 

[Thomas_A]

**FIXED**
Ok I think I found the issue. This was my last shot at trying to fix it. I started cleaning off the flux between solder joints just to be safe, but also cleaned off the extra solder from where I removed the power lines from the Amp board. I think the extra solder that was covering the hole was causing the issue. It's now clean as can be. It would make sense that it started making noise after I did the bypass. I knew I should've tried cleaning that off sooner but I figured it shouldn't be the issue. Guess I was wrong.
Thanks for trying to help everyone!

So it is fixed? Good.

DIY is always something of a risky business - I've done my share of mistakes as well.