Steel String Singer 002 Build - 60Hz Hum - SOLVED

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davebolden44
Posts: 213
Joined: Sun Feb 02, 2014 6:13 pm

Re: Steel String Singer 002 Build - 60Hz Hum - HELP!

Post by davebolden44 »

i still feel that since it is 60 cycle hum that it is being picked up somehow from the power in your home. the circuit may in fact be perfectly fine. im not expert but i think those snubber caps are to smooth out any noise in the rectifier. if shielding the entire circuit doesnt help could you test it in a different environment.
Krinkle
Posts: 192
Joined: Sun Dec 09, 2007 4:51 pm
Location: Pickering, Ontario

Re: Steel String Singer 002 Build - 60Hz Hum - HELP!

Post by Krinkle »

Thanks for the reply Dave. I agree, I've suspected my power for years now. I actually went out and bought 4 switches and removed 4 dimmers from the house. Then my kid comes home and I hear her tell my wife, he forgot one, which I did. I'll be replacing it on the weekend.

I'm going to do a bunch of things tonight/this weekend.

1. Try another amp and check for noise. Maybe something has changed recently, broken wire, that last dimmer failed, who knows. I already plugged a different guitar and different cable into the SSS clone, one with humbuckers, no change. My plexi clone seems to make more noise in my basement than it does at gigs but I think it might be because it is ambiently quieter in my basement. I've been swearing for years that I am going to drive a piece of rebar into the lawn outside my basement window and connect my outlet ground to it.

2. Use a ground lifted AC cable. I have a test AC cable I use to troubleshoot ground loops at practise/gigs. I'll use this one and check the guitar strings for voltage with my meter, I have a healthy respect for AC.

3. Insert my guitar signal after the volume pot. The volume and tone controls change the volume and tone of the noise, so it has to getting injected earlier into the circuit, right? We'll see, with my luck.......
lovetone
Posts: 297
Joined: Thu Mar 20, 2008 6:10 pm

Re: Steel String Singer 002 Build - 60Hz Hum - HELP!

Post by lovetone »

Have you looked at the plate (pin1 and pin 6) on V1 with the scope, probe on AC? with now input signal it should be flat line.
Krinkle
Posts: 192
Joined: Sun Dec 09, 2007 4:51 pm
Location: Pickering, Ontario

Re: Steel String Singer 002 Build - 60Hz Hum - HELP!

Post by Krinkle »

Thanks for the reply Lovetone. Yes, I have very little ripple, mV. What would the value of typcial ripple be in a similar Dumble? This amp seems well filtered, if not a little stiff to me, although I like it.

So last night I put the FET circuit back in, with shielded cable from the input to the FET, then on the output to the grid of V1a. Still noisy but not as bad as before, almost low enough to live with. I checked and with no input I can't really hear any noise, only some hiss, which I would consider normal and not bad for both volumes at 10.

I put the chassis back in the head hoping the extra shielding from the mesh in the head would help make it a little more quiet.

It was noisier and the hum/buzz was back wth no input.

I tried my AC cable with the ground lifte and an Ebtech Humx, to try to see if there was come change in noise to indicate crappy mains power, no difference.

Nect step - I'm going to rewire the tone section. I used a crappy buss on the back of the pots, I'm going to lift and twist the lugs on the pots that go to ground and do the buss that way, I think HAD did it that way also.

I'm also suspicious of my treble pot after it locked up on me when i tried to turn it down past 3 one time, and it doesn't have the same sound or feel when I turn it to 10. It's doesn't click, it feels a little spongy.

And, I only noticed the noise when I swapped the 100k volume pot for a 1M (pulled out of my friend's plexi clone because he wanted CT pots, but they were all working fine)

It may seem like paranoia but I think I have to consider everything.
Krinkle
Posts: 192
Joined: Sun Dec 09, 2007 4:51 pm
Location: Pickering, Ontario

Desperate Cry for Help

Post by Krinkle »

Things I've tried;

1. Installed an isolated input jack. Used twisted shielded pair, grounded at the jack end at V1a cathode resistor/cap ground connection. 1M to ground across the jack, 2 68k's in parallel soldered directly on to V1a grid. I was really hoping this would have fixed it.

2. Installed 0.01uF/1000V ceramic snubber caps across all PT diodes, 6 on the HT 1N4007's and 1 on the bias 1N5408.

3. Installed a ground wire from output jacks to the NFB resistor ground.

I'm injecting a 420 Hz sine wave and I'm seeing a hash on the waveform right at the V1a plate, a hazy glow all around it, albeit very light. I'm not exactly sure that this is the noise though. Volume, bass and treble all affect/increase the noise, so it is injected early in the circuit? I first noticed this noise when I swapped the 100k volume for the 1M. Until I did that the amp was very loud with the master on 2, so I keep wondering if the the volume pot really introduced the noise or if the volume drowned out/masked the noise (for lack of a better description).

I'm at my wit's end. What else should I check/do? I've read a lot of other posts with some great suggestions while other people were having problems so I know there's some pretty smart and experienced people here. Please take a minute and give me some ideas. I'm open to anything right now.

Questions;

1. I have a ground buss soldered to the back of the pots. Is there any chance I have a ground loop? I've done this tons of times before and not had this much noise.

2. Are these amps quiet when cranked, or even at moderate volume?

3. Does anybody know of a particular grounding issue with any of the nodes in this circuit. Anything out of the ordinary that's critical or troublesome?

4. I am using HAD's bias circuit off of one side of the HT like HAD did. As per my post above there is a 60Hz saw tooth wave form as ripple but it is less than half a percent of the rail, 1.3 volts p-p on a 400VDC rail. Is this something else, some other problem that might be caused by doing this, unbalancing the HT, etc.

5. My OT has what has been described to me as a "manufacturer's option" whereby the secondary colors are opposite the norm. During the last mod, I ended up with oscillation and I swapped primaries instead of the output secondaries. Is there any chance that this is causing the issue due some flux band or manufacturing technique of the OT? Any Fender experts around?
tictac
Posts: 610
Joined: Fri Mar 31, 2006 4:42 am

Re: Steel String Singer 002 Build - 60Hz Hum - HELP!

Post by tictac »

Ever thought about going to another location to try your amp just to rule out your home AC?

Seems like you're changing parts helter-skelter without knowing what the source of your problem is....

TT
Krinkle
Posts: 192
Joined: Sun Dec 09, 2007 4:51 pm
Location: Pickering, Ontario

Re: Steel String Singer 002 Build - 60Hz Hum - HELP!

Post by Krinkle »

I've been thinking that for a few days. That's why I tried the ground lifted AC power cable and the Humx. I may have to take it somewhere else.

Don't take this the wrong way because I'm being serious and I appreciate your reply. If I knew what my problem was I'd fix it. I say this with a straight face but that is the crux of my frustration.

I've had a reason for doing everything I've done. I'm just really frustrated man, I've built tons of amps and I'm usually able to track down issues and get rid of them.

Here's what I've done.

I changed the input jack because I have/had noise with no cable plugged in. It seemed to fix the problem, now it's back again. The input jack is a brand new Neutrik isolated jack, how can I still be getting noise with no cable plugged in?

I changed the filter cap in my bias circuit to a 47uF because I didn't have the same value as the schematic.

I added 10nF snubber caps across the PT diodes because of the 60Hz saw tooth waveform I saw when I scoped the bias line.

I used shielded cable on the input jack because the noise increases when I turn up the volume pot so it should be something before that in the circuit and it's the right thing to do.

I'm going to change the volume pot because I first noticed the noise when I swapped it in for the 100k as another poster said it was probably an error in the schematic.

I'm going to change the treble pot because it froze up on me when I tried to turn it down past 3 and it took me about 10 seconds to work the pot and get it to move. Now it feels funny when I turn it to 10, spongy, no click like the other pots.

I'm just trying whatever I can think of, if not, I'll just be sitting here playing a noisy amp.
bcook
Posts: 116
Joined: Sat Aug 05, 2006 12:16 pm

Re: Steel String Singer 002 Build - 60Hz Hum - HELP!

Post by bcook »

If you're using the heater circuit to power the relay circuit, you need to isolate the relay circuit completely from ground, including the ground return from the pedal jack.
Krinkle
Posts: 192
Joined: Sun Dec 09, 2007 4:51 pm
Location: Pickering, Ontario

Re: Steel String Singer 002 Build - 60Hz Hum - HELP!

Post by Krinkle »

Hi bcook, thanks for the reply. I disconnected the heaters like Lars suggested and I didn't hear a change in noise. But I think it's a good idea and worth trying. The noise gets amplified by the FET circuit, of course, but over the last couple of days I was thinking that it was maybe more than normal. I'm going to give it a shot.
Krinkle
Posts: 192
Joined: Sun Dec 09, 2007 4:51 pm
Location: Pickering, Ontario

Re: Steel String Singer 002 Build - 60Hz Hum - HELP!

Post by Krinkle »

Took the amp to my sister's house, no change.

Separated/isolated the relay ground from the rest of the FET circuit, no change. With the chassis out of the head to do the change, I checked and there is no noise with no cable inserted. I can get both volumes to 10 with only some hiss. I'm going to put the chassis back in the head case and if there is noise it has to be a clue as to what is happening.

If I can't figure anything out from that the only other thing I can think of is to remove the treble pot and rewire the ground buss to be on the pot lugs instead of the back of the pots.
markusw
Posts: 451
Joined: Tue Sep 26, 2006 5:10 pm
Location: Vienna/Austria

Re: Steel String Singer 002 Build - 60Hz Hum - HELP!

Post by markusw »

Krinkle wrote: Sun Mar 12, 2017 10:49 pm Took the amp to my sister's house, no change.

Separated/isolated the relay ground from the rest of the FET circuit, no change. With the chassis out of the head to do the change, I checked and there is no noise with no cable inserted. I can get both volumes to 10 with only some hiss. I'm going to put the chassis back in the head case and if there is noise it has to be a clue as to what is happening.

If I can't figure anything out from that the only other thing I can think of is to remove the treble pot and rewire the ground buss to be on the pot lugs instead of the back of the pots.

In your layout the 1M resistor to gnd at the imput jack is missing. Did you skip it?
If there us no noise with no cable inserted it might be that the guitar pickups pick up some hum? Might get better if you add the 1M resistor.
Krinkle
Posts: 192
Joined: Sun Dec 09, 2007 4:51 pm
Location: Pickering, Ontario

Re: Steel String Singer 002 Build - 60Hz Hum - HELP!

Post by Krinkle »

Hi markusw. That's an omission in the layout, the 1M is there. Last night I was doing some critical listening and I think the problem is in my FET circuit. With no cable inserted, there is noise when I turn the volumes to 10 but it's not that much and could probably call it normal. The problem occurs when I engage the FET circuit. The noise gets amplified a lot, and I don't think it is proportional to the signal increase, I think more noise may be introduced. I separated the relay ground from the signal ground and during normal operation the relay uses the normally closed contacts so I only power the relay coil when I engage the FET circuit. I'll grab a clean boost pedal tonight and see if I get the same noise with a similar amount of boost. Thanks for the reply.
Krinkle
Posts: 192
Joined: Sun Dec 09, 2007 4:51 pm
Location: Pickering, Ontario

Re: Steel String Singer 002 Build - 60Hz Hum - SOLVED

Post by Krinkle »

After scoping, shorting points in the circuit, and listening with my cab plugged in, I was able narrow it down to the 100pF cap at the gate of the FET. The high impedance there is a pretty good antenna in my tight Bassman conversion.

Even though my PCB layout is good, IMHO, I still ended up having to lift the 3M3, 100pF, 1M and the gate and solder them together leg to leg. Now the amp is buzz free.

My Strat has the Suhr BPSSC on it and I'm only getting a little single coil noise, depending on where I am in the room and the position of my Strat relative to the amp. I can easily move or turn and get zero single coil noise. I crank the volume and level and I have a minimal amount of background hiss, actually very quiet.

OK, time to create a thread on why my Deep switch does nothing.☺
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