Troubleshooting

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mkel2010
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Troubleshooting

Post by mkel2010 »

I'm still trying to chase down some minor issues with noise coming from my 18 watt build. I've come to the conclusion that I probably need an oscilloscope and signal generator to do it properly.

In researching entry level scopes, I came across the Hantek DS02D10 which has a built-in arbitrary waveform generator. Based on what I've read and looking at the specs, it seems to be adequate but I wanted to get some opinions here first. The whole setup being under $300 puts it within my budget.

Here's a link to it on Amazon:

https://www.amazon.com/Hantek-DSO2D10-B ... 628&sr=8-4

And a link to the info on the manufacturer's web site:

http://hantek.com/products/detail/17182

I'd appreciate any comments or recommendations.

Mark
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JMPGuitars
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Re: Troubleshooting

Post by JMPGuitars »

I would avoid that one. Take a look on my amp tools page for suggestions: viewtopic.php?f=25&t=25173

Take a look at this scope: https://www.amazon.com/Siglent-Technolo ... 01J1MQC3G/

And for the AWG, look at the Tenma 72-505, or Uni-T UTG932E. Don't buy either on Amazon. They're both available much cheaper from other sources. I think I paid about $30 for my Tenma from Newark or somebody like that. And you can find the UTG932E under $100 from alibaba or other sources.

What are the issues you're currently having with your amp?

Thanks,
Josh
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mkel2010
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Re: Troubleshooting

Post by mkel2010 »

JMPGuitars wrote:
Fri 04/30/21 6:14 am
I would avoid that one. Take a look on my amp tools page for suggestions: viewtopic.php?f=25&t=25173

Take a look at this scope: https://www.amazon.com/Siglent-Technolo ... 01J1MQC3G/

And for the AWG, look at the Tenma 72-505, or Uni-T UTG932E. Don't buy either on Amazon. They're both available much cheaper from other sources. I think I paid about $30 for my Tenma from Newark or somebody like that. And you can find the UTG932E under $100 from alibaba or other sources.

What are the issues you're currently having with your amp?

Thanks,
Josh
Josh,

Thanks for the recommendations. I found a US seller who has the UTG932E as an open box for under $100. Alibaba's listings are all over $100 with a 1 month+ wait time.

The amp has had white noise or hiss issues since I built it. When both volume and gain were maxed on either channel, the noise ended up overpowering the guitar. Carbon composition resistors were provided with the kit and I have since changed the 1M input resistors and the 100k V1 plate resistors with metal film. I also have replace the mixed-brand tubes I originally bought with all JJ tubes. I reflowed some of my solder joints that looked questionable.

All of that helped reduce the hiss to the point where it doesn't start to overpower the guitar until both the volume and gain on the TMB channel are over half; on the Normal channel I need to get both volume and tone over half to get to the point where the hiss overpowers the guitar. The hiss is present even without anything plugged into the input jacks; it goes away completely on the Normal channel when the V1 tube is removed but is greatly reduced on the TMB channel, only becoming really noticeable when gain and volume are maxed. Since I made the changes to the resistors, I've also started to get a random popping noise from the Normal channel that I have not yet had with the TMB channel. Hopefully my explanation makes sense.

Mark
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Re: Troubleshooting

Post by JMPGuitars »

mkel2010 wrote:
Fri 04/30/21 11:05 am
Josh,

Thanks for the recommendations. I found a US seller who has the UTG932E as an open box for under $100. Alibaba's listings are all over $100 with a 1 month+ wait time.

The amp has had white noise or hiss issues since I built it. When both volume and gain were maxed on either channel, the noise ended up overpowering the guitar. Carbon composition resistors were provided with the kit and I have since changed the 1M input resistors and the 100k V1 plate resistors with metal film. I also have replace the mixed-brand tubes I originally bought with all JJ tubes. I reflowed some of my solder joints that looked questionable.

All of that helped reduce the hiss to the point where it doesn't start to overpower the guitar until both the volume and gain on the TMB channel are over half; on the Normal channel I need to get both volume and tone over half to get to the point where the hiss overpowers the guitar. The hiss is present even without anything plugged into the input jacks; it goes away completely on the Normal channel when the V1 tube is removed but is greatly reduced on the TMB channel, only becoming really noticeable when gain and volume are maxed. Since I made the changes to the resistors, I've also started to get a random popping noise from the Normal channel that I have not yet had with the TMB channel. Hopefully my explanation makes sense.

Mark
Ah, I guess the prices went up since I got mine (though I did pay around that because I was impatient). You might want to search for the UTG962E, as they were similar in price (962 is 60Mhz max, instead of 30Mhz).

JJ tubes are trash, and could be contributing to the problem. Try some new production Mullard or TungSol tubes. I would replace the tubes, and not make too many crazy changes before then.

If you haven't already, take a look at the solder technique and ground scheme threads in my signature.

Posting some photos of the current state of your build might also be helpful, and some accurate voltages.

In general with this kind of issue, you would want to look at least at your lead dress, solder joint quality, tube quality, and tube socket quality. If you have an extra socket, you could try replacing the socket for V1, after (re)watching the solder technique video.

Thanks,
Josh
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mkel2010
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Re: Troubleshooting

Post by mkel2010 »

JMPGuitars wrote:
Fri 04/30/21 12:19 pm
Ah, I guess the prices went up since I got mine (though I did pay around that because I was impatient). You might want to search for the UTG962E, as they were similar in price (962 is 60Mhz max, instead of 30Mhz).

JJ tubes are trash, and could be contributing to the problem. Try some new production Mullard or TungSol tubes. I would replace the tubes, and not make too many crazy changes before then.

If you haven't already, take a look at the solder technique and ground scheme threads in my signature.

Posting some photos of the current state of your build might also be helpful, and some accurate voltages.

In general with this kind of issue, you would want to look at least at your lead dress, solder joint quality, tube quality, and tube socket quality. If you have an extra socket, you could try replacing the socket for V1, after (re)watching the solder technique video.

Thanks,
Josh
Following your suggestions, here is what I did:

I replaced the JJ in V1 with a Mullard new production CV4004, with no change in the hissing. Prior to that, while getting new voltages, I chop-sticked around and discovered a loose wire on one of the output tubes that was likely the cause of my intermittent popping - now fixed. I wasn't able to generate any new noises or changes with the chop stick until I got to V1. The sound I got sounded like a ring, so I tapped on the tube and got the same ring. I swapped a series of different 12AX7 tubes into that position - and got the same ringing on each one but moving them to V2, the ringing went away. Would a bad socket cause this or could it be something else?

Here are the voltages:

Mains: 121.6
B+ w/Tubes: 355

V1: 145
.95
144.7
.95

V2: 156.3
1.18
257
156.6

V3: 206
51.8
74.8
207
52.8
75

V4: 12
344
333

V5: 12
343
333

V6: 301
355
301

Below are the current pics of the insides.

Mark
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mkel2010
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Re: Troubleshooting

Post by mkel2010 »

I put all my non-JJ tubes back in and the ringing on V1 went away. Not sure how that happens.

I was able to adjust the controls to reduce the white noise while playing except when I crank up the gain past about two thirds on the TMB channel and the volume above half. Even at lower gain levels I can get enough crunch for me at the moment. However, I'll take any suggestions on trying to get the white noise reduced with the gain and volume cranked up on the TMB channel.

Mark
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Re: Troubleshooting

Post by JMPGuitars »

Read or reread and the read my soldering thread again.

You have soldering issues all over. Solder joints should be smooth, shiny, and concave. They should have mechanical support. Your solder joints don't meat those standards, and that can certainly cause some of the problems you're describing. Carbon comps will add to any hiss, and then you have the combination of both.

Zoom in on your photos and tell me if you can see solder joints that are lumpy, dimply, or underdressed. Check and see if your bus wire has any mechanical support across the turrets. Now the bus you can get away with like that, but the soldering has to be better...and it still isn't ideal.

Hit up the soldering thread in my signature, watch the videos a few times, and start cleaning up the build. In the process of doing that, you will hopefully solve your issues.

You also need to read the grounding thread in my signature. I see a star ground near the input, with lots of wires run under the board. Those wires are antennas, just waiting to make things worse. Take a look at the layout in the ground scheme thread and compare that to yours. It doesn't matter that it's not the same circuit version, the theory is the same. I'm not sure what's going on with the pot wiring either.

I could be more nitpicky if you want, but it's bedtime. 😉

Take your time and enjoy the process of cleaning up the build. The only way to improve your soldering skills is to practice, and this should give you that practice. Clean the solder joints, don't just apply more solder. Excess solder makes things worse, not better.

Here's an example of one of my builds for comparison:
_JMP1283.jpg
I avoid the turret tops because wrapping the sides is a better mechanical connection (though the tops are fine with good soldering). The solder joints are smooth, shiny, and concave. There are only 3 ground points: IEC socket, Power Amp Star Ground, and Preamp Ground. Shielding gets its own connection to ground. Everything is done over the board, and wires are insulated. Mechanical connections galore.

Thanks,
Josh
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