Problem with Princeton build
Moderators: pompeiisneaks, Colossal
Problem with Princeton build
I built the Hoffman Amps Princeton Reverb circuit and have a issue where it has a really loud low frequency tone coming from it. Doesn't sound like typical 60 cycle hum. I can put an attenuator between the amp and speaker, set it to 50%, and the tone goes away and my guitar sounds really nice through it, but really loud, even on 1. Hoping someone might have some suggestions as to where to look. I've been through the wiring with a meter ohming everything out. Tried different tubes as well. Voltages all appear normal. Reverb and Tremolo work fine.
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Re: Problem with Princeton build
Sounds like positive feedback from the NFB loop (from OT secondary back to PI). To test, disconnect the NFB wire (yellow wire from output jack to brown resistor on board). If this solves the noise, then you need to swap your OT primary wires (brown and blue wires connected to pins 3 of your power tube sockets).
I build and repair tube amps. http://amps.monkeymatic.com
Re: Problem with Princeton build
May I suggest, while you have that yellow wire disconnected, replace it with a longer wire and route it so it doesn't pass so close to V3.
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Stevem
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Re: Problem with Princeton build
I would remove each preamp tube one by starting with V1 to see if without the attenuation that removing any one of them makes the issue go way.
This would at least prove out that the output stage is good.
I will also ask you to set your voltmeter for ac and report back as to what you have for ac ripple ( millivolts ) showing up on both pins 1 and 6 of V1.
This would at least prove out that the output stage is good.
I will also ask you to set your voltmeter for ac and report back as to what you have for ac ripple ( millivolts ) showing up on both pins 1 and 6 of V1.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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Stevem
- Posts: 4576
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Problem with Princeton build
I would remove each preamp tube one by starting with V1 to see if without the attenuation that removing any one of them makes the issue go way.
This would at least prove out that the output stage is good.
I will also ask you to set your voltmeter for ac and report back as to what you have for ac ripple ( millivolts ) showing up on both pins 1 and 6 of V1.
I would also ask that just for testing purposes you set the negative voltage on pin 5 of the output tubes to the highest ( most negative) it will go.
Also unplug your reverb tank for now and keep the reverb set to 0.
This would at least prove out that the output stage is good.
I will also ask you to set your voltmeter for ac and report back as to what you have for ac ripple ( millivolts ) showing up on both pins 1 and 6 of V1.
I would also ask that just for testing purposes you set the negative voltage on pin 5 of the output tubes to the highest ( most negative) it will go.
Also unplug your reverb tank for now and keep the reverb set to 0.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Problem with Princeton build
Reversing the OT wires fixed the issue. Sounds great now and very quiet. Thanks for the help.
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Stevem
- Posts: 4576
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Problem with Princeton build
Good news and a simple fix!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!