Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: owen on December 06, 2020, 09:34:00 am
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hi all. the 6g2 is the first amp i've built. sounds great but the tremolo is pulsing when the volume pot is at zero.
once i turn the volume pot up 1/16th of a turn or so it sounds scratchy at first, but past that 1/16th once signal from the input comes through, all noise goes away and the amp sounds lovely.
any suggestions on where to begin troubleshooting?
i swapped volume pots but the brand new one does the same thing.
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I'd begin on three. :icon_biggrin:
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I'd begin on three. :icon_biggrin:
unfortunately 3 is way too loud for my apartment.
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Can you provide a bit more info? Is the trem pulse more than barely audible? Does it do it with the trem turned off? Does the noise go down when you turn up the amp, or does it just get drowned out? Scratchy - when turning the pot? Or a constant scratchy sound?
Did you follow the schematic exactly, or is it modded? BTW - despite it being a lower power Fender the 6G2 is pretty darn loud! I built one and am surprised how loud it is.
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OK, so much for my seemingly smartass reply. Sorry. But when you say, "but past that 1/16th once signal from the input comes through, all noise goes away and the amp sounds lovely.", I have to reply, "You don't have a problem."
I think you just need to understand how that tremolo circuit works. That trem circuit varies (or pulses) the output tube bias to produce the tremolo effect. This action continues regardless of the volume control setting. The only way to stop the pulsing is to turn the tremolo off. Sometimes just turning the INT to zero will kill it, but often you have to kill the trem oscillator with the footswitch. So, if you are in a situation such as a church where you need the volume set on zero during prayer, then step on the footswitch also.
There is a trade-off between great sounding tremolo and output tube bias settings. Just as the trem circuit varies the bias voltage to produce the effect, changing the bias setting will also affect the tremolo. But your amp has no bias adjustment so there's nothing you can do, unless you want to install a bias pot. If that appeals to you, just copy Hoffman's Princeton Reverb circuit. Easy mod.
You can also install a diode across the INT pot if the trem pulsing borders on thumping or speaker pumping. Or use a less sensitive speaker. But really, I just think you need to get to know your amp. 1/16th turn is nothing. :wink:
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I'd begin on three. :icon_biggrin:
unfortunately 3 is way too loud for my apartment.
As an apartment dweller, I found my guitar's Volume control very handy in these situations. Sounds silly, but I had a vintage Deluxe Reverb, didn't want to modify the amp by pulling the bright cap, and usually played the amp on 7-8 (even a midnight) to overcome the bright cap's effect. I kept from being evicted by turning the guitar's volume knob way-down. It worked perfectly, and sounded terrific.
hi all. the 6g2 is the first amp i've built. sounds great but the tremolo is pulsing ...
If the pulsing noise only happens with the Volume control very low, perhaps don't keep the Volume control very low.
That said, I've had 2 different brown Deluxes (a '62 and a '63), and both had pulsing noise. There do seem to be some tricks to reduce that pulsing noise (https://www.thegearpage.net/board/index.php?threads/brownface-fender-deluxe-6g3-vibrato-thumping.2206290/) in these amps (which probably apply to the 6G2 Princeton as well). In my case the noise never bothered me while playing, so I left my amps as-is.
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There is a trade-off between great sounding tremolo and output tube bias settings. Just as the trem circuit varies the bias voltage to produce the effect, changing the bias setting will also affect the tremolo. But your amp has no bias adjustment so there's nothing you can do, unless you want to install a bias pot. If that appeals to you, just copy Hoffman's Princeton Reverb circuit. Easy mod.
Sluckey's suggestion is part of the reason I asked if the amp you built was straight stock. Many people, including me, install adjustable bias in their builds of this amp. It allows you to dial in the "sweet spot" on that trade-off. I found the stock bias settings to be very conservative to allow for the variance in the world of 6V6 power tubes. Adjusting the bias has a very noticeable affect on pulsing.
There are some past threads on this subject - both for the 6G2 and the 6G3 which has a similar bias/trem circuit.
Also wondering about that "scratchy" thing. Dirty pot, but you replaced it? DC voltage on the pot?
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that might be trem thump. my 6g2 had the same problem. did you install a footswitch jack? i did not on mine and got that thump. the diode mod sluckey is talking about fixed it for me. i also did the slower trem mod changing all 3 ceramics caps of the tremolo to .02
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I thought it might be helpful to check out mine. Built stock with the exception of adjustable bias, twisted pair heater wiring, and adjustable negative feedback. Trem footswitch off - very quiet amp. Footswitch on - subtle pulse with vol down. Pulse goes away around 3 (go figure.) With trem on there is a very slight noise as the vol knob comes off zero. I never noticed this before, but it is not a scratchy sound that remains.
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Can you provide a bit more info? Is the trem pulse more than barely audible? Does it do it with the trem turned off? Does the noise go down when you turn up the amp, or does it just get drowned out? Scratchy - when turning the pot? Or a constant scratchy sound?
Did you follow the schematic exactly, or is it modded? BTW - despite it being a lower power Fender the 6G2 is pretty darn loud! I built one and am surprised how loud it is.
with all knobs down to "zero", the tremolo comes through despite intensity being rolled all the way down.
turning the volume up the pot sounds like it's scratchy briefly just before you start to hear actual guitar sound come through, then it all works as it should. the scratchy sound stops if i stop turning it, but will resume if I turn the pot to audible guitar level. I'll try to take a video tomorrow, the draconian HOA rules force me to keep it quiet, however.
turning the amp volume up to max, though, there is no trem noise with intensity at zero. only on the beginning of the volume pot rotation.
we're locked down and my DMM is at work so I'll have to see if I can scrounge up another.
the amp is built to the schematic; only raising power handling of some resistors and higher voltage caps of course. funnily enough, I ran wires to the rear of the chassis to install a bias pot soldered to themselves, but in checking the bias it was actually dialed in so well after building i shortened that wire and kept it stock to the intensity pot.
I didn't want to possibly alter the tremolo sound by adding adjustable bias, I wanted to hear what stock was like first.
I recapped a real brown princeton a couple years ago for a friend and I don't recall it doing this, but if it's a common occurrence I feel a little better about it. My concern is something like DC leaking which I'll check when I get another meter here.
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I thought it might be helpful to check out mine. Built stock with the exception of adjustable bias, twisted pair heater wiring, and adjustable negative feedback. Trem footswitch off - very quiet amp. Footswitch on - subtle pulse with vol down. Pulse goes away around 3 (go figure.) With trem on there is a very slight noise as the vol knob comes off zero. I never noticed this before, but it is not a scratchy sound that remains.
that sounds very similar, thanks for checking! the scratch in mine is just for a brief moment between the tremolo pulse going away and guitar becoming audible.
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that might be trem thump. my 6g2 had the same problem. did you install a footswitch jack? i did not on mine and got that thump. the diode mod sluckey is talking about fixed it for me. i also did the slower trem mod changing all 3 ceramics caps of the tremolo to .02
after checking for DC leak when I can, I'm going to swap the trem caps, definitely want a slower speed. The super i'm building requires the 4meg pots which I have to replace with 3m so will need to slow that down quite a bit too.
it does have a jack, I didn't short it to check but will tomorrow.
thanks for the suggestions