Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Bieworm on June 14, 2022, 01:54:33 am
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hi guys
I plan on building the TH30 soon. But I'd like to build only the clean channel and want to ommit the effects loop.
Is leaving out the effects loop going to impact the sound? It's tube buffered, and a substantial part of the circuit. Or shouldn't I worry about that?
thanks
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I think it will work, with some caveats. I'm not the guru here, but it looks like a straightforward amp in the absence of the effects loop (with of course your four glorious EL84 output tubes).
I assume you are looking for a very clean sound here. Your signal into the PI will be attenuated by your tone stack, and to me it will be anemic.
Personally, I'd suggest adding a gain stage and a Master Volume similar to Doug's BJ Conversion schematic -- this is a proven design and works well, even with a slightly altered tone stack as in your schematic.
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I think it will work, with some caveats. I'm not the guru here, but it looks like a straightforward amp in the absence of the effects loop (with of course your four glorious EL84 output tubes).
I assume you are looking for a very clean sound here. Your signal into the PI will be attenuated by your tone stack, and to me it will be anemic.
Personally, I'd suggest adding a gain stage and a Master Volume similar to Doug's BJ Conversion schematic -- this is a proven design and works well, even with a slightly altered tone stack as in your schematic.
Thanks. It's for a friend and he wants a clean pedal platform. He owns a TH30 at the moment but he wants a smaller lighter combo with less features. The OD channel is not requested for he uses only pedals for that.
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+1 for the extra triode stage after the tone stack.
It won't be an "orange" anything after that really, but close enough to have a conversation about it being a modded version of something-or-other.
It'll be one heck of a clean, stompbox friendly tube amp !
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+1 for the extra triode stage after the tone stack.
It won't be an "orange" anything after that really, but close enough to have a conversation about it being a modded version of something-or-other.
It'll be one heck of a clean, stompbox friendly tube amp !
Well it's not my call. My friend wants it that way. I just wonder if deleting the FX loop circuit is going to have impact on the sound. Otherwise it's totally wasted space and parts.. he doesn't use the loop...
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Well it's not my call. My friend wants it that way.
I love it when (usually ill-informed) customers tell me how to do my job. :icon_biggrin:
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I'm not hating on it at all. Sounds like a good custom project 😀
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Well it's not my call. My friend wants it that way.
I love it when (usually ill-informed) customers tell me how to do my job. :icon_biggrin:
Lol.. but the guy already has a TH30 head + cab and uses only the clean channel.. and he's getting lazy. So ge knows what he wants. FWIW I always voice my amps for OD
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+1 for the extra triode stage after the tone stack.
It won't be an "orange" anything after that really...
Why not? The schematic in the first post shows a scratched-out gain stage on the effects loop return. It seems to me like that gain stage is essential for this amp to sound like it's supposed to. Granted, the cathode follower has a resistor divider to knock down the volume on the send, but there is much more gain on the return (56k / 1k5 = approx. 37:1) than there is loss on the send (4k7 / (4k7 + 15k) = approx. 1:4).
With the restored/added gain stage, all that's being left out is the cathode follower, but there's a leftover triode anyway, so it's not like leaving that out is of any particular benefit. If it were me, and I really wanted to keep the tone of the amp, I'd just build it as-is but without the loop jacks and extra pulldown resistors and coupling caps.
Unless someone's got a better idea for that cathode follower triode. :icon_biggrin:
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Put a cathode follower to drive the tone stack and you have almost have a jtm45 front end.
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You could borrow his existing amp and take some voltages, make a quick mod to test it without the effects loop in circuit and see what it's like. There is opportunity in the first 2 triodes to get some more gain, but I would think the effects loop does alter the sound for sure.
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The first triode in blue (12AT7) that is scratched out is not just a piece specific to the loop - that's why there's some dubious reactions to your schematic. You should keep that one, and get rid of the rest of what is highlighted. That's a post-EQ recovery stage as well as the buffer to the FX loop send. You'll want it even without an FX loop.
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Hi Bieworm,
If you go down the jbr... track, you may need to adjust the values of R55, R56. (Good Suggestion jbr :icon_biggrin:)
I have used this same stage in the past, with great results and gives you the opportunity to calibrate the signal to the input to PA (PI Input).
Regards
Mirek
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hi guys
I plan on building the TH30 soon. But I'd like to build only the clean channel and want to ommit the effects loop.
Is leaving out the effects loop going to impact the sound? It's tube buffered, and a substantial part of the circuit. Or shouldn't I worry about that?
thanks
A couple other items of interest I don't think have been stated yet, R34 and 35 are a voltage divider that dumps half the signal going to the tone stack. You can remove them for more gain up front. (Depending on layout, can keep 100K or so as a grid stopper, but not essential)
The 500K volume pot can be changed to 1M, which also retains more gain from the first stage.
These things will impact the sound with the volume turned up. with those changes, it is essentially a standard low gain TMB preamp topology like a fender A763 but with different tone stack values into the el84 based PI and power section.