Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: rdh001 on December 11, 2015, 06:35:57 pm
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I'm looking for a schematic/layout which utilizes mixable bright and normal channels, with a single common tone. Like the BC Audio No7 or Dr Z Remedy. But not the interactive thing the 5E3 has. Does anybody have a circuit with this setup?
Thanks.
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What you are describing sounds like a any early Marshall with jumpered inputs? I believe the Remedy is based on in this. Doug even has a 6V6 version. This could very easily be reproduced internally if needed.
Jim
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Thanks, Jim. yes, sort of like an internally jumpered Plexi, but I don't want the full TMB tonestack, and I'm not sure if the cathode follower is necessary if a single tone control is used instead of the full tone stack. I was hoping somebody with good knowledge might have done a tested schem/layout mixing the normal/bright channels into a single tone, so that I could see how it would be done. Limited skills, here <g>.
Thanks,
Bob
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Check out Slucky's Dual Lite, that would sound interesting! Maybe he will jump in here.
Jim
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It looks like bc audio uses Vox type Cut control as a tone control:
http://www.harmonycentral.com/forum/filedata/fetch?id=31130182&d=1398382836 (http://www.harmonycentral.com/forum/filedata/fetch?id=31130182&d=1398382836)
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Thanks, guys.
Jim, Sluckey's dual lite does look interesting, but I'm sporadically working on rebuilding something into a blues junior chassis, so I have constraints there, and I really wanted to try the two volume/one tone thing. Thanks for the heads up.
VMS -- thanks. So what I was thinking of as a tone control is actually working on the power amp, not mixing two channels into one tone pot in the preamp.
Appreciate the help.
Bob
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So what I was thinking of as a tone control is actually working on the power amp, not mixing two channels into one tone pot in the preamp.
Have you ever played a non-master volume Marshall (reissue or otherwise)?
I used to own a '73 50w Marshall, and played a Strat exclusively at the time. The Normal channel was mud while the Brilliant channel was too shrill to use. The answer for most players in my situation was to jumper the channels externally and balance the two volume controls as a form of tone control prior to the actual tone stack. Worked quite well.
I've never played a BC Audio, but notice the No 7 has 1 input jack and 2 volume controls. With the chassis picture linked earlier, the input stages look similar but the Bright volume has a bright cap and a small cap bypassing its mix resistor (which also brightens that channel).
I'd submit there are 3 tone controls in this amp: The volume controls are your basic means of balancing low/high, while the "presence" control just tims off the highest highs if you choose to smooth the sound going into the output tubes. There's no big midrange cut here (you could add a fixed notch in an amp with a bridged-T filter).
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Hi HBP,
Yes, I first played Marshall's, in the UK, back when the earth was still cooling. Or the 60's. at least. Seems like the same thing. No master volume at that time. Then I bought a 100-watt HiWatt double 4x12 stack when they first appeared. Then a Fender Dual showman with an additional cab with ElectroVoice 12's. Then I thought I'd quieten it down (ha ha) with two AC30s, one top boost and one non. And so on, through my variation of the path we have all taken.
Using the two volume controls for a basic tonal balance is exactly what I had in mind. I thought the two amps I mentioned followed their mixed bright and normal channels with a single tone control, but I couldn't find a circuit like that. I was thinking of voicing the two channels differently, and mixing them through individual volume controls into one overall tone control.
I was looking at the Dirty 18, a variant of the 18 Watt Lite which has only 2 12AX7s, and runs V1a into V1b through a volume control, and on to v2 for the PI. I was thinking of trying to add switching to that, so that one way it is cascaded as above and the other way switches to running V1a and V1b in parallel with the 2 vol/one tone thing.
There's another 18 Watt lite variant which has only 2 12AX7s run in parallel into V2 for the PI. So I figured both series and parallel are possible with just 2 12AXs so it seemed possible to combine them.
Clearly, I'm no expert. I built a few kits and I'm just trying to go a step further and figure out how to put stuff together.
Thanks,
Bob
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Bob
Haha! When the earth was cooling :l2:... You sound like my kids describing me! Sounds like you went through a few musical phases in your career? Yeah I had two small box 50s that I jumpered. I never jumpered the Major back when I played out but I am now. It seems when you play below the pain threshold it sounds a lot better and more rounded - for lack of a better description.
Jim
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I think what you should decide is whether you need control over midrange (scoop vs no scoop).
The circuits you're familiar with using (and apparently contemplating) leave mids uncontrolled. A variable mid-scoop can be some with a bridged-T filter with a rheostat to ground. But your tradeoff might be losing the Cut control late in the amp circuit to tame fizzy highs...
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Jim,
Yeah, more ups and downs than a fiddler's elbow. I went from all that big stuff to a period when I played mostly a Deluxe Reverb, and my 'big amp' was a Vibrolux Reverb. I've gone the other way altogether nowadays and I do my gigs mostly with a 5E3. I put a Celestion Gold in it and, in smaller places, I don't even have to mic it up.
HBP
Thanks for the ideas. I googled 'bridged-T filter' but I can't say I understood what I found -- even RG's usual thorough explanation didn't get through. I hadn't thought of it in the terms you are suggesting. I have a couple of amps which have just volume and tone controls and I have been OK with that. I tweaked the bypass and coupling caps (and tried half-a-dozen different speakers) and was able to arrive at a voicing I am happy with, without thinking much about the mids specifically.
Appreciate the help.
Bob
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Take a look at Hoffman's Stout. It may be a good basis for what you want. It already has v1 in cascade. You just have to do some switching to get to parallel mode. Might be easier to just add another tube.
http://el34world.com/Hoffman/files/Hoffman_Stout.pdf (http://el34world.com/Hoffman/files/Hoffman_Stout.pdf)
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Thanks Sluckey.
I'm looking at that now -- that is a good basis, it looks similar in concept to the Dirty 18 I mentioned above. Assuming I could work out the switching to parallel, with a volume for each channel, where I'm struggling is how to mix the two volumes through a common tone.
Can you expand a little on what you are seeing -- how adding an extra tube would make it easier?
Thanks,
Bob
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Here is a good tone control page:
http://chasingtone.com/yourguitaramp/guide-to-single-knob-tone-controls/ (http://chasingtone.com/yourguitaramp/guide-to-single-knob-tone-controls/)
And here is an crude example of plexi front end into tweed deluxe power amp with two tone options from above page.
Not sure if these would work but hopefully someone will chime in.
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That's really helpful, VMS -- thanks. It looks to me like the top one -- 'A' -- is doing what I am looking for. If the front end of your drawing 'A' works with the power section in the Hoffman Stout, that looks like what I am after.
Thanks again -- appreciate it.
Bob
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Both the Ax84 November and Swamp thing have single input with hi/low mixable triode stages.
I build my Swamper amp using that principle as well.
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Bob
Haha! When the earth was cooling :l2: ... You sound like my kids describing me!
Yeah I had two small box 50s that I jumpered. I never jumpered the Major back when I played out but I am now.
Jim
:w2: ? You're still playing these days?
Here is a good tone control page:
http://chasingtone.com/yourguitaramp/guide-to-single-knob-tone-controls/ (http://chasingtone.com/yourguitaramp/guide-to-single-knob-tone-controls/)
It's been a while since I've seen those... anyway, why not make it interesting and use a paralleled triode (upping the gain a bit closer to the pentode) paralleled with a pentode, then the CF > tone stack > PI > PA section?
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MFowler, thanks very much for providing those pdf links -- really helpful.
jojokeo, nice idea, I wish I was good enough to just run with an idea, but I don't have the design chops to get too far away from stuff that's already been done and proven.
Thanks, guys.
Bob
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you could use a VOX bright and normal channel parallel. mix both tone controls trough a 220K before they go into the PI
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Thanks, birt, I'll check that out.