So, building a nice tube guitar amp for my father's birthday in March. He loves knobs, switches, and extra features, and from his "wish list" of features, I've decided on this so far. He will use it for playing at home, maybe at the occasional recording session, but no large venues.
He requested the 6v6 or el84, and since I've got a bunch of good 6v6 of various makes, I'll give him a dozen to roll in the amp. He also wants basic, easy to find common guitar amp type tubes, so 12ax7, 12at7, etc.
his desired features were-
Presence control (shouldn't be too hard to add since we are doing NFB anyway)
Master volume (at the output tube grids via stereo pot?)
Independent input stages (one is a classic one knob tone control, the other is a Treble, mid, bass style) with independent gain/volume each
Possibly add a switch to cascade the input stages. Allows for high gain and "crunch" (I take this to mean high gain that can be set to clip early for nasty distortion, from what I've been able to research)
Effects loop, (for use with effects pedals) bypassed with nothing connected, takes standard guitar cable. I'm unsure the best way to implement this. It wouldn't be to bad to leave it out if it's not worth the hassle.
Negative feedback with a switch for low or high amounts (just to tighten things up)
Triode/pentode switch (Not to be switched hot, of course)
Standby switch
Solid state rectifier, inline resistance for a bit of supply "sag" (easy, part of the PSU filtering that will be there anyway"
Sounds pretty straightforward, but I'm a Hi-fi guy so I'm sort of picking and choosing bits from various designs here. Any suggestions would be appreciated. I've built tons of tube gear before, but this will be my first guitar amp.
Here's the schematic I drew up to start with. do you think I will have enough gain? Should I drive the other tone control with a cathode follower, since I have the other Triode in the bottle anyway? Would a 12at7 or 12ax7 be a good choice in all preamp tube positions? My phase inverters most likely sit on a CCS to give better swing, balance, and headroom. If it does I'll probably try an lm334z or a discrete NPN "ring of two"
full size pic
Any constructive criticism would be appreciated.
He requested the 6v6 or el84, and since I've got a bunch of good 6v6 of various makes, I'll give him a dozen to roll in the amp. He also wants basic, easy to find common guitar amp type tubes, so 12ax7, 12at7, etc.
his desired features were-
Presence control (shouldn't be too hard to add since we are doing NFB anyway)
Master volume (at the output tube grids via stereo pot?)
Independent input stages (one is a classic one knob tone control, the other is a Treble, mid, bass style) with independent gain/volume each
Possibly add a switch to cascade the input stages. Allows for high gain and "crunch" (I take this to mean high gain that can be set to clip early for nasty distortion, from what I've been able to research)
Effects loop, (for use with effects pedals) bypassed with nothing connected, takes standard guitar cable. I'm unsure the best way to implement this. It wouldn't be to bad to leave it out if it's not worth the hassle.
Negative feedback with a switch for low or high amounts (just to tighten things up)
Triode/pentode switch (Not to be switched hot, of course)
Standby switch
Solid state rectifier, inline resistance for a bit of supply "sag" (easy, part of the PSU filtering that will be there anyway"
Sounds pretty straightforward, but I'm a Hi-fi guy so I'm sort of picking and choosing bits from various designs here. Any suggestions would be appreciated. I've built tons of tube gear before, but this will be my first guitar amp.
Here's the schematic I drew up to start with. do you think I will have enough gain? Should I drive the other tone control with a cathode follower, since I have the other Triode in the bottle anyway? Would a 12at7 or 12ax7 be a good choice in all preamp tube positions? My phase inverters most likely sit on a CCS to give better swing, balance, and headroom. If it does I'll probably try an lm334z or a discrete NPN "ring of two"
An externally hosted image should be here but it was not working when we last tested it.
full size pic
Any constructive criticism would be appreciated.
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Added link to full size pic.
I think the cascaded channels might be a bit much, but when prototyping I can decide whether or not to leave it out.
Would it be a good idea to drive the other tone control with a cathode follower? seems it wouldn't hurt. Might make it a bit easier on that input stage.
I think the cascaded channels might be a bit much, but when prototyping I can decide whether or not to leave it out.
Would it be a good idea to drive the other tone control with a cathode follower? seems it wouldn't hurt. Might make it a bit easier on that input stage.
Hi Lingwendil,
Copy the tone stack and input channels from a Fender Twin Reverb. You can use your 6V6 output stage instead of the 6L6GC monster that this amp is. You might have a look at some Fender P-P 6V6 amps and use that. What works in high end audio is exactly wrong for a guitar head. The resistor in the power supply was a good call.
Why a Fender Twin? Because it can go from clean to dirty and everything in between. In the hands of a good guitarist, he can get any sound he's looking for (unlike a Marshall).
-Chris
Copy the tone stack and input channels from a Fender Twin Reverb. You can use your 6V6 output stage instead of the 6L6GC monster that this amp is. You might have a look at some Fender P-P 6V6 amps and use that. What works in high end audio is exactly wrong for a guitar head. The resistor in the power supply was a good call.
Why a Fender Twin? Because it can go from clean to dirty and everything in between. In the hands of a good guitarist, he can get any sound he's looking for (unlike a Marshall).
-Chris
Is there a schematic around without the reverb circuitry? It's a bit hard to wrap my head around to chop it out.
He is an insanely skilled guitarist and luthier, and likes to play around for his own unique style. also plays on the worship team at church with a metalhead grimmace on his face.
Without simply copying another schematic, what modifications would you suggest to what I put together? He requested the separate inputs and tone controls for the ability of switching between them, so I'm not keen to simply copy over something else, he doesn't really want a chopped and spliced existing design, he wants something different
I can lose the CCS and just sit it on a tail resistor. This should give back a bit more compression, and unbalance the splitter a bit, right?I also considered something based on a "lite" marshall 18w clone, with TMB tone and 6v6 outputs, I built one with 6v6 outputs a while back on commission and my father did the "shred test" and loved it, just wanted the additional switchable tone control input. He lives in Washington now so a bit harder to swap topologies around and have him test it
This will be his only tube head for a while, so that's why he wants it his way. he'll probably have me build another after he lives with it and gives feedback on the features he doesn't use, or at least that's the plan.
Is this the schematic you mean?
Hi Lingwendil,
That's the monster. To delete the reverb, just lose the wire to the grid of V3 and the pot coming off the 7025 (=12AX7A). But, if you left the circuit in, you could add the reverb tank later. They use RCA jacks. It's a straight plug in and go. The vibrato uses a cds cell and a neon lamp in a tube where light is blocked off. You can delete that too. Just ignore the connection to the balance control from the vibrato circuit. You can experiment with tone stacks, but I think the one the Twin uses is an excellent starting point. If he's good with a guitar, he would absolutely love something like a low powered Fender Twin. I think they also made a Twin bassman. Just look at the different tone stacks until you get the idea. BTW, Marshall ripped off the Fender design but messed up on the tone stack. The only effective thing a Marshall has going for it is it does "crunch" well. Fenders can cover a much wider range of effects than the Marshall. One of my favorite amps in the hands of a master.
-Chris
That's the monster. To delete the reverb, just lose the wire to the grid of V3 and the pot coming off the 7025 (=12AX7A). But, if you left the circuit in, you could add the reverb tank later. They use RCA jacks. It's a straight plug in and go. The vibrato uses a cds cell and a neon lamp in a tube where light is blocked off. You can delete that too. Just ignore the connection to the balance control from the vibrato circuit. You can experiment with tone stacks, but I think the one the Twin uses is an excellent starting point. If he's good with a guitar, he would absolutely love something like a low powered Fender Twin. I think they also made a Twin bassman. Just look at the different tone stacks until you get the idea. BTW, Marshall ripped off the Fender design but messed up on the tone stack. The only effective thing a Marshall has going for it is it does "crunch" well. Fenders can cover a much wider range of effects than the Marshall. One of my favorite amps in the hands of a master.
-Chris
I disagree. When you think of R&R you never think if a Twin Reverb. By that time Leo finally got what he was after all these years, a clean machine. He achieved this by running the preamps at a high voltage and scouping out the mids. Didn't hurt any that the scouped sound went well with his Telecasters and Strats. Marshall took his 59 Bassman circuit and copied it but subbed with parts that he could get locally. That and a few tweaks and we have the classic Marshall sound. Mind you a lot of that comes from the speakers also.
There are a few ways of changing the distortion characteristics of an amp. Cold or hot bias the triodes, raise or lower the supply voltage for the stages. The PI can modify things by being a little unbalanced. The tail resistor is used to increase or decrease the balance, it also soaks up voltage causing the PI stage to run out of headroom. The cathode follower also contributes by not doing its job properly. Swap in a Mosfet and it does a great job of feeding the tonestack but cleans things up when we don`t want it to.
The power supply can also be loose or tight and when the amp is driven hard, Class AB not Class A, you get a little compression. Bias shifts also ad an element of fun and not to forget blocking distortion. Each little design choice adds its part but on its own normally does not contribute a big difference to the sound.
I had a student once that wanted to design guitar amps. I said much of what can be done has been tried at some point in time. Years latter I met him and he agreed with me. Nothing wrong with picking up where others spent a lot of time trying to get the sound that they wanted. Or you could put in all kinds of time till you get to know how to get the balance of sound you want.
There are a few ways of changing the distortion characteristics of an amp. Cold or hot bias the triodes, raise or lower the supply voltage for the stages. The PI can modify things by being a little unbalanced. The tail resistor is used to increase or decrease the balance, it also soaks up voltage causing the PI stage to run out of headroom. The cathode follower also contributes by not doing its job properly. Swap in a Mosfet and it does a great job of feeding the tonestack but cleans things up when we don`t want it to.
The power supply can also be loose or tight and when the amp is driven hard, Class AB not Class A, you get a little compression. Bias shifts also ad an element of fun and not to forget blocking distortion. Each little design choice adds its part but on its own normally does not contribute a big difference to the sound.
I had a student once that wanted to design guitar amps. I said much of what can be done has been tried at some point in time. Years latter I met him and he agreed with me. Nothing wrong with picking up where others spent a lot of time trying to get the sound that they wanted. Or you could put in all kinds of time till you get to know how to get the balance of sound you want.
Hi Printer2,
Why I was recommending the Twin was because it is so versatile with the sounds you can get out of it. There are many guitar teachers using these personally. With the Marshall you are getting basically crunch and a tone stack he made a mistake on.
More than one guitarist has said to me over the years that a low powered Twin (any one of the twin models) would be the perfect practice amplifier. These comments stuck with me, and this would seem to be that perfect project. I was designing this kind of amplifier for my daughter before her kids came along. I'll still finish it because I think that when she has time, this would be perfect. Grown up tone stack and features along with a EL84 P-P output stage that would be good enough for a small venue. I've had some great guitarists move from style to style, including R & B on these amplifiers, just tweaking the controls a touch to get those different sounds. They even do clean really well. Having heard this several times, I can't help but to recommend this direction for the OP. Look at the Twins and lower powered amplifiers and take what you need for your own design. After all, that's what Marshall attempted to do in the first place.
-Chris
Why I was recommending the Twin was because it is so versatile with the sounds you can get out of it. There are many guitar teachers using these personally. With the Marshall you are getting basically crunch and a tone stack he made a mistake on.
More than one guitarist has said to me over the years that a low powered Twin (any one of the twin models) would be the perfect practice amplifier. These comments stuck with me, and this would seem to be that perfect project. I was designing this kind of amplifier for my daughter before her kids came along. I'll still finish it because I think that when she has time, this would be perfect. Grown up tone stack and features along with a EL84 P-P output stage that would be good enough for a small venue. I've had some great guitarists move from style to style, including R & B on these amplifiers, just tweaking the controls a touch to get those different sounds. They even do clean really well. Having heard this several times, I can't help but to recommend this direction for the OP. Look at the Twins and lower powered amplifiers and take what you need for your own design. After all, that's what Marshall attempted to do in the first place.
-Chris
Tell that to
Ted Nugent:
https://www.youtube.com/watch?v=HXq73BP5uv4
Anvil:
https://www.youtube.com/watch?v=jDC2e6i6Quw
and MANY others.
Just going by the dad's request for a crunch channel. A Marshall does clean up also, just back off on the gain. As far as the tonestack goes, sure you could put the Blackface values in, just depends on what you are going for.
https://www.youtube.com/watch?v=3ShCv-AEFCQ
Have a cousin that played guitar, I did some sound duty for the band. He had a Twin, I know quite well what they are capable of. Still think the BF amps don't quite do rock well enough. Skipped through a little of Ted, haven't heard some of the songs for must be 35 years or more. Actually he sounds pretty clean to me, just lot of volume causing sustain. The Anvil, not my cup of tea. Still think of all the rock records that came out, not much BF Fender there, the tweeds maybe. But that is really what a Marshall is, a slightly hotter Bassman.
https://www.youtube.com/watch?v=3ShCv-AEFCQ
Have a cousin that played guitar, I did some sound duty for the band. He had a Twin, I know quite well what they are capable of. Still think the BF amps don't quite do rock well enough. Skipped through a little of Ted, haven't heard some of the songs for must be 35 years or more. Actually he sounds pretty clean to me, just lot of volume causing sustain. The Anvil, not my cup of tea. Still think of all the rock records that came out, not much BF Fender there, the tweeds maybe. But that is really what a Marshall is, a slightly hotter Bassman.
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My son and I have been tweaking a custom bedroom/practice amp for a year or so now. In the beginning, he thought he wanted a two channel, two input rig. After many rounds of trial and error, the extra input went away. The front end now resembles a Fender/Peavey design like the 5150/6505 front end, with a clean and a dirty channel that each has its own gain knob and tone/eq control. The two channels come together and signal feeds to a cathode follower that leads to the effects loop jacks. Then there is another cathode follower that feeds the phase inverter and master volume control. Feedback is controlled by presence and resonance knobs.
We started out trying to integrate reverb, chorus/delay, and other effects into the amp. This approach went by the way when my son began experimenting with stompbox pedals. It is incredibly difficult and time consuming to satisfy a musician with a certain effect that can be tolerated and loved forever. It is much easier and more satisfying for my son to go to the music shop, audition some pedals on his amp, and pick the effect of the character he desires.
Fender and Peavey both have "lunchbox" micro-heads aimed towards what you speak of. My son especially likes the EVH/6505 offerings available today. They don't have the same tone we have perfected in the homebrew rig in his bedroom, but they come pretty close. They also play better with industry-standard equipment straight out of the box. The schematics are easy to find on the web, and have been a point of reference for lots of tube and tone stack stages we have tried out.
We started out trying to integrate reverb, chorus/delay, and other effects into the amp. This approach went by the way when my son began experimenting with stompbox pedals. It is incredibly difficult and time consuming to satisfy a musician with a certain effect that can be tolerated and loved forever. It is much easier and more satisfying for my son to go to the music shop, audition some pedals on his amp, and pick the effect of the character he desires.
Fender and Peavey both have "lunchbox" micro-heads aimed towards what you speak of. My son especially likes the EVH/6505 offerings available today. They don't have the same tone we have perfected in the homebrew rig in his bedroom, but they come pretty close. They also play better with industry-standard equipment straight out of the box. The schematics are easy to find on the web, and have been a point of reference for lots of tube and tone stack stages we have tried out.
Lots of good info here on the classic Fender AB763 circuit, which is arguably the best Fender ever made:
https://robrobinette.com/How_The_AB763_Deluxe_Reverb_Works.htm
https://robrobinette.com/How_The_AB763_Deluxe_Reverb_Works.htm
This looks like some good stuff. I'll have to redraw it and play with it a bit. Somehow I find guitar amp schematic drawing style difficult to read at a glance.
That's a helpful link for sure.
My dad practically worshipped ted nugent growing up, and this sounds like the correct direction to go. I'll just chop out the reverb bits, although the idea of throwing in a pt2399 reverb is appetizing...
I think ill draw it up, make a few tweaks, and go from there, just need to find the time and dig out my prototyping stuff. I've also got a tube home theater/surround sound (with pt2399 delay!) project i need to get going on too.
Ok, did a little drawing, and some searches on a non-reverb or "lite" version of the 763- this thing sure is simple. Other than my design having an additional tone/preamp input, and the cathode follower driven tone stack, its close enough to be able to build and do some quick swaps as far as design.
From guys that actually carry their rigs around, and play shows, what would you reccomend, cathode or fixed bias? i like the idea of cathode bias due to its somewhat self-regulating nature, but fixed seems to sound a bit tighter, and the idea of minimizing blocking distortion is always good.
From guys that actually carry their rigs around, and play shows, what would you reccomend, cathode or fixed bias? i like the idea of cathode bias due to its somewhat self-regulating nature, but fixed seems to sound a bit tighter, and the idea of minimizing blocking distortion is always good.
One thing about cathode bias that's frequently overlooked - the bypass cap on the output valves cathode resistor starts to charge up as soon as the valves leave pure class A (i.e., at quite low power).
This happens because once you enter class AB, the decrease in current in one output valve is no longer able to cancel the (much bigger) increase in current in the other output valve during each half-cycle of output signal. This means the average AC current through the cap is no longer zero - instead, it's flowing into the cathode end of the cap, and out of the ground end.
So the output bypass cap charges up, and starts to increasingly cold-bias the output valves as you drive the amp harder. This causes massive amounts of fairly harsh-sounding crossover distortion in the output stage, and can also cause the blocking distortion you mentioned.
Since this is electric guitar we're talking about, one person's "harsh" is another persons "rock n roll". But the take-away is that fixed-bias outputs can be designed to produce a smoother and more well-controlled overdrive distortion, while cathode-biased outputs pretty much always tend to get wild and somewhat harsh when driven hard.
(Fixed bias outputs can also suffer the same sort of problems due to a different capacitor - the ones coupling the phase inverter outputs to the grids of the output valves. So it's possible for a fixed-bias stage to end up with just as much harsh crossover distortion during overdrive as a cathode-biased one. But it's also possible to avoid much of this tendency, if the designer knows what he/she is doing.)
-Gnobuddy
You also might want to look into adding power scaling to your amp:
Power Scaling Kits
I haven't tried it but it sure does look like a damn good thing to have.
Power Scaling Kits
I haven't tried it but it sure does look like a damn good thing to have.
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