Help me design my first amp!

[TheWinterSnow]

So I took out the idea of a preamp out, no real use for it considering the poweramp out and made adjustments to the power section's mono/stereo control, which would bring down the price a lot. I also removed the possible idea of having a reactive load attenuator as with the Variable voltage regulator, power tube saturation can be had at bedroom volumes so there is no point. There will now also be a serial FX loop that bypasses the tonestack that allows for external tone stacks at the same time there will be a bypassable global feedback output which will allow for external feedback controls as well (this would allow for an entire rackmount external tonestack and feedback controls).

I have the schematics for the preamps and power amp section. The only thing left to do is to get the tonestack and FX loop design down on the high gain part of the amp and interface it with the power section.

 

[MatrixClaw]

Honestly, I would rather have a 2 channel amp with two great sounds, than a 3 channel amp with 2 different lead voicing. A lot of people tend to think they want the most versatile amp possible, and all these features, but I have never played an amp, aside from my Diezel Herbert that actually accomplishes this by having every single channel usable by me.

I realize we're on a recording forum right now, so what producers and engineers here are going to want will differ from the musician, who are going to be your main customer. From an engineer's standpoint, I could see needing a British and American voiced lead channel for recording, as you could easily get two different tones out of one amp. From a musician's standpoint, I would rather buy two different amps if that's the case, because implementing that idea is not going to be cheap.

To be completely honest though, I am sick of the SLO clones, there are so many out there right now that not really any of them stand out against the next. Sure, they sound great, but none of them really do anything that I couldn't already do with a 5150, a boost and a separate amp for cleans; for much less. I would like to see something new - Maybe a more German voiced amp, or VHT-like in its ultra-dryness and clarity.

SLO clones have been beaten like a dead horse at this point, I'd say the only way you should go with this amp if you're still going to go with that voicing, is to lean more toward the Recto sort of thing. There are TONS of amps that sound like the 5150 and SLO but really don't make me want to buy them, because in all honesty, they don't really improve much at all on the circuit. I would love to see a 2 channel Recto clone with better cleans and an almost identical lead channel, except with the most clarity possible. I LOVE the Recto sound, but they have always lacked the clarity for me to be able to use them for most of my music; and there's not really a single amp out there (besides Bugera) who is doing a copy of these amps. The 3 channels suck in comparison, so the only way to even get that sound is to just buy a used one; thankfully, they're plentiful, but if someone could break into that market boasting it as being very similar to the Recto, but with a better clean channel and clearer lead channel, I think they could do very well.

 

[TheWinterSnow]

Honestly, I would rather have a 2 channel amp with two great sounds, than a 3 channel amp with 2 different lead voicing. A lot of people tend to think they want the most versatile amp possible, and all these features, but I have never played an amp, aside from my Diezel Herbert that actually accomplishes this by having every single channel usable by me.

I realize we're on a recording forum right now, so what producers and engineers here are going to want will differ from the musician, who are going to be your main customer. From an engineer's standpoint, I could see needing a British and American voiced lead channel for recording, as you could easily get two different tones out of one amp. From a musician's standpoint, I would rather buy two different amps if that's the case, because implementing that idea is not going to be cheap.

To be completely honest though, I am sick of the SLO clones, there are so many out there right now that not really any of them stand out against the next. Sure, they sound great, but none of them really do anything that I couldn't already do with a 5150, a boost and a separate amp for cleans; for much less. I would like to see something new - Maybe a more German voiced amp, or VHT-like in its ultra-dryness and clarity.

SLO clones have been beaten like a dead horse at this point, I'd say the only way you should go with this amp if you're still going to go with that voicing, is to lean more toward the Recto sort of thing. There are TONS of amps that sound like the 5150 and SLO but really don't make me want to buy them, because in all honesty, they don't really improve much at all on the circuit. I would love to see a 2 channel Recto clone with better cleans and an almost identical lead channel, except with the most clarity possible. I LOVE the Recto sound, but they have always lacked the clarity for me to be able to use them for most of my music; and there's not really a single amp out there (besides Bugera) who is doing a copy of these amps. The 3 channels suck in comparison, so the only way to even get that sound is to just buy a used one; thankfully, they're plentiful, but if someone could break into that market boasting it as being very similar to the Recto, but with a better clean channel and clearer lead channel, I think they could do very well.

At this point, the preamp stage is fairly drastic compared to the typical SLO clones. The SLO design was a starter point considering this is my first amp design, I wanted to create an amp that has a tried and true design that is popular but at the same time improve upon the circuit that hasn't been done before. After I get the first amp going, I will indeed begin to find my own signature voice. At the moment I am still trying to find out what makes amps like the Mark IV/V, Pittbull Hundred, and Engl Savage tick so I can use more exotic methods the fine tune the sound I want and fine tune a sound that metal guitarists want. I am really dedicated to hearing the tone and features that other gigging guitarists want at the same time I am trying to take the best of everyamp on the market and put it all into one amp. Its an everything in one head solution so that the gigging guitarist doesn't have to carry around multiple heads and cabs for different sounds. One cabinet and one head would get it all done. Lightweight and actually useful.

In the design itself it isn't an exact drop in of the SLO/5150/Recto preamp, the gain has been changed in the first few stages than normal, on top of utilizing an Engl style stage removal, the rhythm channels for one of the stages actually switches and changes the level of attenuation to the next stage depending on if we are talking about the rhythm or lead channel. Also with the bias selector switch in preamp, by removing the SLO bias you have what almost looks like a very low gain slightly warmer biased Engl Savage.

The Amp voicings will be placed on paper first and then tweaked later. I haven't even began to design the voicing of the tonestacks or global feedback as like I said before it not a direct drop in. The goal is that each voicing is VERY usable, not just some 3 channel amp that has only one usable channel and the rest are meh. Every channel will be usable and will have a separate purpose. And the price to add the third channel, 8 pots, 2 switches, 1 NO pushbutton, 1 optocoupler and physical space on the board and chassis, grand total price per channel would be about $50 which isn't so bad for an amp which it's estimated cost is going to be around $1500.

 

[Wolfeman]

Hey Wolfe, would you be able to pinpoint where the 5150 gets its excessive mids from? Just so that I know beforehand when I start actually building, I think it might have to do with the tone stack modifications on the Marshall stack. I could easily find out by moding the stack on my 5150 to see what it does. Also...since my knowledge of parallel RC (Shelf) circuits are minimal, what the hell is that filter network between V1a and V1b doing other than eliminating bass at lower gain settings (a fixed bright switch?). As for the Rythm filter network, I can't for the life of me make any sense out of it, the schematic is written pretty bad.

And what is the SLO depth you talk about, its not on the schematic, so I am curious as to how Mike achieved it.

Hey sorry I missed this one.

For the tone of the 5150, I think it mostly comes from the slope resistor, the added cap before the stack, and how the stack is getting driven and loaded down. All those slight differences will make a similar tone stack sound different in 'different' amps. I found that adding a pot as the slope resistor works wonders in opening up how the 5150 sounds.

When you refer to the filter network, are you talking about what's going on up around the gain controls? It's pretty much a network of how much high end gets through to the first stage, and also there is some voltage division happening(crunch/no crunch). IMO they went a little overboard there, if you look at the SLO schematic it makes much more sense and has less crap around that area and does just as good of a job.

For the caps over the gain pots, those are simply 'bright' caps as you already mentioned. Put a spst on/off switch on one side, and you've got yourself a bright/normal switch. At a full gain setting, it does nothing though.

The depth mod is simply a resonance control, affecting the lower area of the negative feedback. So as you turn the control up, it takes away negative feedback in the low end, giving you more bass 'response'. IOW it works just like the presence control. See here-
http://sloclone.yesterdaysrevolt.com/schematics/SLOCLONE-OFFICIAL-SCHEM.pdf

 

[Wolfeman]

Matrix, you do realize that the recto is also a 'clone' of the SLO? 5150, Recto, Framus, 5150 III, etc, etc, are all based loosely on the same gain stage topology of the SLO. And yet the small 'tweaks' each manufacture does makes all those amps sound different. So yes, it has been done a lot, but there is still many things you can do differently to make each 'clone' unique.

Sorry I just found it funny that you say you wish amp make\rs would stop doing the 'SLO' thing, but then you recommend an amp that does do the 'SLO' thing.

 

[TheWinterSnow]

For the tone of the 5150, I think it mostly comes from the slope resistor, the added cap before the stack, and how the stack is getting driven and loaded down. All those slight differences will make a similar tone stack sound different in 'different' amps. I found that adding a pot as the slope resistor works wonders in opening up how the 5150 sounds.

The Slope is the same as in most other amps, 47K nearly identical to others but has odd methods of achieving them like the 50K pot with a 47K resistor in parallel rather than using a 25K pot, things like that.

I was doing some reading and came across what the tone stack driver is doing, its just a fancy way of achieving feedback. Gains stages with feedback work similar to DC coupled cathode followers in terms of voltage and current gain but have a slightly increased output impedance. For whatever reason Peavey decided to use two tubes for feedback, rather than taping the signal from the plate back to the grid, they took another gain stage which was in parallel and placed it back at the grid of that stage, the output of the previous. Since they are out of phase it acts like an over-glorified single gain stage with feedback.

Maybe the increased output impedance followed by the filtering between the stack and the driver.

EDIT: Scratch that I can't believe I didn't see this before, the final tube before the tonestack is just a single virtual earth gain stage (or a gain stage with feedback). There are two stages between it and the "slo" stage meaning there is an additional two stages of gain adding coloration to the sound. The second stage actually does not have a cathode bypass cap so I will put money there that this is the stage responsible for a lot of mids or more focus on the lower resonant fundamental frequencies.

 

[MatrixClaw]

Matrix, you do realize that the recto is also a 'clone' of the SLO? 5150, Recto, Framus, 5150 III, etc, etc, are all based loosely on the same gain stage topology of the SLO. And yet the small 'tweaks' each manufacture does makes all those amps sound different. So yes, it has been done a lot, but there is still many things you can do differently to make each 'clone' unique.

Sorry I just found it funny that you say you wish amp makers would stop doing the 'SLO' thing, but then you recommend an amp that does do the 'SLO' thing.

I know, I was recommending that if he does go the SLO clone route, that he takes more of the Recto route, instead of a straight SLO or 5150. There are plenty of amps out there that can get similar to those two amps, but there really aren't any amps out there that sound like a Recto.

 

[TheWinterSnow]

I know, I was recommending that if he does go the SLO clone route, that he takes more of the Recto route, instead of a straight SLO or 5150. There are plenty of amps out there that can get similar to those two amps, but there really aren't any amps out there that sound like a Recto.

I get where you are coming from. Like I said though, since this is my first amp I wanted to try something very popular and tackle the poor design in these amps, particularly the 5150, add other features that I believe that all amps should have, such as stereo FX return with stereo power amp, being able to use ANY octal pentode tube (EL34s to KT88s), built in OD pedal, midi switching etc.

I said before my goal was to find out what makes popular amps tick, find their flaws and make a similar amp or a clone of many different amplifiers with all the good things players want and with as little flaws from each as possible.

By discovering the differences between amps like the 5150, SLO and Recto, I can see at least two separate gain stage design from the differences, let alone the differences when you add amps like the Engl Savage and the Boogie Mark series.

 

[ParsonsMatt]

1 channel with excellent tone?

 

[TheWinterSnow]

1 channel with excellent tone?

Very possible. I was thinking about making the current amp I am designing available in a single high gain version (there will be two versions, an American voiced with 6l6s and British voiced with EL34s), but having a dedicated clean channel because adding the preamp of a 65 twin reverb is so cheap considering its only one valve and the phase inverter and power section for the high gain preamp will be as far as I know identical to that of the 65 twin reverb I figure why the hell not add it, should only add around $20 USD to implement. Get a single high gain amp with a dedicated clean

EDIT: Wolfe, I was thinking about using a Solid State buffered FX loop however I wish to ask, from your experience, does having a cathode follower in the FX loop add to more compression as the Tonestack CF does? That might be something that I will experiment with however, I am leaning towards using op amp buffers to help keep the linearity that FX loops should theoretically have but am concerned about getting as much of a driven sound as possible. I am also concerned about keeping the tube count low and between low tube count plus ultra linear FX loop, I am really leaning towards the SS buffer, but if sonic superiority leans towards tubes I will use them instead.

Should add, I am scrapping the idea of using a 12AU7 for the tonestack drive and will replace it with a 12DW7 that will be bootstrapped, should give absolute maximum amount of gain possible for the tonestack. Should be a VERY stable driver no less.