Tube preamp (do I dare bring up modelers!?!?!?)

OK. I know almost nothing about electronics, but I put together a preliminary layout for an AB763 circuit board based on a number of schematics I pulled up and am hoping I can get some coaching on it. It has an added Mid control as well as an EQ Lift component to it. The big issue for me is the power supply which I'm powerless (ha ha) to design. We can delve into power if I get some basic interest from you guys in debugging this circuit layout. Also, I forgot to indicate the value of the pots, but they're standard Fender values (Mid pot is A10K, EQ pot is A250K) The components show are to scale (looked up the specs) and they are shown mounted on a 2.25" x 2.25" board. Working out the enclosure and location of the pots and tube socket would come after finalizing the circuit board and power supply. Had a couple of specific questions denoted by asterisks 1 & 2 (don't worry with 3 for now). #1 - Most amps have a 120pf bright cap in the area shown on the Gain pot. Should there be one left there or should it be moved to the Volume pot? Also, as guitar players most of us install a treble bleed circuit (cap & resistor in parallel) across our volume pots to accomplish the same thing and it works much more seamlessly than this all-or-nothing approach of the switched cap? Why can't we do that here? #2 - This would be a footswitch instantiating the EQ Lift, the EQ pot determines the amount of "lift". That results in a marked increase in volume, but Kingsley puts a pot on his pedals to control that. Could that be done by placing a standard volume control pot in between the Mid pot and the foot switch? If so, what value?
 

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The first OD pedal I ever used for gigging was a Matchless Hotbox. It was basically a Vox preamp in a (very large) pedal. Then I got a Matchless Dirtbox, then a Bad Cat Two-tone. I used the Two tone for ages because it sounded extremely natural and amp-like and i could stick a delay after it and run it into a non-MV amp.

Then one day I discovered that a good SS pedal could sound just as good. I went through various Jfet overdrives and finally now I build my own ODs. I only recently sold my Bad Cat Two-tone after blind testing it with a couple of trusted op-amp & diode pedals. Bad Cat and Matchless run the tubes at quite high voltages so they do actually wear out, unlike the tubes in Kingsley pedals. I've had a few Kingsleys and they really were excellent but (a) bigger than I needed and (b) sound a bit jazz-fusion for me.

I used to think that only tube distortion was good enough. Now I know that's not true, for me, anyway. But I still love a tube amp!
 
Mike McLane said:
OK. I know almost nothing about electronics, but I put together a preliminary layout for an AB763 circuit board based on a number of schematics I pulled up and am hoping I can get some coaching on it. It has an added Mid control as well as an EQ Lift component to it. The big issue for me is the power supply which I'm powerless (ha ha) to design. We can delve into power if I get some basic interest from you guys in debugging this circuit layout. Also, I forgot to indicate the value of the pots, but they're standard Fender values (Mid pot is A10K, EQ pot is A250K) The components show are to scale (looked up the specs) and they are shown mounted on a 2.25" x 2.25" board. Working out the enclosure and location of the pots and tube socket would come after finalizing the circuit board and power supply. Had a couple of specific questions denoted by asterisks 1 & 2 (don't worry with 3 for now). #1 - Most amps have a 120pf bright cap in the area shown on the Gain pot. Should there be one left there or should it be moved to the Volume pot? Also, as guitar players most of us install a treble bleed circuit (cap & resistor in parallel) across our volume pots to accomplish the same thing and it works much more seamlessly than this all-or-nothing approach of the switched cap? Why can't we do that here? #2 - This would be a footswitch instantiating the EQ Lift, the EQ pot determines the amount of "lift". That results in a marked increase in volume, but Kingsley puts a pot on his pedals to control that. Could that be done by placing a standard volume control pot in between the Mid pot and the foot switch? If so, what value?
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Looks good to me :) You could add in the cap in #1 if you want, but I leave them off in my designs personally. No idea what value pot for #2, I would start with maybe 10k or so?
HamishR said:
Bad Cat and Matchless run the tubes at quite high voltages so they do actually wear out, unlike the tubes in Kingsley pedals.
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I can't speak to Bad Cat as I've never poked around one in person, but Matchless and Kingsley both run their pedals internally at about 250V (the Matchless I measured was closer to 240V, Kingsley was exactly 250V). Matchless does it with a transformer and Kingsley does it with an SMPS, neither is harder or gentler on tubes than the other. Not sure where you got that.
 
HamishR . . . I'm not looking to do an OD pedal, but a straight-ahead tube preamp to run into a power amp of some kind for a good clean Fenderish platform. I realize it could be used as an OD into the front end of an amp, but that's not where I was intending to go.

Vig398 . . . I was waiting for you, buddy! Thx for the reply! Re #1: I can see the non-necessity of the bright cap because as a stand-alone preamp (where your output volume is determined by the power amp) you're going to keep the Gain cranked up where it sounds best, hence, no need to be concerned with a bright cap. I assume that's the gist of what you're getting at. Re #2: Roger that. Now comes the fun part . . . the power supply. I notice in the Harlot shots in another thread that it's built against the side of the enclosure. . . I see a couple of voltage regulators. . . but that's ALL I know. Kingsley uses a 9vdc/500mA source, Tubesteader uses 12vdc/300mA. I would think 9vdc would be more compatible with pedal power units. Any interest in helping out with a layout for a power supply daughter board?
 
Mike McLane said:
Now comes the fun part . . . the power supply. I notice in the Harlot shots in another thread that it's built against the side of the enclosure. . . I see a couple of voltage regulators. . . but that's ALL I know. Kingsley uses a 9vdc/500mA source, Tubesteader uses 12vdc/300mA. I would think 9vdc would be more compatible with pedal power units. Any interest in helping out with a layout for a power supply daughter board?
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I'm not going to pretend to be an expert, but I wrote this up a little while ago, gives a decent starting point if you want a bit of reading. https://forum.pedalpcb.com/threads/tubes-102-intro-to-power-supplies-for-tube-circuits.10652/

I would be more than happy to help with a power supply board layout. I'm actually putting together a PCB order today, I could throw something together for SMD pick-and-place and get some if you want something ready to go. Or if you prefer to do it yourself I could help out with a through-hole layout.
 
I'm thinking thru-hole. . . a pre-drilled circuit board (or a blueprint for diy) with layout diagram and a parts list that hobbyists like me can order and assemble. However, if you think SMD is simpler, cleaner, more compact, etc. (and that we hobbyists need to learn to deal with soldering SMD components at some point) then I would follow whatever rec you had. The point is to make it reasonably doable for dumb shits like me :oops: ("MIRDFDSLM"). I read thru your tube thread and I'm re-thinking the supply voltage thing given that a 12vdc probably simplifies wiring/component requirements on the heater leg of the power supply daughter board. . . MIRDFDSLM. But how does 12vdc power input complicate things when everything else is 9vcd? I don't want to have to get a complicated (read: expensive) power supply.

The whole point of this exercise for me is a DIY (read: inexpensive) tube driven, light weight/portable rig for a working musician (read: broke) for a modern "PA driven" venue. This preamp can't be that expensive, neither would a simple Class D power amp & power supply. Build your own 1 x 12" speaker cab ($50) and load it with your speaker of choice ($100). You're looking at having a BF Deluxe pedal platform for a few hundred bucks. Throw in a few PPCB pedals. . . stick an SM57 in front of it and you have a GREAT gig rig. And its much simpler, uncomplicated and more "bullet proof" than a modeler.
 
Sorry. Spent so much time contemplating my navel that I didn't see your follow up post. YooDaMan!!! Would the thru-hole be a pre-printed PCB or would those be eyelets for "hard wiring"? Also, I see you went with 9vdc input. Great!!
 
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Mike McLane said:
Sorry. Spent so much time contemplating my navel that I didn't see your follow up post. YooDaMan!!! Would the thru-hole be a pre-printed PCB or would those be eyelets for "hard wiring"?
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It's a through-hole fabricated PCB, no eyelets or hand-wiring necessary. It will be very similar to the way Kingsley does it.

The pre-assembled SMD boards are neat, but since the MOSFET and 6V regulator are mounted flat on the board it works out to be the same size as the through-hole board. But I like SMD, and it's only an extra few bucks to get the boards assembled at the factory, so no hand-soldering SMD components necessary.

Both boards are 1" x 2.175"
 
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If PPCB is involved it should be something they can source through their existing vendors. Mr. PPCB (if interested) would have to chime in on that, but my guess would be that a thru-hole requiring user assy is more up his alley (fewer issues of warranties, quality control, etc.). If Sushi were to make it as a finished unit you'd probably want to go the other way. Since my little circuit board strictly involves connections to off board components I'm guessing a simple eyelet or turret board would be all that's required. That said, in looking at your finished dimensions (1" x 2.175") I crunched my board down a bit so all of the components fit "shoulder to shoulder" and reduced the board to 1.75" x 2.25" (see attached). Is there any heating or other issue that would preclude that? At that point you could append your power supply to the same board for a total of 2.75" x 2.25". Probably got some room to loosen that up a bit if need be. I figure it would have to go in a wider box (1590BB?) so that the tube could reside along side the board and have the full depth of the box for breathing room as well. Any of this make sense?

Thanks again for your help!!!
 

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Mike McLane said:
If PPCB is involved it should be something they can source through their existing vendors. Mr. PPCB (if interested) would have to chime in on that, but my guess would be that a thru-hole requiring user assy is more up his alley (fewer issues of warranties, quality control, etc.). If Sushi were to make it as a finished unit you'd probably want to go the other way. Since my little circuit board strictly involves connections to off board components I'm guessing a simple eyelet or turret board would be all that's required. That said, in looking at your finished dimensions (1" x 2.175") I crunched my board down a bit so all of the components fit "shoulder to shoulder" and reduced the board to 1.75" x 2.25" (see attached). Is there any heating or other issue that would preclude that? At that point you could append your power supply to the same board for a total of 2.75" x 2.25". Probably got some room to loosen that up a bit if need be. I figure it would have to go in a wider box (1590BB?) so that the tube could reside along side the board and have the full depth of the box for breathing room as well. Any of this make sense?

Thanks again for your help!!!
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I already ordered both versions of the boards :P Heating shouldn't be an issue, but on the through-hole board I did place the 78L06 on the edge so it could easily be attached to the enclosure to dissipate heat. If you're only heating one tube I don't expect this to be necessary, but if you're trying to run two or more then it may get toasty to the point of thermal shutdown. You won't damage the regulator, but it will shut down and you'll need to wait until it cools back down before you power it on again.

On the SMD version the 6V regulator is only rated for 500mA, which means it's only good for a single tube. As I mentioned in my write-up you can use 9V or 12V directly to the tube heaters without using the 6V regulator, so that's an option for using more than one tube. I tried to get reasonable copper-copper tracing so I'm confident saying you can run this up to 300V, I personally wouldn't take it much farther than that.

As for the size, the main reason I went for the 1" height was so the board can be mounted on the sidewall of something like a 125B. The mounting holes are for M2 diameter mounting hardware, personally I use brass standoffs for things like this. The boards take a couple days for fabrication, then SMD assembly takes an extra day or so, and shipping is 3-7 business days, so I usually get boards in 1-2 weeks. I'll let you know when they show up and I have a chance to test them.
 
Holy cow! We're cookin' now! So you wouldn't go with a single integrated board, but a separate board for power supply for the reasons cited. You're into the territory of how to stuff things into the box and are bringing up considerations that exceeded my knowledge or experience. As far as high voltage goes the old Fender schematics indicate 275V if I read it correctly. Again, all I'm looking for is a basic single channel clean to slight break up BF Fender front end so what you're proposing seems to have some "margin" built into it as I wouldn't want to be running right at the ragged edge of any components ability. Attached are the values of components I've extracted from reviewing the various schematics and layouts. Some guys show stouter specs than some of these shown, but it may involve larger component sizes. I would defer to your judgement if you think they need to be altered. Also, the caps in my DR clone are Mallory M150, but I would again defer to your judgement as to specific brand/model of components.
 

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Kingsley specs 9vdc/500mA for their power source. I assume that's more than adequate for what we're looking at for a single channel unit. I only bring it up inlight of my previous comment on engineering some "margin" into the beast and your comment on the 500mA limit of the 6V voltage regulator. Wouldn't want that to be a weak link in the chain. You know better.

Ya know? The way things are going I might have to learn how to play the guitar :oops:
 
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Mike McLane said:
So you wouldn't go with a single integrated board, but a separate board for power supply for the reasons cited. You're into the territory of how to stuff things into the box and are bringing up considerations that exceeded my knowledge or experience. As far as high voltage goes the old Fender schematics indicate 275V if I read it correctly. Again, all I'm looking for is a basic single channel clean to slight break up BF Fender front end so what you're proposing seems to have some "margin" built into it as I wouldn't want to be running right at the ragged edge of any components ability. Attached are the values of components I've extracted from reviewing the various schematics and layouts. Some guys show stouter specs than some of these shown, but it may involve larger component sizes. I would defer to your judgement if you think they need to be altered. Also, the caps in my DR clone are Mallory M150, but I would again defer to your judgement as to specific brand/model of components.
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I would go with a separate power supply board rather than a single integrated board simply for ease of design. I don't want to take the whole DIY experience away from you, I'm just giving you a tool for your project. When I do preamps I do the whole thing on one integrated board as it makes everything neater and makes less room for error. My thoughts on the component choices:

630V film caps - I use Mallory 150S for my non-SMD preamps and they're rated for 630V and I have no issues with them. They're fabulous.
500V silver mica cap - sounds about right, 500V is one of the more common ratings for silver mica caps
100V electrolytic caps - that's excessive. I wouldn't go below 25V, which is what I typically use for electrolytics on cathodes but it doesn't absolutely have to be as high as 100V.
2W resistors - absolutely not, completely unnecessary. My through-hole preamps use 1/2W carbon comp and my SMD preamps use 1/8W resistors, there's no reason to go as high as 2W in a preamp. Completely unnecessary and a waste of money.
1W resistors - same as above. Unless you're going for a particular look and you have some really cool looking 1W resistors there's no reason not to use 1/4W or 1/2W everywhere.
Mike McLane said:
Kingsley specs 9vdc/500mA for their power source. I assume that's more than adequate for what we're looking at for a single channel unit. I only bring it up inlight of my previous comment on engineering some "margin" into the beast and your comment on the 500mA limit of the 6V voltage regulator. Wouldn't want that to be a weak link in the chain. You know better.

Ya know? The way things are going I might have to learn how to play the guitar :oops:
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I would say 9V/500mA is bare minimum. When the tube is warmed up and you're operating you'll be pulling less than that, but when the tube is trying to get up to temperature it will try to pull as much as it can, which can cause the voltage to sag if the power supply can't keep up. But with a 500mA supply you should still be good after a minute or so.

I've heard you can plug guitars into these, but I haven't had time to try it, I just build them for the sake of building them. The 1/4" audio jacks are for aesthetics :P
 
What kind of enclosure do you envision? I was messing around with stuffing the PS & CB in a 1590BB and still finding room for in/out jacks and DC jack up top (like your units) and two foot switches (on/bypass, EQ Lift) down below and I can't find any place to put my tube !!!:eek: How's a guy supposed get by if he ain't got no place to stick his tube!?!?!?
 

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I only have one tube pedal that uses two footswitches, and I put it in a 1590XX so I don't have to deal with space issues. But if you're set on the 1590BB I would recommend mounting the power supply PCB to the side wall with your signal PCB next to it. You can't completely center the jacks or footswitches as they'll hit the tube, but if you shift things off to the side slightly you should be able to make it work. Obviously exactly what this looks like will depend on what kind of tube socket you have and how you choose to mount it, but this would be my suggestion.

Capture.JPG Capture2.JPG
 
For now let's delete the foot-switchable EQ Lift. I might leave it in as non-foot-switchable, but all of that appears to not involve the design of either circuit board. If left foot-switchable it begs to have an additional volume pot to balance the EQ Lift volume with the base tone. Now you're up to 7 pots! Without a footswitch you can use it to get a more aggressive "tweedy" sound, but that's the tone you get. . . period. I have this on my current amp and even though it's a great feature I generally just set it straight BF Fender clean to edge-of-break-up and use pedals for whatever additional flavor I'm after. After all, that's what PPCB is here for!! So it wouldn't bither me a bot to go straight AB763 for now.

BTW, are you doing all of these nifty renderings in Fusion 360??
 
Mike McLane said:
BTW, are you doing all of these nifty renderings in Fusion 360??
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Nope, these are all in Altium Designer. That's what I use for schematics and PCB layouts, but they've always had limited 3D visual capability and the newer versions keep getting better. For components you can keep the 4D model attached to the library component (like in diptrace) for 3D views, but you can also import additional 3D models like enclosures, jacks, etc. to see how things are going to fit. Not the only way to do it, but it's the way I do it.
 
All my stuff is done in AutoCad, but I'm dipping my toe into Fusion 360 water. I'm a member of a Maker Lab here and made some other guitar related stuff like a backplate noise suppression coil for my Strat and a chambered Tele body. Then I started this "pedal gig". With Fusion 360 I'd like to try my hand at a Strat body. Anyway. . . . back to amp pedals!!!!!

IMG_2309.JPG IMG_2239.JPG IMG_2598.JPG IMG_2525.JPG
 
Mike McLane said:
All my stuff is done in AutoCad, but I'm dipping my toe into Fusion 360 water. I'm a member of a Maker Lab here and made some other guitar related stuff like a backplate noise suppression coil for my Strat and a chambered Tele body. Then I started this "pedal gig". With Fusion 360 I'd like to try my hand at a Strat body. Anyway. . . . back to amp pedals!!!!!

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Oh very cool. I started learning Fusion 360 when I got my first 3D printer, then my work got my a SolidWorks license so I stopped using Fusion :P I always wanted to check out a makerspace, but when I started getting into this stuff I lived in a town that didn't have one, I just started buying all my own equipment and now I don't need a makerspace. My wife calls them all my otherwise useless tax deductions :rolleyes:
 
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