#1
So, starting a new amp build tonight. Last amp I finished, I finished it and posted a couple of pics, and that was that...think I'll do updates on it as I go this time. Don't know how long it'll take me because I'm a full-time engineer and a part-time student. If all goes well, I'll have it done in a week or so...don't know how well it's going to go though (I currently don't have $$ to go and buy stuff, so I'm building this with what I have laying around...). Going to be gutting a couple of amps for parts to get this done, hopefully I can cobble enough to get the parts I need. Building this into a cake pan like my last one, which will be interesting...will be high gain, and I'm trying to pack 6 valves onto a 12x8 cake pan. Probably going to have a valve or two sticking out the sides of the chassis to give it the appropriate "mad scientist" look. Noise will be a concern too. Transformers will be large too...so...yeah, here goes I guess...

The amp itself is going to be a SE amp, probably in the neighborhood of 20 watts or so. The idea right now is to have a 6V6 and a KT77 on it, running parallel. The transformer I'm using is a Hammond "universal" SE OT, so it has several impedences available for the tubes, along w/ 4, 8, and 16 ohms out for the speakers. So, I can hook the 6V6 to 6k which it likes, and the KT77 to 4k which it likes, simultaneously. As far as how that'll work in the transformer, I have no idea. Might end up sounding like total crap, but you never know till you try, so that's what I'm gonna do.

The idea is to bias the 6V6 so it goes into "crunch" mode while the KT77 is still relatively clean, so that there's the transistion to distortion in the poweramp is smooth. Once you start opening it up some and the KT77 starts to get beat on a little bit, it should start to scream. So, the goal being a nice transition and usable sound from fender clean to a screaming 5150, this should be a good "first step" in getting there (the 2nd step being a 90 watt with 6V6s and KT77s in parallel in a push-pull amp). Dunno what the output transformer is going to say about this, so we're starting out a bit smaller...not that I'd ever need a 90 watt tube amp anyways (heck, the 5 watt I have now it too loud for my apt, gonna have to bring it to a friend's house out in the country to get some clips).

Schematic for the preamp, with the exception of having the B+ lines in, is here:



Preamp should be able to go from clean to 5150-levels of distortion. Tone stack is a 4 knob stack (Treb, Mid, Mid shift, Bass) that has enough adjustability to get pretty much any tone curve you want, from a Fender to a Marshall to whatever (so that it'll sound good clean, or mid scooped, etc). Not on the schematic is a prescence/resonance control (that, all it really does is act as a second tone stack, but active this time) that goes between the preamp and the power amp.

Also, there's bunch of diodes under the parallel 12AU7 and 12AX7. Those are actually LEDs, which can be used to bias tubes. Going to put an on-on-on switch on the front to switch between LEDs and give it a creamy -> rock -> scream selector.

So, yeah, enjoy. Hope it motivates others to get into amp building, it's a good time and not as bad as one would expect.
Quote by kcdakrt
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#2
I've heard of push-pull pair amps using dissimilar output stages, in particular a 6v6 and el84. The thing that I notice is the large discrepancy of what the tubes are designed to be maximally operated at. 9W vs 25w (12 v 32 if we count the actual absolute maximum). This may cause the amp to have its own challenges. Should be an interesting project though, once I get my first self designed amp built I want to try some dissimilar output stage types. I will definitely be watching this thread.

edited:
Another possible problem I see is having two different tubes hooked up to two different transformer taps. Does it have any taps around 2.5k? Maybe also try hooking both tubes up to one tap.
Last edited by XgamerGt04 at Jan 24, 2009,
#3
wow looks like it should be a great amp, let us know when you have clips should sound awesome.
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#4
Parallel Push Pull, nice! I like that power design.

I have been experimenting lately with biasing with LEDs as well. I had a hell of a time to bias up some 12AU7s so sound good. What type of LED you using, color? You obviously know but the voltage drop (which is different for all LEDs) is what makes the bias work.

Why are you using 12AU7s for voltage amplification in the pre-amp btw?
#5
Quote by XgamerGt04
I've heard of push-pull pair amps using dissimilar output stages, in particular a 6v6 and el84. The thing that I notice is the large discrepancy of what the tubes are designed to be maximally operated at. 9W vs 25w (12 v 32 if we count the actual absolute maximum). This may cause the amp to have its own challenges. Should be an interesting project though, once I get my first self designed amp built I want to try some dissimilar output stage types. I will definitely be watching this thread.

edited:
Another possible problem I see is having two different tubes hooked up to two different transformer taps. Does it have any taps around 2.5k? Maybe also try hooking both tubes up to one tap.


The discrepancy in output power is what I'm looking for...I want the 6V6 to start distorting before the KT77s (and they will) so that I get a nice clean > OD > distorted transistion in the poweramp. I fully expect the 6V6 to be completely square by the time the KT77 starts to scream. That's OK too, that's actually a design goal of this amp. How well is going to work in real practice? I haven't the foggiest idea. The P-P version of this amp sims up great in SPICE, never got around to a SE version tho...output transformer saturation may be an issue, which is why I'm using a Hammond (which are conservatively designed) 25watt (when I'm expecting less than that).

The OT taps thing...no idea how that's going to go. But, I have the taps for each tube, why not load match each tube? Most OTs don't give you the option of different primary impedences (except UL OTs, those could work the same), so I don't know that this has been done before. So...yeah...maybe it sounds like total crap and I have to run them through the same tap. Or, maybe I discover something that sounds really really sweet.
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#6
Quote by lbj273
wow looks like it should be a great amp, let us know when you have clips should sound awesome.


Problem with that is that I suck at playing. I'll try to get something up eventually though.
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#7
how much will this cost you to build
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#8
Quote by kurtlives91
Parallel Push Pull, nice! I like that power design.

I have been experimenting lately with biasing with LEDs as well. I had a hell of a time to bias up some 12AU7s so sound good. What type of LED you using, color? You obviously know but the voltage drop (which is different for all LEDs) is what makes the bias work.

Why are you using 12AU7s for voltage amplification in the pre-amp btw?


Actually, parallel single ended!

I've been working on the side w/ a few people from AX84 on this, basically the quality of the LED makes a difference...usually, the darker/dimmer/crappier ones sound best.

Recall that the LEDs are on an on-on-on switch... setting 1 will be red LEDs (1.2 volts-ish?) for both the 12AU7 and 12AX7, setting 2 will switch the red on the 12AU7 to a yellow (1.6 volts-ish?), and setting 3 will switch to a pink LED for the 12AX7 (which, according to the package gives a drop of 4.2 volts, so that is the definition of a "clipper" stage). should be a sweet creamy > rock > hard rock switch.

As an aside, the 12AU7 || 12AX7 stage is a JJ 12DW7, which has a 12AX7 and a 12AU7 triode in the sample tube. SCORE!

Regarding 12AU7s... I dunno if you've been to ax84.com or not, if you do check out their "projects" and then the LeadII preamp...that's a 5 gain stage (+ CF) that had 4 12AU7 stages into a 12AX7 stage (with 12AX7 CF). I was loosely involved in designing it...I built up John H.'s version after he was done, but into a 50 watt PP poweramp. Simply put, that was the most touch-sensitive amp I've ever heard. Brutal distortion but you can still hear each individual note well. So, part of the goal of this is to see how much of that "mojo" (if there is such a thing) is from the LeadII topology, and how much is the 12AU7.

Further regarding the 12AU7...the typical high-gain amp has a bunch of 12AX7s strung together for a theoretical gain of millions. Of course, you're only going to get a gain of 100-200 (assuming an input of a volt) before the signal is completely squarewave...from there, all you're doing in amplifying noise, making it hiss more, pop more, etc etc, a few millions of times louder...not good. So...why not use 12AU7s for lower gain? Because they aren't running completely wild like a 12AX7, you don't need to put a resistor in front of the gain pot, so it can run a little more full-tilt and give you better range of adjustability along with lower noise amplification along with more stability. Seems like a win-win-win to me.

The 6au6 (which is actually an EF86 btw) will have a gain of about 200...enough to clip the stage after it if desired...more than likely though, it'll OD it a bit and then clip the stage following that one. Should do it in a very smooth fashion. From there, you go through the tone stack (bassman with a mid-shift pot so you can vary the mid-cut from 300Hz to 2kHz) to the || section...which reportedly does the clean > scream thing really well.

So, yeah.....
Quote by kcdakrt
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Last edited by DLrocket89 at Jan 25, 2009,
#9
Quote by rancidryan
how much will this cost you to build


Um...$2.99 for the cakepan, that's about it...all the other stuff I'm gutting from other builds.

I were to start from scratch, probably on the order of $500 maybe?
Quote by kcdakrt
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#10
Chassis punched and tube sockets added:

Homework is slowing this down. Gotta gut another amp I have for the transformers, that's on the docket for tomorrow. For now, homework and sleep...
Quote by kcdakrt
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#11
we need sound clips when this is finished

I wanna know how the cake tin goes, are they alright for building amps?
#12
Quote by guitarcam123
we need sound clips when this is finished

I wanna know how the cake tin goes, are they alright for building amps?


I wouldn't try putting a 50 watt in it or something similarly big. Working great for prototyping new preamps (or, preamp AND poweramp in this case) into a simple poweramp w/o reverb and whatnot. It helps if you're willing to do things like have tubes hanging off of the sides, no pilot light, input on the side and not the front, etc, like what I've done. Kindof a pain to drill because the metal is so soft. Also, make sure you get the cheap kind that don't have the stick-free surface...the stick free surface is teflon, which makes a lovely insulator, so your ground connections don't connect and then you get fried.

If this preamp works right, I'm going to have custom made a freaking huge chassis and build this preamp plus two other preamps that I have that rock into a huge-ish amp, probably powered by a 6V6 quad (for 50 watts), double reverb (short and long tanks in parallel), tremolo, FX loop, footswitched, etc...whole works into basically the amp of my dreams (where, if I own it I can say I don't need another amp). Might end up going a pair of 6V6s and pair of KT77s in that amp, hence me trying it out here. ...and then I go buy an attenuator... that's prolly a year or four off yet, would probably be a $1500 project.
Quote by kcdakrt
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#13
This sounds like a very interesting project. When it is finished, you should put up a demo video. This sounds like something that Egnator forgot to think of.
#15
I want me and you to go into business if this sounds good.
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#16
Quote by sesstreets
I want me and you to go into business if this sounds good.


Hah! Actually, in the process of starting a business now. Didn't get any forward progress last night because I was in the middle of getting set up as an amp tech at the local amp store. Apparently, I'm the only one w/in about 80 miles. Score.

What have you done for amp stuff? I've been at this 5 years now and am just feeling comfortable working on other people's stuff/selling other people things I make...
Quote by kcdakrt
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#17
Quote by end_citizen
This sounds like a very interesting project. When it is finished, you should put up a demo video. This sounds like something that Egnator forgot to think of.


it'll have to be audio I'm affraid. Should be pretty sweet though, I have a mini recording rig w/ decent mics, so it should sound better than most videos...
Quote by kcdakrt
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#18
Quote by DLrocket89
Hah! Actually, in the process of starting a business now. Didn't get any forward progress last night because I was in the middle of getting set up as an amp tech at the local amp store. Apparently, I'm the only one w/in about 80 miles. Score.

What have you done for amp stuff? I've been at this 5 years now and am just feeling comfortable working on other people's stuff/selling other people things I make...


Well. You build the amp. We sell it for 500 dollars, you get 9% of every amp sold, I get 5%, the rest goes towards parts.
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#19
Quote by sesstreets
Well. You build the amp. We sell it for 500 dollars, you get 9% of every amp sold, I get 5%, the rest goes towards parts.


Heh...or, I build the amp, I sell the amp for $2000, and I keep 100% of it...

Sorry...I've put about 2,000 hours over the last few years into this and probably $10,000 of my own money over that time...takes me about 40-60 hours to build an amp from scratch. I'm trying to recoup some losses here.

Quote by kcdakrt
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#20
Quote by DLrocket89
Heh...or, I build the amp, I sell the amp for $2000, and I keep 100% of it...

Sorry...I've put about 2,000 hours over the last few years into this and probably $10,000 of my own money over that time...takes me about 40-60 hours to build an amp from scratch. I'm trying to recoup some losses here.



Can i get an A-Men-uh
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#21


Heater wiring in. Always the most obnoxious part of building an amp...ug.

Used a hot glue gun this time to tack down the wire and keep it more in place, came out better than most of my heater wiring jobs...especially considering the tubes aren't in a row (and aren't even in the same plane...). So..yeah...progress, hopefully more tomorrow. Next step is mounting transformers and drilling holes for pots, jacks, etc.

Quote by kcdakrt
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#22
Sounds like a cool amp!
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#23
Lmao I was just joking dude xD no reason to get all up tight.

I'd still want to hear it.
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#25
^ lol
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#26
Quote by sesstreets
Lmao I was just joking dude xD no reason to get all up tight.

I'd still want to hear it.


No worries. I've received other things like that from people who were very serious...

Should be cool...hoping to get it over to the music store and plug it into a 1960 full stack and do some recordings...it'll be awhile before it's done tho, school is taking up a lot of time (not to mention the full-time job).
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#27
Quote by hotmusic
wahh.. great amp.. anybody know how much it?


huh?
Quote by kcdakrt
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#28
Quote by hotmusic
wahh.. great amp.. anybody know how much it?

You r pro troll.
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#29
Currently debating between two different power transformers. one should give a B+ voltage of 385V, the other one 490. The 6V6 tube I'm using maxes out at 500V...so...might be fireworks. I'll try to get a video when I first fire it up.

Quote by kcdakrt
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