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Thread: My worst idea ever? Greatest? Both? (12 stage pre)

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    Senior Member NorCalTuna's Avatar
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    My worst idea ever? Greatest? Both? (12 stage pre)

    So, I built this amp for an old bandmate of mine, into an amp he didn't really like and had a taste for power caps: an ampeg vl-1002. I build him a sweet, sweet ass two channel thing that suits him perfect, i'll spare y'all details. I ended up with the VL, which is cool because i'll build a dumble or something brawny with the trannies, I think. BTW? Fav amp is my DR build, i just like building silly things in my spare time.

    So i'm cleaning my workshop last night and I'm moving the thing for the umpteenth time (duval's rule: the frequency with which an item needs to be moved is directly proportional to it's mass, times its volume) and I think, hey, this thing has potential.

    The trannies are already mounted, and one's prolly still good after all the abuse, and it has that nice driver tube hole over by the power tubes, switches... etc...

    oh yah, and 6 preamp tube holes.

    I'll put it out front- i've built a buncha unique and good amps, but i'm not a primarily mathematical builder, so this is a stretch. I'm gonna go order the parts and do this anyhow, but i'll ask to see if anybody's done something this foolish before. Luckily- no fear of failure or endless rework. Is there any reason, besides lead dress, that the typical 100k/1-2.2k/meg pot or divider stage and knockdown resistors couldn't continue to be scaled up to, say, 12 stages, or 11 with a cf to drive the tone stack? I'm thinking of just propagating the entire front of the amp with gain knobs. Then, I can start tapering the fool thing back down so the range through them actually is functional. If it never works, well, I can break it down and build a multichannel back into it or use it to prototype stuff.

    I guess I am asking for some starting points on the coupling caps, really the only spendy part in the thing to start messing with. I'm betting the largest in the whole thing is .022, but even that seems large as a starting point. I'm anticipating theres going to be very minimal cathode bypass in this pre, and a cold stage, so that'll perhaps come later. I'm never going to ask any stage to do much so I don't have to throw it away and I suspect that adds to the compressed feel of typical ultra gain amps.

    (sug)jest away! There is no goal here but a dumb amount of gain, but with more feel than the triple rec/krank space. The newest 5150, iirc, has 7. This is five louder!

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    With that many dual triodes to work with I would just do one of everything: cascode input, parallel triode stage, cathode follower, coupla common cathode gain stages, and maybe a couple of triodes wired as diodes to provide clipping/limiting. All 12AU7's, no cathode bypass, maybe some diode or LED cathode biased stages.

  3. #3
    Supporting Member Chuck H's Avatar
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    I think you'll end up minimizing the DB of each stage to get the amp under some control. And at that point there will be more series resistance overall in the signal chain resulting in a ton of hiss noise that is avoidable by reducing the number of stages.

    Of course we'll never know what kind of extreme high gain can happen if we don't build one. Could be at least interesting.

    To my thinking a better idea would be to build a more typical high gain preamp, a dedicated clean preamp with a seperate tone stack, include an effects loop and reverb. If you still have a tube left over add a trem.

    Chuck

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    My amp has 6 preamp stages, and then a PI. Of coure, one can get lots of preamp overdrive from fewr stages, but I wanted to try using lots of preamp stages, and over driving each one quite mildly, attenuating the signal from the previous stages using split loads, and seeing how it sounds. I use .047u coupling cap after the first stage, but from then on use .1u coipling capacitors with 220k grid resistor, and I dont have any apparent problems with blocking distortion. The firt few stages I over drive kinda lightly, but the 6th stage I over drive kinda hard to get the overdrive sound that I want. But that hard overdriving gives it an edgy sound, so I'm thinking about adding in another preamp valve so I can get it as saturated as I want using mild overdrive all the way. The clean tone (low volume after the first preamp stage) is really sweet. So, I'd like to see how you project turns out.
    A

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    Senior Member NorCalTuna's Avatar
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    Chuck, thats the kind of thing I was worried about, was s/n artifacts. I was planning to use my favorite rn65 plate resistors to minimize hiss. Perhaps this is one of the reasons noise gates have shown up in this sort of rig- that might be a fun tech to work with, too, but it doesn't really seem like anybody's really got that right, ever! Active gain lowering like a radio might be neat... I may also step up to the 1w dale rn70 for the plates and do 1/2w 65s for the rest. Those resistors are ridiculously awesome- robust, stable, quiet!

    You're right, there's an empirical imperative here. Must... Adventure... Forth! Here's my plan B, incidentally. Clean Channel: fender (2 stage) non reverb, then that stages up to a d-inspired thing. Thats 2 dual triodes. That leaves 8 triodes for high high gain, a la slo+ or 5150+. A loop might be cool here! I'm totally pimped on the belden digital reverb, which should be cool for something like this.

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    Old Timer tedmich's Avatar
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    you've seen this right?>



    IME you don't need so many stages to get gut wrenching dist. and sustain, even the 5 stage 5150 has one set up for unity gain. check the Ax84 LeadII with 3-4 tubes or even the (2 tube) Ax84 Ubergain pre

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    Re: Carvin Quad-X. The only thing I can think of when I look at that schematic is "To me, quantity IS quality!"

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    It's fun to see how every other stage is throwing almost the entire signal away! That kinda proves the point made in the above posts!

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    Old Timer tedmich's Avatar
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    Quote Originally Posted by octal View Post
    Re: Carvin Quad-X. The only thing I can think of when I look at that schematic is "To me, quantity IS quality!"
    Companies still markets their amps as "having an extra tube for more gain" or some such...people (men?) are often too eager to go down the "more is better" road witness various porn actors...and this guy's amp:

    The Big Ass Guitar Amplifier | ken-gilbert.com
    nice guy...crazy amp...

    Hmmm never noticed the (Al foil?) cap "crazy hats"...

  10. #10
    Senior Member NorCalTuna's Avatar
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    Well, tedmich, that carvin schematic certainly took the wind out of my sails. I guess I can than you for saving me a benjamin in parts!

    what to do with the monster is the question. I found it a nice place where I won't have to move it until I figure it out!

    thanks guys-

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    Old Timer defaced's Avatar
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    Quote Originally Posted by tedmich View Post
    Hmmm never noticed the (Al foil?) cap "crazy hats"...
    Someone over at the slo forum was talking about getting shocked from the cap ends. Makes me wonder if its tape to insolate the ends.
    -Mike

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    Quote Originally Posted by defaced View Post
    Someone over at the slo forum was talking about getting shocked from the cap ends. Makes me wonder if its tape to insolate the ends.
    Ken said specifically that the tape over the caps is the result of those caps floating at high voltage. It's out there on the forum or his website somewhere.

    jamie

  13. #13
    Old Timer tedmich's Avatar
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    Quote Originally Posted by imaradiostar View Post
    Ken said specifically that the tape over the caps is the result of those caps floating at high voltage. It's out there on the forum or his website somewhere.

    jamie
    I find that a little odd, check these series caps rated at 550uf 1800VDC that Apexjr sells for $35
    just an Al rail on the ends....

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    Yeah, it does seem odd. I was just repeating what I thought I'd read.

    jamie

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    kg
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    no, you're right about those caps and why the tape is there.

    the issue is not their voltage capacity, which is 500vdc--it's the fact that they're stacked in a full wave voltage doubler supply, which means the "ground" of the "top" caps is at B+/2. in this case, 305vdc.

    trust me, i only had to brush my palm on them once before the tape got added.

    -ken

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    Thanks for the reply. I think your BAGA is pretty amazing! I've been stockpiling parts a little at a time for a largish amp build.

    jamie

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    kg
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    i've got two more 1650w opts and a couple of 1k4va power trannies (one donut, one EI) waiting to be put together.

    i used to work a lot with my amps, but then i had a daughter, bought a house, had another daughter. :lol:

  18. #18
    Supporting Member Chuck H's Avatar
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    Aahhh... I had wondered why your posting tapered off some time ago. Building amps is great fun but building a home and family is funner.

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    Quote Originally Posted by kg View Post
    i've got two more 1650w opts and a couple of 1k4va power trannies (one donut, one EI) waiting to be put together.

    i used to work a lot with my amps, but then i had a daughter, bought a house, had another daughter. :lol:
    Yah I wondered what had happened to you also Ken. Maybe in time you can get your daughters to work on amps too.....haha. On second thought they probably won't be interested.....time to have a son!

    Greg

  20. #20
    Supporting Member Chuck H's Avatar
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    Quote Originally Posted by soundmasterg View Post
    Maybe in time you can get your daughters to work on amps too.....haha. On second thought they probably won't be interested.....time to have a son!
    Maybe the girls won't want to build amps, but they may want to learn how to play instruments. I'm thinking bass and drums

    Chuck

    PS, I talked with a guy who owned one of those Carvin Quad amps and he said it was a hiss machine.

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    I remember decades ago when I first started fooling with this stuff, I had a Sound City 200 that had a couple of extra unused holes for preamp tubes. So knowing that I didn't know what I was doing I filled them with additional gain stages with tone control and level pots on each stage so I could dial in my excess. Ended up with one input jack and the other three holes filled with concentric pots for the level and tone pots. Yes, there was a surplus electronics shop right up the street from me. It actually ended up sounding pretty good. Unfortunately, despite all the knobs there were only like three good sounds in the thing.

  22. #22
    Noodle of Reality Steve Conner's Avatar
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    And what were those three good sounds?
    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

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    Old Timer Gtr_tech's Avatar
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    That Carvin Quad thing sounds like processed cheese. Retarded design. The plate rail is low.....around 100v IIRC. I got one years ago for a good price and ended up adding another plate supply xfmr and associated caps/stuff to get a 320v rail. After that I jumped out a ton of bandwidth limiting SS circuits and redesigned the channel gain stages. I used a 3 stage for the dirt channels and left the clean alone for the most part other than some resistor/cap value changes. It sounds good now. Was a lot of work tho....
    The farmer takes a wife, the barber takes a pole....

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    Gtr_tech wrote:

    That Carvin Quad thing sounds like processed cheese.

    I like cheese:

    YouTube - 0110_Carvin Quad-X-Amp - cabinet voicing sound demo

    You have to stick around to get to the nutso 9-triode channel.

    The noise gate triggers off the input, and gates at the output.

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    Some of the tones are pretty interesting. It drives me crazy the way the background music ducks and returns and the way his voice is delayed from right to left- but it's a good show of what the unit is capable of. If I were the shredding sort of player I'd probably really like that box.

    All of this leaves me wondering- wouldn't you rather have a bogner shiva and a delay pedal? It has enough distortion for 90% or more of music. I'll make an exception for really crunchy stuff that sounds good with an SLO or Dual Rect- but as far as I'm concerned 3 or 4 stages of 12ax7 gain is plenty.

    jamie

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    Old Timer Gtr_tech's Avatar
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    Quote Originally Posted by BackwardsBoB View Post
    Gtr_tech wrote:

    That Carvin Quad thing sounds like processed cheese.

    I like cheese:

    YouTube - 0110_Carvin Quad-X-Amp - cabinet voicing sound demo

    You have to stick around to get to the nutso 9-triode channel.

    The noise gate triggers off the input, and gates at the output.

    The nutso channel has 11 stages in series. Watching that video brought back the hour or so I played around with mine it its stock form. Hated it then....hate it now. Total squash....no dynamics. Artificial sounding at best.....
    The farmer takes a wife, the barber takes a pole....

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    Supporting Member Chuck H's Avatar
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    Quote Originally Posted by imaradiostar View Post
    but as far as I'm concerned 3 or 4 stages of 12ax7 gain is plenty.
    Four is plenty for sure. It's entirely within reach to get to a well refined and fully square wave form with four. You could actually get there with three but it won't sound as nice. My personal amp uses three but there's actually quite a bit of attenuation. The preamp clips in cutoff at full tilt but no crazy OD there. But this amp is built to be cranked so that means the PI and power tubes are in OD. So that's three stages clipping and/or over driving which I guess would be about the same as four preamp stages (one to OD the next a little, then two more). I like it both ways really. A good high gain preamp is fun if you have the power to amplify it. I think a true fifty watts minimum for this kind of amp since you never really want to OD the power tubes. Part of the point of the high gain preamp is being able to EQ the distortion. Clip the power tubes and that gets lost. But my amp of choice will always include power tube OD and then EQ by transformer choice and speakers. With a 4x12 I can get a very appropriate "metal" tone from my personal build, but "I" like it best through it's own 1x12 combo speaker.

    Then there's the classic Marshall with a distortion pedal. Who doesn't love that??? I've done many recordings and gig's with such a rig and I can't think of a good reason to pick a Soldono instead.

    Lots of ways to get high gain.

    Chuck

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    thanks Chuck. I'll make another rampant generalization if you'll allow it.

    Most 3 stage preamps (early master volume marshall or bogner shiva, for example) clean up reasonably well with the volume knob. I've never heard a 4 stage mesa or SLO or similar do that quite as well.

    Thoughts?

    Maybe this is less of a stages thing and more of a cold cathode thing- perhaps that 39k cathode resistor is making that 12ax7 into a good crispy distortion element but destroying its ability to pass a clean tone.

    jamie
    Last edited by imaradiostar; 10-01-2010 at 02:45 PM. Reason: /hard heard /make making

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    Old Timer Gtr_tech's Avatar
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    Quote Originally Posted by imaradiostar View Post
    Most 3 stage preamps (early master volume marshall or bogner shiva, for example) clean up reasonably well with the volume knob. I've never heard a 4 stage mesa or SLO or similar do that quite as well.

    Thoughts?
    The way I play, that is an absolute must. Not only to clean up to get close to a clean tone, but to get different sounds from the same pickup....without stepping on buttons. I need versatility rather than "insane gain"....
    The farmer takes a wife, the barber takes a pole....

  30. #30
    Old Timer defaced's Avatar
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    Quote Originally Posted by imaradiostar View Post
    thanks Chuck. I'll make another rampant generalization if you'll allow it.

    Most 3 stage preamps (early master volume marshall or bogner shiva, for example) clean up reasonably well with the volume knob. I've never heard a 4 stage mesa or SLO or similar do that quite as well.

    Thoughts?

    Maybe this is less of a stages thing and more of a cold cathode thing- perhaps that 39k cathode resistor is making that 12ax7 into a good crispy distortion element but destroying its ability to pass a clean tone.

    jamie
    VHT Deliverance in the "more" mode (4 stages) can clean up well with the volume knob, see video below. 10k cold cathode stage, though I'm not sure that's where all the trickery is.
    YouTube - vht deliverance 60 dynamics
    -Mike

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