Preamp suggestions for modular amp design

[KingNed]

I'm in the process of building a bit of a modular amp design-type-thing. I have a stereo QSC poweramp; and in the 1U space above it in the rack case, I'm going to have 2 preamps in half rack enclosures that I plan to chop and change depending on what sound I'm going for. My initial design is one side being a Sunn Model T preamp, and the other side being a Fender style preamp. I'm keeping it all solid state.

I have all the stuff to build the Model T preamp ready, and I have someone more skilled than me working on a schem/pcb for a Fender preamp. However, the latter isn't going to be ready very soon, and I'm recording in early April. I need to get one other preamp finished ASAP, and I'm drawing a blank on what to build. I'm looking for a PCB that's readily available. I've tried many a tagboard build, but I'd rather not use one (mainly as I can rarely get them to work). I don't have time either to design and prototype a PCB design, although feel free to suggest ones for future builds.

I was considering one of the amp emulations from ROG, but couldn't find any information about how they would behave going into a poweramp. Another one I was looking at was the OLC Orange Peel but, again, not much information on how it works straight into power amps. Has anyone built a preamp/amp emu/amp-in-a-box that they've used going either into an effects loop or power amp which they can recommend building? I just want something clean/crunchy which I'll drive with fuzz pedals.

[HamSandwich]

Hmmm how about the Azabache?

http://diy.thcustom.com/shop/rog-azabache-pcb/

[KingNed]

Hmmm how about the Azabache?

http://diy.thcustom.com/shop/rog-azabache-pcb/

Yes, I've considered that.  It looks like a cool option but I'm not sure if it would have the headroom to drive a power amp.  Although maybe i could chain it with an LPB to bring up the volume going into the power amp?  Hmm...

[thesmokingman]

my problem with this post is wrapped around terminology. words are important and it is important to make a distinction between a preamp and an effects pedal because they are not the same thing. so when you tell me you have a sunn model t preamp or a fender style preamp, those are both tube preamps. keeping them solid state doesn't mean you go out and get a wampler black 65 and an earthquaker acapulco gold pedal and feed those into the power amp like that is the same thing.

[KingNed]

my problem with this post is wrapped around terminology. words are important and it is important to make a distinction between a preamp and an effects pedal because they are not the same thing. so when you tell me you have a sunn model t preamp or a fender style preamp, those are both tube preamps. keeping them solid state doesn't mean you go out and get a wampler black 65 and an earthquaker acapulco gold pedal and feed those into the power amp like that is the same thing.

I'm a bit confused by what you mean. I suppose it's a bit of lax terminology, but what i was looking for was something like a FET emulation of the preamp section of an amplifier.  That's what the Model T preamp I mentioned is.  I wasn't suggesting that I plug an acapulco gold straight in as that's a fuzz pedal rather than a tone-shaper.

I was looking for a pseudo-preamp in a pedal kind of thing?  Or does that confuse things more?...
I thought it would be understood what I was looking for - effectively a circuit to colour and add harmonics to the front end of a clean power amp so that it becomes useable as a primary amplifier.

Hope i've clarified things, although i might have just confused things more...  I'm not very good at explaining this type of thing lol.  I know what *I* want, but others may not get that.

[HamSandwich]

I took the thread as asking for a pedal-like tone shaping device to feed into something like a chip amp, where you're basically taking the sound it's fed and turning it up. Although I'm not sure now as you're saying it needs to drive the power amp, in which case you could be looking for something that puts out 10+V or.. an actual preamp lifted from an amp?

[gordo]

Something like the http://www.madbeanpedals.com/forum/index.php?topic=7139.0 might get you in the right direction.  You'll need to get it up to line level.  Have you heard the Sunn into your power amp yet?  You may find that in order to get the grunt of a T (or the Fender for that matter) you may have to route them thru a cabinet simulator.  Sort of the same idea as using a Line6 POD with the "Air" setting on and choosing a speaker configuration.

Barry's SunnT over at GuitarPCB sounds pretty nice but again, I don't believe it has enough output to drive a power amp without sounding a bit anemic and noisy.

The L5 preamp that Aion sells would be perfect but is a pretty involved build and the idea of rack mounting it with all the pots on flying leads to a front panel gives me a rash just thinking about it :-)  Would be worth taking a look at the schematic to see how it's getting so much output with a low noise floor though.

I'll keep an eye on this thread cuz I'm curious to see what you end up with!

[reddesert]

Line level, instrument level, and mic level: http://www.ovnilab.com/articles/linelevel.shtml

A preamp has about two basic functions: to bring instrument level up to line level, and to do some overdrive and EQ/tone control if needed/wanted.

A guitar has a signal level of maybe 0.1-0.2 V rms depending on the pickups, and high output impedance. Line level is about 1 V, which is sometimes referred to 0 dBv (and about 0.1 dBu). A typical mixer output, tape deck or CD line out or line in, and so on, is at line level. A power amp expects a line level input.

But, it isn't that hard to get a 1V signal out of a circuit that runs on 9V. With a lot of pedals, if you turn the volume knob down it will be close to instrument level (so no volume drop/gain vs. bypassed). But if you turn the volume up it will be putting out near 1V or line level, and be suitable for input into a power amp. Most of the ROG "amp emulation" circuits should do this. Even a venerable circuit like the DOD 250 Overdrive/Preamp is intended to allow it.

[KingNed]

This has all given me a little bit to think about...

I understand the difference between line and instrument level, although i was under the impression that I could add a simple booster circuit at the output of the "preamps" to bring them closer to line level.  Also, I've been told that inserting a buffer circuit between the Treble and Volume pots on the Sunn circuit greatly improves tone and volume due to loss from the tonestack. 

The input sensitivity on my poweramp is just above 1v, and the input impedances are 10K ohms unbalanced and 20K ohms balanced.  I should be able to get close to that with a booster circuit like an LPB after each preamp to boost the level up and bring the impedance to 10k... right?

I found a cool looking JCM800 emulation which looks quite nice (http://uk-electronic.de/onlineshop/product_info.php?cPath=105_248&products_id=941&osCsid=7676696ac9f3fed0bf317787b4be071f)

You may find that in order to get the grunt of a T (or the Fender for that matter) you may have to route them thru a cabinet simulator.  Sort of the same idea as using a Line6 POD with the "Air" setting on and choosing a speaker configuration.

Oh really?  The poweramp will be running through some cabs, so won't this sound a bit weird/blanketed?  A speaker sim going into a speaker?

[gordo]

Duh, yeah, you're right.  I'm thinking it's going to the board.  Fingers flying with the brain disengaged :-)