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PAiA stack-in-a-box guitar preamp kit
PAiA stack-in-a-box guitar preamp kit
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Old 14th July 2012, 03:50 AM   #11
cyclecamper is offline cyclecamper  United States
diyAudio Member
Join Date: May 2010
Location: Chicago IL, Long Beach CA, Vienna VA
Yes, I've had a dozen of those "starved plate" devices and it's not at all the tube sound I like. I had a 'blue tube' and a Chandler and several others. I don't find the sound meets my intent of being 'emotive'...going from realy clean to really complex by both how hard I pick and how many strings are involved.

I'm not really big on any power supply sag type of compression and its related distortion either.

Getting the sound I am pursuing involves a tube at that critical first stage of interaction between the coils and grid, then treble pre-emphasis, one or two more stages adjustable for the exact point of distortion generation, then treble de-emphasis. Usually at least 4 single-ended tube stages in a row at a minimum. If I get one stage to go in and out of distortion with my touch just as I prefer, I find it just sounds much better after the output's phase is shifted 90 degrees and repeats the process. I don't really know whether it's the effect on the waveform or the amount of compression, but IMHO blues is all about whatever sounds good, and IMHO it sounds good. I have nothing against op amps and transistors in their appropriate place, like in my accurate reproduction amps. But my guitar preamps are part of my instrument and sound generation. Perhaps the last stage for recovery of the gain lost in the final tone de-emphasis stage could be an op-amp. But I don't find een powered pickups work as well as a tube first stage, and that stage has to add enough gain for my preferred pre-emphasis. Then when the next stages do (or don't) add distortion, there is so ridiculously much treble that I can roll it off and make the treble less obnoxious and what we used to call 'creamy' yet still have plenty of treble content. The way the sound from multiple strings mixes in those treble-boosted distortion stages is incredible, and makes all kinds of interesting beat tones which become more prominent when you filter the excess treble out later. The original guitar sound goes thru pre-emphasis and somewhat matching (well, not exact) de-emphasis, but the disortion generated between only goes thru the final de-emphasis.

THAT's how to get the emotive guitar sound I prefer. It's not just tone, and it's not achieved by just adding a plate-starved distortion, generator or a saggy power supply.

And, with slight adjustment to the knobs and via playing technique, I can avoid generating distortion in those intermediate stages, and get a little gain at each stage and achieve a ridiculously beautiful clean treble sound.

Thinking like Nigel Goodwin makes for preamps like this PAiA and it's not bad, it's just not anything special IMHO and not worth my time building as it can't do what I require. I'd rather modify both channels of an Alembic preamp into one really special channel.
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Old 14th July 2012, 12:18 PM   #12
Printer2 is offline Printer2  Canada
diyAudio Member
Join Date: Apr 2010
I would just find a HV transformer and run the tubes at normal voltages. I tried tubes in the sub 100V range and do not care for it much. Mind you I want to try the 6SJ7 at about 100V to get a 30's - 40's amp sound. I did the back to back low voltage transformer thing, it works well enough for a preamp. As Loudthud says though, there is a bit of voltage drop from the primary resistance and the added turns they put in to get their voltage. Don't be tempted to feed a 6V transformer from a 12V one though, the 6V one seems to loos a lot of voltage and behaves badly a slight mismatch seems to work. I would just run a voltage doubler off the boost transformer. Should get an easy 250V.
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Old 15th July 2012, 05:03 PM   #13
Minion is offline Minion  Canada
diyAudio Member
Join Date: May 2006
Location: Cowican Bay , vancouver island
I built a stack in a box several years ago and is a nice sounding preamp and the speaker simulators sound great. It doesn't have nearly enough gain but that can be fixed by nodding the gain of the input opamp.
I use mine as a preamp that then goes into a 15 band equalizer then into a dbx compressor/gate then into my diy 2 channel tube amp.

It's the only starved plate tube preamp I have tried that actually sounds like a real tube preamp.

Since then I have built several for friends who love them. You really need to use an equalizer offer as it lacks any tone controls.

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Old 19th July 2012, 01:44 AM   #14
cyclecamper is offline cyclecamper  United States
diyAudio Member
Join Date: May 2010
Location: Chicago IL, Long Beach CA, Vienna VA
I was looking at some Weber kits. I'd like to buy the Fender Twin copy and modify it to suit my tastes, convert both 2-input channels into one 1-input adjustable-gain channel, with a switch to bypass 1 stage. Would need to make my own panel w/ labels...

They sell reverb spring units made by Belton. How do they compare with Accutronics?
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