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Question about preamp, boost and line-stage
Question about preamp, boost and line-stage
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Old 14th February 2013, 06:36 PM   #1
felipemuniz is offline felipemuniz  Brazil
diyAudio Member
Join Date: Mar 2012
Default Question about preamp, boost and line-stage

Well, I have been searching in the last weeks a way to give more amplitude on a final stage from a instrumental line. I decide to create this topic here on tubes / valves and not on instrumental forum, because generally speaking, what I need here, is not specifically to use with guitar or any other instrumentals, and also, I want to use tubes on this. But if the moderation decide that I'm wrong, no problem, I'm just want be cooperative.

The situation is:

I have a signal audio coming from a lot of digital effects racks and digital pedals. They process the signal that comes from the guitar and stuff.

After all this way, I have a stereo audio signal that are going for two solid state guitar amplifiers, each one on a channel, but to have in a pratical way, lets think with just a mono path, because the both channels need to work with the same way. They are the Vox Pathfinder 15R. I found they diagram here:


This amp are designed to distort the sound, and I think that is the wrong type of amp to use, since that we want just have amplitude, and not distortion (the effect pedals is there for this, right?) but the amps are already there, so I need a solution from this now. From now, I need ideas, but first, I'll tell some things that I have tried.

Between the amps and the pedals and stuff, we have tried a Boost, the Bravo audio booster.

Bravo Audio

In fact, my client have tried this, not I, but looking this, to me it is a circuit Valvecaster based, like (I can be wrong, since I dont have the Bravo here)

Click the image to open in full size.

He said that the Bravo gives the "warm up" that he need with the harmonics and stuff, but not with much "power".

It's hard to hazard a guess, but I think that maybe, a line-stage preamp design, like from schematic below, using the tube 12AU7 maybe can solve the problem, but is really hard to say.

Click the image to open in full size.

To test purposes, I made a cheap clone the VOX 15R here using the 4558 op amp and tda2009 not the 2030, as schematic says. I used just one channel from 2009, that is a AB amp, like the 2030, but is stereo.

I don't made the tremolo and EQ parts. And on place from LT9914, I just placed a 1Mohm resistance (look on schematic if you dont understand).

So, I recorded a sample here. I used my guitar connected to a Zoom Pedal G1XN to simulate the pedals path that he have there. I connect the Zoom to the 12AU7 line-stage preamp, I used the same configuration from the schematic above. In the end, after the C2, I added a B500K pot, with the C2 on right, ground on left and output on the middle.

After this I connected my clone from the Vox and recorded a simple sample here:


I need some opinions from people here. Maybe someone have a idea that can work better that my until now.

Really thank you for reading this. Greetings
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Old 14th February 2013, 09:18 PM   #2
Gilgy is offline Gilgy  United Kingdom
diyAudio Member
Join Date: Oct 2009
Felipe - you'll get a better response in the Instrument Amps forum. This one's really just for hifi.

Instruments and Amps - diyAudio
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