Single Channel Deluxe Reverb

[yohanmishkin]

Hello everyone,

I'm very new to all of this so please bare with me, but my interest has taken me towards a '65 Deluxe Reverb. However, I'm only interested in having a single channel with no vibrato or reverb included (so not exactly a '65 Deluxe Reverb). I assumed the best place to start would be the schematic. I was hoping to find some help with that. My intuition tells me that large portions of the current schematic can be completely "cut out.," but obviously this is something I don't want to mess up. The channel I'm interested in keeping is #1 on the Vibrato Channel, but completely disregarding the vibrato and reverb circuits.

I'm aware that there are many starter projects available on the net, but I really have my heart set on this. Thanks a lot!

http://www.ampwares.com/schematics/deluxe_reverb_ab763.pdf

[tubesornothing]

Cut out everything in the red boxes.  Re-draw the schematic (or be nice to tubenit), post it and we'll take a look.

[tubenit]

Here is a starting place. Download the FREE ExpressSCH program and you can use these schematics to redraw your own
schematic and layout.

http://www.el34world.com/Forum/index.php?topic=579.0

I personally would probably have a mid pot and use a smaller value than the 3.3M resistor like maybe a 1M.  However, anything less than the 3.3M resistor will allow more overdrive/gain. I'd probably start with the bias control as shown in the schematic I posted but it may need to be tweaked? And if so, look in HOFFMAN's Library of Info about bias control information.

With respect, Tubenit

[yohanmishkin]

Thanks a lot! I'm gonna get right on this, I really appreciate the quick responses.

[yohanmishkin]

Ok, I took one of the schematics listed on the forum and I tried adding a Middle Control as well. I'm not 100% confident that it's in the correct place.

It appears now, that without the other channels and no reverb or vibrato, there is a total of 5 tubes (3 - 12ax7 and 2 - 6v6). I don't quite understand how the volume control functions exactly. It looks like the volume control is essentially acting as a preamp volume control, similar to one you might see on a Marshall JCM 800. If so, would it be possible to add a sort of "master volume" control?

Thanks for all of the help, the resources here are amazing.

[tubenit]

The schematic already had a mid pot prior to you drawing a second one.

You will have to experiment to see if a 500k or 1M audio master volume is to your liking.

With respect, Tubenit

[tubesornothing]

If you wanted to add a master, then add it right before the PI coupling cap.  You will have to add a coupling cap before it though after V3a plate.  I.e.  the coupling cap from v3a isolates DC geting to the master pot, and the coupling cap on the PI prevents the zero DC on the master volume pot from messing with the bias of the PI.

Lets see,

Your first gain stage will bump up the signal about 40 times.  Lets say from 200mV to 8V pk.

Your tone stack (without a CF) will cut the signal about 1/3, so from 8V down to 2.6V pk.

On your next gain stage at 100% volume, gain will be again 40 times, so we are back up to 104V pk.  BUT really its going to hit its limits, so lets say around 60V pk.  This stage is the start of your preamp distortion.

Then we hit the 3.3M resistor.  This will drop the gain a lot about 70times, so your signal is back down to 0.85V pk.

Now into v1b about a 40x gain, so signal is up to 34V.

If your master was on 100% - or you had no master at all, you would be cramming 34V into the PI.  On a clean swing the PI could probably handle 2V pk before some kind of distortion starts to happen, which is OK, the PI is used for distortion on a lot of circuits.

So looking at it this way, a master would be a good thing to help you get more clean out of the amp. You also have two places for distortion:  V1b and the PI. My suggestion, once you have this built, is to replace the 3.3M drop resistor with, say  a 50% voltage divider.  This will give you a lot more signal into V3a and help you shape more distortion on the other side of the wave.  By adjusting the plate and cathode resistors on V1b and V3a you could really get lots of saturation or lots of hard clipping distortion on both sides of the wave.  Anwyays, food for thought.