Deluxe Reverb Normal Channel Mods?

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Deluxe Reverb Normal Channel Mods?

Postby Cygnus X1 » Wed Apr 23, 2008 12:39 am

67 vintage Deluxe Reverb:

I've seen the Dumble mods at Schematic Heaven, and heard some clips.
They are oriented towards getting different "clean" sounds out of the
otherwise underused Normal channel, I guess. But, I love the sound of the
amp as it is, clean.

Are there any simple mods (easily reversible!) that utilize the normal channel
to be used as a gain (actually overdrive) to the vibro channel? Bridging channels on this amp doesn't work, because the inverse phase relationship to the reverb channel cancels out.

Since it's 95% original, I don't want to change anything for the reverb side.
I was just musing on the possibility of putting that unused normal side to use.
Perhaps using the pots on that side as sort of a Master volume?
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Postby Junction » Wed Apr 23, 2008 4:56 am

I have modified a Fender Twin for a friend who wanted the Normal Channel to sound like a Marshall, a bit of experimentation and what I came up with is you need more gain to get that Marshall overdrive and maybe a bit fatter in the bottom end. I ended up using the Bright switch (no longer as a bright switch), and rewired it in series with the ground connection from the tone stack, switching up, lifts the ground connection which added a significant level boost, at a guess maybe 10dB, this then drives the next stage with lots more gain and gives a really nice tube overdrive sound, the tone stack is still partially in circuit as it is now in series. I cant remember but I think treble and middle now have little or no impact and there seems to be a bass heavier shift, this actually resulted in quite a realistic marshall type overdriven sound.

I'll try to hunt down the modified schematic I have floating around home somewhere to verify exactly what I did.

He now uses an A/B swicth on the front end to switch between Normal and the Vibrato channel, works reall well. Does this sound remotely like what you are wanting to do?

Michael
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Postby Cygnus X1 » Wed Apr 23, 2008 8:01 am

Sounds good, Junction.
I would appreciate a drawing or schem.
I already have a toggle in the #2 normal input, and another slot
available where the ground switch is.
Best to put it up front, though. I'm pretty sure placing a signal path next
to the mains would be asking for trouble.
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Postby Junction » Wed Apr 23, 2008 8:40 am

Okay, you'll just have to give me a couple of days to find the schematic ... had a major cleanup last week and now I can't find anything!!

Michael
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Postby Cygnus X1 » Wed Apr 23, 2008 9:26 am

Thanks!
I really appreciate it.
Hopefully I can return the favor somehow, someday.
:)
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Postby dhuebert » Wed Apr 23, 2008 12:39 pm

I'm going to keep plugging Randy's website because I like it. For a good read:

http://tone-lizard.com/Table_Of_Contents.htm

Don
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Postby Junction » Thu Apr 24, 2008 11:21 am

Junction wrote: ... give me a couple of days to find the schematic ...


Cygnus, well I found some scribblings which resemble a schematic of some mods, but something doesn't look quite right ... I have this bad habit of cooking up mods and then not documenting properly ... hmmm!!

I have another Fender amp here I am fixing, might take a while, but when I finally get it working, I can try modding it and then let you know then. I don't want to steer you up the wrong path of some possibly experimental scribblings that may not work or screw up your amp.

Sorry for the initial bum steer.

There is one thing you can try, I am sure I did but I dont recall the resulting sound, but you could safely lift the connection from the Middle Pot to ground, this should give a serious gain boost and will surely push the next stage into overdrive.

Michael
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Postby Cygnus X1 » Thu Apr 24, 2008 2:56 pm

The DR doesn't have a mid control, if that's what you're suggesting.
Maybe lifting the bass?

As of now , I'm going completely stock on everything to make sure
all is in order before doing anything with the normal channel.

I have seen the Tone Lizard site, some good stuff there!

Thanks!
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Postby wyatt » Thu Apr 24, 2008 5:09 pm

I have not seen a mod that will drive the the Normal Channel into the Vibrato Channel, and I would think it may be a pretty invasive mod for a vintage amp.

I do know people have reworked their Normal Channel for a more Tweed tone, lots of midrange and more aggression, but can't seem to find info on this mod.
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Postby Junction » Thu Apr 24, 2008 7:31 pm

Cygnus X1 wrote:The DR doesn't have a mid control, if that's what you're suggesting.

Sorry I didn't look at the DR schemnatic, assumed it was the same as the TR.

Just had a look at the 67 Blackface DR schematic, I assume this is the same as yours? ... from one side of the bass pot there is a 6.8K resistor to ground, just remove one leg of this resistor from ground and you will get a significant gain boost.

Passive tone control circuits do not and cannot add gain or boost to any signal, they merely attenuate the signal when all controls are in the mid position and when you turn up the bass or treble, it is just attempting to restore the level back toward the normal level, but because there will still be resistive and capacitive components in circuit, connected to ground and in series with the signal path and from a simplistic point of view, acting like a voltage divider, there will still be attenuation of the signal even with all controls at maximum.

Therefore disconnecting the ground connection will reduce the attenuation, the treble pot will still partially in series with the signal path, if you turn the treble pot to maximum, it is no longetr in circuit and this should provide you the maximum amount of gain with this mod. With the ground cionnection lift, the tone controls will no longer act as tone controls, bass will do nothing, treble will affect the volume just a little.

Try it, it is an easy mod and can be reversed if you don't like it. Alternatively if you want significant gain increase you will need more tubes, this is much more serious mod and needs to be designed properly.

There are other mods that can be done to change the gain, but generally they may only squeeze a dB or two here and there and will probably not really get you into that zone of a highly saturated/distorted sound, that maybe you are looking for.

Michael
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Postby Junction » Thu Apr 24, 2008 7:40 pm

Just realised your DR doesn't have a Master Volume, so my suggested mod probably means your amp will be frighteningly loud, nevetheless if it does get you the crunch tone you are looking and it is now too loud, we can try experimenting with resistor values after the next tube stage to reduce the gain, or could possibly move the volume control after the next tube stage to do the same.
Michael
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Postby Cygnus X1 » Fri Apr 25, 2008 12:20 am

Junction wrote:Just realised your DR doesn't have a Master Volume, so my suggested mod probably means your amp will be frighteningly loud, nevetheless if it does get you the crunch tone you are looking and it is now too loud, we can try experimenting with resistor values after the next tube stage to reduce the gain, or could possibly move the volume control after the next tube stage to do the same.
Michael


Thank you Michael. You did a lot of homework for me!
I'm busy undoing all those mods (after I did the recap, and some shakey resistors) that I put in. Seems every rocker that has a Fender goes through a "Marshall Mod" phase at some point. LOL...
It just, dang, that Normal channel is just sitting there wasting it's time.
Oh, well.
I have a tweed to build, and just brainstormed something else.

I have a free curbside 70's Kustom Commander roll tuck I'm using to hold my other combo's up in the air. It might make a great platform to build into a Bogner clone. Hmmmm. Yeah, leave the vintage Fender stock, and play where it hurts nothing. Or at least, a lot less.

Thank you so much for your effort!
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Postby Cygnus X1 » Fri Apr 25, 2008 12:27 am

Looking back, I realised I didn't point out that this is an original AB763
BF circuit. It's one of those drip-edge silverfaces that was completely blackface inside. It has '66 iron, and '67 circuitry.
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Postby Cygnus X1 » Fri Apr 25, 2008 8:45 am

Alright!
The Deluxe Reverb is restored. Sounds good. I just need to bias it.
I did leave one mod in...the switch is connected to the negative feedback.

The Normal channel already sounds a lot richer than the Vibrato channel.
I'll leave it stock.
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Postby Cygnus X1 » Fri Apr 25, 2008 7:37 pm

Junction wrote:Okay, you'll just have to give me a couple of days to find the schematic ... had a major cleanup last week and now I can't find anything!!

Michael


BTW...I found a similar mod (I think) at this site:

http://blueguitar.org/schems.htm

"Hot rod Normal Channel on AB763 Super Reverb".[/url]
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