Diaz Vibroverb Project

[bnwitt]

So I am thinking about including the Diaz mods on the vibroverb project.  The Tube/Silicone rectifier seems easy enough.  A SPDT switch along with an added sand rectifier board to switch the B+ source to the standby switch.

 On the other mod I need some advice.  What's the best way to use a dpdt switch to disable the normal channel and tremolo tube to achieve the extra gain and overdrive?  Anyone know?

[phsyconoodler]

You can 'disable' the normal channel simply by using no shared cathode resistors.Have a separate cathode resistor/cap for each of V1 & V2.That effectively removes the normal channel from affecting the reverb channel.By using a switch to lift the 6.8k resistor off the bass pot you can add a boost.That disables the tone stack however.
   Then you can use a switch to lift the cathodes of the trem tube so they stop conducting current.Or better yet,just lift the lead off the trem intensity control.That will give you more oomph.

[bnwitt]

Ok, so on Doug's layout with the 6G16 bias vary tremolo I'll have to lift the lead of the intensity control that is labeled "10" so I still get bias to the tubes from 12 through 11 of the control right?

[sluckey]

Killing the trem on Doug's AB763 won't give you any kind of gain boost. There is a mod for a full blooded AB763 that puts a switch in series with the intensity pot. When the switch is open, the 50K pot is removed from the Vibrato channel signal path. This 'unloading' of the signal gives a significant signal boost.

If this is what you have in mind, you can accomplish the same thing on Doug's AB763 board by putting a switch between this 47K and ground. Just lift the bottom end of the resistor from ground and put the switch in.

[bnwitt]

Steve,
thanks a bunch.  I'll put that in and see how it does.

[blueznet]

Steve,
thanks a bunch.  I'll put that in and see how it does.

Bnwitt, I think I still have a leaked out schem and layout for the Diaz Vibroverb from Fender. As soon as I locate it want to have a lookie?

Those few mods are worth the effort believe me.

Darrell
Tx Amp

[Fresh_Start]

Killing the trem on Doug's AB763 won't give you any kind of gain boost. There is a mod for a full blooded AB763 that puts a switch in series with the intensity pot. When the switch is open, the 50K pot is removed from the Vibrato channel signal path. This 'unloading' of the signal gives a significant signal boost.

If this is what you have in mind, you can accomplish the same thing on Doug's AB763 board by putting a switch between this 47K and ground. Just lift the bottom end of the resistor from ground and put the switch in.

Steve - can you help me find that 47K resistor to ground in either the AB763 or 6G16 schematic(s)?  I've looked over both and just don't see it.  It looks like it comes right after the coupling cap between V4b and the phase inverter.  I don't understand it's purpose.

EDIT: just re-read the thread.  That 47K resistor a substitute for the 50K intensity pot in the vintage AB763 circuit, correct?

Also, Barry's original idea of switching out point "10" on the Intensity pot would disable the tremelo.  Would that reduce potential noise from the tremelo circuit even with Speed at 10 and Intensity at 1?
Thanks,

Chip

[sluckey]

That 47K resistor a substitute for the 50K intensity pot in the vintage AB763 circuit, correct?

Yes

Also, Barry's original idea of switching out point "10" on the Intensity pot would disable the tremelo.  Would that reduce potential noise from the tremelo circuit even with Speed at 10 and Intensity at 1?

I'm not quite sure what 'potential' noise is.  :) If you set the intensity control Max CCW then the 47uF bias cap should remove any unwanted trem signal. But if it doesn't, just engage the footswitch to the closed position. That will totally kill the trem oscillator.

Here's an actual schematic of the Hoffman AB763 layout. It might make it easier to see the circuit operation. Certainly makes it easier to see the effect of that 47K

http://home.comcast.net/~seluckey/Hoffman_AB763.pdf

I just recently drew this schematic to help with another troubleshooting challenge. Hope Doug doesn't mind.

[topbrent]

http://www.cpthorntonguitars.com/TQRAug07.pdf

Barry,

Here is a link to the tonequest article where they recovered a stolen SRV/Diaz vibroverb.  Documentation of the Diaz mods.

Might be of some use to those happy folks (like myself) following this thread.

Brent. :)

[bnwitt]

Thank you everyone for the contributions.  I think I have it pretty sussed out and will get back to the drawings next weekend.  Hopefully this project will be complete on paper in a couple of weeks and in amp form shortly after that.
Barry

[Greasehorse]

Steve,
thanks a bunch.  I'll put that in and see how it does.

Bnwitt, I think I still have a leaked out schem and layout for the Diaz Vibroverb from Fender. As soon as I locate it want to have a lookie?

Those few mods are worth the effort believe me.

Darrell
Tx Amp

Can I possibly get a copy of that also?...My nephew in Marble Falls is a SRV fanatic and has just bough a vibroverb he wants me to go through after I finish his Hoffman DRRI conversion...fee gratis of course..lol..kids! Plays at Poodies on Weds nights ...

[topbrent]

http://www.prowessamplifiers.com/schematics/fender/64_VibroVerb_Custom_SRV_DIAZ-This_is_the_new_64_Vibroverb_custom_with_the_Diaz_SRV_mods.html
(PDF) http://www.prowessamplifiers.com/schematics/images/64%20Vibroverb%20Custom%20Schematic.pdf


I just might know the "leaker" ;) 8-)

[bnwitt]

Ok everyone here we go.  I have modded the standard Hoffman AB763 board for both the 6L6GCs and now for the Diaz mods.  Everyone take a look at the board and help me find any errors.  The 6L6GC mods are explained in the archive section thread on that subject.  As far as the Diaz mods, I have taken the reissue schematic and applied three out of four of those mods and Sluckey's mod for the tremolo defeat to increase gain.   Until I post the layout it may be a little difficult to understand the mods but I'll describe them:

1. On the V2-a cathode I have changed the 1k5 resistor to a 2k7 and added a 3k3 resistor in parallel.  When not in the mod mode you have both resistors to ground giving you the stock 1k5.  When in mod mode you lift the 3k3 from ground and you get 2k7 ohms.

2. On the V2-b cathode I have changed the stock capacitor/resistor to a .68uf/2k7 and added a parallel 22uf/3k3  When in normal mode the two cap/resistor setups are in parallel and you've got 22.68uf/1.5k on the cathode.  When in mod mode you've got .68uf/2k7

3. The third mod is an off board mod which ( in mod mode) disconnects the normal channel from the phase inverter by breaking the connection of  the output of the V1-b plate .047 coupling cap to the 220k resistor before the phase inverter.  A 10meg resistor is placed on the second pole of the mod switch to ground when the connection is broken as in the Fender schematic.

4. The last mod is Sluckey's boost mod mentioned in this thread which lifts the 47k resistor of the V4-b plate from ground.  You'll see on the board that the ground buss wire does not extend to that resistor from the adjacent components as it does on Doug's normal layout.  This connection will simply go to the 4th spdt section of the mod switch and break the ground connection in mod mode.

The layout will also have the dual rectifier switch to choose between tube or silicone diode rectifier.  

So, please take a look at the board and I'll post the layout as soon as it is done.

[LooseChange]

Where you added the mods to the cathodes for V2b.  Add a 100k between the grounded cathode resistor/bypass cap and the free end of the cathode resistor you will be switching in for the mod.  Then when you add the switch across that 100k you will minimize the bump sound.

NICE work!

[bnwitt]

LC,
I'll try that out.  I have updated the boards pdf in reply #12 of the thread.  I added the little board that allows the tube/silicone rectifier choice.  I can't post the layout yet as it is too big even in PDF to fit the forum 100kb limits.  In gif or jpg it's too blurry.  I'll figure out a way to shrink it or link to it.

[HotBluePlates]

Here is a link to the tonequest article where they recovered a stolen SRV/Diaz vibroverb.  Documentation of the Diaz mods.

I haven't finished reading the article yet, but there are at least several details about the mods to the Vibroverb that, while the info on the mod may be accurate, the details of what change it would make to the sound are wrong or at least misleading. I don't know who the author is, but while they've had amp techs write articles in the past, this one looks like a non-tech who used crib-notes from a tech, but made a few errors on details...

[bnwitt]

Well, I 've basically gone by the leaked schematic and Sluckey's boost mod so it should be fairly accurate.  If not, I'll tweak the heck out of her.  This is going to be one fine sounding amplifier for sure.

[PRR]

> I haven't finished reading the article yet

I agree that some of the explanation may be muddled.

What I got from the story: SRV's "sound" was in his soul and his fingers. The amps' job was to stay together through soul/finger pounding. The guy was killing E130s! That's heavy air.

[bnwitt]

There are just so many glaring errors in that article (like the reference to AA764 and AB764 which of course should be 763)  that I can't take it seriously.  I decided to go with the mods that Cesar worked out with Fender, the beefier transformers (with proper impedance matching) the 3/4" baffle and Sluckey's mod.  A regular Hoffman Vibroverb AB763 produces a great SRV tone in itself so I think with these mods it will sound great.  Hopefully I'll have it up and running in the next couple of days.

[bnwitt]

Ok a little update.  I found a couple of value mods in the Diaz unit's preamp caps and I've made those to the layout.  .022s for the orginal .047s.  Also, I completely redid the filter cap board to the way Diaz had SRV's with the 220uf and 47uf series cap assemblies for stages 1 and 2 for the increased bass response and the higher voltage capacity to accomodate the silicone rectifier.  The last thing is the 100k resistors in place of the 68k resistors on the input jacks.  I may have to play with the value of the resistor that drops in and out on the bias feed until I get it right with the bias vary tremolo.

With the exception of Doug's brownface bias vary trem and of course the subsequently required boost mod by Sluckey this will be alot like SRV's amps when in the mod mode.  The board file in reply 12 has been updated.  Still working on the layout while building the amp.

[Geezer]

I'm going to throw something in here for consideration, since the article mentioned the OT being a 2 ohm unit & the EVM-15L being 8ohm..........maybe you would want to add the ability to purposely mismatch the output (?)

To support this, I'll give personal experience (and at the same time testify to the extreme toughness of the old Fender amps.)

I had a 1969 "drip-edge" Super Reverb (Silverface, but I suspect it was BF circuit) when I was 18 years old & playing in a glam-rock band back in the 70's. Bought it from an old lady's basement sale for $50.00, put new tubes in it & hit the road....no biasing, no stinkin' tube matching..just cranked it up & played.

Wanting to give the soundman maximum control over the mix out front, I disconnected the 4x10's & ran it into a "monitor style" closed back cab on the side of the stage that had a mic stuck in front of it. The monitor was loaded with an EVM-12L / 8 ohm.......yes, a 2 ohm OT into an 8 ohm load.....wide open (ALWAYS wide open), as that's how it sounded best. I'd just rake my hand across the controls & max everything  to "10" (except the reverb & trem, of course).

That amp was the BEST sounding rock amp I have ever played! I played it @ hundreds of gigs, it never failed me, and (being the stupid kid that I was) I never even had a backup amp!! That poor 2 ohm OT must've HATED me! (but she never gave up the ghost!)

Anyway, a multi-tapped OT (very beefy, of course) may be another "mod" that would allow one to fully explore all the tonal possibilities of this amp....maybe 2-4-8 ohm(?)

[bnwitt]

I'm going to throw something in here for consideration, since the article mentioned the OT being a 2 ohm unit & the EVM-15L being 8ohm..........maybe you would want to add the ability to purposely mismatch the output (?)

Geez, I've been mulling that over.  It goes against my engineering soul to mismatch the OT P and S, but I am using a Super Reverb rated PT and OT, and the OT has a multi tap secondary so it would be a simple thing to add a rotary switch.  The C15N I have is 8 ohms too.

The only down side is I've already had my plates made but I guess I could do some Trainwreck style label maker stuff ;D  Subsequent models could be laid out that way.  I think I'll try it matched and mismatched to hear the tonal variance before committing.

[Geezer]

I have a Bandmaster Reverb head cab & a Weber chassis that I'm eventually going to built this circuit into.

Weber has the MM Toneclone Super Reverb OT w/ 2-4-8 taps (# FBFS-O40MM) for ~120.00...not too bad.
Anyone know where to get any better MM prices out there?

[sluckey]

boost mod by Sluckey

Just for clarity, I didn't dream up this AB763 mod. I've seen it all over the net but don't know who may have thunk it up and labeled it as a boost mod.

I did struggle with just the opposite when I built my TDR. I had omitted that resistor in my scaled down single channel DR and when I fired it up, the gain was a bit hairy... much more than I remembered an AB763. It took me several hours to find the mistake. I kept looking for a problem between my schematic, my board layout, and the actual board and build. The same ole song, I've looked and looked and it's wired right.

...but my schematic was wrong. Once I put in the 47K resistor (later replaced with a MV) the gain tamed down and sounded like the classic BF Fender.

[bnwitt]

boost mod by Sluckey

Just for clarity, I didn't dream up this AB763 mod... when I fired it up, the gain was a bit hairy...

Steve,
I could very easily wire it up where the 47k resistor is grounded or another value takes its place, like 82k.  Do you think that would tame the gain a little?

[bnwitt]

Geez,
after mulling over the impedance thang I have changed the amp layout.  I put in a 3 position selector switch where I had the Stock/Hi Gain switch and moved it to the preamp end of the chassis which will make for shorter wires to it anyway.  This allows the user to mismatch if he wants and of course to use extension cabs.  More versatile all around.  Take a look at the plates in the attached file.

[sluckey]

I could very easily wire it up where the 47k resistor is grounded or another value takes its place, like 82k.  Do you think that would tame the gain a little?

I don't think you'll hear a difference between 47K and 82K or even 250K. I think the switch is the answer. Remember, I was looking for a classic Black Face clean sound. If I had wanted a higher gain with some dirt I would have left the resistor out.

Don't you have an AB763 amp that you can lift that 47K resistor (if Hoffman) or Intensity pot (if true AB763)? The sound difference is obvious. And very usable as a boost. I just wasn't looking for that sound when I built my TDR

[bnwitt]

Don't you have an AB763 amp that you can lift that 47K resistor (if Hoffman) or Intensity pot (if true AB763)?

I do, but with the multiple changes in the preamp and power sections of this amp, I think it will be better to just finish this one and see how the boost sounds combined with the other changes.  If I think it's too much I'll just eliminate it from the mod switch.

[Fresh_Start]

Greasehorse - my experiences with Mercury Magnetics have all been pretty positive.  Sorry you had a bad time.  The +25 pricing makes complete sense from a business point of view.  Wait!  They are a business!!!

As far as Doug carrying MM iron, why would he?  He's got Heyboers made the way he wants 'em and Doug's prices seem very fair to me.  (don't know if all of his trannies are made by Heyboer, but I've got complete confidence in the product)

Respectfully,

Chip

[sluckey]

And the "Hey they are a business" reply was just flat rude.

I certainly didn't see it as rude. But then my communication skills are often deficient. So, what did your off topic rant contribute to this thread?

[sluckey]

Rant?

While not offensive to me, your comments about MM and Angela certainly sounded like a rant.

[sluckey]

I got it. Still a rant. And no reason to jump in Chip's sh#t.

[jhadhar65]

Okay, now, which way is it spelled:  "[size=14]sh#t[/size]" or "[size=14]sh$t[/size]"?

Also, that's nine last words, by the way.  Unless you break the hyphenated one into it's two natural parts, then you have ten.

Don't you city folks know nothin' about the three R's - Readin', Ritin', and Rithmetic?  Sheesh!

I wonder if Barry's amp is finished yet?

[Dynaflow]

 Wow the forum lost its happy thoughts for a moment...  [smiley=cussing.gif]

Regards,

Dyna

[bnwitt]

I wonder if Barry's amp is finished yet?

Not yet, I keep getting interupted by service customers.  I just got a 93 reissue AC30 back out the door and I'm finishing up an SWR Red face Bass 350.  Both solid state PIA's to work on.  I hope to finish the BFVV tomorrow. If I do, I'll post comments and pics.

[bnwitt]

Well gang I have finally finished the SRV Vibroverb.  Along the way I had a little mishap that an experienced builder like me shouldn't have had.  I put the B+ wire on the two series 47uf caps on the wrong darn turret.  Blew those two caps and the PT. :'(  Shame, shame, shame on me for not paying close enough attention and for not using my light bulb limiter on start up.  Thank you sir may I have another!!!! 

Since then I've been playing the "solid state service guy" and the amp has been sidelined.  Today I swapped out the trannie and two filter caps and cranked her up.  I am here to say that the amp (as everyone in here helped me design it) sounds fantastic!  I am really pleased with the stock/hi gain switch and what it does to the amp.  With Tube rectifier and stock settings it is a beautiful quiet on idle Hoffman AB763 BFVV but with sand rectifier and hi gain setting it is a real crunchy beast indeed. 

Thank you everyone for the help.  I did put in the multi tap secondary but haven't tried the 2 ohm / 8 ohm OT/speaker mismatch yet.  This amp is already sold but I will try to get some sound samples from the new owner's try out session.  I have attached some pictures but because of the size restrictions of this site they aren't very good.  I'll try to get some up on my photobucket site tommorrow.  I will try to get the layout finished soon and share it with everyone.

[bnwitt]

Here are two Pdf files.  One on the final plates and one on the partial layout.

[bnwitt]

Ok, so there doesn't seem to be much interest any longer in this design so if anyone wants info IM me.

[6G6]

Hey Barry,
It looks like you just did get that wrapped up by year's end.  ;D
Thanks for working out all the details and sharing with everyone.

[Fresh_Start]

Ok, so there doesn't seem to be much interest any longer in this design so if anyone wants info IM me.

You're kidding, right?  It looks great! :D

Thanks for sharing your design and development process.  Sometimes I just learn more from lurking than I do from asking questions.

Happy New Year,

Chip

[LooseChange]

Ditto what Chip says!  Great work and very informative.

[bigdaddy]

I just recently read the whole thread.

I read a long time ago that Diaz used Twin reverb output transformers.

That's what he said in the interview.

That would make it an 8 ohm load for the speaker......am I right? So there was no mismatch.

[bnwitt]

I just recently read the whole thread.

I read a long time ago that Diaz used Twin reverb output transformers.

That's what he said in the interview.

That would make it an 8 ohm load for the speaker......am I right? So there was no mismatch.

What I read was that he used a Super Reverb PT and OT.  That means the OT was a 2 ohm secondary and the speaker was 8 ohms so there was a mismatch.  Even with a Twin there would have been a 4 ohm secondary OT and an 8 ohm speaker and still a mismatch.  My amp uses SR trannies with a multitap secondary on the OT.

[bnwitt]

Ok believe it or not I am finally back on this SRV Diaz modded Vibroverb.  The buyer backed out and I shelved it.  He found himself an actual Fender 64 Custom Vibroverb for $1,300 used.  Even I understand why he bought the Fender. 

The amp is working on the silicone rectifier mode but I've developed a problem on the tube rectifier mode.  On the tube rectifier mode I started getting weird VDC reading fluxuations out of pin 8.  I had the tube rectifier wired to the PT HT VAC wires upstream of the silicone diodes.  So I thought I would wire it like the Fender version which basically ties pins 4 and 6 of the the tube to the married output of the two silicone diodes.  Switched it on and my 5AR4 recitifier started flashing internally.  So now I'm scratching my head.  Take a look at the attached shot of the Fender dual rectifier set up.  Anything wrong with the way it's setup?

[bnwitt]

Here is how I had it wired before.  I'm hoping this is just another JJ tesla GZ34 rectifier gone bad.  I've had alot of those in the last year.  I am out of GZ34s at the moment so I ordered some sovtek and Rubys.

[sluckey]

You may like this idea. You can use a DTDT if you want to also switch in a sag resistor.

[bnwitt]

Fellows you're never going to believe this one.  I have just discovered that the key on the socket base of JJ Tesla GZ34 tubes is so small (shallow) that you can insert them into a standard fender octal socket in any position without lining up the key and slot.  I tried it with several bad ones I had in a box and the one I just put in and they're all the same.  I did find a new working one in my stock and found the same thing.  I was very careful to line up the key in the slot before putting it in.  I tried 4 different tubes which were purchased two years apart.

[bnwitt]

Ok, I just did a little more testing and some octal sockets from the same batch won't allow the JJ bases to be inserted incorrectly.  Looks like it may be the sockets and not the tube bases.  And I paid good money for these things.

So all is good with this amp.  Nice and quiet on idle, great vibroverb tone in the stock mode, roaring gain in the SRV mode.  I'm going to try and get the origninal buyer to bring his Fender version over for an A/B comparison if I can.  I'll try to finish the wiring layout in the next few weeks.  This is a very good amp for future builds.

[bnwitt]

Sluckey,
your schematic is how I had it wired in the first place.  I am currently using a DPDT switch, but the second side is bypassing an extra in line bias resistor to maintain tube bias in the two different rectifier modes like in the Fender.

[bnwitt]

Ok, I had the shootout between the Fender SRV Vibroverb and the Hoffman Vibroverb with the brown era tremolo and the Hoffman version won hands down.  So many similarities but the Hoffman version had a purer tone on all settings.  The owner of the Fender unit started asking me about modding it to come closer to the Hoffman unit.  Major success tonally.  Hooah!  It feels great when things go well.