Vibrolux 1-channel clone w/d*mble OD circuit - need advice

[markmalin]

Hi, all.

I built up this circuit last year.  It's a single channel Vibrolux (67'ish schematic) with no vibrato, and a D*mble style OD circuit which is switchable.  I love the tone of this amp!  Now I need to figure out how to better suit the OD to this schematic, though.  Basically the OD works, but it has so much gain that I can't really get a distortion sound out of it (like in the D-clones that I've built in the past) without turning the level almost off and gain almost up and volume way up.  This basically makes the "level" control on the OD circuit act like a master volume.  Where I fall short in my skills, and where I'd like your design input, is how to modify the OD circuit to make it function correctly for this amp.  Do I need to add a master volume?  Is there some way I can modify the gain (or overall level) of the OD so it's more usable at reasonable volumes?

Thanks guys!

Humbly,
Mark.

[Willabe]

Hi markmalin,

There are many guys here that know a lot more than me, but you could try lifting the ground end's of the 2, 5uf k bypass caps on the extra gain stages (V2) and see what happens? Wont hurt anything, and if you don't like it or it does'nt help, just solder them back to ground.   If disto tone is better but too dark now, you could 1. - take out the 270 pf thats on V2a plate to cathode, 2. - change V2a plate CC,  0.01uf to a smaller vaule, maybe 0.001uf or so, and/or 3. - bypass series R's 100K and 180K that are hooked up between the plate CC and the OD drive/OD level pots, with maybe 100pf or 250pf caps. You may also need to put in a voltage divider, by hanging a resistor off the 100K or 180K (maybe both?) to ground, maybe 100K to 470K, just guessing, or make V2a grid stop larger.          

    Just my $0.02.          Brad              

[tubenit]

On the Clean channel.  I'd get rid of the 22uf cathode caps and use 2.2uf  and/or I'd use a 5751, 12AT7 or 12AY7/12AV7.



ON the OD channel ......

This is what I personally would try starting with the 5uf caps becoming 2.2uf.

Then I would try a 5751, 12AT7 and then 12AV7 in that order.

With respect, Tubenit

[sluckey]

Is this OD switch really wired as drawn? I see the OD level pot connects thru the switch to the input of the reverb driver, thru the reverb tank, recovery amp, and reverb pot before being mixed back into the dry/clean signal just as the reverb would normally be mixed? This makes no sense to me. Is the drawing just wrong or am I missing something?

[Geezer]

Is this OD switch really wired as drawn? I see the OD level pot connects thru the switch to the input of the reverb driver, thru the reverb tank, recovery amp, and reverb pot before being mixed back into the dry/clean signal just as the reverb would normally be mixed? This makes no sense to me. Is the drawing just wrong or am I missing something?

Yes, IF it's wired as drawn, you have the od circuit and the reverb circuit in series......you want the reverb parallel, right?

[Willabe]

Oohh, now I see it, I think. In series with the reverb the OD would "over drive" and muddy up the verb, possible giving the reverb cir. fits. If the verb is in parallel with the OD/dry signal, the verb stays clean and is independent of the OD settings?


          Brad,                        

[JayB]

Oohh, now I see it, I think. In series with the reverb the OD would "over drive" and muddy up the verb, possible giving the reverb cir. fits. If the verb is in parallel with the OD/dry signal, the verb stays clean and is independent of the OD settings?


          Brad,                        

Yup. he also has the reverb mixer in circuit to, which isn't a bad thing, that will add a tad more overdrive at higher volumes.

[markmalin]

Is this OD switch really wired as drawn? I see the OD level pot connects thru the switch to the input of the reverb driver, thru the reverb tank, recovery amp, and reverb pot before being mixed back into the dry/clean signal just as the reverb would normally be mixed? This makes no sense to me. Is the drawing just wrong or am I missing something?

It is as drawn, yes.  My thought was that I wanted reverb available when the OD circuit is engaged.  Not a good idea??

[markmalin]

Is this OD switch really wired as drawn? I see the OD level pot connects thru the switch to the input of the reverb driver, thru the reverb tank, recovery amp, and reverb pot before being mixed back into the dry/clean signal just as the reverb would normally be mixed? This makes no sense to me. Is the drawing just wrong or am I missing something?

Yes, IF it's wired as drawn, you have the od circuit and the reverb circuit in series......you want the reverb parallel, right?

Thanks Geezer.  Yes, I have them as shown.  I want to say up front here that I'm probably in over my head here with this design -- so that being out of the way and my ignorance being established---should I rather have it in parallel?  Can you help me understand why?  Again, the idea was to take a very Fender'ish circuit and add a D*mble OD to it.  I realize the D' doesn't have a reverb (and when folks add reverb it isn't typically a 2 tube configuration).

[markmalin]

On the Clean channel.  I'd get rid of the 22uf cathode caps and use 2.2uf  and/or I'd use a 5751, 12AT7 or 12AY7/12AV7.



ON the OD channel ......

This is what I personally would try starting with the 5uf caps becoming 2.2uf.

Then I would try a 5751, 12AT7 and then 12AV7 in that order.

With respect, Tubenit

Thanks Tubenit.  I'll play around with the 2.2uf in the OD circuit and try some lower gain tubes.  Good idea.  As for the normal pre-amp section ("clean") I love the tone so I may hold off on changing anything there.  It is a very sweet throaty Fendery tone.

[markmalin]

Oohh, now I see it, I think. In series with the reverb the OD would "over drive" and muddy up the verb, possible giving the reverb cir. fits. If the verb is in parallel with the OD/dry signal, the verb stays clean and is independent of the OD settings?


          Brad,                        

Yup. he also has the reverb mixer in circuit to, which isn't a bad thing, that will add a tad more overdrive at higher volumes.

Hm...this is intersting.  I do notice the OD overdriving at higher volumes.  I've heard of people switching the Reverb out of the circuit when using this OD -- but I want to be able to keep it in.  Sounds like maybe I would rather have the Reverb in parallel so it's independant of the OD settings.

[Willabe]

Keeping the sound of the Fender "clean" (less OD mod) channel is why I suggested working on the OD's R,C values and not the Fender 1'st 2 triode (1 tube) stages R,C values. With that said, tubenit --IS-- one of the "go to men" here with-out a question IMHO, for this kind of thing. I would listen to him way before any thing I would have to say! I'm trying to learn from him.

Look at a recent thread on Fender cathode bypass caps, should help you very much with this build and others.  

You can have still have reverb on both the clean and OD channels, but you'll have to change the dry/ wet signal "tap" in the circuit to keep both the clean and OD channels in parallel with the reverb.

It's been done before, (nothing new under the sun) with two separate/independant reverb controls for both clean and OD channels, so you can have different levels of reverb on both channels to your personal taste.

The guys here will be able to help you with a different switching schem.

        Hope this helps you,      


              Brad              

      

[tubenit]

Here's an idea for you ..............

On clean, you have typical Fender.  I think with the insertion point AFTER the OD that you'd still have plenty of reverb to spare without the reverb becoming distorted.  Note the 1M reverb pot.

On Overdrive you have Fender two first gain stages then the OD.

This method eliminates that "5th" gain stage that may be making the OD "too distorted & unuseable"?

Hopefully Sluckey or Geezer or someone more knowledgeable can comment?

I always have wondered how to get that clean Fender tone and then have a D_mblish OD also? Maybe this would work?

I probably would still do three things using this schematic:  1) lower the Fender cathode cap values to 2.2uf-5uf range  & 2) add a master volume to the Fender clean AFTER the "3rd" Fender gain stage & 3) add another filter cap on the B+ rail. I think you have alot of stages hooking up to the "D" node.

With respect, Tubenit

[markmalin]

Thanks, guys.  I truly appreciate the input and explanations.  Brad, thanks for the explanation on the R,C values.  I know enough to be dangerous...or should I say, enough to get myself in over my head.     But learning from you guys is great! 

Tubenit, you drew up schematics!!!  Thanks!  I'm going to take some time this week and play around with these.  I need to see if I have enough components.  Also looking forward to the other guys' input.

Cheers,
Mark.

[tubenit]

Mark,

PLEASE don't rewire anything until Sluckey and/or Geezer comment on my schematics.  I left them a PM requesting their input.   I think what I drew will work but would feel more comfortable hearing from them.

With respect, Tubenit

[markmalin]

Mark,

PLEASE don't rewire anything until Sluckey and/or Geezer comment on my schematics.  I left them a PM requesting their input.   I think what I drew will work but would feel more comfortable hearing from them.

With respect, Tubenit

Sounds good :)  Thanks for the heads up.

Cheers,
Mark.

[markmalin]

Hi Tubenit,

Hey, I'm looking at your schematics and I see you have the reverb located after V3a whereas in the original Fender schematic (that I used to cut/paste for my version) the reverb is before V3a.  Isn't V3a considered the "tone recovery" part of Fender's schematic ... which would be after the reverb?  (I'm sure it's something I'm not understanding, but it's puzzeling to me)

Mark.

Mark,

PLEASE don't rewire anything until Sluckey and/or Geezer comment on my schematics.  I left them a PM requesting their input.   I think what I drew will work but would feel more comfortable hearing from them.

With respect, Tubenit

[sluckey]

There are several ways to do this, but, I suggest using this drawing as a good starting point. All you gotta do is rewire the switch. This puts the Vibrolux circuit back to original configuration and inserts the OD circuit between the Vibrolux preamp and PI (just like it would be in a passive FX loop).

Then you can work on taming the gain in the OD circuit. I suspect that one gain stage may be plenty.

[tubenit]

Hey, I'm looking at your schematics and I see you have the reverb located after V3a whereas in the original Fender schematic (that I used to cut/paste for my version) the reverb is before V3a.  Isn't V3a considered the "tone recovery" part of Fender's schematic ... which would be after the reverb?  (I'm sure it's something I'm not understanding, but it's puzzeling to me)

I am personally not convinced that you need the V3a as a tone recovery on the Fender and it does add some gain to the reverb. Every LTPI amp that I have added reverb to ....... has been done as I have drawn in the suggested schematic.  The FX-Reverb Unit that I recently built has ALOT of reverb to it and the insertion point (again) is just before the LTPI.  Not saying it's better. But I will say it sounds very good to me and I like it.

Having said that,  ......... I'd follow Sluckey's suggestion.

With respect, Tubenit

[markmalin]

Thanks, Gents.  Tubenit, I'm going to give Sluckey's rewiring of the switch a quick try (it's easy enough to do!) before moving any further and see what happens.  Thanks so much both of you guys for your help.  I love that about this forum :)

So if that works better, on to taming the OD...

[markmalin]

Just wanted to report back - I rewired the reverb per Sluckey's schematic and it seems to work great.  I started tweaking the OD and it's pretty descent sounding.  Maybe having them inseries was just too much gain?  I think in an ideal world I would have a master volume on this amp because on a Dumble you need to crank the first volume (kind of acts like an input gain) in order to drive the OD circuit hard enough to get that Dumble sound.  In my case with this amp, w/out a Master volume I kind of have to play the amp loud to get into that range.  So that's one option - adding a Master.

I think tone wise the OD is sounding Ok.  It's a bit bassier than the clean, but I'm good with that - I'm thinking if it weren't on the Bass side it would get too fuzzy.

Incidentally, I tried a nice Telefunken 12AT7 I had in the OD socket.  It gave the OD less ability to distort, so I may stick with the 12AX7.  I need to experiment some more today, though.

Thanks again guys! I think I'm heading in the right direction. 

One thing - is it conceivable that I could have a master volume which would only switch in when I turned on the OD, or does that sound kind of stupid?

Mark.

[sluckey]

...I could have a master volume which would only switch in when I turned on the OD...

I would think that your "OD Level" pot already does that. It sits just before the PI like a pre PI MV. It would be trickier if you want a post PI MV though.

[markmalin]

...I could have a master volume which would only switch in when I turned on the OD...

I would think that your "OD Level" pot already does that. It sits just before the PI like a pre PI MV. It would be trickier if you want a post PI MV though.

It kind of does.  I mean, if I turn the level WAY down (like barely on) and increase the Volume to about 35% I can get some serious overdrive at something just above livingroom volumes.  The slightest nudge of the OD level and it's major "Honey, will you turn that thing down!" volume.  Maybe I need to think of a different value pot for the level?

I've been tweaking the OD input pot (the 100k on the board) and it's sounding pretty nice, by the way. Lots of punch, gain and sustain.  Not a Dumble by any means (not that creamy Santana distortion) but I really don't want that, so I'm OK with that.

[sluckey]

Change that trim pot to a 1meg audio taper and maybe even remove that 220K on top of the trim pot. That will allow more signal into the OD stage. Be sure to use audio taper pots for the "OD Drive" and "OD Level" pots. You should easily get bedroom level distortion.

[markmalin]

I bypassed the 220k with a clip-lead and it really does drive it harder.  More distortion is on tap.  I must admit, though, I think I like the tone with that in.  Kind of fun playing around with it, though ;)  I'll have to  pick up a 1M trimpot and see what difference that makes.

Thanks again for all the help!
Mark.

Change that trim pot to a 1meg audio taper and maybe even remove that 220K on top of the trim pot. That will allow more signal into the OD stage. Be sure to use audio taper pots for the "OD Drive" and "OD Level" pots. You should easily get bedroom level distortion.