Carolina Overdrive Special conversion to Carolina Special - RT (TON mod)

[tubenit]

I'm looking at stealing one triode in the gain stage and converting it to Sluckey's Vactrol tremolo mod.  I tried removing the 12AX7 triode and just using the 5879 pentode instead and it still sounds fantastic to me.

Attached are the original COS with active FX loop and the converted COS with tremolo and reverb.

With respect, Tubenit

[tubenit]

This is what the layout board will look like with the TON conversion and then changing the FX into reverb.  Note that the Vactrol will be mounting on a super tiny board and that board mounted on the back chassis panel inside the chassis.

EDITED out layout board view as I changed the orientation of components.

[tubenit]

Here is a photo of the chassis interior and the tiny vactrol board and another turret strip that I will screw down on to the present layout once I remove the wiring from turrets 11 thru 13.

Does this look feasible?  I presume I'll need to do some trouble shooting but that's OK?  Does the basic approach seem reasonable?  Would you expect any noise problems at idle?

The amp sounds great as it is, but I'm intrigued by the Vactrol tremolo with reverb idea. 

If this seems reasonable with a potential of success, I'll order some parts from Doug and start this weekend or early next week on the conversion project.

With respect, Tubenit

[sluckey]

Yikes! Your schematic shows the Vactrol LED connected to the plate. That should be connected to the cathode of the tube.

The Vactrol is fragile. You may want to build the oscillator, but substitute a red LED for the Vactrol. The LED anode will connect to the tube cathode. When the LED is blinking, then put the Vactrol in.

PS... Just saw the pic of the amp. The Vactrol is sitting a long way from the INT pot. Be sure to use shielded cable for both connections to the pot. Speed pot doesn't need shields.

[tubenit]

Yikes! Your schematic shows the Vactrol LED connected to the plate. That should be connected to the cathode of the tube

.

Yes, you're right and I corrected the schematic

The Vactrol is fragile. You may want to build the oscillator, but substitute a red LED for the Vactrol. The LED anode will connect to the tube cathode. When the LED is blinking, then put the Vactrol in.

I am understanding the oscillator to mean the components (caps and resistors) on the board?  So, use the red LED and when that confirms the circuit is correct by  blinking then wire in the Vactrol?  Am I understanding this correctly?

Can you point me to a schematic (or link to one) using the LED and not the vactrol, please?

PS... Just saw the pic of the amp. The Vactrol is sitting a long way from the INT pot. Be sure to use shielded cable for both connections to the pot. Speed pot doesn't need shields.

Thanks for the head's up & yes I will do that.  Having a VERY quiet amp at idle is super important to me.

THANKS and with respect, Tubenit

[sluckey]

The Vactrol is an optocoupler, sometimes called opto-isolator. It contains two devices, a LED that shines on a LDR (light dependant resistor). You can't see the LED because it's encapsulated in the device. That's OK because the LDR can see it.

Here's a familiar schematic that shows an LED replacing the VTL5C1...

[tubenit]

As I am understanding the schematic,  the LED itself is NOT connected to the intensity pot but simply wired in to show a pulsating LED light which indicates the tremolo circuit is working?  Once the LED shows the circuit works, then I use the Vactrol to hook up to the intensity pot.     Is this understanding correct? 

Thanks and respect, Tubenit

[sluckey]

That's correct. The only connection between the LED and the LDR is the light beam, hence opto-isolator.

[turtle441]

Hate to jump in on a thread without something substantial to add, but before you pull that amp apart, any chance you've got a recording of it in its current state?  I've been looking at the Carolina Overdrive Special as I feel the need for another 2-channel amp in the stable, but have been struggling to find a demo.

[tubenit]

I don't have a recording of it's "current" state unfortunately. 

[tubenit]

Got some progress done on the conversion.  The OD is converted to the single 5879 now.  I cleared some rows of turrets needed for the conversion & I removed pots to be ready to install the ones needed for the conversion.   I ordered some parts from Doug that I need to do the tremolo mod.  Tomorrow I will get the one tube reverb going and wait for the tremolo parts.

However, I've run into a glitch.  V2-B is not wired up EXCEPT for pin 5 the heater wire.  I am getting a terrible buzz/hum with the V2 tube in.  V2-A is hooked up with a gain stage.  I tried different 12A_7 tubes with no success in reducing the buzz/hum.  I tried grounding pins 6,7 & 8 with alligator clipped wires and it did nothing to lower the buzz/hum. 

IF I remove V-2  and bypass it straight into into V3 the 5879 pentode, the amp is dead quiet at idle and sounds quite good. And the foot switched relay works fine that way.

I am thinking that with V2-5 heater wire hooked up that this is inducing the hum/buzz.  Could this be correct?

* See attached schematic.    V2-B will be used for the Vactrol tremolo.

With respect, Tubenit

[sluckey]

I am thinking that with V2-5 heater wire hooked up that this is inducing the hum/buzz.  Could this be correct?

I don't think so. There should be no problem with connecting pins 4 and 5 together, even with pins 6,7,8 totally disconnected.

[Joel]

I don't have a recording of it's "current" state unfortunately.

If I've learned one thing since I joined this forum, it's that Mr. Tubenit doesn't have a "current" state.  Everything is in a constant state of upgrade or teardown.  Dunno how you find the time mate.

[sluckey]

Jeff, since you are limited for space and you plan to have the Vactrol on a small board, you may also be interested in this TON version by 2deaf...

     http://el34world.com/Forum/index.php?topic=24472.0

[tubenit]

Mr. Tubenit doesn't have a "current" state.  Everything is in a constant state of upgrade or teardown

I resolved some years ago to not have more then 3 electric guitars, one acoustic and 3 amps. So, IF I want something different ………. then I have to sell an amp or rebuild one.      That's why you occasionally see me modifying something.  Honestly, most of the changes are small ones like changing FX to reverb, or changing something in the preamp. LTPI to power amp stay the same yr after yr.

Steve, I'm gonna stick with the tube triode for the Vactrol tremolo.  I don't have any of those mosfets LND150's & I've already cleared out some turret rows to try this out. 

With respect, Tubenit

[tubenit]

There should be no problem with connecting pins 4 and 5 together, even with pins 6,7,8 totally disconnected

Well, for some inexplicable reason ………… these ultimately seemed to be a problem on my particular amp.   

I ruled out tubes.   
I ruled out the relay switching.
V1a and V1b gain stages were super quiet  & the relay would click into the overdrive and it was quiet. So problem was V2-a.
I replaced the wiring on V2a and some components.
I had tried grounding 6,7 & 8  with no luck at all in reducing hum.

I was headed towards replacing the tube socket as I was running out of ideas of what could cause the problem. However, I noticed moving the heater wires would change the buzz/hum very dramatically even though I could NOT move them enough to reduce the noise to an acceptable level.

So, I decided to hook up pin 6 to pin 1,  pin 7 to pin 2, and pin 8 to pin 3.  I ended up paralleling V2 triodes knowing that it increases gain by 30%. I was concerned this would simply increase the buzz/hum, but it didn't!

That resolved the issue!  Amp is very quiet at idle & the heater wires no longer act like an antennae.  I think on my particular amp having pin 5 hooked up without pins 6,7 & 8 hooked up made the heater wires like an antennae and induced some awful loud buzz/hum.   I will not confess how many hours it took to find this solution. 

Issue resolved …………. on with installing the one tube reverb and then wait for the tremolo parts to arrive. 

[tubenit]

So far this amp is a great success for me.  The one tube reverb works excellent and can even get cavernous reverb.  I'm dialing it about "2" for what I want.  I'm currently using a 1M dwell resistor but may change this to 680k or a dwell pot.

The amp is amazingly quiet at idle even when the volume is turned up louder then I'd normally play at.

Just have the Vactrol tremolo to install now & I'm sure hoping that will work well and NOT add any floor noise as I strongly prefer a quiet amp at idle.

With respect, Tubenit

[tubenit]

Current state is the amp sounds really great and I'm waiting for some parts to install the tremolo. 

In the meantime, I've reconfigured the tremolo layout on the board from what I originally had.  This makes more sense to me and keeps the B+ on the tube side of the board and allows the turrent to the speed pot to be closer.

IF any of you see any mistakes, please voice them.  I hope to finish this over the weekend or Monday.

With respect, Tubenit

[tubenit]

I keep having spring projects delaying my finishing the tremolo up on the amp and then starting tweaks.  However, I am pleased with how it's going and I've installed the tremolo pots and wired up the turret board tremolo components.

And today I'm going fishing as the weather may prevent me from getting out this next 7-10 days.  Fishing trumps soldering in the springtime hands down.   

So, I'm at the point where I just need to hook up the B+ node to the tremolo system and then temporarily wire in the LED light to see if it's pulsating.  I plan to finish this tomorrow Thursday.  The speed pot is wired in but the intensity pot is not as I am understanding this to be wired in after the Vactrol is installed. 

Node A is 365v      B is 364v     C is 330v           

Q1)  Would any of these work or is there a strong preference?

Q2)  The LED anode connects to V2-8 cathode & the LED cathode connects to ground?  Correct?

With respect, Tubenit

[shooter]

fwiw;
my B+ tap was ~280vdc and got a good oscillation with an AX7
anode to tube, cathode to ground is correct.  I was measuring ~ 1.6vdc at tube cathode, LED flashed well

[sluckey]

I would use node B since the ripple is much less.

[tubenit]

Sluckey and Shooter,

THANKS for the info.  I'll plan to use node B and see what happens.  I can always lower the 470k if need be to increase voltage.   My plan is to work on this tomorrow Thursday

With respect, Jeff

[PRR]

> Node A is 365v      B is 364v     C is 330v 

The highest node is probably buzzy. Tremolo is thump-thump and feeding with the lowest-level stages may bleed bad? AND... it is one wire. Tack it in and try A or B or C. This year's Fantasy Baseball is no match for actually whacking horsehide and running bases; same for over-thinking musical electronics.

[tubenit]

Well, I was all braced to trouble shoot and tweak for the next several days to get the tremolo working properly.   

However, the amp tremolo is a whopping success!!!  I will admit that the only thing that threw me off was it working flawlessly to my satisfaction from the start!!      I'm just not used to that when experimenting. 

Yrs ago, I sold my Dano Centurian, and I've always thought that I will never ever have a tremolo that sounded that good again.  I don't have that amp to make a side by side comparison, but I will say this Carolina Special -RT is every bit as good as what I remember that Dano sounding. 

On PurpleTele's thread, I posted a YouTube of Paul Black and the FlipKings because that was the tremolo sound I wanted.  Well, this tremolo mod can easily do that or Creedance Clearwater Revival.  It's got that deep intensity and throbbing tremolo "thang" going just fantastic!

My main concern was that it would add floor/idle noise to the amp, but the amp is one of the quietest amps at idle that I've ever built and it can crank up amazingly loud also.  I can NOT tell that the tremolo addition added any noise at all. Not in the slightest. 

Sluckey (especially as he came up with this idea ), PurpleTele, Shooter and all the others that helped with this design ………… a HUGE THANKS!!!!  You guys knocked it out of the park!  It sounds sooooooo good! 

I am not sure why but the "one tube reverb" on this sounds "better" then my more Fenderish 12AT7 paralleled driver on my other amp. 

With the reverb around 2-3 and the intensity around 3-4 and the speed around 3,  I can get this incredible "swirly 3-D" type tone out of the amp now. It has a big rich tone to it.  I will try to do a demo and record a song sometime in the next week to 10 days and post the results.

I used node B as Steve suggested.   V2-6 goes from around 155v-240v,  V2-8 goes from around 1.12v - 1.36v  when the Intensity is "6" and the Speed is "4".

The Carolina Overdrive Special was a great amp before the conversion.  This Carolina Special -RT is also a great amp but just in a different way.  Instead of delay in an active FX loop,  I now have both reverb and tremolo.  The COS had more overdrive, but this Carolina Special - RT does still have a nice "boost" tone (not as overdriven) with just the 5879 pentode.

THANKS, gentleman!   This has been a fun project!   I will post an update in a week or so IF I tweak anything.  As of this post, my schematic is accurate. 

Best regards and with respect,  Jeff 

[tubenit]

The amp has NO business being so quiet at idle, but it's amazingly quiet.  Quieter then the original Princeton Reverb I had years ago at idle with the same volume set.

This chassis has gotten pretty messy looking as this is the 3rd or 4th iteration of the original amp.  I am somewhat embarrassed to show the messy work, but I thought maybe it might encourage someone to give this mod a try knowing it's still possible to have a quiet amp after the mod (IF it's done right)

Note the little board that I riveted on to the main board (& covered the rivet with silicone).   And note the littler board that has the Vactrol on it.  And it was a long run from the Vactrol board to the Intensity pot but all of this mod added ZERO floor noise to the amp.

I will eventually post the final schematic and layout in the ExpressSCH library for others.

With respect, Tubenit

[tubenit]

OK,  here is a quick demo of the tremolo on 4 brief rhythm/chording tunes.  I did NOT play any lead over this on purpose.  3 slower songs and one that was a little faster tempo and strummed.

https://soundclick.com/r/s8ckvt

To be honest, I think it sounds even better in person.  I'm not sure this was the best way to record it? 

What do you guys think?   One triode tremolo with 5881's.   I'm happy with it! 

Thanks Sluckey, 2 deaf, shooter, PurpleTele and everyone else who contributed to the success of this! 

It seems like it was a very easy to do installation that added zero to little floor noise.

With respect, Tubenit

[sluckey]

Here are two of my all time fav trem songs...

[tubenit]

Those are FANTASTIC songs!   I saw Canned Heat at the New Orleans Pop Festival in 1969 during the same summer as Woodstock,  Texas Pop Festival and Atlanta Pop Festival.  They did that song! 

[tubenit]

I am continuing to enjoy the amp.  It's quiet at idle and the vibrato works fine.

I am curious though ……………………………..

Looking at this schematic,  could the vibrato be effective at the LTPI entrance (indicated by a yellow/orange circle).

OR by connecting it to the juncture of the post LTPI caps and 220k resistors to ground.  In other words, connect to both sides there?

I won't have time to experiment with this for a few days, but I thought I'd ask IF those could possibly work?  IF so, I'll give them a try and report back.

I don't "need" to try this to correct anything.  Just like experimenting to see if I can improve something good to be even better.   

With respect, Tubenit

[sluckey]

A couple points I think would be worth trying are points R and RV. Don't connect to V5-2 because of the healthy bias voltage present there.

[tubenit]

OK, great!  Thanks for the guidance.  I'll give this a go later this week and report back.  Appreciate the help.

With respect, Tubenit

[Joel]

I've been wanting to build one of your Carolina Special amps for a long time.  Work and life keep getting in the way. One day... Until then this thread is just a tease... 

Given the choice between the active FX loop of previous Carolina amps and onboard reverb and trem, which do you currently prefer?  I'm not really a delay guy, but I love a good reverb and trem.  Having both built in is probably a bit too complicated.

[tubenit]

I'm not sure if I can answer that question.  I love the active FX loop with delay or reverb pedal  &  I like the reverb and tremolo.  I've been trying to learn more jazz as of late ………… so currently it's nice having the reverb and tremolo (set very light).  And that's more with a clean tone.

With overdrive, definitely prefer FX & delay.