Carolina Overdrive Special 5879 plus

[tubenit]

Goal was to have a 3 gain stage clean channel that stays clean at a higher volume and an overdrive channel with the 5879.

One of the things I like about this amp is the clean stays cleaner and there is more contrast between clean and the OD channel.

http://el34world.com/Forum/index.php?topic=21803.0

CHECK for ERRORS!    Compare schematic with layout.  IF there is a discrepency, go with the schematic.

with respect, Tubenit

I have made some tweaks that significantly improved the smoothness of an already smooth OD

[tubenit]

Someone PM'd me about a Carolina Overdrive Special 5879 plus with one tube reverb.

CHECK for errors!    Compare schematic with layout.  IF there is a discrepency, go with schematic.

With respect,Tubenit

[tubenit]

]I continue to experiment with mods. Currently, I am enjoying this version ALOT!  Mods to note are the 68k on the OD level pot to ground.
And the mid cap switching going to the 250k mid pot in the tone stack.   I am finding that I use the mid cap switching more then I use the midboost switching.

I finally got around to trying a James Tone Stack in the OD channel.  This has been a winner for me! I think IF you try this build getting the right plate resistors  (either Vishay Dale RN65 from Mouser or Kiwame 2W carbon film from Parts Connexion & Orange Drop PS series caps are important for the tone. I suspect there are some other caps that may work well also? You might try Hoffman's Jupiter caps or the Xicons? While the 4-2019 schematic shows a master volume, I actually don't currently have that installed yet and I am still debating about whether to install it.

With respect, Tubenit

[Auke Jolman]

Here's the layout I made for building the COS.

In the layout are switches drawn, but I will be using relais. The powersection for the relais is already drawn.

With regards,

Auke

[Auke Jolman]

The PDF-file I uploaded did not show everything as clear as I thought. So I changed it a bit and uploaded it once more...

[tubenit]

Auke,

What a fantastic job you did on the layout!  VERY impressive!   Here is what I found that is either different or a mistake.

1) the boost resistor on yours is 270k from the 150k resistor.  I use 120K    (270k is fine)

2) the cap going to the send pot of the FX is .22 instead of .02 that you list.  I would use .22 or .44

3) you have a 330k resistor going from grid to plate on the 5879 tube.  I use 470k    (330k is fine)

4)  the NFB resistor is not wired right in your layout.   The NFB resistor should be between the NFB (notation) and the speaker.
     In other words, the NFB notation should be in between the presence pot and the 6.8k resistor. 

5)  It looks like you have both a Marshall style master volume and a PPIMV.  I'd use one but not both.  I had a PPIMV in mine
     but recently removed it & I am considering using the Marshall pre-phase invertor style master volume instead.  The PPIMV
     defeats/neutralizes the negative feedback when the PPIMV is turned up higher. 

I did not find anything else.  You really did a magnificent job on the layout! 

With respect,  Jeff

I sent you a PM about component parts.   

[Auke Jolman]

Hi Jeff,

Thank you very much for your kind words and for taking the time. It means a great deal to me.

I've changed the layout according to your findings. In addition I've changed the cap-value of the relais power to 4700 uf. I've been using a switching kit from Tube-Town on several occasions and they always added some kind of noise. They use a 1000 uF cap. In the forum I've seen others using a 4700 uF cap and decided to up the value.

I'll report back when the build is on the way.

With regards,

Auke

[Auke Jolman]

Totaly missed your comment on the PPIMV. I've removed it and added the changed layout!

[tubenit]

Don't forget your 220k resistors to ground now that you've removed the PPIMV.   

You've really done a great job on the layout!   Jeff

[Auke Jolman]

Can't thank you enough!

Added the changed layout.

[tubenit]

Here is the voltage chart of my amp in it's current state.  The PT is 300-0-300 using a GZ34.  I would advise paying attention more to the voltages on the nodes then on the preamp tubes. 

The reason for that is I will sometimes change those out.  For example,  I usually use 12AY7 in V1 but sometimes use 5751 and those tubes give different voltages  (with 12AY7 giving lower plates voltages).  I sometimes use a 12AX7 in V2 but typically a 5751.  I sometimes use a 12AY7 or 12AV7 in V4 (FX loop).   I usually use a 12AT7 in the LTPI but also a 12AX7. All those change the readings.   So focusing more on the output tube plate voltages and the voltages on the nodes of the B+ rail is a more helpful focus, IMO. 

It should be noted that I've also used a 5Y3GT and 6V6 tubes in this amp as well as a 5V4 rectifier tube.  Each gives the amp a little different feel and tone.

With respect, Tubenit

[Auke Jolman]

Jeff, thanks for the voltage chart.

I also use a PT 300-0-300. All the B+ voltages are in the same ballpark as yours.

Did wonder about the voltages of the 5879 tube. I thought they were lowish, but that's probably how it's supposed to be.

[tubenit]

Since the amp seems to bright for your Tele's and Strat's on the clean channel, try these modifications.  IF those don't work, try changing the silver micas in the clean channel to ceramics.

With respect, Jeff

[tubenit]

Auke, 

Maybe try these ideas to tame the distortion on the higher frequencies on the clean channel?

Jeff

[Auke Jolman]

Jeff,

Thanks for your ongoing support!

I'm sure I will get there. There must be some wiring error or whatever. I will check that first.

[Auke Jolman]

Jeff,

I've added the local feedback and also the cap between anode and cathode with no result I'm afraid.

Checked the wiring etc. in relation to the schematic and could not find anything out of order . Next thing to do is take out all the gain stages and add them 1 by one in the circuit again to hopefully detect where the added distortion starts. If you have any pointers as to where to start, there always welcome.

[Auke Jolman]

I thought that something in the preamp was wrong, as it turns out, I had miswired the 390 resistor on the Presence pot 

The amp sounds much better now. Did not dare to crank the MV, but will be able to do so tomorrow. I'll try to make some new soundbits.

[tubenit]

Progress!!!!    Hooray!!!       Please. keep us posted.  Thanks!

[tubenit]

I've done ALOT of work with this general amp design over a year period trying different things.  It has led to some of these changes:

-  one tube reverb instead of active FX  AND using a passive FX loop with the reverb.  This has worked fine with my delay pedals
   In fact, I honestly can't tell any difference in how good or less good the passive FX loop is from the active FX loop the amp
   originally had. Maybe the one tube reverb plays some role in that? 

-  I am now convinced that the James tone stack in the OD section works well to accent the mids for more of that vowel tone
   with some blooming of notes. Looking at Duncan Tone Stack calculator.  Watch what happened when you turn down the
   treble and bass on the James tone stack.

- this schematic gives a clean not that unlike Fender and an overdrive fairly similar to the Tweed Overdrive Special. I would say
  the overdrive is closer to the TOS tone then the Dumble clone YouTubes I've listened to.  The 5879 tube in the OD section adds
  some chime that I like.

- the large pot values in the OD section  250ka trim,  500ka drive and 1MA level allow for a very overdrive tone or dialed down
  to almost a boosted clean tone.  The OD section is pretty versatile in dialing in a range

- playing the amp about 6-8 ft away "testing" it today,  some of the notes would bloom into almost a feedback tone but retained
  their note definition. (the cab and speaker were facing away from me)

- there are some other minor changes in component values, adding some components and deleting a few not needed

- lastly I tried p2pAmps suggested of a floating buss wire and the amp has ZERO hum even when cranked loud.  It has the
  typical hiss of a high gain amp but any hum from grounding issues is completely resolved.  I find that significant for a high
  gain amp

The wiring is NOT neat.  It was moderately neat at the start but this amp has had it's fair share of experimenting with it and the neatness factor is lessened in doing that.  I am simply attaching the photo of the interior not because I am proud of it but simply to illustrate how I laid mine out.  Again, the amp is super quiet with no hum. 

With respect, Tubenit

[ChopSauce]

I just noticed this update accidentally. Thanks for sharing!

Your work is pretty inspiring.

I couldn't find a reference for that "floating bus wire" though.