Carolina Overdrive Special 5879 plus

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10thTx
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Carolina Overdrive Special 5879 plus

Post by 10thTx »

I am continuing to experiment with different Dumblish inspired designs where you have a clean and an overdrive channel. The Hammond PT on this one is 300-0-300 173ma. I used a Classictone OT 40-18000

My goal on this one was to use 3 gain stages in the clean channel to try and keep the tone reasonably clean up to 12 noon on the volume dial. I feel like I succeeded reasonably well with this. It has nice full tone to it, IMO and has some musical sweetness in the tone. It is reasonably Fenderish but slightly less mid-scooped.

One of the things that really surprised me was how quite the thing is at idle. Even at volumes beyond what I will normally play at, the idle noise is very very quiet. The original Princeton Reveb I owned once was more noisy at idle then this is. I think it could be easy to walk out of the room and forget to turn the amp off? However, when you hit a chord, it is surprisingly loud.

The overdrive is also to my liking and is very touch responsive with the 5879 tube. I may try tweaking this some more, but if it never got any smoother, I'd still be very happy with it. The 5879 tube does have a little chime inherent in it's tone.

This has more contrast between the clean truly being clean and the overdrive being more noticeably overdrive compared to the clean tone.

There is an editable ExpressSCH file for this on the 3rd page of this thread that was posted 4/9/2017. On the 3rd page of the editable schematic it shows the B+ rail.
http://ampgarage.com/forum/viewtopic.ph ... 0&start=30

with respect, 10thtx
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Last edited by 10thTx on Tue Apr 11, 2017 9:23 pm, edited 2 times in total.
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sonicmojo
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Re: Carolina Overdrive Special 5879 plus

Post by sonicmojo »

Very nice 10thtx!

Considering how modular you are with your schematics and layouts, do you do the same for your physical amp experiments? Or did you make this one a regular boxed up amp? I'm curious if you have any tips for how you experiment with all your ideas.
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Phil_S
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Re: Carolina Overdrive Special 5879 plus

Post by Phil_S »

10thTx wrote: Mon Apr 10, 2017 10:35 am There is an editable ExpressSCH file for this on the 3rd page of this thread that was posted 4/9/2017. On the 3rd page of the editable schematic it shows the B+ rail.
http://ampgarage.com/forum/viewtopic.ph ... 0&start=30
Hi there. I found the files dated 4/9/07. Each one seems to be only one page. No power supply or B+ rail found. Can you help? Thanks.
Phil
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pompeiisneaks
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Re: Carolina Overdrive Special 5879 plus

Post by pompeiisneaks »

I just opened them in jschem on mac and can see all 3 pages, page 2 has the B+. What app are you using to view them?

This is the exact link:

http://ampgarage.com/forum/viewtopic.ph ... 30#p371366

also its 2017 not 2007 :)

~Phil
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lovetone
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Re: Carolina Overdrive Special 5879 plus

Post by lovetone »

10thtx

Have you ever designed anything similar that use's the EF86?

We have plenty of these in the U.K.
10thTx
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Re: Carolina Overdrive Special 5879 plus

Post by 10thTx »

Have you ever designed anything similar that use's the EF86?

No, I have never tried one. I've heard enough complaints about microphonics to stick with 5879's. I have tried 6AU6 and 5654 with good results though.

with respect, 10thtx
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Phil_S
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Re: Carolina Overdrive Special 5879 plus

Post by Phil_S »

pompeiisneaks wrote: Tue Apr 11, 2017 7:08 pm I just opened them in jschem on mac and can see all 3 pages, page 2 has the B+. What app are you using to view them?
Hi Phil. This one gets a "D'oh <headslap>." I didn't see the sheet tabs at the bottom of the app's window. I'm using Jschem. Thanks for the help!
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pompeiisneaks
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Re: Carolina Overdrive Special 5879 plus

Post by pompeiisneaks »

No problem, we Phil's need to stick together! :)
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10thTx
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Re: Carolina Overdrive Special 5879 plus

Post by 10thTx »

The PAB on the original Carolina Overdrive Special 5879 plus wasn't being used much as it had a BIG jump in volume and had some high end hash/grind that I didn't care for.

I removed it and used the relay switch to add a Carolina Eclipse boost mod (installed it yesterday about an hr before the solar eclipse). This involved switching in a bypass cap on the 3rd gain stage in clean channel where there previously was only an 8.2k resistor unbypassed.

Nothing new about switching a bypassed cathode cap. However, I typically see them added to a plate/cathode ratio of 100/1.5 Obviously, 120k/8.2k is a very different ratio and ended up producing some sweet harmonics in this amp. I spent 2 hrs trying all kinds of values of bypassed caps from 2.2uf to 100uf and many different resistor values paralleled with the 8.2k and combinations of bypass caps and paralleled resistors.

I settled on 10uf/100v and 10uf in series with a 5.6k resistor paralleling the 8.2k cathode resistor.

The relay switching to ground is dead silent. The toggle switch allows either 10uf or 10uf in series with the 5.6k. The 10uf directly to ground adds a lot of sustain and a pushed overdrive tone with some grind. The 10uf with 5.6k in series has a moderate boost in sustain and volume and a VERY smooth overdrive. I think paralleling the 8.2k (larger then normal value resistor with 120k plates) is part of that formula.

Don't know if this would produce sweet harmonics on other amps? But thought I'd share the idea of a larger value cathode resistor being bypassed with relay switching.

ExpressSCH file for schematic and layout are on this thread on the 3rd page: http://ampgarage.com/forum/viewtopic.ph ... 66#p371366

With respect, 10thtx
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