John Suhr Provided Details Regarding the SL68 (JMP SL clone)

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Re: John Suhr Provided Details Regarding the SL68 (JMP SL cl

Postby vh junkie » Sat Jan 26, 2013 11:30 am

Pretty sure the Xicon resistors being used would be 1 watt (not 1/2 watt)... can you confirm? Half-watts would be kind of puny.

I know that sometimes 1000v caps are used, but usually that is because of their longer lead lengths (they can reach across a 3.125 inch board). The SL68 looks to use a narrower board (and closer lugs), so the caps could very well be 500v to 630v; but who knows, maybe the 1000v sound better!
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Re: John Suhr Provided Details Regarding the SL68 (JMP SL cl

Postby bmf5150 » Sat Jan 26, 2013 11:45 am

I was told long ago that the 1000v cd where the way to go, never tried the smaller volt ones
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Re: John Suhr Provided Details Regarding the SL68 (JMP SL cl

Postby EddyInChicago » Sat Jan 26, 2013 1:09 pm

My mistake. The resistor in the picture I posted is a 1 watt Xicon, NOT 1/2 watt. I was mistaken in thinking Suhr uses 1/2 watt for his builds. Still, that confirms, what I said before in my post. Those caps are larger/longer than the 1 watt resistor, implying they are around 200pF (I think).

Sorry for the confusion.
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Re: John Suhr Provided Details Regarding the SL68 (JMP SL cl

Postby projectx102 » Sun Jan 27, 2013 4:54 pm

Do we know for sure what value that fat cap is?
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Re: John Suhr Provided Details Regarding the SL68 (JMP SL cl

Postby projectx102 » Tue Jan 29, 2013 3:44 pm

That fat cap has to be a 250uf. A 25 is smaller in size and based on the gut pic, the V1a and V2a caps are the same size
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Re: John Suhr Provided Details Regarding the SL68 (JMP SL cl

Postby projectx102 » Sat Feb 09, 2013 8:30 am

Would it be giving away a huge secret to tell what the filtering is in the SL68? All I want to know is what the pre-amp cap is
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Re: John Suhr Provided Details Regarding the SL68 (JMP SL cl

Postby johnnybgoood » Tue Feb 12, 2013 10:20 am

projectx102 wrote:Would it be giving away a huge secret to tell what the filtering is in the SL68? All I want to know is what the pre-amp cap is

I wish someone could have helped you with a concrete value as well. I have a 250uf Atom cathode cap on V1a in my plexi. The cap is over an inch long. The caps in the SL68 aren't that large. An educated guess would be that the cap is no larger than 25uf.

See the post in the following thread. Hope this helps. Peace.
viewtopic.php?f=4&t=1845&start=7

Flames1950 wrote:250-330uF like Marshall used is way too much cap for the application. A simple 25uF like Fenders use should give a gain boost to all frequencies relevant to guitar or bass.
To lower the bass response you could use a smaller cap in place of the 250uF to focus the gain boost away from the bass frequencies. A 3 to 5uF cap would focus that boost on some nice hot midrange and high frequencies.
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Re: John Suhr Provided Details Regarding the SL68 (JMP SL cl

Postby projectx102 » Tue Feb 12, 2013 3:22 pm

I have a few of the 25uF Atoms and they are smaller than the Atoms in the SL68 gut pic
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Re: John Suhr Provided Details Regarding the SL68 (JMP SL cl

Postby projectx102 » Tue Feb 12, 2013 3:29 pm

As far as filtering goes looks like the two positives of the screens caps are tied together. So it's possibly a total of 32uF on screens.
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Re: John Suhr Provided Details Regarding the SL68 (JMP SL cl

Postby projectx102 » Tue Feb 12, 2013 3:31 pm

The 8uF 150v Atoms look to be the proper size. That seems to be a really odd value for those spots though
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Re: John Suhr Provided Details Regarding the SL68 (JMP SL cl

Postby Roe » Tue Feb 12, 2013 5:45 pm

projectx102 wrote:As far as filtering goes looks like the two positives of the screens caps are tied together. So it's possibly a total of 32uF on screens.


yes, that's my guess too (unless its 16uf caps)
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Re: John Suhr Provided Details Regarding the SL68 (JMP SL cl

Postby projectx102 » Tue Feb 12, 2013 11:35 pm

Well going with what Pete Thorn said: "low but not too low" I'm going to say the screens are a total of 32uF. Preamp cap in my amp is 32/32, mains are 50uF, PI is 100uF and now my screens are 32uF. Sounds pretty damn close but I'm still curious as to what value the two Spague Atoms are.
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Re: John Suhr Provided Details Regarding the SL68 (JMP SL cl

Postby sinasl1 » Sun Feb 17, 2013 3:57 pm

EddyInChicago wrote:Gentlemen,

Something I noticed in the gut shot John Suhr provided. Also, a few mentioned the specs; in particular the mixer and tone stack capacitors. I believe, 470-470/470pF mixer and 500pF (or 560pF) tone stack caps is incorrect. Looking at the picture carefully, I noticed a few things regarding the mixer cap and tone stack caps; the caps are longer than the resistors around them. And, I'm sure we can agree that John is using 1/2 watt resistors (they look to be Xicon).

So, what is my point? Glad you asked :) I've provided a picture that compares a 1/2 watt Xicon resistor to the CDE mica caps that are used in John's amp. The top cap has a value of 200pF (1000v) and the bottom two caps are 500pF and 560pF (1000v). All three caps are of the same type. I have (obviously) the 200pF, 500pF and 560pF CDE's. So, I think, the mixer and tone stack caps are closer to 200pF than 500 to 560pF.

John has also mention that every SL68 amp he builds, is put on a piece of lab equipment (he did say, but I forgot the name. It's an analyzer of sorts) and the EQ is swept to match the "Holy grail amp". In Pete Thorn's demo video, it's my opinion, that the amp almost nails the EQ part of Ed's sound, however a bit too much gain and clutter to my ears. EVH's amp, to me, sounds less distorted and more open and articulate. However, since the EQ (or voicing) of the amp is nailed, we get the impression that everything "falls together".

So, this is my contribution, opinion and detective work to this topic, for what it's worth. Check out the pic and let me know what you think.

Thanks....Ed

P.S I do believe that, as someone mentioned here, that the power tranny is switched from it's input. For example, two sets of leads that tap different points of the primary of the power transformer.




Hi guys, thought I'd chime in... cool thread! You guys amaze me with your knowledge. Most of it (90%) is greek, to me... :mrgreen:
Anyways, wanted to say, the "gain & clutter" thing you hear may be the fact that in my demo, I was using a 1-12"- even attenuated, there's something that happens with a 1-12" vs a bona fide 4-12".... I find that with a 4-12" things hold together better, I assume it's because you are spreading the amp output to 4 speakers instead of nailing one, as well as just the increased physical size of the cabinet. So that may be what you hear, or at least it's something to consider... the amp sounds killer no matter what, but it just really all comes together 100% when using a 4-12"

I have a new studio now, where I can use 4-12"s... and last week I was able to dime my SL68 into a greenback loaded /13 68 Marshall repro cab I have.. no master, no attenuation. Jesus, what a sound. I just live for that tone, ha :) Not very practical, but it is just the quintessential rock tone, to me. Often imitated, never to be equalled :rock: I think I will try and do this at least a couple times a week, it's a grounding experience for me, ha!
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Re: John Suhr Provided Details Regarding the SL68 (JMP SL cl

Postby Tone Slinger » Sun Feb 17, 2013 4:14 pm

You are a lucky man to be able to do that (dime your plexi, with no attenuation).I sure wish I lived somewhere that could handle the volume,or have a soundproofed studio.
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Re: John Suhr Provided Details Regarding the SL68 (JMP SL cl

Postby sinasl1 » Sun Feb 17, 2013 4:23 pm

Tone Slinger wrote:You are a lucky man to be able to do that (dime your plexi, with no attenuation).I sure wish I lived somewhere that could handle the volume,or have a soundproofed studio.


Ya, I lucked out, with my new studio. It's a commercial space, with some other guys with studios that work mostly biz hours in the same space... and after biz hours and on weekends, I'm generally the only one in there. Free reign to crank it! Now I just gotta get to work and make some music in there...
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