Soldano Cold Clipper..

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midnightlaundry

midnightlaundry

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So, I think what I don't like about this amp (JCA 50) is the fuzzy mega compressed gain caused by the 39K Cathode Resistor... The clearest I can get the amp with the right amount of distortion is with the Gain on 3.5.. LOL The amp lays over when I dig in and doesn't clean up with the guitar volume. I want less gain and more dynamics..

I read about rebiasing this stage but I might get Grid Clipping on the next State. I don't think I want this.. I could up the Grid Stopper to like 500K?
I'll putz with it latter, but if I bias that stage with a regular 1.5-1.8K resistor what else could/should I do to achieve my goal??
 
If you reduce that 39K resistor you'll get a lot of grid clipping and bias excursion on the next stage.

If you want to do that then you should probably increase the grid stopper on the next stage and potentially put a divider in there to knock the signal down a bit. You can also decrease the coupling cap value (say 2.2nF instead of 22nF). You could try, say a 3.3K cathode resistor, increase the grid stopper to 470K and decrease the coupling cap to 2.2nF. You may want to put a treble peaking cap across the grid stopper to recover some of the lost highs (470pF or so).
 
the 39K cathode is not your problem. Go further down to the first CF stage and reduce that 220k plate resistor and your fizz, and too much gain will be fixed.

Looks like R28 on the JCA50 Schematic
 
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BackCrack said:
Have you tried swapping tubes? 12AT7, 5751, or a 12DW7?

The 5751 worked for mine....back when I owned it.
Click to expand...
Switching to lower gain tubes always dulls the final product if the stage wasn't designed for that tube.. And it doesn't change the overall bones of the amp.. I need to mutate this thing..
 
CrazyNutz said:
the 39K cathode is not your problem. Go further down to the fist CF stage and reduce that 220k plate resistor and your fizz, and too much gain will be fixed.

Looks like R28 on the JCA50 Schematic
Click to expand...
Shit, did that a LONG time ago..
 
C
cliffc8488 said:
If you reduce that 39K resistor you'll get a lot of grid clipping and bias excursion on the next stage.

If you want to do that then you should probably increase the grid stopper on the next stage and potentially put a divider in there to knock the signal down a bit. You can also decrease the coupling cap value (say 2.2nF instead of 22nF). You could try, say a 3.3K cathode resistor, increase the grid stopper to 470K and decrease the coupling cap to 2.2nF. You may want to put a treble peaking cap across the grid stopper to recover some of the lost highs (470pF or so).
Click to expand...
Cool, thanks..
I was thinking about lowering the Plate resistors on the earlier stages to like 47K, 82K ???
I fixing to jump in the rabbit hole this weekend.. LOL
I'm not trying to reinvent the wheel, but I just wanna make it a bit better for what I like..
 
midnightlaundry said:
C

Cool, thanks..
I was thinking about lowering the Plate resistors on the earlier stages to like 47K, 82K ???
I fixing to jump in the rabbit hole this weekend.. LOL
I'm not trying to reinvent the wheel, but I just wanna make it a bit better for what I like..
Click to expand...
If the input stage has a 220K you can lower that to 100K and that'll cut your gain quite a bit.
 
CrazyNutz said:
Good deal.

I've lowered the 39k cathode, but to me it loses it's character, starts to sound sterile, and you just end up with more gain LOL
Click to expand...
I understand that 39k was a mistake. Mike grabbed the wrong resistor and ended up keeping it.
 
psychodave said:
I understand that 39k was a mistake. Mike grabbed the wrong resistor and ended up keeping it.
Click to expand...
I've developed parts of my circuit this same exact way. Things I would of otherwise never thought of trying.
 
K2fq0.jpeg
JCA50HPOWER_zpsabf14bc1.jpg
 
So far, I tried a few things.. The easiest was switching in a 1M resistor with a 470p cap in parralel at R29. This allowed me to turn the gain up to 5.5 and have the same response as 3.5 on the Gain.. But the rollback is still dead like a Boogie Mark.. It's just lifeless.. Cranking the gain on this things is just a woofy, bloated mess.

I'm going to try lowering the bias on the early stages with a 2.2K cathode resistor in thoughts of keeping the overall freq response..

This guy has it all figured out. This page must be old, but it's new to me..
https://robrobinette.com/How_the_Saldano_SLO-100_Works.htm#Long_Tail_Pair_Phase_Inverter
 
Lowering cathode resistors is only going to shift the operating point for a given grid reference voltage. You need to stop thinking about cathode resistors only and start thing about load lines to achieve your goal of removing compression and fizz.

Example:

If you lower the cathode resistor, the cathode is less positive than the grid, meaning the grid is less negative than the cathode, meaning you're more sensitive to oscillation and instability for large peak to peak swings.. Your previous coupling cap will have to be reduced to prevent blocking distortion. The voltage divider on the grid of the same stage also changes the input impedance of the grid which has a massive change to your tone. As you flow more current through the tube, you'll find your voltage divider will play a more important role.

Another piece of advice - changes made further down closest to the power tubes will make more drastic changes tonally than starting at the input stages. It's definitely a sum of its parts type of mentality, but you'll have to be careful - increasing gain from tubes makes layout, solder joints, and lengths of wire more important to prevent instability.

I hope this helps a bit.
 
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I would first start with changing out the gain pot for a 250k. If it’s still too much try a 100k. Your 3.5 range will turn into 6.5 on the dial/pot. Other than the loop, the SLO is quite the perfect design.
 
I’d drop the first cathode bypass cap from 1uf to .68 to boost more mids and less bass. If you like it do it again for c26. It will also take some gain out as well.

To take out some bass and gain I’d remove C19 completely and put a 100k resistor in parallel with R29 to drive the stage harder. You can play with R29 and see what you like - 100k up to 470k.

Bypass C33 with a jumper - it’s a huge tone hit having such a large cap there.
 
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I appreciate the help..(y)
Man, I've had this thing a long time..
I actually did pull that cap on C33 years ago. There's another on C34 that I pulled as well.
I ended up changing the 1st stage bypass cap to .47uF, the second stage to .68uF, and I left the .1uF on C19.
I also changed the PI Coupling C10, C11 from .022uF to .047uF like the SLO..
It sounds way better to my ears., and is not nearly as gainy or muddy. The gain is on 5 now.. :ROFLMAO:
The Depth Control fills in the sound with the open back Combo Cab set on like 9:30-10:00..
I switched out the Stock Eminence with another Eminence I had laying around that has the small Dust Cap construction. I think the large Dust Cap speakers have a hardness to them that I just don't like..
 
I threw a mic on it. Recorded at a low volume with the Amp behind me. You can hear me pick with headphones on..
At a real volume the speaker would add some rip to the sound for sure, but not bad for a Combo Amp sitting in a bedroom..



IMG_20210926_162808783_HDR.jpg
 
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