Snubber question

[jamme61]

Is it best to use snubber caps on the plate resistors or on the Preamp tubes? On the preamp tubes is it best plate to ground or plate to grid? Thanks for info on this

[iknowjohnny]

I've tried them pretty much everywhere they are used. There is no best place, theres only the best place for your amp and ears. For me personally, i prefer not to use them by trying to voice the amp so it doesn't need them to begin with because i don't like what they do to the way the tone cuts thru a mix. It can make it NOT cut. I find using them at the PI is ok in that regard, but putting them in the preamp stages tends to kill the top that needs to be there when distortion is being created. I find it best to used them AFTER the OD generating stages. Not that they can't sound good there, but like i say, it then has problems cutting IMO. As for how, i have tried them from plate to plate of one stage to the other and across one given plate resistor. the differences are subtle and hard to describe. It's best just to try it since it's simple and quick experiment. You could even alligator clip a cap and try it quickly then do the same with different values is necassary.

Also, to tell you the truth i find it takes too large a value to really attenuate highs to any degree that will help a bright am,p, but it does it in a bad way once the value gets high enough to do so IMO. Thats why i tend to dislike them. In fact, i came to hate what they do when the valuse is high enough to tame highs, and using small enough values not to cause that i began to hear other things instead of hi end attenuation, and i liked what i heard. But in the end that too hurt the to as far as cutting thru a mix. I believe someone here was experimenting with them and called them "smoothing caps" because of the way they seemed to smooth out the top. I liked that at first but in the end i felt it hurt the tone overall and it was better to reh\shape the overall tone with couplers and bypass caps and such. One last thing....in a non master amp with no preamp generated distortion via cascaded stages, you may find very different results. Heck, you may in ANY amp since we all hear different and expect different results. But i suspect everything i said would be invalid in say a fender twin.

[BTF]

If it's any help, my favorite niche in building is preamps, everything from acoustic to low gain clean to high gain. I've found that high end attenuation gives you a much more pleasing tone than simply building a JCM800 preamp in a box. That tends to give you a sound like you get with a direct out on an amp- very bright and edgy to the point of being harsh.

So, for my own taste, I've found the most pleasing option is to use an attenuating cap between the plate and the cathode of a gain stage. Carefully chosen, it rounds the highs off without the dark "tone turned down" sound of a cap from grid to ground or a cap across the plate resistor. I've developed a gradual attenuation over several stages, rather than trying to kill everything at one stage.

Hope this helps.

[jamme61]

Thanks for the time on this. My problem is dealing with a bogner ecstacy that i love but, it can sound a little muffled. You can dial up treble, mids, presence but, it's always there. I love the feel of this amp (very compressed IMHO in a good way) There's two caps- one on the second gain stage -1000pf (effects blue and red channel) and another -500pf on the third stage(only effects red channel). I've messed with both using clips and changing values but, its a balancing act that I feel I can't win. It's a compromise which I guess Bogner already dealt with in the design. best I've come up with is just lowering the first 1000pf to 250 pf and leaving the 500pf alone. There's also a 500pf in the negative feedback structure circuit that kills the highs a lot too. So far the amp sounds better without that too. sorry to go on so long. Thanks again

[Tone Lover]

If it's any help, my favorite niche in building is preamps, everything from acoustic to low gain clean to high gain. I've found that high end attenuation gives you a much more pleasing tone than simply building a JCM800 preamp in a box. That tends to give you a sound like you get with a direct out on an amp- very bright and edgy to the point of being harsh.

So, for my own taste, I've found the most pleasing option is to use an attenuating cap between the plate and the cathode of a gain stage. Carefully chosen, it rounds the highs off without the dark "tone turned down" sound of a cap from grid to ground or a cap across the plate resistor. I've developed a gradual attenuation over several stages, rather than trying to kill everything at one stage.

Hope this helps.

BTF give us an example of values so we can experiment to.
Thanks Bill

[sepulchre]

So, for my own taste, I've found the most pleasing option is to use an attenuating cap between the plate and the cathode of a gain stage. . . . . I've developed a gradual attenuation over several stages, rather than trying to kill everything at one stage.

Hope this helps.

This is the method I've used with great success in a few amps. Using at least a small snubber on two (or more) stages with varying values works best. It does indeed smooth out harshness without muddling the tone. I've used as much as 1000gF but more usually they're in the 250pF to 500pF range and sometimes less. The effect can be subtle but I A/B'd a lot to get just the right amount. They can make the difference between 'okay' and 'Deluxe' tone.

Like iknowjohnny said, it's better not to need them but in certain circumstances they can be the perfect way to attain the tone you're after IMHO.

[BTF]

I think the plate to cathode cap doesn't lend that "tone turned down" sound to the preamp, but rather warms up the stage. The stage doesn't seem piercing, and still has a nice round top. When I first began building rack preamps in the 80's, I was frustrated at how nasty the top was.

As to values in preamps, I've progressed to a cross-stage method. It depends on the circuit as to the values, but for instance:

In the lead preamp I built for myself years ago, it is essentially a tweaked JCM800 preamp with the option of using a Marshall or a Vox AC30TB tone stack. In the first stage I (to the best of my recollection) used a 1000pf cap PTC (plate to cathode)- I use Fenders, so I want to thicken the 1st stage sound a bit , a 500pf on the next stage, and an 820pf on the 3rd stage . I've found that if the cathode resistor has a bypass cap, the attenuation will be more dramatic as the PTC cap will decouple the highs through the cathode cap. That's why the 3rd unbypassed stage has a slightly larger cap. You pretty much have to experiment with preamp attenuation, as a 59SLP preamp needs less attenuation than a Soldano or Boogie preamp. If I were using humbuckers, I might have made that first stage attenuator a 500pF, or 820pF if the pickup is bright.

My clean preamp is a Super Lead preamp with a Bassman tone stack. The values on it (I believe) were 500pF, 500pF, 500pF. Note that the idea here is to warm the preamp and give it more of a "whole amp" sound in unison with the power amp. If your preamp is actually an amp preamp, you may not need all this.

Not much help, but if I can help I'll be happy to. Bill.

[BTF]

By the way, a good example of this PTC high end decoupling occurs on the Rivera-era Fender amps. I think warming might have been a side effect and that the actual reason for the PTC caps was to eliminate cross coupling in the spaghetti-like tangle of leads inside their higher gain amps!

I believe Boogie also used it on some of their II or III-series reverb drivers.

I tried this method after seeing it in my copy of the 1959 Radioman's Handbook. It's used in a speech clipper to round off the highs while keeping intelligibility intact.

Hope this helps! Bill.