grid blockers

[iknowjohnny]

I never seemed to need them in my main amp (marshall style home brew) even tho it's got a fairly hi gain pre. But i tried them for the umteenth time and this time with the circuit in it's 9 millionth incarnation they seem like must what the doctor ordered. Or at least to some degree. They are taming the hi end for me where other methods just didn't feel right. I suppose part of that is the elimination of any oscillations too. so heres the question....i tried 470k's, then 270k's. Both left my hi gain tones sounding fabulous and i couldn't tell too much difference. But when i roll back the guitar for clean tones they both sound ok but lack a bit of sparkle. I DO realize the top that they eliminate is where a lot or all of that is, but still i wonder if theres a way to have my cake and eat it to? To get that rounder less biting tone but still have some sparkle when i clean up.

[Jana]

"still have some sparkle when i clean up."


aw... you're mom would be proud!

[iknowjohnny]

Very funny miss Jana.....tech savy AND a comedian !

Now, to the grid blockers. Last nite i tried a 220k on the V1A plate. had one there B4 but went to a 100k for the cleaner more articulate tone. But the 220 gives a softer smoother tone. That+grid blockers=mud city. great for high gain on the higher notes but not much else. The 100k goes back in, now the grid blockers are just right. they give me a smoother tone and cut the harshness w/o any mud like with the 220k plate.

The one thing that drives me crazy about tweaking amps is like you said before....change one thing, many other things are not no longer optimal. You could do this for decades before nailing it, and in fact Jana i believe you said as much in a PM.

[Structo]

So you are talking about grid stoppers on the first stage of the amp?

Unless you are talking about the swamper resistors on the power tubes, I think those high values will alter the tone and output.

Typically you don't find them in that range of resistance.
Up to a point they won't cut much from the signal level but in the range you are in I think they do in fact reduce input.

Most of the time you see them well under 100K.
They are useful for high filtering as in RF coming into the amp but the amount you have there, I would think it would be detrimental to the tone and signal strength.
Typically you see values from around 22K to 68K and the highest I can recall was 100K.

[iknowjohnny]

No, i'm talking about grid stoppers or blockers, whatever you wanna call them, on the first few stages of a high gain preamp, not the input stage. I already have the typical 68k on the input. Or actually, i think it's a 47k, but that makes no difference. But the first stages of a high gain pre they really make a nice difference. I was just wondering about how to get that nice taming of the highs w/o losing sparkle on the top when i roll the guitar off. But i think since i went back to a 100k plate on the first stage they are sounding pretty good. i just need to fine tune the values. It's looking like probably 100k at the first stage after the input stage, then a 270-470k on the next, but i'm not certain just yet.

[Merlinb]

I was just wondering about how to get that nice taming of the highs w/o losing sparkle on the top when i roll the guitar off.

That roll-off is entirely due to the input stage. I would try reducing the input grid stopper to 10k or so, or add a bright cap to your guitar's vol knob.

[iknowjohnny]

no, thats not what i'm talking about. I have a cap in my guitar, and in fact even have it in series with a pot to djust how much high end it retains as i lower it. I'm talking subtle but very noticable (to me at least) loss of sparkle when i roll off. Not total mud like you get with no cap in the guitar. As to the input grid stopper it's 47k, but i never used anything there that made any difference that i noticed.

[Merlinb]

The trouble is that when you roll down the guitar vol pot it adds resistance in series with the input of the amp. Reducing the input grid stopper may help with this, but otherwise you can try a bright cap on your guitar vol pot to bypass the high-s around the pot's resistance. This is not really the same as the tone pot in your guitar.

[iknowjohnny]

Thats what i was saying...i already have a cap on the guitar's volume pot. .001 from wiper to input, and i have a 50k pot in place of one of the tone pot slots (i don't use tone controls) and it's in series with the cap to adjust it's amount of affect.

[Structo]

My favorite treble bleed on a single coil guitar is to use a 1000pf (.001uF) and a 150K resistor in parallel across the volume pot (250K).

It seems to load the pot differently and makes a smooth volume transition along with retaining the treble as you turn down.

[Merlinb]

Thats what i was saying...i already have a cap on the guitar's volume pot. .001 from wiper to input, and i have a 50k pot in place of one of the tone pot slots (i don't use tone controls) and it's in series with the cap to adjust it's amount of affect.

Oooh, now I get you. In that case perhaps you could try a bright cap or two in parallel with your attenuating resistors of grid stoppers, elsewhere in the amp?

[iknowjohnny]

Thanks merlin, but w/o exaggeration, yesterday i made what i consider the final and key discovery and the amp now sounds like the amp of my dreams. I've thought this before but this time i am positive because it's just so obvious and every issue i ever had is gone gone gone ! I'm only going to try a few different values in key areas where i have tried a few and not yet sure which i prefer, then zip her up either for good or for a long long time. Oh, and add a resonance pot since i have an unused pot hole i need to fill. the amp is truly the best sounding "marshall" i've ever owned. Now it's time for a new and very different build that i've been looking to do for a long time. Look for my thread about it....maybe you'll have some ideas for me.

[Merlinb]

Thanks merlin, but w/o exaggeration, yesterday i made what i consider the final and key discovery

Well, what was it?

[iknowjohnny]

It was a feedback network that Jana drew for me. Not much different from what i had but there was a R/C network at the beginning that apparently did the trick. At least thats what i think. There are a few ways to wire up a NFB loop that i've tried in the past, and possibly the way i was doing it wasn't the best for this amp, who knows. But it may have been partially that, partially that R/C pair, i dunno. I just know the amp is perfectly balanced now, all high end harshness is gone, the bass is now tighter, that squishy feel is there in spades, and i honestly cannot hear or feel a single aspect of the tone that isn't now very right. I had it close before this, but this just perfected everything. I should take a moment here to thank her publicly because she truly deserves some major kudos for going the extra yard in spending her time trying to help me. Few ever go to that length, and i appreciate that more than i can say. I spent somewhere between 1 and 2 years trying to make this amp sound like this, and she has helped me get it there. W/O that help i may never have gotten there. Even the tweak a week before this one which got me close to perfection was based on things she said. I have never played an amp i thought was perfect in my eyes, but this one just may be, and if not it's awful close. Thank you Jana !

[Jana]

You're welcome, now about the bill.... lol.