help with d'lite OD

[bigmik]

hello everyone I finished my D'lite about three months ago and after fixing a few wireing mistakes in the tone stack it has been up and running ever since, in stock form it is a really good sounding amp and I always liked the clean sound but was never totally satisfied with the OD so I began to tweak the circuit with some of the great info provided by dogears, kelinm and others.the list of things that have been done are

changed choke resistor to 330, dropping string 3k,15k,2.2k with 150k fet resistor[voltages are 190's v1 202 v2 280's PI and 430 on the 6l6] PI plate resistord 110/100 ,grid resistors to 470 swamper's to 3.3, negative feedback resistor to 4.7 k rewired prescence the dumble way changed v2 plate resistors 150/220 with appropiate cathode resistors and bypass caps,v1 cath. bypass caps to 4.7 uf ,upped v2 a/b snubbers to 330 pf ,treble cap to 330 pf and possibly a few more that I don't remember right now . the overall tone of the amp has improved and seems more vibrant but was still not satisfied with the sound of the od,for lack of a better word it sounds HARD and brash not sweet and smooth like I would expect it to, I have tried adjusting the od trim ,re flowing all the connections nothing made any difference so tonight out of sheer despiration I tried a 47 pf capacitor across the plates 0f v2 like you do across the PI to check for osscilations and the sound drastically improved it sounded much smoother not hard and brash and for the first time I really dig the sound of the OD.So all of this to ask this simple question ,is the cap across the plate of v2 a bad thing? and is this pointing out a more serious issue with the amp ?

thanks
big mik

[keithrick]

Bypassing the Plate is one way, several amps have this feature. KOC talf about this in TUT-3.

I am not familiar with the D'lite circuit but you could increase the snubbers on V2 (if you have them) instead of the 47pfcap across the plate. Which is how Dumble did it.

Good Luck!

[bigmik]

hey kethrick I have tried upping the snubbers ,got 330 pf in there now it did help some with the high end ,but I am not bypassing the plate with the 47 pf cap but have it going plate to plate .is this still bypassing the plate?Ialways think of bypassing as going from positive to negative. thanks for the reply

[odourboy]

Hey Mik,

Approx. what value do you have your pre-OD trimmer set to? Where do you run your volume at?

[bigmik]

hello odourboy I got a resistence readin of 68k legs 1 and 2 of the od trimmer and i usually run my input volume between 11 and 2 master at around 10 and od level wherever it takes to balance it with the clean channel

thanks
big mik

[odourboy]

I'm not sure if leg 1 is up or down - so just try setting the trimmer to about 25K from wiper to ground as a starting point. It may be that you've simply got too much going into the OD1. That's going to make your tone harsh and grainy. I try to keep OD1 running in the compression zone - just shy of clipping - with max input. (For me, that's usually voluime at about 1:00, 6 on the dial). Let OD2 do the work.

[bigmik]

hey odourboy i tried you suggestion and lowered the trim pot to 25k to ground and it definately helped I think i'll keep it there for now .could you tell me what adding the capacitor from plate to plate on v2 actually does,Ican hear the effect's but what's going on technically?thanks.

[odourboy]

hey odourboy i tried you suggestion and lowered the trim pot to 25k to ground and it definately helped I think i'll keep it there for now .could you tell me what adding the capacitor from plate to plate on v2 actually does,Ican hear the effect's but what's going on technically?thanks.

Off the top of my head, I'd say that 47p cap is creating a local negative feedback loop which is only passing the highs - so it's like an active tone circuit to cut the highs. I'd rip it out if it were mine. It's just muddying the picture.

[bigmik]

Thanks for the explination ,it doesn't really sound muddy IMO it just seem's to take the trash off of the top end,but i'll probally pull it out and try upping the snubbers to 500 pf to see how that sound's,maybe I just need more appropiate speakers

[odourboy]

Sorry Mik. I didn't mean it would be making the sound muddy - I meant that it's not a 'Dumble standard' circuit component and it's behaviour in the circuit is going to be unpredictable, thereby making it difficult to nail down and fix the real issue(s).

For instance, if you turn your drive down really low, that cap might actually feed forward and act as a 'bright' cap. At higher levels, it will probably be providing negative feedback and tame the highs as I suggested in my previous post.

[bigmik]

no need to be sorry I apperciate your input ,I completely understand that it's a band aid and that is really the reason of this post that it might be pointing out other issues ,i'll post some pictures later and maybe you or someone else will point out some areas that can use some tightening up

THANKS

[odourboy]

no need to be sorry I apperciate your input ,I completely understand that it's a band aid and that is really the reason of this post that it might be pointing out other issues ,i'll post some pictures later and maybe you or someone else will point out some areas that can use some tightening up

THANKS

Go for it! If you've been following RJ Guitars' tone issues thread:
https://tubeamparchive.com/viewtopic.php?t=4506

Discussion and posted pics lead to uncovering three wiring errors, all of which would have adverse effects on his tone.

[bigmik]

here's some pics please have a look and let me know if you see any problem areas

thanks

[bigmik]

two more

[keithrick]

Bigmik,

I would look at the white wire from the treble pot to the volume pot. It looks like it is connected to the volume pot in two places in the first pic.

I would also check your grounds on the cathodes again. I assume the resistor to the first cathode is the treble bleed?

I am sure others will have more suggestions.