Need help tweaking OD

[Tonegeek]

Problem:
When my OD channel is on, the breakup is not as sweet as I think it could be (kind of buzzy), nor is the tone as "fat" as I would like. I could use some help on tweaking. I have 2 sound clips to illustrate with. One is clean channel no boost, bright, deep, etc. (although it may have mid boost - forget), and the other is with OD, PAB and mid boost on.

Just found out I have a bandwidth limit so try the other links if these fails
http://www.geocities.com/tonegeek/dcloneclean.mp3
http://www.geocities.com/tonegeek/dcloneod.mp3

alternate links
http://www.freewebs.com/tonegeek/odsample.mp3
http://www.freewebs.com/tonegeek/clean.mp3

Test Conditions:
Mex Strat w/stock ceramic Pups, except bridge pup that has had about 1000 extra windings added for more mids and output. Guitar controls wide open.
50 watt HRM, Marshall iron, currently with El-34's biased to 40ma (Not tried 6L6's yet), onboard loop, Sprague PS caps (see attached schematic which includes my voltages. also, I used values NOT in parenthesis)
Earcandy open back Boa cab w/2 12" Avatar Hellatones. Upper Mids and highs on this speaker/cab combo are very evenly balanced but are somewhat overpowered by the bass/low mids regardless of what amp I use. With adjustments at the amp the cab is still useable. Neg FB resistance is 8k-10K (trimmer is almost all the way up). I worked with the NFB a good while and it just sounds too thin with the trimmer below about halfway. The sound opens/fattens up with less FB.

I did my clips with the loop completely bypassed, plugged directly to the input of the amp. I used an SM-57 about 8" slightly off axis from one speaker into my PC with an impedance matching xfrmer.

Clean channel:
I am getting a good, full tone from the clean channel with all deep, bright, and PAB switches off. I can tweak the settings with the bright and or mid boost on and get good sounds as well. For the clean sample I have the treble, and mid controls all the way up. Bass control is about 35%. Mid boost is on I think. Presence is backed off a bit from full (the taper is all wrong so it is real sensitive from 80% to 100%) I crank the volume up and keep the clean master down to get slight distortion on hard playing. The tone is full and clean normally but With Pre-amp boost, on it starts to break up really nice. So far, no complaints except that I hope I never need more high end (I think different speakers would help this). I have a very useable bright switch (reduced stock value to 100pF), but it seems to make the OD situation worse. BTW- while researching my lack of top end, I removed all shielded wire (2 - 6" pieces). I could detect no difference in the tone, so I put the two pieces back.

OD channel:
I can get the OD channel to sound pretty good clean, but when I push it, the distortion is not quite right. People report the OD channel is better with PAB on and I agree, but it still does not sound sweet enough when it is breaking up. I have tried it with lots of drive and just a little (preferred). I just need a good blues lead sound (think Robben on Mystic Mile). I like a really fat, mid slanted sound for leads, but I am getting some top end buzziness. For the OD clip My OD stack is set:
Bass 25%-30%. This control is very sensitive and at about 30% it suddenly jumps way out of control. I basically just matched the bass level I get on the clean channel if that helps describe it.
Mid 80% up
Treble 50% up
PAB on
clean tone stack and switches the same as clean sample other than mid and pre amp boost switches on.

I have tried the OD entrance trimmer at different positions but not sure it makes a lot of difference. It seems to be a bit better cranked. As you can see on the schematic, my clean master is out of the circuit when OD is on. I have tried turning down the clean volume just in case it was overloading something but it does not help. I can get the OD channel to clean up so I doubt my gain structure is contributing to the buzzy distortion. I can't imagine the 12pF bleeder on the OD master is contributing much to the problem, as the sound is fine until pushed. Other areas I am looking at are:
OD2 plate resistor- maybe it needs to go to 150K
clean master treble bleeder- if I up it then I might be able to turn down the treble control which would also affect the OD

Maybe my guitar is the problem. I do seem to want it to sound like a Les Paul for leads and realize single coil pups are a challenge. I would love to try a guitar with Humbuckers, but don't have one. However, since I have other amps that this guitar works well with, I think tweaking the clone is what is needed. Any ideas?

thanks,
Whit

[Bob-I]

You didn't mention what tubes you're using. I've found that the EH 12ax7's tend to sound smoother at higher gain settings.

I've also found some of the additional TS switches to be tone suckers, especally the bass boost and rock/jazz but it doesn't look like you have one of them. Try removing them temporarally to see the results.

Try lifting that bright cap off the OD master, it may have more effect than you think. I've adjusted OD1 coupling cap on mine, .0022uF to .0033 and even to .01.

[Tonegeek]

You didn't mention what tubes you're using. I've found that the EH 12ax7's tend to sound smoother at higher gain settings.

I think I took your advice earlier and got EH 12ax7's. BTW someone else mentioned a bad batch of them and I had one go bad after only a few hours of use. AES is kindly sending out another one gratis even tho it was 2 months ago that I bought them. I guess they understand builders may not get around to using something for months. I have an old Groove tube in there now. The EH went bad in the middle of my testing so not sure if the Groove tube is affecting the sound, but it may be. I tried a Sovtek LPS, but it definitely affected the sound (too much gain), so I took it out. Also If you notice my voltages on CL are 187, 194. Last week I only had the clean channel working so I removed the OD tube which put my voltages about 10 volts higher. I swear it sounded better last week, (the clean channel that is). I will do an A/B test tonight with just the clean channel using last weeks conditions to be sure (my guess is I won't hear a difference with just 10 volts, but who knows).

I've also found some of the additional TS switches to be tone suckers, especally the bass boost and rock/jazz but it doesn't look like you have one of them. Try removing them temporarally to see the results.

no jazz, deep is off (effectively out of circuit)

Try lifting that bright cap off the OD master, it may have more effect than you think. I've adjusted OD1 coupling cap on mine, .0022uF to .0033 and even to .01.

The bleeder is an area to try. The coupler seems OK only becuase I seem to have enough bass already. If I increase it, I will have even more, but of course the corner freq. of it may be different (thats why I can see spending months on just tweaking- the possibilities are endless!).

I used mostly ceramic pF values, but I am however using a silver mica for the .002 treble cap in the CL (the 390 treble cap is ceramic). I have a ceramic on hand of the same value, so I may swap them just to cover that base. Even though my clean channel sounds good to me, I guess it could have an effect on OD. If the first stage is off, then it just gets worse, don't you think?

It seems like I need to some how brighten up the clean channel, not that I need it, but I am running my treble control maxed out which for me is unheard of. I was thinking about increasing the clean master bleeder. That way, I can turn down the treble control which will give less highs going to the OD (the master and its bleeder are out of circuit when OD on). At this point I am honestly not sure if I have too much highs on the OD. It is more of the way it breaks up rather than too much high, if you know what I mean. But, I will keep working with it until i get a better feel for what it sounds like to me.

[heisthl]

Nice playing on the clips - Maybe its me but I don't hear any note bloom or enhanced harmonic overtones in these clips (read sterile sounding). I would adjust filtering and NFB to get more life in the sound before OD tweaking. Maybe I'm just used to hearing the non-Marshall transformer versions.

[Normster]

If your amp sounds better with V1/V2 10 volts higher, try changing the 150K dropping resistor to 220K. BTW, I thought the amp sounded pretty good and didn't notice any extraordinary fizz, but as heisthl said, maybe a bit 2-D sounding. You'd be surprised how much the right speaker and cab will effect that, however.

[Bob-I]

Also If you notice my voltages on CL are 187, 194. Last week I only had the clean channel working so I removed the OD tube which put my voltages about 10 volts higher. I swear it sounded better last week, (the clean channel that is).

Yes, these ckts are sensitive to voltage, much more so than other amps. Try adjusting the PS rail resistors.

The bleeder is an area to try. The coupler seems OK only becuase I seem to have enough bass already. If I increase it, I will have even more, but of course the corner freq. of it may be different (thats why I can see spending months on just tweaking- the possibilities are endless!).

The bleeder can make it a tad harsh. I don't have them on my amps.

It seems like I need to some how brighten up the clean channel, not that I need it, but I am running my treble control maxed out which for me is unheard of.

That's simply wrong. I usually run treble at about 10-11:00 and I use Hums. Yes I make adjustments when using a Strat, typically more on the mids though.

I was thinking about increasing the clean master bleeder.

I wouldn't. The clean bleeder works in reverse when in OD mode. Think about it.... when you have the OD switch on, the clean bleeder is connected to the OD entrance. Depending on the clean master setting some highs can be bleed off through the master.

It almost sounds like you're losing highs somewhere, perhaps an oscillation or something bleeding the highs to ground. It's very odd to have to crank the treble that way.

[Tonegeek]

I don't hear any note bloom or enhanced harmonic overtones in these clips (read sterile sounding). I would adjust filtering and NFB to get more life in the sound before OD tweaking. Maybe I'm just used to hearing the non-Marshall transformer versions.

Yep, I agree, it is 2D, sterile, even accounting for the fact it was recorded totally dry. I don't have much experience making comparisons between one dry recording and another, they all sound bad to me. If you guys know of some dry Dumble clips with bloom and overtones I could listen to, then let me know so I can get used to what to expect.

It seems like I need to some how brighten up the clean channel, not that I need it, but I am running my treble control maxed out which for me is unheard of.

That's simply wrong. I usually run treble at about 10-11:00 and I use Hums. Yes I make adjustments when using a Strat, typically more on the mids though.

I was thinking about increasing the clean master bleeder.

I wouldn't. The clean bleeder works in reverse when in OD mode. Think about it.... when you have the OD switch on, the clean bleeder is connected to the OD entrance. Depending on the clean master setting some highs can be bleed off through the master.

Actually if you look at the schematic I used, the master bleeder is out of circuit when in OD, but I agree something is up with the highs. I never had an amp where treble was maxed. Maybe oscillation. time to look for a scope...

You'd be surprised how much the right speaker and cab will effect that, however.

Agreed. I know my speakers are not right for this amp. Still I feel there is work to be done on the amp.

[heisthl]

I'll post one of the "Butcher" in the files section under "Total Butchery"

[Tonegeek]

I'll post one of the "Butcher" in the files section under "Total Butchery"

Excellent. just what I need for benchmarking. If a Strat was used (sounds like humbuckers though) all the better.

[Tonegeek]

I tried a .047 mid cap in the clean tone stack, I axed the Groove tube for an EH and cut back my bias to 36ma. Also worked with the NFB. The lack of highs I was experiencing is now gone (mostly due to the cap change). It completely changed the response of the whole stack. I can now put treb, mid at 12oclock, bass at 3-4 and get a very full sound with my Strat. I can't believe anyone is happy with the .01 mid cap (Skyliner EQ).

I still have the OD issues, I think, but it was midnight so I could not crank too loud. I will have to re-adjust the OD stack anyway so maybe this weekend I will make some headway on that. I am going to get up with a friend and try a Les Paul also to see how much the Strat is fighting me (isn't it love/hate for all Strat owners!) May also get to try different speakers (definitely needed).

I plan on tweaking my plate voltages (thanks Normster) soon too and trying some other suggestions from you guys.
Will report back when something changes...
whit

[dogears]

The .047 has virtually no effect on the OD tone as it is designed to be run with the PAB on. Fwiw, the .01 sounds way better with hum guitars on the bridge. Strats can go either way with many liking the .047 If the .01 is that bad, you have other serious build issues.

Lastly, I'd adjust teh post stack to bass 40% on, mids no more than 50% on, and treble about 1/3 on. Mids at 80% is unplayable on mine.

I tried a .047 mid cap in the clean tone stack, I axed the Groove tube for an EH and cut back my bias to 36ma. Also worked with the NFB. The lack of highs I was experiencing is now gone (mostly due to the cap change). It completely changed the response of the whole stack. I can now put treb, mid at 12oclock, bass at 3-4 and get a very full sound with my Strat. I can't believe anyone is happy with the .01 mid cap (Skyliner EQ).

I still have the OD issues, I think, but it was midnight so I could not crank too loud. I will have to re-adjust the OD stack anyway so maybe this weekend I will make some headway on that. I am going to get up with a friend and try a Les Paul also to see how much the Strat is fighting me (isn't it love/hate for all Strat owners!) May also get to try different speakers (definitely needed).

I plan on tweaking my plate voltages (thanks Normster) soon too and trying some other suggestions from you guys.
Will report back when something changes...
whit

[heisthl]

Excellent. just what I need for benchmarking. If a Strat was used (sounds like humbuckers though) all the better.

I'll post a strat clip in the Butchery files section thread

[Tonegeek]

If the .01 is that bad, you have other serious build issues.

That is possible, but it may be because with the .01 I hated the way the mid sounded when I turned it down, which is what you have to do to get a perception of more highs, so I had my mid all the way up which forced me to put treble all the way up. Either that or one of the other tweaks I made had an affect. I did swap a tube and adjust the bias at the same time i switched the cap. I messed with NFB too, but not much. I will say I have double and triple checked the layout and schematic and could find no errors in my build. I could have a bad part. I have checked for the wrong values, but can find nothing wrong there either. Well for now the .047 has made a large difference so I will revisit that after I work some more on the OD.

Lastly, I'd adjust teh post stack to bass 40% on, mids no more than 50% on, and treble about 1/3 on. Mids at 80% is unplayable on mine.

Before I read your reply, I had just finished tweaking the tone stack to almost that very same percentage. Should I be getting a similar sound from the OD, only with more breakup/singing and of course PAB? I feel like the clean channel is fuller. It seems to be in the low mids or bass where it is missing something. Not sure. I did not play with the entrance trim today, so maybe I should look that over. It seems like I will need to either up the .0022 cap off the OD1 plate, or up the 1uF cathode bypass on OD2 to get some moe fullness. (Sorry bobi, this contradicts what i said the other day when I thought i had too much bass - so maybe your suggestion is the way to go - upping the .0022)

One more thing: on mine, PAB does fatten up the OD, but mid boost also makes it fatter, louder on top of that. Does this jive with what others experience. I tend to want mid boost and PAB on when in OD. It may just be a personal taste issue. Really, I just want it to work like the real deal for now, and try to hold off on my personal preferences until I get a benchmark. does that make sense? in other words - I am shooting for what most people here generally agree is great tone - like say the Matt sloppy clip (his words - not mine - it is awesome).

[dogears]

The midboost will dramatically fatten up the PAB tone as you will get much more bass when in PAB mode. I'd change the SM or ceramic .002 to a PS series .002 Also, measure your 390pf ceramic treb cap. Make sure you have a full sized one. If it is small, like some are, you will lose fullness in PAB mode.

You can also change the OD1 cap to a .0025uf PS series. They have them at tubesandmore.com What does your OD drive pot measure? Is it low? If it is 230k for example, you will need to raise the cap since the knee will be too high.

Try changing the OD2 grid resistor to a 150k. That will restore some highs.

I am alarmed that you needed to so dramatically alter your NFB loop. That is way way suspicious. I have a 50w Marshall output in my Glaswerks and 4.7k is perfect.

[Tonegeek]

The midboost will dramatically fatten up the PAB tone as you will get much more bass when in PAB mode. I'd change the SM or ceramic .002 to a PS series .002 Also, measure your 390pf ceramic treb cap. Make sure you have a full sized one. If it is small, like some are, you will lose fullness in PAB mode.

You can also change the OD1 cap to a .0025uf PS series. They have them at tubesandmore.com What does your OD drive pot measure? Is it low? If it is 230k for example, you will need to raise the cap since the knee will be too high.

Try changing the OD2 grid resistor to a 150k. That will restore some highs.

I am alarmed that you needed to so dramatically alter your NFB loop. That is way way suspicious. I have a 50w Marshall output in my Glaswerks and 4.7k is perfect.

I just went PS to ceramic on the .002 mid cap, but I will put the ps back in and check the 390. With NFB, I havent actually measured the trimmer at its current setting (75%), but I think 4.7 would sound good too. I tried it halfway up and it sounded about as good as at 75%. Pretty much anything over halfway is doing it for me, but I should be more scientic (less lazy) and desolder/measure. Also just to verify, i have NFB on the 4 ohm tap. I still have only 390 on the PI tail (across the 2k pres. pot). Should I up that to 1K? like some suggest? Since I put the .047 mid cap in, I have been able to back off presense to about 50% with good results. I am actually happy with my clean tone at the moment but want to do whatever is necessary to get the bloom/harmonic content going better. I will implement all these suggestions in the coming days.
thanks,
whit