Fine tuning/Blueprinting your amp-

[Funkalicousgroove]

I did a re-voice for a guy last week, and it got me thinking about what mods/changes have the largest impact, versus mods/changes that have little to no impact. Here are my thoughts, and I'd love to hear yours-

1. Obviously there are huge differences between the "Classic" and "Skyline" EQ section, and I find that the "Classic" voice (.05 mid cap, 100 or 150K slope, 100K mid pot, 250K bass pot) is much more useable with a strat, and the Skyline voice seems to have more of the familliar "Honk" associated with the ODS

2. Changing Preamp tubes- As a simple fix, this had a HUGE effect on the overall tonal characteristics, Going from Long plate tubes to short plate tubes, one brand to another, or simply trying different tubes in different positions. the amp had a Mullard(new) in V1, and Beijing production 12ax7's in v2 and v3. The guy complained that the amp was a tad too bright, so replacing V1 and V2 with JJ ECC83's and moving the mullard to V3 not only took care of the brightness, but opened the amp up substantially.

3. v2B Grid stopper- Changing this resistor seems to have a HUGE impact on overall tonality and response, 150K seems brighter and livelier, 180K sounds smoother and sweeter (but may make for mud in the wrong application).

4. Resistor after V2B coupler (Usually 150K) I found that 180K takes the "Edge" off but going really big makes for MUD CITY. Also, Carbon Film seems to sound best IMHO.

5. Plate load resistors- Going from 100K/1K5 to the 220K/3k3 150K/2k2 setup has a VERY large effect, seems to make the amp "Browner" and more "Living room friendly".

What my findings tell me is that different Preamp tubes are the place to start to tune brightness or darkness, Mid cap is what to change to make amps "Strat friendly" and the Plate loads and Grid stopper are for fine fine tuning of overall brightness/darkness. So tell me what you've found!!

[jelle]

How about NFB? I tweak that part too, whenever I tweak the preamp to balance the overall sound again.
Balance/inbalance of pi tube is also very worthwhile...

[odourboy]

Great post Funk!

[Tonegeek]

General (mostly OD) tweaks by type that worked for me with a Mex Strat:

Overall response (feel): Plate/cathode resistors (220k,150k on v1,v2), choke to sag resistor. going to Bluesmaster PI but keeping NFB on 8 ohm tap (tames the upper mids a bit more than the 4ohm tap) Of these, the plate load changes made the most difference. The amp had more authority, a better growl and more touch response.
Taming fizz: I went to higher resistance in OD entrance (470k + 180k to a 100k trimmer), I put the OD entr. 47p bypass cap across the 180k. a smaller HRM mid cap gives more mids with a perception of less fizz
Tightening low end: adjusting coupler and bypass cap values (5uf Ck across works for me)
Fattening up: smaller mid cap value in the HRM circuit. This is one of the most productive changes I made to the amp. It fattens up and tames the fizz at the same time. I can switch between 3 mid cap values for distinct sounds depending on what I need. The .02 cap does not do it at all for me. About the highest value I can use is .01

Tweaks for clean:
I have a Skyliner stack. treble caps are either 324p or 820p depending on mid boost. I like the tamer 820p over the .002 which works better for me when I get into OD with no PAB. With the .002, I just don't get a useable OD unless PAB is also on. This way, OD is useable with just mid boost on. Its nice and fat with the Strat character shining through for Hendrix/SRV type stuff.

I tried .047 mid cap but like the .01 slightly better. Seems lots of Strat players like the .047 with a strat and it may be that I need to make all the changes (100k mid pot) etc for that to work correctly. Would love to try that sometime.

[Guitarman18]

Excellent stuff, you've just inspired me to get my soldering iron out yet again! Could be a long night ahead.

[fabiomayo]

You guys are too good...

Thank you so much for this post, Funk!

[Structo]

I found the Rp change on V2 ( 220K/150) along with the Rk of 3K3/2K2, had the biggest effect to get what I want tone wise.
I have a 330pf treble cap.
Still have the .05 uf mid cap and 100K mid pot.

So now V1 and V2 have the same Rp and Rk values.
It became much more reedier, honky, like I hear on Dogears clips.

110K/120K Rp on the PI. 47pf ceramic across the PI plates.
470R screens and 3K3 grid stoppers on the 6L6 power tubes.

But I still have a bit of high end fizz on both OD and Clean.
There are a couple things I am going to try to tame that.

I still haven't done the OD entrance mod as I will have to pull the board to do that one.

I also added a dual bias mod with two 25K pots and 15K tails.

[Funkalicousgroove]

First off, I am a STRONG believer in "if it aint broke don't fix it" so I think if you are happy with your amp leave it alone!

Tonegeek, you don't need to change the pot, there is 100K between 0 and 250K Did you try the 100K slope with the .047?

So those of you who have been messing with your amp for a while (or built a few) please come out of the woodwork and add your $.02!!

[heisthl]

I'm a big fan of playing with the dropping string upstream of V2 (and V1) or the FET simulator resistor with the philosophy that voltages that are higher = harsher and lower = smoother (to a point).
As pointed out tube relacement can do this too...

[ampedup]

this is great stuff, keep it comin. i would say the biggest improvement i made on my dclone was sheilding all the OD wires, made the distortion so much better. the 330p treble cap helps too. i want to try some of the plate resistor changes but i would like to get more of the dales for that. i changed to the traditional FB layout on the 4 ohm, but not sure if its better or not.

[heisthl]

4. Resistor after V2B coupler (Usually 150K) I found that 180K takes the "Edge" off but going really big makes for MUD CITY. Also, Carbon Film seems to sound best IMHO.

This is actually a good thing to change along with the mid cap if you have a "single coil/Humbucker" switch. You can use a smaller value (or none!!) on humbuckers but need something larger to be Strat friendly.

[Tonegeek]

4. Resistor after V2B coupler (Usually 150K) I found that 180K takes the "Edge" off but going really big makes for MUD CITY. Also, Carbon Film seems to sound best IMHO.

I have a 100k off the treble wiper of the HRM stack. does that count or is this in addition to, or maybe a non-HRM tweak?

Tonegeek, you don't need to change the pot, there is 100K between 0 and 250K Did you try the 100K slope with the .047?

DOH! so the sloper is what I need to change to give it a true test...

[rutledj]

Well, I finished my non-hrm and really haven't changed anything in it. I really like it. I included a switch to switch the mid cap between .05 and the standard. It seems to make the clean sound better with a strat but still doesn't do a lot for the od and strat.

I really want to thank all of you that graciously offered advice/help. I'm sure I could not have done this without you.

Next project? Build a tele so I can see what that sounds like through my amp!!


Rut

[Normster]

I agree on the tubes. Not only do they effect the overall tone, but within the same brand and type they effect plate voltage.

V1 grid resistor is a good place to tweak for light or heavy touch. I prefer 22k for my personal amps but have used 24k or 33k to minimize first stage clipping for heavy-handed players with high output pickups.

Slope resistor is a good place to tune bass content. Higher = Tighter. I typically stay with a 150k slope resistor, except on the bluesmaster. The 100k can help compensate for a bright speaker in a small cab (which can sound boxy).

I haven't played around much with plate/cathode resistors. The only amp I've built with 100k/1.5k also has Trainwreck iron and a tube rectifier so it's hard to judge the effect of the resistors.

Bypass cap on the overdrive entrance. (470k/180k/100k style) I treat it like a bright cap. Larger = Brighter. I like 47pF to 68pF, but have gone as high as 100pF. OTOH, I don't use low capacitance shielded cable. I use 22AWG PTFE cable with a capacitance of 58pF per foot so some of the bypass cap tweaking may be compensating for cable capacitance.

I've tried 470R, 500R, and 1k on the screens and honestly can't hear or feel a difference. I'm sure there are others with better ears than mine who would disagree.

NFB circuit. Great place to tweak the "attitude" and sensitivity of the amp. With the Bluesmaster PI, I like 100k but have used as low as 47k. The presence pot is also a significant tweak, if only in perception. If the amp seems too dark overall, try using a smaller pot value. I find the 25k pot has very little use outside of the 0-8k range so I'm leaning towards a 10k pot.

Clean Master bright cap. For HRM/BM circuits, I like 68pF but have gone as high as 100pF. I don't use a bright cap on the non-HRM master.

As far as CF versus MF resistors, I'm still acting on blind faith. Haven't done any tweaking in this area.

Well, you asked for my .02, and that's about what it's worth.

[Funkalicousgroove]

Just for clarification, Lets make sure that we specify whether we are talking about amps with or without the HRM module.. All of my notes this far are in regards to an amp without the HRM.