D'lite to Bluesmaster migration testing

[deiseldave]

Well, even though I don't think it's fully done yet, I got to listen of my little Blue Frankenmaster Delight. Lol.
Several things have improved a lot. Earlier breakup of clean channel is just right. Love it. I also think the lower value caps used for the BM make it less tubby, and more focused.
I only mostly converted clean channel, from D'lite to BM, because I didn't know how to deal with the tonestack. I'm just not sure how to get to BM spec from where I am. Largely due to a mod (which I like) that I previously did to D'lite PAB like this: https://tubeamparchive.com/viewtopic.ph ... 9&start=15 , which has mid pot pin 1 going to one half of the PAB relay where NC is grounded, and NO has 500K pot to ground to adjust amount of lift, and bass pin 1 -> 10K -> 2nd half of DPDT NC to ground and NO to 500k pot -> ground.
Changing all that to get the tonestack to look like BM looked like a nightmare trying to get to the relay board, etc. Plus I like the flexibility of that PAB design. So, I just left it the way it was, for now...
Is there a way to keep bass and mid separate on the PAB relay like I have, and have the same tonestack effect as BM?
I also had a "deep" switch wired in for D'lite that when off uses .01uf mid cap, and when on, parallels the .01uf with a .047uf. Not sure what I should do there. Removing all that to replace with .02uf lowers flexibility, and removing the switch would leave a hole. I mainly play a strat, and sometimes a Les Paul style (Guild Bluesbird). What would be the best values to switch between for strat and LP type?
I also converted the PI. But still have some work to do on GNFL to presence. Still need to swap 2K pot for 10K? or 25K?, and 390R between presence pot pins 1 & 3 with 4k7.
Like I said, I fired it up as is, and it seems pretty sweet. I think it just needs a couple more things wrapped up before I mount back in it's combo cab.
On a side note. Like I said, I bit the bullet, and turned all preamp tubes 180 degrees, so the side of tubes facing the input jack were going to 6, 7, 8... I was hoping it would not make a difference, and then could file that info in the "meaningless" folder. However, the amp is quieter now. Not drastic. But, noticeably. I guess it could be something else that lowered hum. After all, I did make a lot of other changes.
But, then again, it could be the reversing of the tubes. Just sayin'.
Thanks in advance for any guidance.
Dave

[Smokebreak]

Nice!
I would encourage you to draw a schematic of your tonestack, as-is, then compare it to the BM ts. You can keep your PAB and convert the rest over by moving 1 wire. It's the NC one(to ground) on the Bass pot side of the switch. Instead of going to ground, you put it at the top of the mid pot. Then change the stack caps, pots,slope.
You can still keep your "deep" switch that parallels in another mid cap. Just make it 22n and 47n and season to taste.
25K pot is fine, or see 5F6A schem for "scratchy" presence, if you have a 5K. Don't forget about the 100K FB resistor.

[deiseldave]

Nice!
I would encourage you to draw a schematic of your tonestack, as-is, then compare it to the BM ts. You can keep your PAB and convert the rest over by moving 1 wire. It's the NC one(to ground) on the Bass pot side of the switch. Instead of going to ground, you put it at the top of the mid pot. Then change the stack caps, pots,slope.
You can still keep your "deep" switch that parallels in another mid cap. Just make it 22n and 47n and season to taste.
25K pot is fine, or see 5F6A schem for "scratchy" presence, if you have a 5K. Don't forget about the 100K FB resistor.

Thank you, Smokebreak. I already have the 100K FB resistor in place. I just need to change the presence pot, and add the 4.75K and .1uf cap.
So, if I'm thinking right, the BM will have less GNFB than the D'lite. Is that right?

[Smokebreak]

That is correct. You can look at the ratios :
D'L 390r : 4K7 = ~12
BM 4K7 : 100K = ~21

So the BM will have less NFB, resulting in a dirtier/wilder amp, so to speak. If you need to tighten up the bottom end or if it's too wild for your liking, drop the 100K down to 56K and you'll have about the same amount as the Dlite had. Or put the thing on a pot and call it a "soul" control.

[deiseldave]

That is correct. You can look at the ratios :
D'L 390r : 4K7 = ~12
BM 4K7 : 100K = ~21

So the BM will have less NFB, resulting in a dirtier/wilder amp, so to speak. If you need to tighten up the bottom end or if it's too wild for your liking, drop the 100K down to 56K and you'll have about the same amount as the Dlite had. Or put the thing on a pot and call it a "soul" control.

Awesome. Thanks a ton. Probably won't have time to get the rest completed until the weekend. But, I'll try and post some clips when I do. Thanks again.

[deiseldave]

Sorry to bother you again. But, I have been reading a ton of presence control stuff, and I'm seeing people get steered away from 25K pots towards smaller (5K) pots. Also reading that the presence pot should be about 5 times the tail resistor. In this case, the Bluesmaster is 4k75 tail, so I would thing 25K is about perfect. But, I am a greenhorn on the subject.
In my parts box, I found both a 5K linear, and a 25K linear. Which should I use for the Bluesmaster?
Also, can you point me to where I can learn how to calculate the presence pot behavior with different values? Caps, pots size, taper, etc.
Thanks - Dave

[deiseldave]

Nice!
I would encourage you to draw a schematic of your tonestack, as-is, then compare it to the BM ts. You can keep your PAB and convert the rest over by moving 1 wire. It's the NC one(to ground) on the Bass pot side of the switch. Instead of going to ground, you put it at the top of the mid pot. Then change the stack caps, pots,slope.
You can still keep your "deep" switch that parallels in another mid cap. Just make it 22n and 47n and season to taste.
25K pot is fine, or see 5F6A schem for "scratchy" presence, if you have a 5K. Don't forget about the 100K FB resistor.

Sorry for being slow on the uptake. I wasn't sure what you meant by "scratchy" presence. But, at first it didn't sound like it was something I wanted. Until, I read: https://tubeamparchive.com/viewtopic.ph ... ce&start=0
Sounds like "scratchy" 5K is for me. After I had read about it, I thought "you know... my Plexi6v6 presence is scratchy". Looked at the scheme, and sure enough that's what I have in it.
I didn't know the scratching was normal. Lol. It just never bothered me that bad. Picking the lesser of evils, I would rather have a smooth taper and live with a little scratching.
Sheesh. You guys sure know your stuff. I frequently go back in these comments, and think "oooh... Thats what he meant".
I apologize for being a little slow on the uptake, and thank you for the sage advice.

[deiseldave]

Got all changes complete. So everything except OD stage has Bluesmaster config. Everything sounds amazing, except PAB. It is way too bassy.
I really liked how the previous tonestack / PAB config, allowed independent control of the amount of lift applied to both bass and mids. Now that I have the other side of the PAB relay open, could I do something wierd like switch in a cap to high pass some of that bottom end?
Sorry if I'm being a pain. Thanks in advance for any ideas.

[Smokebreak]

Yes, If you look at the evolution of the 5F6A presence from Fender to Marshall, you'll see that ultimately Marshall ended up going with a 25K pot with a 4K7 strapped across it, which gives you a tail of ~4K. Close enough. Someone please correct me if I'm wrong here, but the 25K pot helps keep the cap charged which eliminates the scratchies, since the pot is in series and underneath the cap, so to speak. Hopefully someone can elaborate more on that point.
Presence is one of those things that is difficult for me to describe verbally, but basically, it attenuates frequencies(based on the RC values) in the NFB loop. By attenuating certain frequencies, these frequencies are NOT fed back, and therefore are boosted in what comes out of your speaker. That's why presence gets brighter as you turn it up. Those high frequencies are actually attenuated in the NFB loop. Depth or Resonance works by the same principle but with low frequencies. If you want your mind blown, look up Martin Manning's "Presonance".
Now, when you put in a higher cap in a typical 5K (or 25k with a 4K7) in the circuit, it starts to let some mids bleed to ground, thus having the effect of boosted mids. Some like it, but it sounds kinda unnatural to me. I prefer to hump mids elsewhere if that's what is called for.
Also, the amount of NFB, via the resistor, has an effect on the perceived treble boost, as well.

I would try a handful of different pot and cap values to see what you like, but personally I would start with 5K/.1

[deiseldave]

Yes, If you look at the evolution of the 5F6A presence from Fender to Marshall, you'll see that ultimately Marshall ended up going with a 25K pot with a 4K7 strapped across it, which gives you a tail of ~4K. Close enough. Someone please correct me if I'm wrong here, but the 25K pot helps keep the cap charged which eliminates the scratchies, since the pot is in series and underneath the cap, so to speak. Hopefully someone can elaborate more on that point.
Presence is one of those things that is difficult for me to describe verbally, but basically, it attenuates frequencies(based on the RC values) in the NFB loop. By attenuating certain frequencies, these frequencies are NOT fed back, and therefore are boosted in what comes out of your speaker. That's why presence gets brighter as you turn it up. Those high frequencies are actually attenuated in the NFB loop. Depth or Resonance works by the same principle but with low frequencies. If you want your mind blown, look up Martin Manning's "Presonance".
Now, when you put in a higher cap in a typical 5K (or 25k with a 4K7) in the circuit, it starts to let some mids bleed to ground, thus having the effect of boosted mids. Some like it, but it sounds kinda unnatural to me. I prefer to hump mids elsewhere if that's what is called for.
Also, the amount of NFB, via the resistor, has an effect on the perceived treble boost, as well.

I would try a handful of different pot and cap values to see what you like, but personally I would start with 5K/.1

Hey Smokebreak. I wired in the 5K / .1uf, and am completely happy with it. Also had previously checked out Martin's "Presonance" threads, but didn't quite understand how the control worked. It's on my list of "to do's", probably will try on a prototyping rig that I plan on making as soon as I finish with the Bluesmaster hybrid, and 1959/2204 hybrid.
Any advice on how to reduce bass on PAB? I really liked how the previous tonestack / PAB config, allowed independent control of the amount of lift applied to both bass and mids. Now that I have the other side of the PAB relay open, could I do something like switch in a cap to high pass some of that bottom end when PAB is on?
Thanks - Dave

[Smokebreak]

Got all changes complete. So everything except OD stage has Bluesmaster config. Everything sounds amazing, except PAB. It is way too bassy.
I really liked how the previous tonestack / PAB config, allowed independent control of the amount of lift applied to both bass and mids. Now that I have the other side of the PAB relay open, could I do something wierd like switch in a cap to high pass some of that bottom end?
Sorry if I'm being a pain. Thanks in advance for any ideas.

No worries at all man. Ok how do you have the PAB wired? Same concept as before, but it's just not to your liking do to the rearranging of the mid pot? I don't understand why you have a free 1/2 of a switch. You can still lift both the mid and bass pots independently, or have them stock

[Smokebreak]

Try a .1 for your mid cap

edit: come to think of it that won't do much if you are in PAB mode. I'd need to see how you have it wired now

[deiseldave]

Got all changes complete. So everything except OD stage has Bluesmaster config. Everything sounds amazing, except PAB. It is way too bassy.
I really liked how the previous tonestack / PAB config, allowed independent control of the amount of lift applied to both bass and mids. Now that I have the other side of the PAB relay open, could I do something wierd like switch in a cap to high pass some of that bottom end?
Sorry if I'm being a pain. Thanks in advance for any ideas.

No worries at all man. Ok how do you have the PAB wired? Same concept as before, but it's just not to your liking do to the rearranging of the mid pot? I don't understand why you have a free 1/2 of a switch. You can still lift both the mid and bass pots independently, or have them stock

Thanks, I think you just made me realize what I did wrong. I tied the ground side of bass pot right to the top of mid pot, and then mid pot ground side to one side of PAB relay.
I'm guessing that instead, I should have tied bass pot ground to common of the second side of the PAB relay, then NC to top of mid, and PAB 500k bass trim between common and NO, and NO to ground? Sound right to you? Thanks.

[Smokebreak]

Yea, so you just lifted the ground of the mid pot, is all. That's fine, and a common way to do it.
But i think this is what you were trying to do ? One way is normal, and the other variably lifts both bass and mid. I'm curious how this one sounds with a Marshall stack.

[deiseldave]

Yea, so you just lifted the ground of the mid pot, is all. That's fine, and a common way to do it.
But i think this is what you were trying to do ? One way is normal, and the other variably lifts both bass and mid. I'm curious how this one sounds with a Marshall stack.

Cool. That is pretty much what I drew out at work. That lets me know I'm starting to think about some of this stuff the right way. I appreciate you taking the time to do that. - Dave