2nd gen hybrid - very little mid pot range

[rogb]

Hi all,
I have virtually no sweep on the mid pot. Very strange
.01>250K pot
Treble cap 500pf>500K pot
Bass 0.1>1M pot
Slope 100K

Treble comes in at 4 and 6 and bass at 3, which seems pretty normal to me.
I have changed the pot and the cap, but there is very little action. I do like my mids so I can only get that by adding mid boost in.

It's quite confusing, any ideas?
The amp sounds great but I would like to switch off the mid boost sometimes.
Thanks
Roger

[Dr d]

Hi Rog! From my experience, I think this is perfectly normal....if a little frustrating at first. I believe its due to the design of the tone stack i.e. large bass and treble caps and smallish mid cap. The mids are in there, but not very adjustable. The small special works really well without the mid pot, and it is very similar in design to the 2nd gen. I found the presence very subtle too on the hybrid. Ended up with 1K pot and 2.2uf cap.
Hope this helps!

[rogb]

Thanks Doc! Yeah the presence is VERY subtle too. I might go to a 2.2uF tant but as usual I'm getting away from the original design

[Dr d]

Hi again Rog! On my version of the hybrid, I used the 2nd gen GNFB values and remembered Marcos saying that he had been advised by HAD to use either a 500R or 1K pot and play with cap values to suit (anything up to 4.7uf) when changing from an accent switch to presence control. I found 1K and 2.2uf suited my ears! Hope that helps! Cheers.

[rogb]

Thanks for the advice, I will try the 2.2uF

[Darkbluemurder]

I have the Skyliner stack in my converted Bassman which also has the 0.01uf cap and the 250k log midpot, and it's also more subtle than I expected. I tend to turn it down for cleans and up for overdriven tones.

Cheers Stephan

[rogb]

I have the Skyliner stack in my converted Bassman which also has the 0.01uf cap and the 250k log midpot, and it's also more subtle than I expected. I tend to turn it down for cleans and up for overdriven tones.

Cheers Stephan

There's very little to turn up or down in this case - maybe my mids have gone from my hearing?

[jelle]

Look closely at the tonestack design. The answer is there. If unclear, ask.

[crbowman]

My 2nd gen build had the same issues. The mid control did very little to nothing. Jelle, I'd love to hear an explanation of exactly why.
I changed the slope to 150K, and treble cap to 390p and this helped quite a bit on mine. With the stock 2nd gen tonestack the OD really roared, but the cleans were just kinda meh.

[rogb]

Well I never tried it before but I downloaded TSC and ran Mid on 0 and Mid on 10 with the values as best as I could.
Here are the results.
Looks like the Mid pot does zip from 0 to 10.....
why would HAD do this? Didn't clients bitch or were they too afraid!

[stevlech]

Two issues w/ the Tonestack Calculator:
Dumble's Tonestack is much more complex and can't be accurately simulated in the calculator. Just as well the value you've used in the calculator for the mid control is 250 OHMS which will have little impact. Although this is not accurate at all, try 250K for the mid control and see what happens.

[rogb]

Good catch! I did say I had never used it before
It looks like there is a mid scoop that only flattens out at near 10.

[marcos]

Hi roger,
the reason the mid pot does very little in a 2nd generation
Dumble is the .02 cap on the bass pot, if you remove it you´ll
have something similar to a 3rd generation amp,different tone though, actually one
of my earliest Dumble mods in 1987.
These days, my personal amp has something similar to a Skyliner
tonestack, and I feel the 250k pot/ .01 cap combo is actually very
effective, not as much sweep as a "classic" tonestack, but musically very useable.
hope this is helpful
Marcos

[rogb]

Thanks Marcos! Very useful information for which I am grateful. You know, I am not sure I need any mid pot range as it is sounding absolutely fantastic at the moment. This is why -
I have been spending a LOT of time on this amp, trying to get it as good as I can.
This week I finished a TL806 cab with a Swamp Thang. This sits at the bottom of the stack with the G12-65 above.

I also picked up a Lexicon MPX500 to upgrade the TC G# I have been using.
The reverb is FAR better but I am not sure on the delay yet. I will play it out on Thursday so I will have a chance to get some opinions on it.

I also went through my Dlastor, upgrading some parts and correcting an error in the wiring which had caused some hiss
I had a low hz hum that was not level dependant so I went through the amp chopsticking. Turns out I had my V3 and V1 tubes mixed up, giving a microphonic V1 causing the hum. It is now whisper quiet.

So far, I think this is the best sounding D style I have had. THe OD and clean are amazing with this speaker setup.

[Dr d]

Hi Rog, and for anyone else interested, there is a great discussion on this topic in the files section https://tubeamparchive.com/viewtopic.php?t=12113.
I would guess that an obvious mod would be to incorporate a push/pull switch on the Bass pot(or separate switch!) so that you could switch in and out the 0.02uf cap. Then you would have a 2nd/3rd gen hybrid!!!! Try it....it definitely makes for a more versatile tone stack.