Help me mod my 102 - it's too bright!

[Audiodog]

My presence is very noticeable as it sweeps. 9 o’clock to noon is a big difference. On all my amps. Something is either wrong with the amp or the ears if you can’t hear the presence effect below noon. This is on every amp I have and every amp I have modded. I can always here noticeable presence effects at lower settings. In fact, I hear the effect of it just being connected but off!

Fairly major breakthrough: changing the trimpots from the small bourns to Piher PT15's had almost as large an effect as removing the master bright cap. I did also change out the 390pF mica to ceramic which also definitely helped. I'm now playing with treble, mid and bass all at noon. Almost feels like I should try and get a little bit of sparkle back I like it so much better on both the clean and dirt channels now.

For reference, here is where I had my treble and middle set for each stage of part-swapping:

No modification: treble and middle completely down

Master Cap removed: treble and middle about 2 to 3.5

Ceramic cap 390pF in place of mica: treble about 4 and middle about 3.5

Piher trimmers in place of Bourns: Treble and middle at noon


I may now experiment with a polypropylene mid cap and or bringing back a little brightness through a lower value master cap as you guys suggested.

Also, I'm still going to try a tantalum for the presence cap. It doesn't really seem like my presence knob is doing anything? Is this a volume thing? I thought I read an old post by Tony that said the presence knob doesn't really come into play until the amp is turned up...

***Pictures to come

The presence control doesn't really do much until about 1 o'clock then you should be able to hear something move. Amount of signal (volume) does make a difference. Also install the Tant and see how that does?. Also you can now tweak the Bright master to taste(after the 716) with either mica or a ceramic there. Mica's have a bit more sparkle. As far as the 716 it will brighten up the mids quite a bit. Give it some time and play around with it. It takes a little getting used too and your settings will change. This mod sounds better on a stage with a band and not sitting at home sitting directly in front IMO. Just to give you a heads up. Speakers also matter.

Glad you got it sorted out!
Parts matter
Tony

[talbany]

AFAIK The Dumble presence control has a reputation for being pretty "lousy"..Back in the good ole days when people started building these amps several here noticed and complained about it,
There were even several remedies tried like using different tapered pot's and Gil I believe recommended a reverse log pot, others tried adding different value resistors across the pot to try and improve it's range.

The use of a linear pot here makes the control pretty lousy, IMHO. The best solution I have ever found was to use a reverse log pot... but the only ones commercially available, as far as I know, would be the ones used by Fender in their reverb amps, and they're not a good match (value-wise) for the Dumble's presence circuit needs.

https://ampgarage.com/forum/viewtopic.p ... ce#p144172

In the end, I got used to the rather horrible feel of the normal Dumble control (using a linear pot, whether it be the classic style or Blues Master style). Most of the time I keep the control well within its useless range (so say just below 2 o'clock); some times when playing live I turn it up some more.

https://ampgarage.com/forum/viewtopic.p ... 68#p112168

Tony

[Audiodog]

102 has the 2.2uf cap. This makes the presence control fr more effective and noticeable. Something is wrong with ears or amp if one can’t hear the sweep from off.

AFAIK The Dumble presence control has a reputation for being pretty "lousy"..Back in the good ole days when people started building these amps several here noticed and complained about it,
There were even several remedies tried like using different tapered pot's and Gil I believe recommended a reverse log pot, others tried adding different value resistors across the pot to try and improve it's range.

The use of a linear pot here makes the control pretty lousy, IMHO. The best solution I have ever found was to use a reverse log pot... but the only ones commercially available, as far as I know, would be the ones used by Fender in their reverb amps, and they're not a good match (value-wise) for the Dumble's presence circuit needs.

https://ampgarage.com/forum/viewtopic.p ... ce#p144172

In the end, I got used to the rather horrible feel of the normal Dumble control (using a linear pot, whether it be the classic style or Blues Master style). Most of the time I keep the control well within its useless range (so say just below 2 o'clock); some times when playing live I turn it up some more.

https://ampgarage.com/forum/viewtopic.p ... 68#p112168

Tony

[talbany]

The presence control doesn't really do much until about 1 o'clock then you should be able to hear something move.

Scott
I agree! I never said that the entire range was inaudible? My point was the null point (mine! was 1 Gil's was 2) where it's most noticeable. I also never said? up too that point it doesn't do anything. I said it doesn't do as much (even with a 2uF cap?).Your still getting signal sent through that cap below 1:00 as the amp tightens, however this might not be as audible from 1 to full off...Perhaps i should have explained it better, but can assure you the ears are fine
Thanks for checking.
Tony

[ayan]

The presence control doesn't really do much until about 1 o'clock then you should be able to hear something move.

Scott
I agree! I never said that the entire range was inaudible? My point was the null point (mine! was 1 Gil's was 2) where it's most noticeable. I also never said? up too that point it doesn't do anything. I said it doesn't do as much (even with a 2uF cap?).Your still getting signal sent through that cap below 1:00 as the amp tightens, however this might not be as audible from 1 to full off...Perhaps i should have explained it better, but can assure you the ears are fine
Thanks for checking.
Tony

Great, Don T! Throw the guy that facilitated 124 to the world under a bus. After all these years, I still believe the linear taper of the ODS presence control is definitely not ideal... and I don't like the 2.2 uF cap there either.

Cheers to all!,
G.

[talbany]

The presence control doesn't really do much until about 1 o'clock then you should be able to hear something move.

Scott
I agree! I never said that the entire range was inaudible? My point was the null point (mine! was 1 Gil's was 2) where it's most noticeable. I also never said? up too that point it doesn't do anything. I said it doesn't do as much (even with a 2uF cap?).Your still getting signal sent through that cap below 1:00 as the amp tightens, however this might not be as audible from 1 to full off...Perhaps i should have explained it better, but can assure you the ears are fine
Thanks for checking.
Tony

Great, Don T! Throw the guy that facilitated 124 to the world under a bus. After all these years, I still believe the linear taper of the ODS presence control is definitely not ideal... and I don't like the 2.2 uF cap there either.

Cheers to all!,
G.

Oh no BUSTED!!
I know? you pioneers catch all the blame (Gil said) ..For some reason I remembered you complaining about that dang presence control ..I'll move the bus now

Tony

[PicknStrum]

The presence control doesn't really do much until about 1 o'clock then you should be able to hear something move.

Scott
I agree! I never said that the entire range was inaudible? My point was the null point (mine! was 1 Gil's was 2) where it's most noticeable. I also never said? up too that point it doesn't do anything. I said it doesn't do as much (even with a 2uF cap?).Your still getting signal sent through that cap below 1:00 as the amp tightens, however this might not be as audible from 1 to full off...Perhaps i should have explained it better, but can assure you the ears are fine
Thanks for checking.
Tony

Great, Don T! Throw the guy that facilitated 124 to the world under a bus. After all these years, I still believe the linear taper of the ODS presence control is definitely not ideal... and I don't like the 2.2 uF cap there either.

Cheers to all!,
G.

Been a while since I checked back on this thread - glad to see it's still alive.

I did listen more intently recently to the presence control - I notice a tiny bit of change over the sweep of the presence control on clean. Can't say that I could tell much on the OD channel which is where I expect to hear more of a difference. Don't think there is anything wrong with my ears - although I do have meniere's disease, it only flares-up once in a great while

Any suggestions on making it more useable? I read your post in the thread that talbany posted - sounds like you think a reverse log pot may do the trick but it's tough to find one in the correct value (If I remember correctly). Have you tried anything else?

[ijedouglas]

What is your expectation of the presence circuit? If you run the pot at 0 and then at 10, do you get enough effect? If not, changing the taper will not help.

[PicknStrum]

What is your expectation of the presence circuit? If you run the pot at 0 and then at 10, do you get enough effect? If not, changing the taper will not help.

I was just curious if anyone has messed with it. Really don't have an expectation. Right now, I pretty much just leave it around "2", which is fine.

[ijedouglas]

What is your expectation of the presence circuit? If you run the pot at 0 and then at 10, do you get enough effect? If not, changing the taper will not help.

I was just curious if anyone has messed with it. Really don't have an expectation. Right now, I pretty much just leave it around "2", which is fine.

I haven't other than swapping the polarity of the cap. I have found there is definitely one way that the cap sounds better, regardless of the polarity. I have also read that the tantalums don't like the wrong polarity but if you look at the #124 pics, Mr Dumble had the cap in the "wrong" way.

[PicknStrum]

Hey guys - I owe you an update - this is more than 2 years overdue. I haven't had a ton of time to dig into my amps over the preceding 2 years - mainly because of my 2 kids under four!

But, I've finally swung back around to the #102 and figure out what was going on with my dang presence control. My thoughts were either something was wrong with the wiring or something was wrong with my hearing. I started digging into that part of my circuit. I tried different feedback resistors, different presence caps and different bypass (?) resistors (ie the 390r). The only thing that seemed to affect the amp at all was the type of presence capacitor. I quadruple checked continuity and specs on the parts around that circuit. I had resolved that maybe I just couldn't hear the presence frequencies and I'd just have to live with it or that it was so subtle that I didn't notice it.

This led me to put it on my oscilloscope (which I don't use a ton but will start using much more often (foreshadow)). I noticed with the scope, there was also no change in the signal while moving the presence pot - even with higher frequencies. A breakthrough: it wasn't my ears that were the problem. That provided some relief so I started pouring of the schematic and layouts again and finally found my problem. The feedback resistor was connected to the OT but was completely open on the other side!!! I've been basically playing this guy without negative feedback and a presence control since I built it.

I like how it sounds much much better now! It's almost like having a new amp again. I think one of the problems with the original point of this thread was that the amp was super bright (especially in the mids) and with this, it definitely seems to have evened out much better. Also, I absolutely love the presence control. Here's a shot of the where I was missing the jumper - the red line is where I threw in the jumper:

IMG_4886.JPG

***Note: I used an older photo so the presence cap in the above-picture is different. I put a tantalum in there based on your all's recommendations.

[ijedouglas]

I like how it sounds much much better now! It's almost like having a new amp again. I think one of the problems with the original point of this thread was that the amp was super bright (especially in the mids) and with this, it definitely seems to have evened out much better. Also, I absolutely love the presence control. Here's a shot of the where I was missing the jumper - the red line is where I through in the jumper:

Awesome that you got that sorted out! Congrats

[jelle]

Glad you found it!!!

[PicknStrum]

Glad you found it!!!

Thanks Jelle - I experimented a bit with the 390R vs. the 330R you provided in the NOS resistors. I preferred the 330R. Seemed to tame the presence so the change from 3 to 5 on the presence pot (thinking about clock hands) felt slightly more subtle.

[jelle]

Yes, those Dralorics sounds better than most resistors out there.

jelle