External OD Trimmer Pot

[bigmik]

looking good ,I also had to redo my d-lite as a result of to much "tweaking ",I was wondering what value is the bright cap that you used on the master? stuck a 47 pf in mine the other day but it was to much in OD and didn't have anything smaller at the time I would like to try a 15 to 30 pf at some point .Didn't you also buy a choke ? did you ever give it a try to hear the difference.

thanks

[Structo]

looking good ,I also had to redo my d-lite as a result of to much "tweaking ",I was wondering what value is the bright cap that you used on the master? stuck a 47 pf in mine the other day but it was to much in OD and didn't have anything smaller at the time I would like to try a 15 to 30 pf at some point .Didn't you also buy a choke ? did you ever give it a try to hear the difference.

thanks

Yes after a lot of tweaking and modding, my amp looked like crap.
It's still not on par with some people's amps here but it is definitely neater than it was.

I have a 47pf bright cap on the master.
I liked it there because I normally don't play the amp very loud at all.
As you turn up the master the bright cap does less and less.
I would like to try some other values as well.

You can also hang one on the OD level pot as well if you like.

I did have a choke at one time, it just never ended up in this amp.
I built a guitar amp out of a Hammond organ amp and used the choke in that.

I was wondering if a choke would get rid on the tiny amount of hum I have.
But it isn't audible until the volume and master are cranked up almost all the way.

The amp is much quieter then before.

Many thanks to Tony (Talbany) for helping me on that.
He encouraged me to use the #124 grounding scheme.

He also advised me on the back panel OD trimmer.
Something I hadn't considered is that a smaller pot there is going to brighten the tone.
It acts just like the volume pot in a guitar, where as the higher in value you go, the brighter the tone.

I'm going to listen to what I have in there but most likely will swap it out for a 100K pot.

[talbany]

Tom
Glad I could help!!..We should all be grateful to Gill for posting 124... We all live quieter lives now...
When the wife leaves play the amp LOUD!! for me!!!..

"Let's face it, the non HRMs are easier to play, there, I've said it." - Gil Ayan... AND HE"S IN GOOD COMPANY!


Tony

[bluesfendermanblues]

the back panel OD trimmer.
Something I hadn't considered is that a smaller pot there is going to brighten the tone.
It acts just like the volume pot in a guitar, where as the higher in value you go the darker it will sound.
Like a humbucker uses a 500K and a single coil usually uses 250K volume pot.
I'm going to listen to what I have in there but most likely will swap it out for a 100K pot.

Tom, interesting and thorough post.

Regarding the pot values, I think it's the other way around.
A higher in value pot gives a brighter sound
a lower in value pot gives a duller sound

agree??

[talbany]

the back panel OD trimmer.
Something I hadn't considered is that a smaller pot there is going to brighten the tone.
It acts just like the volume pot in a guitar, where as the higher in value you go the darker it will sound.
Like a humbucker uses a 500K and a single coil usually uses 250K volume pot.
I'm going to listen to what I have in there but most likely will swap it out for a 100K pot.

Tom, interesting and thorough post.

Regarding the pot values, I think it's the other way around.
A higher in value pot gives a brighter sound
a lower in value pot gives a duller sound

agree?? :?:

This is true with both pots turned all the way up...Although a 25k pot set at max will be brighter than a 100k set at 25k.. Bright caps... I think this is what he means...

Tony

[Structo]

Arrrggg, yes I got that backwards as far as the guitar pots go.....
Mistake corrected.

[bluesfendermanblues]

Arrrggg, yes I got that backwards as far as the guitar pots go.....
Mistake corrected.

huh, thought I had to resolder my amp.

[dogears]

Guys, the pot value means nothing to the brightness if you keep the total load the same.

Fig A: 220K feeding 100K trimmer. Trimmer set at 25K from ground.

Fig B: 270K feeding 50K trimmer. Trimmer set 25K from ground.

Fig C: 300K feeding 25K trimmer. Trimmer maxed.

All three have a total load of 320-325K. The divider is constant. No difference in tone, unless there is something gained by using a nice carbon resistor to feed the smaller trimmer.

Now, if one leaves the 220K feeding a 25K trimmer, then things change. You reduce total load to 245K. This reduces bass content and changes stage loading. And, if trimmer is still maxed, you will have much more gain. Less series resistance too. So, yes it is thinner, gainier, and brighter.

[Structo]

Thanks for the clarification Scott.

[butwhatif]

470k is more like it for me---feeding the 68k and the trimmer -so the trimmer is just the ground ref. --that way the tone doesn't change as much, just the gain. fwiw

[talbany]

Now, if one leaves the 220K feeding a 25K trimmer, then things change. You reduce total load to 245K. This reduces bass content and changes stage loading. And, if trimmer is still maxed, you will have much more gain. Less series resistance too. So, yes it is thinner, gainier, and brighter.

The same holds true for installing master volumes..Even with the 1 meg pot set wide open your still putting a 1 meg load on the PI...Both tone and feel changes..This is why many people use push pull master volume pots to take that load off...Quite a difference


Tony

[Structo]

Guys, the pot value means nothing to the brightness if you keep the total load the same.

Fig A: 220K feeding 100K trimmer. Trimmer set at 25K from ground.

Fig B: 270K feeding 50K trimmer. Trimmer set 25K from ground.

Fig C: 300K feeding 25K trimmer. Trimmer maxed.

All three have a total load of 320-325K. The divider is constant. No difference in tone, unless there is something gained by using a nice carbon resistor to feed the smaller trimmer.

Now, if one leaves the 220K feeding a 25K trimmer, then things change. You reduce total load to 245K. This reduces bass content and changes stage loading. And, if trimmer is still maxed, you will have much more gain. Less series resistance too. So, yes it is thinner, gainier, and brighter.

So as with ODS #124, the trimmer measured 345.5K (although it is rated at 500K).
So with the 220K + 345K = 565K
We don't know if that trimmer was altered or faulty but it measured 345.5K.

Now I thought it was agreed that #124 was a very good amp.

So maybe a 470K resistor into a 100K trimmers is more on par with a real Dumble. But it is confirmed that #124 had a 220K resistor before the trimmer.
So that is a quandary.

The 470K would roll more highs off at around 2.2kHz and thicken the tone but I'm not sure how much the 25K-35K trimmer setting plus 68K grid stopper would shave off as well.

[talbany]

Guys, the pot value means nothing to the brightness if you keep the total load the same.

Fig A: 220K feeding 100K trimmer. Trimmer set at 25K from ground.

Fig B: 270K feeding 50K trimmer. Trimmer set 25K from ground.

Fig C: 300K feeding 25K trimmer. Trimmer maxed.

All three have a total load of 320-325K. The divider is constant. No difference in tone, unless there is something gained by using a nice carbon resistor to feed the smaller trimmer.

Now, if one leaves the 220K feeding a 25K trimmer, then things change. You reduce total load to 245K. This reduces bass content and changes stage loading. And, if trimmer is still maxed, you will have much more gain. Less series resistance too. So, yes it is thinner, gainier, and brighter.

So as with ODS #124, the trimmer measured 345.5K (although it is rated at 500K).
So with the 220K + 345K = 565K
We don't know if that trimmer was altered or faulty but it measured 345.5K.

Now I thought it was agreed that #124 was a very good amp.

So maybe a 470K resistor into a 100K trimmers is more on par with a real Dumble. But it is confirmed that #124 had a 220K resistor before the trimmer.
So that is a quandary.

The 470K would roll more highs off at around 2.2kHz and thicken the tone but I'm not sure how much the 25K-35K trimmer setting plus 68K grid stopper would shave off as well.

Here is something to think about?...

If a load is just a load I wonder why Dumble went through all the trouble to pull a trimmer apart and scratch off the trace to come up with the strange 345K value...He could have done this with a number of different combination's of resistors and set trimmer pots as Scott points out to obtain the total 565K....We should maybe consider the method to the madness...I smell a clue?Any Ideas?

Tony

[ampdork]

Has anyone here taken apart a pot and scratched the carbon to get a smaller resistance value?

In all my trials I could get more resistance but not less.

Did I miss a memo?

[ampdork]

Maybe he simply popped a 350K track in there?


No wait this is dumble so it would have been a 250K track, scratched up to 350K and stuck in a 500K case...