presence cap questions

[grtamp]

If I watch the photo of #124 , I seems that the positive of the presence cap is wired to ground or I'm wrong?
If I watch the #124 layout in the "file section", I don't see the ground wired with presence cap instead in the schematic this is tie to cathodes of V2.
Can anyone explain me .
Thanks very much

[Guitarman18]

Hi grtamp,

Welcome to TAG.

The blue presence cap is a tantalum cap and does look as though it's wired in reverse. Have you looked thru the file section to see if there are any references to this? Most aspects of #124 have been covered in fine detail. Maybe HAD should answer this one!

The ground in the schem shows it connecting to the cathodes of V2, which then ground to the chassis via the loop return jack.

Hope this helps.

Cheers,

Paul.

[mbeldyga]

Isn't tantalum caps one of many kinds of electrolytic caps?

[ampdork]

Tant's do have a polarity and it does appear to be backwards in that picture.

[talbany]

Tant's do have a polarity and it does appear to be backwards in that picture.

+1
It will work in both directions but really - should go to ground..+ to the pot..Taint right..

Tony

[sergio]

Maybe this mod?

I always tied (+) to Pot.

Sergio

[grtamp]

Hi guitarman18,

I looked better and now the layout is okay, I had not seen the dotted line of the earth under the board!
but looking the schematic , I'm not sure for the cathodes of V2 , they could be tied to cathodes of V1 as layout show.

[Guitarman18]

grtamp wrote:

I'm not sure for the cathodes of V2 , they could be tied to cathodes of V1 as layout show.

HAD used a couple of different variations for V2 cathode grounding. On #124 they reportedly ground at the return jack, but others have been observed with V2 cathodes daisy chained to V1, which then ground to the lugs near the guitar input jack. Either way works well.

On the layout, Tony has V2 grounds going to the trimmer and then to ground. Other amps sometimes have a tail resistor (4.7K) coming off the trimmer in order to get the loading into V2 correct from what I understand, so going from V2 straight to V1 and then connecting the trimmer to V1, makes things easier.

All my amps have V2 grounds connected to V1 then ground, and if you comply rigidly to HAD's grounding scheme, the results are astounding, if not a little disconcerting. (so quiet that you wonder if it's working at all!)


Cheers,

Paul.

[Structo]

Interesting about the tant presence cap.
I've read before that if a tant cap is installed backwards it ruins them.
I guess that may not be correct.

[talbany]

Interesting about the tant presence cap.
I've read before that if a tant cap is installed backwards it ruins them.
I guess that may not be correct.

Yeah.. I think that applies to voltages..In the presence it's just signal there.(RC time constant)

Tony.

[talbany]

grtamp wrote:

I'm not sure for the cathodes of V2 , they could be tied to cathodes of V1 as layout show.

HAD used a couple of different variations for V2 cathode grounding. On #124 they reportedly ground at the return jack, but others have been observed with V2 cathodes daisy chained to V1, which then ground to the lugs near the guitar input jack. Either way works well.

On the layout, Tony has V2 grounds going to the trimmer and then to ground. Other amps sometimes have a tail resistor (4.7K) coming off the trimmer in order to get the loading into V2 correct from what I understand, so going from V2 straight to V1 and then connecting the trimmer to V1, makes things easier.

All my amps have V2 grounds connected to V1 then ground, and if you comply rigidly to HAD's grounding scheme, the results are astounding, if not a little disconcerting. (so quiet that you wonder if it's working at all!)


Cheers,

Paul.

Paul totally agree!!
I've tried running/ splitting up the V1/V2 cathodes/ trimmer grounds and didn't notice any difference there.. FWIW..the 4.7k tail is part of the HRM low gain network.. 470K bypass 47pf w/220k..Not a big fan
Like Paul says follow Dumbles grounding scheme and the skies will clear the seas will part and Heather Graham will bring you a Beer!!..Quietly

Tony

[dogears]

Naked on roller skates??

....the skies will clear the seas will part and Heather Graham will bring you a Beer!!..Quietly

Tony

[BobW]

The only issue I have w/ the #124 presence, is mine doesn't work until it's past a 2 o clock setting. Otherwise it sounds great and the reason why the chassis hasn't been pulled.

"On roller skates..." LOL! that a good one.

[talbany]

Naked on roller skates??

....the skies will clear the seas will part and Heather Graham will bring you a Beer!!..Quietly

Tony 8)

[Guitarman18]

Sorry Heather,

If that's all you have to offer, don't bother. On the other hand, if you have some 'Old Speckled Hen', you can come round any time!

Paul.

BTW, nice roller skates!