Real-Deal Pres/Feed Ckt

[UltraHookedOnPhonix]

I know this subject has been bludgeoned to death but maybe someone can shed a light on it.

Does anyone know the presence/feedback circuit of a “real-deal” 80’s-or-later 50W ODS?

Here’s the schematic for the 100W:
[IMG:269:624]http://i205.photobucket.com/albums/bb17 ... edback.jpg[/img]

[UltraHookedOnPhonix]

I found this quote in the 97 ODS Notes from schematic heaven:

"My clone uses a 3.9k FB and a 390 ohm PI reference to ground as does the one I saw and the 50w that is posted. It also had the 1mf (electrolytic) cap with a 2k presence control".

I just want to get it right for the sake of accuracy.

Electronic archeology is difficult sometimes...

[dogears]

The only 50 I have seen was a Bluesmaster with the regular 100W Bluesmaster PI. 100K on 4 ohm tap and 4.7k tail.

[UltraHookedOnPhonix]

Thanks Dogears!

So I guess it is safe to assume that there's 50W amps out there that are running the standard PI values from the 100W version (that's what they are doing in half power mode anyways!)

I'm going to simply replace the 1K/8.2K that I have in there now for 390R/4.7K and see what happens.

[ic-racer]

Thanks Dogears!

So I guess it is safe to assume that there's 50W amps out there that are running the standard PI values from the 100W version (that's what they are doing in half power mode anyways!).

I know you are asking about real Dumble 50w amps, but from what I can tell from the 50w Ceriatone, there are about 1700 posts on the Ceriatone forum about that 50w amp and I have not seen any negative comments or tweaks on the NFB loop (which has the #124, 100W values). BTW there is one small change from 100w values in the PI of the Ceriatone, of unknown significance to me. The PI plate resistors are 110k and 120k instead of 100k and 110k.

[dogears]

Real Dumbles used lots of different PI plates. 91/110, 100/110, 1110/120, 120/130 among others. So 110/120 is fine. That is what I use btw.

Standard 100W feedback in a 50W is good for me too. Unless it is a Bluesmaster. They get a bit raw then, for my tastes.

I know you are asking about real Dumble 50w amps, but from what I can tell from the 50w Ceriatone, there are about 1700 posts on the Ceriatone forum about that 50w amp and I have not seen any negative comments or tweaks on the NFB loop (which has the #124, 100W values). BTW there is one small change from 100w values in the PI of the Ceriatone, of unknown significance to me. The PI plate resistors are 110k and 120k instead of 100k and 110k.

[UltraHookedOnPhonix]

WHOOPS!!!! I meant standard NFB values but it's interesting about the PI nonetheless.

I have a 100K/110K, 5K trimmer combo right now that I'm going to change to 100K/110K 25K trimmer to simulate the higher plates.

[ic-racer]

I know this subject has been bludgeoned to death but maybe someone can shed a light on it.

Does anyone know the presence/feedback circuit of a “real-deal” 80’s-or-later 50W ODS?

I know you asked about a "80s or later" amp, but have you seen the pictures of #40? That is 50w and looks to me like it has an 820R NFB resistor.

[Funkalicousgroove]

I think 3K9 sounds better in the 50W amps, they need a tad more dampening to my ears, YMMV.

That #40 is a whole different thing, the real early amps had a whole different PI, 47K/51K plate resistors, .05uf coupling caps, 100K grid leak resistors, 1.2K grid stoppers, 820R feed back, 100K tail, and an "Accent" switch

[UltraHookedOnPhonix]

I use to have the 1K/8.2K combo but it sounds way to open and the bass is overpowering so I've subbed for 390R/3.9K and I'm going to fire it up sometime next week. I'll report back with my observations.

[Structo]

My D'Lite still has the 6.2K/390 with a 2K pot for presence.
Been thinking about changing the 6.2K to a 4.7K
Or trying a different tap.
Right now it's on the 4 ohm tap.

I'm also using the 110K/120K plate resistors on the PI.

[UltraHookedOnPhonix]

The largest difference I noticed by switching the NFB circuit was that the operation of the presence control shifted somewhat. Other than that, I didn't notice a huge difference. Maybe a bit tighter.

I'm scratching my head trying to figure out why there's such bass overload on this thing, in OD mode I'm running the bass control at virtually zero to avoid whooof-ing...

Currently I'm running a ported 2x12 with EV12L speakers. The amp is non-HRM, Skyliner, 220K/150K plates and old-style PS with an external Dlator.

[dogears]

Could your cabinet be woofy? Is it woofy on the bridge pup?

The largest difference I noticed by switching the NFB circuit was that the operation of the presence control shifted somewhat. Other than that, I didn't notice a huge difference. Maybe a bit tighter.

I'm scratching my head trying to figure out why there's such bass overload on this thing, in OD mode I'm running the bass control at virtually zero to avoid whooof-ing...

Currently I'm running a ported 2x12 with EV12L speakers. The amp is non-HRM, Skyliner, 220K/150K plates and old-style PS with an external Dlator.

[UltraHookedOnPhonix]

Well, I've tried a heap of guitars: Strats, Teles, Pauls, Music Mans and it really shows up in the lower registers on all of them to a more or less extent. Feels like the walls are about to crumble around me from the vibrations!

Also, I've tried differet cabs: Marshall 1960AV, Hermida 1x12, Harry Joyce, Marshall with Alnicos etc and same there (again to a more or less extent).

In OD mode, I'm running it in PAB mode to avoid the ginormous bottom this thing has.

Maybe an Ayan Smooth-n-Slim is in order...

[UltraHookedOnPhonix]

Forgot to actually ANSWER your question Dogears!

It is woofy on the bridge as well, yes.