Overdrive Special Reverb........#60

[Aaron]

Hi Eric,

There's no second page. I might have planned on drawing the power supply on another pager but have managed to squeeze it all in.

I've started working on the schem again after drawing #13.

I'm still trying to get my head around the mixer stage, fifth valve from the right, back of amp facing. I can't believe it's been over 18 months!

Any ideas?

Thanks,
Aaron

EDIT:- Revised schematic posted.

[PaisleyTube]

thinking out loud:

- 470k-dry-signal-mixing-resistor goes to the input of the reverb-driver

[Aaron]

Hi Paisley,

You mean something like this??

Has not been tested, so assume it has errors!

Cheers,

Aaron



EDIT:- ERRORS CORRECTED AS POINTED OUT BY SERGIO

Thanks Sergio, it helps to get a fresh pair of eyes, I double checked and still missed it!

[sergio]

Hi Aaron ,good work!, where is 220k bias feed resistors , there is "D" node marked instead of the bias point.
Maybe "D"node is for recovery reverb stage?
"H" node missed?
"6" in the Fet circuit?

S.

[sergio]

Aaron , well done!!
looks like there is another resistor in series with LNFB on V3 driver reverb! (blue wire of reverb trafo) maybe is 2,2M - .005uF - 10M?

S.

[PaisleyTube]

Hi Paisley,

You mean something like this??

Has not been tested, so assume it has errors!

Cheers,

Aaron

!

Yeah, like that!
Is the local neg. fdbck. correct on the very last pre-amp-stage?

tia!

[Aaron]

Yeah, like that!
Is the local neg. fdbck. correct on the very last pre-amp-stage?

tia!

Hi Paisley,

Do you mean the 470k on V5B?

Aaron[/quote]

[PaisleyTube]

yeah, different compared to other d-style neg.fdbck.-loops........

[Aaron]

yeah, different compared to other d-style neg.fdbck.-loops........

I wasn't to sure either, but I noticed the Bassman AB165 uses the same neg.fdbck loop as well. I'm guessing putting a capacitor in series would effect a certain frequency, where no capacitor would effect the overall level.
I assume that's how HAD tunes the SSS circuits as well.

Cheers,
Aaron

[martin manning]

But note on AB165 (and other Dumble FB loops) the feedback resistor comes directly off the plate, where you have it downstream of the coupling cap, which will create a bit of a hi-pass filter with a break at ~30hZ.

[Aaron]

But note on AB165 (and other Dumble FB loops) the feedback resistor comes directly off the plate, where you have it downstream of the coupling cap, which will create a bit of a hi-pass filter with a break at ~30hZ.

Thanks Martin,
Indeed it does. I've just started reading and trying to understand all these design characteristics. Valve Wizard has some really good articles, and has one on neg fdbck loops in triodes. Aitkens site is still a bit to full on for me at the moment.

Cheers,
Aaron

[talbany]

But note on AB165 (and other Dumble FB loops) the feedback resistor comes directly off the plate, where you have it downstream of the coupling cap, which will create a bit of a hi-pass filter with a break at ~30hZ.

Sure we can run the numbers to figure out the -3Db break point but just as important "How does FB loops effect harmonic content" Same with use of Global FB loops

Tony

[martin manning]

True, the proof is in the listening, but an estimate of the frequency range that will be affected (even a very crude one like I made) will tell me where I should be listening ;^)

[talbany]

yeah, different compared to other d-style neg.fdbck.-loops........

I wasn't to sure either, but I noticed the Bassman AB165 uses the same neg.fdbck loop as well. I'm guessing putting a capacitor in series would effect a certain frequency, where no capacitor would effect the overall level.
I assume that's how HAD tunes the SSS circuits as well.

Cheers,
Aaron

Yeah, like that!
Is the local neg. fdbck. correct on the very last pre-amp-stage?

tia!

Hi Paisley,

Do you mean the 470k on V5B?

Aaron

The 470k's are the mixer resistors..Used to isolate the Clean/wet signals..I don't think they are part of the FB circuit..
I think the .005 is there for 2 reasons..
He doesn't want the return mixer to hard clip, (no added harmonic content)
He wants to flatten frequency response (to prevent oscillations) allot of signal there coming from the OD side!!!

In the reverb sections in the SSS he uses NFB to help control harmonic content (to help increase headroom)..Same kind of thinking was used in the return amp of the D-lator...I personally don't think in these type circuits frequency response was a big concern to him as much as it was to try and keep that stage clean!....IMO

Tony

[Bombacaototal]

Hi Aaron

I was checking the original handwriting versus the schematic and I am wondering why the tonestack is different

The handwriting has 250ka treble while schematic has 250kb. The Handwriting has .01 mid cap while the schematic has .05

Regarding the Phase Inverter load I notice this amp uses 100k with 110k. What is the difference between this and the #102, #124 ODS which use 110k with 120k (the rest of the PI is identical)?

Thanks

Hi Paisley,

You mean something like this??

Has not been tested, so assume it has errors!

Cheers,

Aaron



EDIT:- ERRORS CORRECTED AS POINTED OUT BY SERGIO

Thanks Sergio, it helps to get a fresh pair of eyes, I double checked and still missed it!