Friedman Twin Sister Circuit?

[psychepool]

If this question violates the forum rules, please let me know.

I became interested in build the Friedman Twin Sister.
I was able to find the Dirty Shirley schematic by searching here and other web pages, but I couldn't find the Twin Sister schematic.

https://ampgarage.com/forum/viewtopic.p ... ty+shirley

Twin Sister is guessed to be a configuration of two Dirty Shirley preamp that can be switched.

The gain switch probably has the same configuration as the Dirty Shirley, but the difference from the Dirty Shirley is that a bright switch has been added.

My guess was that this was the treble bleed cap on gain pot pins 2 and 3, but after checking with some gutshots, I can find no switching was applied to the gain pot.

Does anyone have any information about Twin Sister's Bright Cap? If it is not applied to the gain pot, I think it is likely to be a cap applied in parallel to the 470K stopper after the second stage. If anyone has accurate information, please share.

[Littlewyan]

I believe it's a cathode bypass cap on the last gain stage. I think Dave said so on one of the other forums.

[psychepool]

I believe it's a cathode bypass cap on the last gain stage. I think Dave said so on one of the other forums.

Thank you for answer.
Is that the bypass cap you mentioned, the red boxed spot in the image below?
If you don't mind, can you tell me where this forum is mentioned?

bypasscap.jpg

[Littlewyan]

No it's on the stage before the cathode follower and I can't honestly remember I'm afraid. Would have likely been gearpage.
What you're looking at is a capacitor used to shave off some high end.

[Tone Lover]

Try a 22u on that 820k resister and see what you think. If to much bass go lower

[Solder&Sparks]

Late to the discussion here, but I’m building a Little Sister and, after hours of staring at gut shots, have solved this mystery. The DPDT Bright/Tight switch, when ON, adds a 0.0022uF coupling cap in series after the 0.022uF coupling cap after the second gain stage. It also adds a 0.68uF electrolytic bypass cap in parallel with the 820R cathode bias resistor on the the third gain stage. When Off, the switch shorts around the 0.0022uF and adds a 1M resistor (to ground) in series with the 0.68uF cap.

[psychepool]

Late to the discussion here, but I’m building a Little Sister and, after hours of staring at gut shots, have solved this mystery. The DPDT Bright/Tight switch, when ON, adds a 0.0022uF coupling cap in series after the 0.022uF coupling cap after the second gain stage. It also adds a 0.68uF electrolytic bypass cap in parallel with the 820R cathode bias resistor on the the third gain stage. When Off, the switch shorts around the 0.0022uF and adds a 1M resistor (to ground) in series with the 0.68uF cap.

Thank you for sharing the information.

According to what you mentioned, it seems possible to create a less fluffy, more modern gain sound by cutting the low end and then providing gain compensation.
I naturally thought that this would be a mode that connects 470pF in parallel to the 470K after the second gain stage, such as a bright switch connected to a gain pot or a JCM800, and I think it was impossible to interpret it because I only looked at the gutshots from that perspective.

I was sure that this was a mode that bright switch connected to a gain pot or connected 470pF in parallel to the 470K after the second gain stage like JCM800. So I think it was impossible to interpret it because I only looked at the gut shots from that perspective.

Since I've been building very difficult amplifiers recently, I've been taking a break and looking for the next amplifier circuit for a long time. In fact, this circuit has been pushed down the priority list at the moment, but the information you provided has made me interested again.
I once made a Bogner Ecstasy, and the dirty channel circuit was almost similar to the classic Marshall circuit, so I modified it by inserting numerous switches. Since this circuit also has a fairly similar to the classic Marshall circuit, many modification ideas come to mind.

Thank you again. I hope your Little Sister builds beautifully!

[Ray Barbee]

Late to the discussion here, but I’m building a Little Sister and, after hours of staring at gut shots, have solved this mystery. The DPDT Bright/Tight switch, when ON, adds a 0.0022uF coupling cap in series after the 0.022uF coupling cap after the second gain stage. It also adds a 0.68uF electrolytic bypass cap in parallel with the 820R cathode bias resistor on the the third gain stage. When Off, the switch shorts around the 0.0022uF and adds a 1M resistor (to ground) in series with the 0.68uF cap.

Not correct.

[pdf64]

Late to the discussion here, but I’m building a Little Sister and, after hours of staring at gut shots, have solved this mystery. The DPDT Bright/Tight switch, when ON, adds a 0.0022uF coupling cap in series after the 0.022uF coupling cap after the second gain stage. It also adds a 0.68uF electrolytic bypass cap in parallel with the 820R cathode bias resistor on the the third gain stage. When Off, the switch shorts around the 0.0022uF and adds a 1M resistor (to ground) in series with the 0.68uF cap.

Not correct.

And correct is ... ?

[two tone]

I would also like to know how the Bright Switch works…

[GlideOn]

I think what makes a Friedman 'Dirty' circuit are a few key ingredients:



- 220k plate resistor V1.

- No peaker cap in the mixers.

- 470k vs 1M one half of the PI (compensating for earlier V1 Plate R?).

- .1uf couplers in the power amp.

- Tube rectifier.


Shifts a mid of the high mids to more "mid-mids," IMHO.

Still a Cascaded preamp like a JMP/JCM800.

I think the rest of the bells/whistles cut or add, but the core and ingredients above keep what it is intact.