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Babelfish M25, SissySIT - general building tips and tricks
Babelfish M25, SissySIT - general building tips and tricks
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Old 11th November 2019, 03:57 AM   #1331
twitchie is offline twitchie  Canada
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Location: Toronto
Babelfish M25, SissySIT - general building tips and tricks
Quote:
Originally Posted by Juntuin View Post
Hmm, would it come with too much trouble to convert my M25 to SissySit SITís are already awaiting in my drawer.

For once time is not problem, since Iím unemployed very soon.
See Post #1 for both schematics for M25 and Sissysit.

You would be best checking yourself but what I can see:

M25 - D1, D2, D3 (no D4, D5)
Sissysit - remove D1 and D2 and install at D4 and D5

Reverse the direction of install for zeners - ZD1 and ZD2

Remove RS(R and L), P1 goes from 1K to 2K

R19 47K in M25, 36K in Sissysit (R18 stays 43K in both)
R15 270R in M25, 1K in Sissysit

Q3 device changes of course and don't forget the 100R resistor on the gate pin of the SIT.
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Old 11th November 2019, 04:51 AM   #1332
rhthatcher is offline rhthatcher  United States
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Join Date: Dec 2018
Location: Beachwood, Ohio (Cleveland Area)
Babelfish M25, SissySIT - general building tips and tricks
Looking for help.

Left channel board is alive and singing. Dead quiet on test speakers. And makes beautiful music.

Right channel board offset is not settling down as nice.

So I thought I would try the driver bias and live with more offset on test speakers.
Set 20mV on R8. Check.
JP to Gnd = 2.7V. Turn increase R7 and voltage goes up. What could be the problem? It is NOT acting like the other channel. Need some insight. Hope the board pix are helpful.
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Old 11th November 2019, 05:56 AM   #1333
Zen Mod is offline Zen Mod  Serbia
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Babelfish M25, SissySIT - general building tips and tricks
be sure that you're measuring on proper pin of JP , vs. GND

one pin is looking at xformer , another one to buffer output

I'm damn sleepy right now, we arrived at SR less than 2 hours ago , so I'll post nice pic with marked pins for setting buffer DC offset , for both channels

good night ......

btw. your soldering could be better
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Old 11th November 2019, 06:45 PM   #1334
Juntuin is offline Juntuin  Finland
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Quote:
Originally Posted by twitchie View Post
See Post #1 for both schematics for M25 and Sissysit.

You would be best checking yourself but what I can see:

M25 - D1, D2, D3 (no D4, D5)
Sissysit - remove D1 and D2 and install at D4 and D5

Reverse the direction of install for zeners - ZD1 and ZD2

Remove RS(R and L), P1 goes from 1K to 2K

R19 47K in M25, 36K in Sissysit (R18 stays 43K in both)
R15 270R in M25, 1K in Sissysit

Q3 device changes of course and don't forget the 100R resistor on the gate pin of the SIT.
Thanks, nicely summed up gotta double check, but Iím usually quite blind when modifying circuit.
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Old 12th November 2019, 12:50 AM   #1335
cal3713 is offline cal3713
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Join Date: Mar 2014
Quote:
Originally Posted by rhthatcher View Post
Looking for help.

Left channel board is alive and singing. Dead quiet on test speakers. And makes beautiful music.

Right channel board offset is not settling down as nice.

So I thought I would try the driver bias and live with more offset on test speakers.
Set 20mV on R8. Check.
JP to Gnd = 2.7V. Turn increase R7 and voltage goes up. What could be the problem? It is NOT acting like the other channel. Need some insight. Hope the board pix are helpful.
As ZM pointed out, you've got quite a few open through-holes in the soldering. My first build was an F4 and I didn't get the solder to flow fully through the holes, it created a lot of unstable oscillation behavior... got things steady walked away for a second and turned around to see smoke. Things calmed down when I re-soldered everything so that the solder went completely through the holes (and was filled on both sides)...
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Old 12th November 2019, 08:00 PM   #1336
twitchie is offline twitchie  Canada
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Join Date: Jul 2004
Location: Toronto
Babelfish M25, SissySIT - general building tips and tricks
Quote:
Originally Posted by twitchie View Post
See Post #1 for both schematics for M25 and Sissysit.

You would be best checking yourself but what I can see:

M25 - D1, D2, D3 (no D4, D5)
Sissysit - remove D1 and D2 and install at D4 and D5

Reverse the direction of install for zener - ZD1 ONLY!!!

Remove RS(R and L), P1 goes from 1K to 2K

R19 47K in M25, 36K in Sissysit (R18 stays 43K in both)
R15 270R in M25, 1K in Sissysit

Q3 device changes of course and don't forget the 100R resistor on the gate pin of the SIT.
I made a mistake - ZD2 does not need to be reversed between M25 and Sissysit, only ZD1 is reversed.
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Old 15th November 2019, 09:33 PM   #1337
rhthatcher is offline rhthatcher  United States
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Join Date: Dec 2018
Location: Beachwood, Ohio (Cleveland Area)
Babelfish M25, SissySIT - general building tips and tricks
I'm just returning from a biz trip. I'll have to fire up the soldering iron this weekend.
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