OK, then the problem might be with the secondary tranny coil. Because I was seeing the dip also on VR1 output with that primary coil attached and your plot for VR1 looks great.
-Frank
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GK rails in a pedal?
- Thread starter sprag
- Start date
OK, then the problem might be with the secondary tranny coil. Because I was seeing the dip also on VR1 output with that primary coil attached and your plot for VR1 looks great.
-Frank
The plots I posted of the TY250 many pages ago were done with True RTA. Try just the tranny with T-RTA and see if your plots match.
-Frank
-Frank
I calculated the primary at 3.9H using the cap and coil trick looking for the resonant peak. So, your 3.66H is probably the good measurement.
-Frank
John, looking at your plot I think the tranny was wired wrong... I bet one of the secondary coils is backwards. Send a test sig into the primary and see if either secondary coil is 180 degrees out. 5-6 or 7-8
Also, the DCR of the secondary should be close to 170 ohms with 6-7 tied together.
-Frank
Also, the DCR of the secondary should be close to 170 ohms with 6-7 tied together.
-Frank
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- Feb 16, 2008
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BTW, the 400RB is probably the best GK amp knon for its 'driven on the rails' tone but the 700RB is great too.
here's my RTA result for the TY250P (and it looks GREAT!
here's my RTA result for the TY250P (and it looks GREAT!
BTW, the 400RB is probably the best GK amp knon for its 'driven on the rails' tone but the 700RB is great too.
here's my RTA result for the TY250P (and it looks GREAT!
This does not make any sense. Can you hook the tranny to VR1 output and take another listen?
-Frank
- Feb 16, 2008
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the primary DCR measures 167.6 ohms
and the secondary with 6&7 tied together measures 165.9 ohms
and no, i'm positive that the tranny was wired properly for the freq test (at least as per your schematic and the TY-250P tech sheet.
- Feb 16, 2008
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I just hooked up that series 1K to the primary and the secondary has a 1K VR2 load and looked at the response. The response looks great. This isn't making any sense at all.
-Frank
-Frank
John. when you ran that freq plot with the bad tranny response was VR1 and VR2 turned all of the way up?
-Frank
-Frank
- Feb 16, 2008
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With VR1 at 100% that will be very close to the sig level seen on the primary + 1K resistor. So with your VR1 sig looking so good (better than my simulations, BTW) the output of the tranny should look very close to VR1 response. You proved it by running the tranny alone on T-RTA...
One more test... Can you hook the primary to the output of VR1 (the sig looks fantastic there) and run T-RTA with various VR1 settings like 25% 50% 100%? This will tell us if the tranny has a problem with levels.
-Frank
It would be great if we can get the tranny to play nice, because then you would have the worlds first pseudo "GK" DI box too. 
-Frank
-Frank
I'm such a dummy-head! I just measured the output resistance of my sound module at 47K... totally forgot to take test equipment loads into account.
Try a 47K resistor from 2-4 primary and it will duplicate your stand alone test of the transformer with T-RTA.
-Frank
Try a 47K resistor from 2-4 primary and it will duplicate your stand alone test of the transformer with T-RTA.
-Frank
- Feb 16, 2008
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so you want the tranny tested by itself with a 47K across 2&4 or in the circuit?
First naked tranny (nothing else)
pin 2 to VR1 wiper
pin 4 gnd
T-RTA connected to amp input and tranny secondary output
Take various T-RTA plots with VR1 100% 50% and 25%
-Frank
