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GK rails in a pedal?

#203
John, after we get those DC voltages and they check out, install a 062, 072 or 082 with pins 6&7 tied together. You will have to bend pin 6 out of the socket to make this connection so that it is only connected to the output of U1b. I want to remove all the local error correction from U1b for Q1/Q2 and only let it run as a unity gain driver... we will let U1a handle all of the error correction like the original GK amp does. Also to protect the output of U1b from faulty Q1/Q2 transistors you can lift pin 7 out of the socket and connect a 1K in series from pin 7 to the junction of D2/D3. So lift pins 6&7 and connect them together and then attach a 1K from 6&7 to the junction of D2/D3. BTW, We may have to insert the distortion detector in another location if this works.

I was looking at the 800RB pre amp and the J113 output amp can drive a 12Vp-p signal to the power amp. So this amp is able to accept large input signals without issue.

-Frank
 
#204
here's the chip socket voltages without the chip with the 10K resistor across pins 6&7. power supply is a 1spot into the LT1054 for the negative voltage. V+: 9.43V V-: -9.25V
Pin:
1: .024V
2: .015V
3: .004V
4: -9.25
5:-.429V
6: .028V
7: .030V
8: 9.43V

with the chip (TL072)

1: 2.80V
2: -.010V
3: -.035V
4: -8.85
5: -.460V
6: -1.30V
7: -1.45V
8: 9.43V

let me know if you need any other voltages........
 
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#205
Thanx!! Just what I expected!!! U1b is fighting with U1a or there is something wrong in the copper... pins 5 & 6 should only have a few mV difference with the opamp installed.

Please make the connections that I described in the post above your last post.... we need to remove global feedback from U1b.

-Frank
 
#206
johnk_10 said:
here's the chip socket voltages without the chip with the 10K resistor across pins 6&7. power supply is a 1spot into the LT1054 for the negative voltage. V+: 9.43V V-: -9.25V
Pin:
1: .024V
2: .015V
3: .004V
4: -9.25
5:-.429V
6: .028V
7: .030V
8: 9.43V

with the chip (TL072)

1: 2.80V
2: -.010V
3: -.035V
4: -8.85
5: -.460V
6: -1.30V
7: -1.45V
8: 9.43V

let me know if you need any other voltages........
Click to expand...

The output of U1a should be a few volts negative like -2.5V to -3.5V when everything is idle. I Expect that when we get this other issue resolved then that output will look good.

BTW,Did you put the LED's back in?


-Frank
 
#214
Q1 and Q2 are too low. You should see +/-9V minus the LED drops plus a small drop from the 10R resistors with the LED's.

When idle you should see:

TP1 = -2V to -3.5V or something close (depends on Q3/Q4 gain)
TP2 = approx 0V to a few tenths of a volt
TP3 = same as TP2

At the opamp:

pin 1 = TP1
pin 2 and pin 3 = a few mV
pin 4 = -Vcc
pin 5 = TP2 = -100mV to -700mV
pin 6 = pin 5 +/- a few mV
pin 7 same as pin 6
pin 8 = + Vcc

-Frank
 
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#217
***IMAGE REMOVED- WE HAVE A NEWER VERSION LATER IN THIS THREAD***

John, I have put all of the changes that you have made on your V3 in this V4. Please check D8 on your PCB to see if it is connected correctly... if the anode is still connected to the junction of R1/R2 it may make some awful sounds.

-Frank
 
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#218
boomertech said:
John, I have put all of the changes that you have made on your V3 in this V4. Please check D8 on your PCB to see if it is connected correctly... if the anode is still connected to the junction of R1/R2 it may make some awful sounds.

-Frank
Click to expand...

man, traffic was a bitch and i just got back home.

cool. rather than keep jury-rigging my protoboard, i'm going to etch a completely new one tomorrow morning according to the latest V4 schematic since the first one was getting pretty gnarly, sloppy, & confusing to work with with all of the later changes I made to it.
I should have the new one built, & ready for testing by noon and i'll take voltage measurements of it too.

thanks again. i'd like to get it running in 2014. ;)
 
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#219
johnk_10 said:
man, traffic was a bitch and i just got back home.

cool. rather than keep jury-rigging my protoboard, i'm going to etch a completely new one tomorrow morning according to the latest V4 schematic since the first one was getting pretty gnarly, sloppy, & confusing to work with with all of the later changes I made to it.
I should have the new one built, & ready for testing by noon and i'll take voltage measurements of it too.

thanks again. i'd like to get it running in 2014. ;)
Click to expand...

Great! Thanks for sticking with it! I have a feeling that this will be it... but test it with the 072 first.

Punch list:
*********************************************
I will finalize the schematic after you have figured out what the values of R16, R7 are best for AC gain and max output level. We still will need to figure out where you want the foldback clipping set (R19/R20). You can do some asymmetrical foldback clipping by making R19/R20 different values.

You will also have to let me know what NPN's and PNP's you used, so I can get those numbers on the schematic.

We will also need the taper of VR2 when you get the chance to test drive the tranny... I don't know for sure whether audio or linear taper feels best. I have VR2 as A1K now, but you could use a larger value pot for more max output, maybe 5K or 10K.

I would also like to put some voltage readings on the schematic for anyone that might take on the task that you have.
*********************************************

I had to change 3 resistor values for the distortion detector with it in the new location.

Dist detector.jpg


-Frank
 
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