Drip Opto6 Voltage issues

[morls]

Hi,

I've just finished building this, and although it's up and running, passing audio and compressing, there are a few voltage anomalies I need some advice on, if possible. I've gotten the voltage test figures from the drip PCB and also the LA2A-deconstructed.jpg posted earlier on this site:

Running from the transformer output (hammond 240V):
Red leads from secondary 274VAC each; Greens 3.3VAC

Test point at PS caps (275V) - 250V
Test point at R1 (240V) - 207V
Test point at C2 (131V) - 111V
Test point below 12AX7-2 (110V) - 90V
Test point at R12 (1.2V) - 1.03V
Test point at R35 (136V) - 116V
Test point at R36 (9V) - 8.2V

R9, at 12AX7-2 should be (205V, 115V) - 195V, 106V
R34 should be 275V, 135V - 249V, 88V

I'm running a tube rectifier. The NE2 bulb is also flickering, not on-off but lower-higher.

I have a Hairball VU meter, which wants 3.6 to 5.2V. I've connected the 6.5V taps, and it is glowing a dull orange colour.

Is the voltage drop at the PS caps significant? Would this account for the lower voltages throughout?

Any help would be greatly appreciated.

Many thanks

Stephen

 

[joaquins]

Hi,

I've just finished building this, and although it's up and running, passing audio and compressing, there are a few voltage anomalies I need some advice on, if possible. I've gotten the voltage test figures from the drip PCB and also the LA2A-deconstructed.jpg posted earlier on this site:

Running from the transformer output (hammond 240V):
Red leads from secondary 274VAC each; Greens 3.3VAC

Test point at PS caps (275V) - 250V
Test point at R1 (240V) - 207V
Test point at C2 (131V) - 111V
Test point below 12AX7-2 (110V) - 90V
Test point at R12 (1.2V) - 1.03V
Test point at R35 (136V) - 116V
Test point at R36 (9V) - 8.2V

R9, at 12AX7-2 should be (205V, 115V) - 195V, 106V
R34 should be 275V, 135V - 249V, 88V

I'm running a tube rectifier. The NE2 bulb is also flickering, not on-off but lower-higher.

I have a Hairball VU meter, which wants 3.6 to 5.2V. I've connected the 6.5V taps, and it is glowing a dull orange colour.

Is the voltage drop at the PS caps significant? Would this account for the lower voltages throughout?

Any help would be greatly appreciated.

Many thanks

Stephen

Voltages are all in the ballpark, a bit low but not a problem unless you can't reach specs in distortion, level or something like that.

Don't do that to your rectifier, rectifier tubes ask for lower voltages to avoid using the same winding as the others and usually are connected to the cathode of the tube. Get a proper 5V for it.

You may be having some troubles with the transformer rating, does it have enough juice? If it does you probably need a higher voltage transformer.  There may be ways to avoid changing it, tweaking the circuit a bit.

JS

 

[morls]

Thanks for the reply Joaquins,

I've been looking at it some more, and although the meter is showing gain reduction, there isn't actually any compression occurring. I had a trim resistor at R25, which I'm going to remove and replace with the fixed 33k option. I also had a 1M trimmer pot for the frequency response which I'll remove and just use the jumps on the board which bypass pin 7 on the 2nd opto cell.

There is also continuity between the 6.3V taps and ground, which has me concerned.

Cheers

Stephen

 

[morls]

The levels are all good, plenty of gain, just no compression and the strange 6.3V ground issue. I'm getting this without the rectifier in place.

I'm not sure what you mean by getting 5V for the rectifier - is it running on the 6.3V? If so, would this mean getting a different transformer with 5V rather than 6.3?

I'm using a Hammond 369JX. Secondary voltage of the transformer (measured) is 548V, circuit calls for 500V.
specs:
Secondary output 500 VAC CT
Power Rating: 50 VA
Secondary Current Rating: 69 mA

 

[morls]

I've isolated the transformer, and there is continuity between the 3V AC wires and their centre tap, which is grounded. This is why I'm getting a connection from the 6.3V to ground. Is this normal?
Thanks
Stephen