PL 700 II REPLACEMENT MAIN VOLUME POTS

I’m leaning toward hardwiring the input jacks to the control board and leaving the volume pots in place, unwired, to retain the original appearance. Chances are somebody will flip that switch when the amp is on and speaker parts will go flying.

besides, adding a switch will add wire and contacts that are potential resistance, yada yada
 
You can try this, taken from Joe's Cylon instructions for the 400. 500 Hz, 3.198298 Vpp (sine wave peak to peak) input to the RCAs. Should get you 40 Vrms output per channel at the speaker jacks.
In the past, output has always been right on so I didn't measure it this last time. You can zoom in and see these settings. You can also see my right meter needed one additional tiny turn of the precision pot to get 0 dB.
 

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Actually, I think I adjusted the left meter down 1 segment. Joe specifies adjust until LED #31 just turns on. That leaves one LED off just below 0 dB. Difficult counting all those segments.
 
Ok…I will give that a try, but I had tried both 60Hz and then thought the protection relay might not have liked that and so I went for 1KHz and that did the same. Note I had the generator connected to one channel and about 50mv when I powered it up both times. The idea was to ramp the input volts until I got to that 40V RMS output. No connection to the output jacks, except the oscilloscope…and also tried a DMM that reads true RMS. Admittedly, I ramped the power through the variac as it was within reach when I was testing..not sure if that comes into play.
 
e30m3mon said:
Ok…I will give that a try, but I had tried both 60Hz and then thought the protection relay might not have liked that and so I went for 1KHz and that did the same. Note I had the generator connected to one channel and about 50mv when I powered it up both times. The idea was to ramp the input volts until I got to that 40V RMS output. No connection to the output jacks, except the oscilloscope…and also tried a DMM that reads true RMS. Admittedly, I ramped the power through the variac as it was within reach when I was testing..not sure if that comes into play.
Click to expand...
The Variac in circuit may have been a factor. Try bringing both channels up slowly to 3.198. Probably a volt at a time, then the final .198. No Variac or DBT needed at this point. Good luck!
 
George S. said:
The Variac in circuit may have been a factor. Try bringing both channels up slowly to 3.198. Probably a volt at a time, then the final .198. No Variac or DBT needed at this point. Good luck!
Click to expand...
I was thinking the variac might have played a role as well…but easy enough to go back and give it a shot later today.

I was too interested in HEARING the difference! The meters are fun to watch, but the door to my rack is usually closed, so the meters are out of view anyway
 
My 400 meters were fairly close, the 700s were way off. And both were precisely adjusted before the mod. A good indication of the change of input impedance.
I've also noticed the Cylons are now more responsive, even at low volumes. Joe has these designed such that the leading LED varies in brightness. Not sure sure how many stages each LED goes through from off to full brightness, but I'm seeing more of this in direct proportion to the bass with no lagging. A mechanical meter doesn't come close in terms of response and accuracy. WOAD Cylons are a major upgrade to these amps.
 
I could probably design something. Then it's a matter of getting it made, which I could also do.

"speed's just a question of money. How fast you wanna go?"
 
Plenty of 700B owners out there. Maybe conduct a poll to see if it would be worth your time.
 
My now deceased bud in Phoenix wanted a 400 with dual outputs. One through the DC protect board and one set straight through. He said he could hear a difference. Dont know if I did. Pots were evil to him also..
The second set of output jacks were installed between the backplane boards...
 
laatsch55 said:
My now deceased bud in Phoenix wanted a 400 with dual outputs. One through the DC protect board and one set straight through. He said he could hear a difference. Dont know if I did. Pots were evil to him also..
The second set of output jacks were installed between the backplane boards...
Click to expand...
I've often wondered about this after seeing Joe's build with no DCP.
 
George S. said:
I've often wondered about this after seeing Joe's build with no DCP.
Click to expand...

My personal 400 II WOPL is not getting a DCP but the Volume Pots, On/Off switch and the meter sensitivity switch are staying. These amps are so clean and quiet that I HEAR NO DIFFERENCE. YMMV

Same for the next pair of 700 II's

It ain't like the Distortion Police are coming in and fining me for distortion they can't hear. I don't mind if MY bandwagon is empty. My stereo isn't open to the public anyway. :)

But, I may let the goats in occasionally.
 
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