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- Jan 14, 2011
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- Halfbiass...Electron Herder and Backass Woof
PL400 Restoration
- Thread starter jtatknox
- Start date
- Joined
- Jan 14, 2011
- Messages
- 74,877
- Location
- Gillette, Wyo.
- Tagline
- Halfbiass...Electron Herder and Backass Woof
Right now my strategy is just to never turn it off. No noise, no latching if you never shut it down. 
I soldered up the WOPL driver board yesterday afternoon and installed. Came up fine first try. ~1 mV DC offset. Kudos to White Oak for making a very nicely organized kit. I particularly like the use of high power small form factor Vishay resistors. I use those all the time when a lower power resistor burns through in a guitar amp and I love them because they fit in the old form factor and I feel like they'll still be running when I'm dead.
A few comments and questions:
1) The PCB is VERY high quality and it made the job a lot easier. I don't have a digital soldering iron, just one with an analog knob. I was still able confidently solder up the board. It looks like the pads are very thick and pre-tinned. Even though this was about 10x bigger than any previous job I have done, I felt like it went much smoother.
2) All of the grounding problems I have had with this unit were fixed by replacing RCA input jacks. On my particular unit, there was a bus wire leaving these jacks for audio ground as well as 3 ground wires (2 black and one white) leaving the audio ground to the old driver board. When I installed the Watts Abundant kit, I cut the bus wire and ran a new wire to the filter cap ground busbar. I think that given the topology of the circuit at the time, this may have exacerbated grounding problems at the janky RCA jack. One nice thing about the WOPL driver board is it that grounds the board to the bus bar using a separate ground path than the audio ground. This ends up complementing the Watts Abundant kit perfectly.
3) I'm getting a little more tweeter hiss, but I feel that this is a feature not a bug. I think the old worn out driver board wasn't giving up the treble frequencies from the program material. I aim to do some listening today.
4) I don't have a scope. Does anyone bother to check the output on a scope of it doesn't sound bad by ear and came up fine? I did some frequency sweeps and my "ear scope" is happy.
5) I also installed the new VU meter board so I wouldn't have to change the lamps. When I first tested this w/ the old board the meters were both pegging at power down, so I didn't use the amp until I could get the new driver board in. I don't see the needles moving even with the internal jumpers at the most sensitive setting. I checked my input source and it's -70 to -60 dBFs and the meters move if I crank it to touch -40 dBFs. I think I just want them to be a little more sensitive. Maybe I can increase R14 but I don't know the right calibrated values.
Cheers,
J.T.
P.S. nobody get in trouble with their SO answering my questions on Valentine's day!
A few comments and questions:
1) The PCB is VERY high quality and it made the job a lot easier. I don't have a digital soldering iron, just one with an analog knob. I was still able confidently solder up the board. It looks like the pads are very thick and pre-tinned. Even though this was about 10x bigger than any previous job I have done, I felt like it went much smoother.
2) All of the grounding problems I have had with this unit were fixed by replacing RCA input jacks. On my particular unit, there was a bus wire leaving these jacks for audio ground as well as 3 ground wires (2 black and one white) leaving the audio ground to the old driver board. When I installed the Watts Abundant kit, I cut the bus wire and ran a new wire to the filter cap ground busbar. I think that given the topology of the circuit at the time, this may have exacerbated grounding problems at the janky RCA jack. One nice thing about the WOPL driver board is it that grounds the board to the bus bar using a separate ground path than the audio ground. This ends up complementing the Watts Abundant kit perfectly.
3) I'm getting a little more tweeter hiss, but I feel that this is a feature not a bug. I think the old worn out driver board wasn't giving up the treble frequencies from the program material. I aim to do some listening today.
4) I don't have a scope. Does anyone bother to check the output on a scope of it doesn't sound bad by ear and came up fine? I did some frequency sweeps and my "ear scope" is happy.
5) I also installed the new VU meter board so I wouldn't have to change the lamps. When I first tested this w/ the old board the meters were both pegging at power down, so I didn't use the amp until I could get the new driver board in. I don't see the needles moving even with the internal jumpers at the most sensitive setting. I checked my input source and it's -70 to -60 dBFs and the meters move if I crank it to touch -40 dBFs. I think I just want them to be a little more sensitive. Maybe I can increase R14 but I don't know the right calibrated values.
Cheers,
J.T.
P.S. nobody get in trouble with their SO answering my questions on Valentine's day!
Last edited:
- Joined
- Oct 15, 2014
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- ---not quite right
I had a blast building two of them driver boards. I had never assembled a board before and I enjoyed the process very much, as you said the quality made it a breeze! So your VU meters aren’t moving at all when playing music? Test them for continuity, test for AC (signal) voltage at the meter and also you can disconnect your speakers and turn the amp up some should get them dancing... possibly you’ve made a connection error or (hopefully not) otherwise damaged them (open meters)???