Scratchy left channel

O

Ohioriver

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Jan 30, 2022
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Ok, I am loving my original PL700B. I had to take it to a shop in louisville to work the bugs out. It had been running well for many hours, but..... I now have a scratchy noise on the left channel. I have switch everything an been able to isolate it to the left channel of the amp! It is only scratchy on the highs frequencies especially at the begin of songs when it is quiet. Any thoughts? I may put it back in the shop but then I will not have the amp for awhile. Any suggestion on why I might have a scratchy noise from the left channel of my amp.
 
Last edited:
Ohioriver said:
Ok, I am loving my organic PL700B. I had to take it to a shop in louisville to run the bugs out. It had been running well for many hours. I now have a scratchy noise on the left channel. I have switch everything an been able to isolate it to the left channel of the amp! It is only scratchy on the highs especially at the begin of songs when it is quiet. Any thoughts? I may put it back in the shop but then I will not have amp for awhile. Any suggestion on why I might have a scratchy noise from the left channel of my amp.
Click to expand...
Try "exercising" the left channel attenuator back and forth about 20 times. Does moving the attenuator cause scratchiness or a increase in static?
 
I agree with George, that was the first thing I thought of, dirty pot.....use some Deoxit and work it back and forth.
Corrosion can happen any time, but if the potentiometer is "parked" on your 700b as we tend to do, it will take a set so
to speak, corroding quicker. That's where I would start anyway.....check your connection from your pre as well coming into
the amp (turned off of course) and make sure that is making good contact. Simple troubleshooting, but a good start anyway.
I hope that does it.
By "organic 700b" do you mean it is not WOPL'd?.........boards are 45 years old?
 
Perfect George,
It is that "Slowly returning to the earth from which it was formed" that had me concerned o_O.
You put a smile on my face.
 
Should I excersie the pot with power on it or no power? It precious had zero effect when I had adjusted it, but never for 20 minutes. Just a time or two. I will exercise it for sure.
 
Funny. I only took about 5 minutes of excercising to figure it out. I need a new pot! It is really bad now. Any recommendations for replacement pots?
 
Definitely power OFF.
Did you spray it well with Deoxit?
Let that work in and do it several times.
Sometimes you will have to pull the top cover, and really get to it, and catch the corrosion as it comes pouring out.
They can get really cruddy (technical term) and a good cleaning (hopefully without disassembly of the pot) will do the trick.
Hope that helps.
 
In my experience, the best potentiometer for you would be the high quality Bourns 100K pot available from Mouser under this part number:
652-PDA241HRT02104B0
https://www.mouser.com/ProductDetail/Bourns/PDA241-HRT02-104B0?qs=itG3xFeL1F3d8lnCDEh%2B6Q==

For the price of $3.87, I would order two and replace them both. These pots have the straight shaft and work perfectly with the knobs that use a set screw. If your knobs require pots that have a half-round shaft, you will have to modify the shaft with a Dremel tool (fast) or a file (slow).

Mark
 
I second Mark's suggestion of replacing both at the same time, if you need to replace one. I had a broken original on the last 700b, that I WOPL'd and replaced the pair. Works like new. It will definitely take care of the scratchiness.
 
Well I was going to order and replace the pot asap but they are 19 weeks out. In a quick search I only found quants of 300+. An other places or recommendation on the potentiometers? I can easily ( as old electronics go) remove and replace but I want to make sure I get the right ones.
 
Ohioriver said:
Well I was going to order and replace the pot asap but they are 19 weeks out. In a quick search I only found quants of 300+. An other places or recommendation on the potentiometers? I can easily ( as old electronics go) remove and replace but I want to make sure I get the right ones.
Click to expand...
You get your first HUH???

They have 433 in stock.
 
The Mouser link that Mark sent you says they have 433 in stock.
It is the correct Bourns 100k with .250" shaft.
 
19 weeks factory lead times. Not sure what the HUH means but I don't want to wait 19 weeks.
 
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