Bottlehead Finished Products > Legacy Products
Extended FP III with 60 Hz buzz
mingles:
I have an Extended Foreplay III with 6SN7. I've had it since 2009. The previous owner said it was built by Bottlehead as a demo for a show. It's had a 60 Hz buzz since the day I got it. It's been in storage for many years. I just pulled it out. The buzz doesn't change with volume. It's the same at volume 0 as it is at 10. The buzz disappears while music is playing, but it's obvious between songs. Swapping tubes and changing sources does nothing. This isn't a ground loop problem. Other preamps are dead silent in its place. The Foreplay sounds absolutely spectacular otherwise. I'd really like to fix the problem. I have decent troubleshooting skills. Unfortunately, I don't have voltage check instructions for the Extended version. Searching through the forums, I found someone with a similar problem that was resolved by replacing the 220uF power supply caps:
https://forum.bottlehead.com/index.php?topic=2249.msg17356#msg17356
If the solution to my problem is this easy, can someone point me to the correct 220uF 250V caps that are drop in replacements?
Thank you in advance for your help!
Mark
Paul Birkeland:
The first thing you want to do is to listen to a 60Hz tone and a 120Hz tone and let us know which you hear.
The other thread you found is for a stock Foreplay III without the extended upgrade, and what's being gone after in that preamp isn't present in yours.
Is this noise in both channels or just one channel?
Doc B.:
Just a minor point - a buzz is 120Hz. 60Hz noise will typically be a soft tone associated with the radiated magnetic field of nearby transformers. I don't see anything in your description that completely rules out a ground loop problem. A simple test is to use a cheater plug on the FPIII and see if it changes anything. It's possible that 13+ year old electrolytic caps are causing the problem, or bad tube pin connections, or oxidized switch contacts, or oxidized attenuator contacts...
So my suggestion is eliminate the easy to test stuff first. Along with the cheater plug try cleaning tube pins, sockets and switch contacts as well as the rca jacks. Only after all that consider replacing components.
mingles:
I cleaned the tube pins with Deoxit and installed a cheater plug, but that didn't change anything. The buzz is in both channels. It's present when the volume is at zero. It increases slightly with the volume knob. The buzz is the same when the source is switched. I can't tell if it's 60 or 120 Hz. It sounds similar to a phono ground problem. Here is a recording that I made:
https://drive.google.com/file/d/196wV_eVJ03fYCKJf-jN2_lFUrdS64ujJ/view?usp=sharing
Thank you again for your help.
Mark
Doc B.:
The extended FPIII has a lot of gain and will tend to boost the noise floor more than other preamps. That 120hz buzz sounds like it could be an open ground or a ground loop. Try disconnecting all the interconnects of your source components from the input jacks on the FPIII, turn the volume control all the way down and see if that changes the noise level.
Navigation
[0] Message Index
[#] Next page
Go to full version