Foreplay II buzz-need help with snubbers

[Grainger49]

Tom,

I'm going to look and see which terminal I should have suggested be connected to T13. (I'll post here to verify whether T12 was right or wrong.)

Looking at your quote in Red, this makes some sense, depending on which diode you connected the Cree after.  That is, it should be after the diode that is connected to the positive on the first capacitor in the power supply filter.

Looking at your quote in Green, I'm not sure what was done.  If it is connected between the power supply common and the anodes of the two diodes that are connected to the power supply common then that is where it should be inserted.

Cree diodes negate the need to install the RRSF since they have no reverse recovery spike.  I'm pretty sure one between the + of the bridge to the first filter capacitor should block all the reverse recovery spikes that the stock filter could pass.  So if the red text is correct the bridge is not your source of buzz.

So I tried connecting terminal 12 to the ground leg of the power, very loud hum. Terminal 14 is connected to terminal 13, as suggested in one of the previous posts.

I tried one of the Cree diodes (I have 4), connected after one of the existing diodes (being careful to connect the cathode end correctly). The buzz is a little quieter, but not much. I tried connecting a second Cree to the other diode that is oriented in the same direction, a lot more buzz. Removed it, of course. So I have only one Cree diode installed.

One issue that may be related is a grounding noise when ever I touch the volume. It does have a stepped attenuator. I appreciate all the help so far. I feel that I am getting somewhere, slowly but surely. Just that last bit of buzz....

[manfred99]

I put the first diode after the diode that is pictured here on the right, the second diode I installed was to the diode next to it. Both diodes have the banded(cathode) end going toward the cap. I will take another pic this afternoon of what I did.

 (http://i146.photobucket.com/albums/r271/manfred8/foreplay3.jpg)

Tom

[Grainger49]

Tom,

This sounds like you put a Cree diode from a diode cathode to the terminal strip.  Is that right?

Looking at your picture it seems the terminals are numbered from top (1) to bottom (5).  What should help is putting a Cree diode from (anode) terminal 2 to (cathode) the blue wire.  I.E. in series with the blue wire.  This should guard against reverse recovery spikes.

This all assumes that your problem is caused by reverse recovery spikes.

[manfred99]

Well, this is what I did. So it should have gone from the blue wire, cathode end,to the second diode, anode end? I have a pic with a line drawn as to wear the diode should connect.
(http://i146.photobucket.com/albums/r271/manfred8/cree1.jpg)
(http://i146.photobucket.com/albums/r271/manfred8/cree2.jpg)

Tom

[Grainger49]

Tom,

The simplest way to do it is in series with the blue wire.  I would try to swap the UF4007/Cree combination on the left with the diode that is second from the right.  Be careful to keep the directions right, that is, both have to be swapped to give you a full wave bridge.

I wouldn't try to mess with the other diodes, just swap 1 and 3 (numbering from left to right).

[manfred99]

I put the Cree diode as per your previous message, Cree diode from (anode) terminal 2 to (cathode) the blue wire.  I.E. in series with the blue wire, the buzz didn't change.

So I have enclosed another pic with the wires numbered 1-4, please explain again, I didn't quite understand which left and right.

(http://i146.photobucket.com/albums/r271/manfred8/cree3.jpg)

Tom

[Grainger49]

Tom,

The Cree diode is not really where I suggested.  For the Cree diode to be as I suggested it would have the anode on terminal 2 and cathode soldered to the blue wire.

However, I saw something completely different in your previous picture.  I don't know why.

What you did is put the Cree diode in series with one of the two diodes that feeds terminal 2.  That would eliminate 1/2 of the RRS noise.  Another Cree diode with its cathode on Terminal 2 and in series with diode 3 (last picture) would eliminate the last half of the RRS noise.

I'm still wondering why I didn't see the Cree diode correctly in the picture.  Age maybe?

[manfred99]

Sorry, that was a previous pic, just to get the numbers on. Here's how I have it. Cathode on the blue wire, anode to terminal 2. Still have the buzz. I'm pretty sure at this point that the buzz is coming from somewhere else.

 (http://i146.photobucket.com/albums/r271/manfred8/cree4-1.jpg)

[Grainger49]

That is just as it should be.  If there is buzz the diodes are not at fault.  No RRSF will help.

What is your situation now?

[manfred99]

Buzz remains. I have a spare preamp to use. I may take it to a local tube audio repairman. Not sure what else to try. Filament snubbers? I'll make a copy of Voltseconds web page when I take it in.  I never learned to read schematics.

Thanks for your time and effort.