Diodes and Noise

[C Moore]

I am rebuilding a 1969 Bassman head. So I am just wondering about those old, silver, RCA diodes. I am replacing them just because I am inside the amp, and I am replacing all the other components.
Is there any "noise" associated with diodes? Can a diode get noisy with age, or maybe some brands might be "better" than others?
So....can diodes be a source of noise?
Thank You
I am talking about solid state diodes by the way. I should have stipulated that already. Something like a 1N4007....

[tubeswell]

Look at Merlin's page on power supplies.

http://www.freewebs.com/valvewizard/fullwave.html

The part where you put high voltage 0.1uF snubber caps in parallel with each diode works well for eliminating diode switching noise - I have used this method to great success with 1N4007s.

Otherwise schottky diodes are hi-speed switching and are not as noisy as other types.

[C Moore]

Look at Merlin's page on power supplies.

http://www.freewebs.com/valvewizard/fullwave.html

The part where you put high voltage 0.1uF snubber caps in parallel with each diode works well for eliminating diode switching noise - I have used this method to great success with 1N4007s.

Otherwise schottky diodes are hi-speed switching and are not as noisy as other types.

Thanks for the link. I will give that a good read.
Thank You

[iknowjohnny]

what does this switching noise sound like?

[PlinytheWelder]

I used Silicon Carbide diodes in my Express with good results. They don't need snubbers for low noise. Google them...

To go farther, Google Silicon Carbide Jfet... Interesting technology.

[labb]

Use FREDs

[selloutrr]

this will solve any issue

[David Root]

I recommend the Fairchild Stealth dual diode hexfred that is 8A per side, 1200V rating, you only need one of them, Mouser charges about $1.00 each, you cannot beat them with two sticks.

No noise, soft recovery, one simple TO-220 package does it all. In audio applications they are barely ticking over.

Separate anodes, common cathode, just what you need, good for 400-500 Vp with no nasties.

Mouser P/N 512-ISL9K8120P3. They are not ROHS compliant.

[rp]

For a while I was sticking soft recovery hexfreds in any tube hifi I found that used diodes including a CJ MV52 Amp I had bought new. Sounded amazing to me, really obvious improvement. I will keep doing this if I ever have a tube hifi again

I read on the ol' internet somewhere that hexfreds (and solens for filter caps) don't sound at all good in guitar amps (was it Gerald Weber?) I don't believe everything I read on the internet but I like sussing out knowledge from debates.

I swore long ago that I'd never put fancy hifi parts in a guitar amp ever again but I'll read posts about it.

Where are the ampgaragers on this?

[20to20]

what does this switching noise sound like?

It doesn't sound like anything. The typical switching time for the common power diodes is measured in microseconds and nanoseconds. That translates into hundreds of khz. and Mhz. They are small ultrasonic pulses that are inaudible. They are also well beyond an amps frequency response even if you could hear those frequencies. A dog couldn't hear them even if they made it through the filtering and OPT roll-off.

[iknowjohnny]

what does this switching noise sound like?

It doesn't sound like anything. The typical switching time for the common power diodes is measured in microseconds and nanoseconds. That translates into hundreds of khz. and Mhz. They are small ultrasonic pulses that are inaudible. They are also well beyond an amps frequency response even if you could hear those frequencies. A dog couldn't hear them even if they made it through the filtering and OPT roll-off.

Ok, but then what are they all talking about here?

[20to20]

what does this switching noise sound like?

It doesn't sound like anything. The typical switching time for the common power diodes is measured in microseconds and nanoseconds. That translates into hundreds of khz. and Mhz. They are small ultrasonic pulses that are inaudible. They are also well beyond an amps frequency response even if you could hear those frequencies. A dog couldn't hear them even if they made it through the filtering and OPT roll-off.

Ok, but then what are they all talking about here?

Misinformed myth and imagination. Just passing bad information from one to another. Just because the diode does its switching on and off at 120hz doesn't mean the pulse lasts that long. The pulse is a one quick high frequency blip riding the carrier of 60hz.

[Structo]

Hadn't heard that one before.

Do you have any data to back up your claim?

When I installed new diodes in my amp I included the snubber caps
The diodes are the UF5408's.

I had originally had 1N4007's in it and I could hear a high frequency buzz.

After the new diodes and snubbers no noise.

[jaysg]

I recommend the Fairchild Stealth dual diode hexfred that is 8A per side, 1200V rating, you only need one of them, Mouser charges about $1.00 each, you cannot beat them with two sticks.

Interesting part. I've used UF4007 and IXYS DSEI-12 parts. Fwiw, you only need 4 if you go with the UF4007 or UF5408...two of the DSEI-12. There are six in all those Fenders because they weren't 1000V parts.

[20to20]

Hadn't heard that one before.

Do you have any data to back up your claim?

When I installed new diodes in my amp I included the snubber caps
The diodes are the UF5408's.

I had originally had 1N4007's in it and I could hear a high frequency buzz.

After the new diodes and snubbers no noise.

The diode data sheets give switching times. Also, here is a link to a technical experiment on the switching times of diodes used as snubbers on relay switch coils to measure how fast they were.

Plenty of scope pix to show that the turn on and off pulses are faster than the rise and fall time of a Mhz square wave.

www.cliftonlaboratories.com/diode_turn- ... htm#1N4007

Your noise may have been from one faulty diode making much more noise than just switching spikes. Did you also change the PS filters at that time? Heat the solder pads to the PS caps? Clean any jacks?