Snubbers: The leakage inductance of the trafo AND the capacitance of the rectifier diodes creates a resonant "tank" circuit which can, under certain circumstances, cause PN junctions to conduct when they otherwise wouldn't.
Snubbers in audio circuits have been flogged to death, employed without any knowledge of the parasitic inductance of the transformer or capacitance of the rectifying diodes.
There's a real, existential need for a snubber in an SMPS power supplies. Elsewise measure first, listen, and report back.
Snubbers in audio circuits have been flogged to death, employed without any knowledge of the parasitic inductance of the transformer or capacitance of the rectifying diodes.
There's a real, existential need for a snubber in an SMPS power supplies. Elsewise measure first, listen, and report back.
I am in the process of getting all the parts to build a Pearl 2.
I have a couple of questions.
First the cartridge loading resistor. I am using a Kiseki purpleheart cartridge. It has an output of 0.4mV and an impedance of 6R.
What value of cartridge loading resistance would you suggest?
Second, will I still need to use a SUT with the Pearl 2? In my current setup I am using a Bob's devices SUT (30dB gain) with a Bottlehead Eros which has 50dB of gain
Thanks
Debra
I have a couple of questions.
First the cartridge loading resistor. I am using a Kiseki purpleheart cartridge. It has an output of 0.4mV and an impedance of 6R.
What value of cartridge loading resistance would you suggest?
Second, will I still need to use a SUT with the Pearl 2? In my current setup I am using a Bob's devices SUT (30dB gain) with a Bottlehead Eros which has 50dB of gain
Thanks
Debra
Debra! Great to see you here in this thread. 
Load - well, that depends on if you are using the SUT or not...
If you directly run the cartridge to the Pearl, then I'd start at 1K or so. Adjust to taste.
If you use the SUT, then at the Pearl inputs you need to load the transformer, not the cartridge, so just use the regular 47K. (The Bob's transformers are expecting to 47K on the secondary.)
Try both ways, but I bet you'll prefer the sound with the SUT.
Order a couple extra ZVP3310, they are VERY static sensitive, and about 1/2 the builders zap one or two during the build, and it's easier to have spares on hand right away.
Load - well, that depends on if you are using the SUT or not...
If you directly run the cartridge to the Pearl, then I'd start at 1K or so. Adjust to taste.
If you use the SUT, then at the Pearl inputs you need to load the transformer, not the cartridge, so just use the regular 47K. (The Bob's transformers are expecting to 47K on the secondary.)
Try both ways, but I bet you'll prefer the sound with the SUT.
Order a couple extra ZVP3310, they are VERY static sensitive, and about 1/2 the builders zap one or two during the build, and it's easier to have spares on hand right away.
Your two questions are interconnected.
Cartridge loading:
It is often recommended to load at least at ten times the internal impedance. So I'd try with 100ohms at first.
With your current set-up, the load with your 30 dB SUT (1:29.5 ratio) is 54 ohms (47000/29.5²). So, if your happy with it, you can try that.
I f I were you, I'd buy several values (50, 100, 200, 400 ohms) and choose by ears once the Pearl is finished.
Gain:
If you really need the 80dB gain of your current set-up, certainly the 55dB (or 65dB) Pearl 2 will be a little "weak". You will have 711mV output (with 65dB) instead of 4000mV (which is really huge).
On the other side, maybe less gain in the phono stage will give a more usable volume control in your setup.
If you want to try the SUT with the Pearl 2, buy a 47k input resistor in addition to the other I listed above.
Sorry I didn't post schematics originally, it took me this long to figure out how mark them up.
I would like to pursue this a little farther. Still trying to get my head around how removing these parts could make such a dramatic difference in sound.
I appreciate the information about the PN junction conducting, I'm reading about that. Still, it seems like there could be more to it. Could the output snubber somehow be reacting with the onboard regulation?
If you want to get all science-y, you can replace the fixed 1 ohm resistor with an adjustable resistor (a potentiometer) and then find the resistance setting which results in the GREATEST sonic difference between [red "Output Snubber" = YES] and [red "Output Snubber" = NO]. Possibly DigiKey part # CT2150-ND might be a good choice. It's a 5 ohm, 5 watt device, giving you plenty of adjustment range.
Once you have dialled in the MAXIMUM SONIC DIFFERENCE value of snubbing resistance, it's time to start snapping lots and lots of oscilloscope photos. What, if anything, is different on the oscilloscope between [red "Output Snubber" = YES] and [red "Output Snubber" = NO]??
Once you have dialled in the MAXIMUM SONIC DIFFERENCE value of snubbing resistance, it's time to start snapping lots and lots of oscilloscope photos. What, if anything, is different on the oscilloscope between [red "Output Snubber" = YES] and [red "Output Snubber" = NO]??
Mark was probably too modest to promote his own thread, but this is awesomely useful! http://www.diyaudio.com/forums/powe...sformer-snubber-using-quasimodo-test-jig.html
I know! This is cool too: http://www.diyaudio.com/forums/powe...dirty-transformer-snubber-bellringer-jig.html
47k may not load correctly.
For the correct load disconnect the first stage from the RIAA network. If you don't have an analyzer which goes out to 100kHz you can use a 10mV square wave @1kHz and observe the ringing on the leading edge on a scope. Just like Goldilocks, not to hot and not too cold.
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