Single diode supply for DAC

[fedde]

Hi guys,

I was wondering if anyone of you has done some experiments with a single diode supply instead of a bridge with four diodes. I've heard that the Shigaraki and Progression DACs of 47 Labs use only a single diode.

I did some experiments and found out that there quite a difference in sound between these setups. I did not reach a final conclusion, but the sound with a single diode seems to be more detailed and open.

I think that the single diode supply could have more advantages beside cost, size and circuit complexity reduction. The diodes have switching noise and are a non-linear component, so I'd guess it is an advantage to have only one diode in the power supply path. A disadvantage is the greater ripple. This can be compensated for with a larger cap. Or you could see it as a trade-off between ripple and HF noise. The regulator after the diodes will have far less trouble with 50-60 Hz ripple than HF noise...

Any thoughts???
(or better: measurements with spectrum analysers )

Fedde

[ThorstenL]

Konnichiwa,

Originally posted by fedde
I was wondering if anyone of you has done some experiments with a single diode supply instead of a bridge with four diodes.

I only ever compared bridges to full wave rectification, generally preferring the latter.

Originally posted by fedde
I've heard that the Shigaraki and Progression DACs of 47 Labs use only a single diode.

So have I.

Originally posted by fedde
I did some experiments and found out that there quite a difference in sound between these setups.

I would expect so.

Originally posted by fedde
I did not reach a final conclusion, but the sound with a single diode seems to be more detailed and open.

Maybe just "brighter"? With the natural HF rolloff of the NOS DAC this may help ofsetting some of the "darkness"?

Originally posted by fedde
I think that the single diode supply could have more advantages beside cost, size and circuit complexity reduction. The diodes have switching noise and are a non-linear component, so I'd guess it is an advantage to have only one diode in the power supply path.

Maybe. But you also end up putting a significant DC load on the mains transformer. You must severely derate any mains transformer used with such a rectifier. Not an issue if you use a 170VA Transformer to draw 100mA or so, but potentially an issue if you use a "wallwart".

Originally posted by fedde
A disadvantage is the greater ripple. This can be compensated for with a larger cap.

I would suggest against this. Keep the cap's small(ish). Modern Regulators do well enough in killing ripple.

Originally posted by fedde
Any thoughts???

I suggest you compare single diode and full-wave rectification (needs centertapped secondary) to bridge. It might be interresting. If you find that Bridge and Fullwave sound similar or identical the cause for the change in sound is the higher noise level with the single diode or possibly the fact that ripple is 50Hz not 100Hz. If you find the Single Diode and Full Wave to sound similar then the HF noise signature is most likely the issue.

Sayonara

[fedde]

Thanks Kuei for your response!

So you suggest full wave rectification with two diodes !? Doesn't that also have the DC loading problem !? I do have a centre-tapped toroid, so I can try that... (well, a double secondary toroid, but that'll work too)

Brighter? Yeah, I guess it is brighter! Too bright for my taste, I have to say... (but I also use different components 4xMUR860 vs 1xSchottky, I'll do better experiments lateron)

"I would suggest against this. Keep the cap's small(ish). Modern Regulators do well enough in killing ripple."

Yes, that was the next experiment I wanted to carry out. I currently use 1000 uF P. FC, but that could be too large...

Fedde

[tiroth]

I would not use smaller caps than that! I would not expect more than 60dB ripple attenuation, so to put ripple below the noise floor of a good reg you still need to deliver < 5-20mV of ripple to the input of the regulator.

I was experimenting recently with 2200uF + 10mH/3R + 2200uF + R + 680uF next to the regulator. I would choose R to control the ripple, as the current draw was relatively constant. This would not work well for very dynamic current draws of course.

[moamps]

Originally posted by Kuei Yang Wang
I would suggest against this. Keep the cap's small(ish). Modern Regulators do well enough in killing ripple.

Hi,

With small caps we need higher secondary voltage for proper regulators work. Current impulse thru diode is than higher. HF noise is function of diode current. I see circle here.
Using two diode-double secondary full wave rectifier is IMHO good idea, half wave rectifying isn't at all.

Regards

[ergo]

One aspect in all this subject that I have been thinking of is that the 100Hz ripple has harmonics also.

So, you do not only get 100Hz + any HF garbage but also some harmonics @ 200, 300, 400 etc. Hz.

What I'm getting at is that perhaps there is one more point why half wave rectification sounds better. There you get 50Hz ripple + 100, 150, 200 Hz etc. harmonics + less HF garbage. All this means less colouration to the critical midrange, doesn't it ?

Ergo

[peranders]

If you have the opportunity, use a fullwave bridge. This is the cleanest way to rectify. Other methods creates more harmonics and losses in the transformer. It's nicer to the smoothing caps also with fullwave rectification.

[peranders]

Originally posted by moamps
Using two diode-double secondary full wave rectifier is IMHO good idea, half wave rectifying isn't at all.

Using a fullwave bridge is even better because using two diodes is also halfway rectification of each half in the transformer, which creates more losses and harmonics.

[moamps]

Originally posted by peranders

Using a fullwave bridge is even better because using two diodes is also halfway rectification of each half in the transformer, which creates more losses and harmonics.

Hi,

Sorry, I don't think so.
Transformer is full wave loaded. Current flow thru only one diode all the time instead of 4diode-bridge where are two diodes active.

Regards

[peranders]

Originally posted by moamps
Sorry, I don't think so.
Transformer is full wave loaded. Current flow thru only one diode all the time instead of 4diode-bridge where are two diodes active.

Think how currents flow. Through each winding you will have current on a half period only. 50% of the time no current will flow. The transformer is driven harder with a 2-diode rectification. The thing is halfwave rectification times two with the two sections 180 deg separerated apart. This creates fullwave rectification with only two diodes.