Bride of ZEN zener diodes

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BOZ Transformer

The sound stage of BOZ is greatly enhanced, as are all the other good qualitys of the preamp, if you use an oversized transformer.
It draws a constant 40 ma. per channel or so, so it shouldn't make a difference if you use a 500 ma. or a 3 amp transformer, but it surely does in mine.
I tried it both ways, and the difference is NOT SUBTLE.
It makes a wonderfull improvement going from a 30va to a 180-230 va Avel Lindburgh transformer.
Fast/soft recovery diodes seem to help also when used in place of the specified rectifiers in the p.s. section.

I am using a 300VA 25-0-25 trannie at the moment and I must agree the sound excellent. My next project is the BSOZ as it has been mentioned on this forum time and again that it is supperior to the BOZ. I intend to use an oversized transformer on this one as well. I have not used fast diodes but they must be worth a try since they are only a few cents more than ordianry diodes.

We...and by we, I mean a lot of people from 'round these parts...never came to a conclusive, all-encompassing, definitive conclusion on audibility of fast vs. slow diodes. Never even managed to draw battle lines and take sides, for that matter. Go look for a thread about it about two or three months back. Got a good running start, tilted at the windmill...and decided not to decide.
All of which to be construed as a long-winded way of saying that no one really was able to say for sure whether fast/soft/slow/whatever diodes actually sound better.
I've used them on some projects & not on others. But, and here's the rub, I've never built a circuit, listened, then pulled out diode X and put in diode Y, then listened again. Nor had anyone else, at least as of the time of the thread. I believe Geoff had swapped diodes in a circuit, then later swapped them back, but ended up confused as to whether he had actually heard an improvement either way. There are theoretical arguments both pro & con, but little in the way of actual listening to lend creedence to either school of thought.
If you've got time, and an extra dollar, please do try both and report back. I, for one, would be interested in the results.


For my BLS pre-amp (some say Bride of Son of Zen), I used 1 watt Motorola Zenor diodes. I liked the silver/greyish colour of these diodes over the generic, smaller wattage, glass like, orangee variants.

As for oversized transformers. Well I would say i'm far from oversize in my pre-amp. Only 24 VA for each power supply board (48VA total) and running 4 channels! Furthermore, the higher voltage rails (40vdc on the mosfet drains) will draw a lot more than originally specified.

The sound is incredible (more full sound with extended response than running the source direct to the amp). I chose not to use toroidals and most likely will never replace the current double split bobbins used now.

For large unregulated power supplies - then I can see the gain in massively oversized transformers. Actually, I would think using larger size capacitors would yield more improvement than oversized transformers in pre-amps?
Super BQ,

The main reason for my using a 300VA transformer is that I had it lying around. When I finally decide on a final design (I'm just building all sorts of circuits on scrap pieces of timber at the moment to see how they sound) I don't think I will be quite so extreme, however the cost difference between 80VA toroidals and 30VA is minimal so I will probably opt for those.


time permitting I think I will experiment with fast/normal rectifier diodes, when that will be? who knows?

Something else I was curious about is:

If I replace the 750Ohm biasing resistors in the BOSOZ with CCS as discussed in another thread will I need the RC regulation on the negative rail (i.e. 1000uF and 22Ohm)? I figured that the regulation of the CCS would not require extra filtering.

Will you need to regulate the rail?
But I tend to prefer locking in as many variables as possible. When I use current sources, I still regulate the rails...but that's just me being excessive.
Set up the current source on a separate, small circuit board with two leads coming off at the same spacing as the 750 ohm resistor. Then you can use either resistors or a current source daughter board, whichever suits you (read: whichever you think sounds better). It would also give you the option of trying other current source topologies if you were to start feeling experimental later on.

Disabled Account
Joined 2002
Hi, Tob

I heard about fast speed diodes (=fast recovery type that is
known as ideal for switching).

I however never heard about the fast zener diode.
I :no: heard about the soft zener diode, either.
I :no: found the fast/soft zener diode in the product cataloges.

If you have them of the same zener voltage, you could likely replace them.


PS. Any of you against me, please write.
I don't think there is such a thing as a fast or soft-recovery Zener diode.

Basically Zeners don't need to recover like a rectifier. Usually a Zener is biased backward (purposely) so that it produces a reasonably constant voltage reference.

The gate-source Zeners are there to clamp the voltage to +/- (some value < 20V) to protect the gate from punch through due to a voltage transient. Should such a transient strike, I'm not sure I'd be concerned so much with the reovery of the diode as my ears and my poor speakers. :)

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