ESP Death of Zen preamp vs BOZ

Hi!
I'm about to build a preamplifier and I'm wondering which of these two I should choose :
1) The Bride of Zen from Passlabs
2) ESP project#37 Death of Zen Preamp

Both preamp have great specs. I already built a Leach amplifier and I'd like to build the best preamp that would goes with it. I read that the Bride of Zen has a high gain (15db) to match the Son of Zen that doesn't have a high gain for an amplifier. The Esp project has a lower gain (10db). Should I take the ESP project for this reason (I guess my leach amplifier doesn't need a high input).

Thanks a lot for your ideas!
David
 
gretzteam said:
Both preamp have great specs. I already built a Leach amplifier and I'd like to build the best preamp that would goes with it. I read that the Bride of Zen has a high gain (15db) to match the Son of Zen that doesn't have a high gain for an amplifier. The Esp project has a lower gain (10db). Should I take the ESP project for this reason (I guess my leach amplifier doesn't need a high input).

Well, both amps have a low input sensitivity (much lower than the Leach)... you can tweak with both preamps' gain (i beleive that the DOZ pre had info on doing just that; haven't checked on the BOZ), without problem. On the sonics.... well, i haven't heard either, but they're both superb designs for sure.
 
DoZ vs BoZ

Having built both DoZ and BoZ preamps, yes, both the preamps' gain are adjustable by changing the value of one resistor (the 1K 3W resistor in the BoZ). In the BoZ, by changing the value to 600 ohms (parallel 2 units of 1.2k), this will solve the unsymmetrical clipping problem too, giving you a gain of about 5 (about 14dB, if I'm not mistaken) unloaded. Nelson Pass recommends a pot at the input to eliminate the clipping problems that may occur with too high an input level to the BoZ (for example a CD player at 2V!). The output of the BoZ will clip at around + - 15V peak.

Unless you are using a source with low output (ie below 500mV), a gain of 3 (10dB) is more than enough for the Leach Amp, which needs an input of 2V for full output.

All things said, both are good, solid designs and sounds good too! I'm using both, but I may prefer the DoZ preamp just for its negligeble heat dissipation (in 30 degree C weather, it IS a major consideration) and extremely compact size (if you buy the boards from ESP).

As for the "another few zeros after the decimal point" distortion, I have to confess I can't hear the difference between 0.1% distortion and 0.01% distortion. Maybe I need to upgrade my ears for a change......
 

grataku

Member
2000-12-31 9:31 am
-
I built the DoZ, sounded like crap (IMHO), very bright, dry, definitely annoying to my ears. That's not to say that Rod did a bad job. I used off the shelf components and I made my own pcb. Maybe it requires very careful component selection to sound better, I don't know. From my experience I can't recommend it.
 
Having built both DoZ and BoZ preamps, yes, both the preamps' gain are adjustable by changing the value of one resistor...

I'm not too sure what you guys mean when you're talking about tweaking the preamp gain. I'm a hardware guy so I don't know much about the theory of audio preamplifiers.

Do you mean that since the Leach does not need a high input, I should diminish the gain of the preamp I decide to build? If so, what would be the gain I'm looking for?

Thanks a lot
 
gretzteam said:
I'm not too sure what you guys mean when you're talking about tweaking the preamp gain. I'm a hardware guy so I don't know much about the theory of audio preamplifiers.
Do you mean that since the Leach does not need a high input, I should diminish the gain of the preamp I decide to build? If so, what would be the gain I'm looking for?

Well, this is the idea: input sensitivty is the signal voltage needed to drive the amp at full power; for the leach amp that's about 1,5 - 2V and for the DOZ, it was something like 6V... So, yes, you need to reduce the gain (or keep the volume pot down :) ). Gain in preamps is usually set by one or two resistors, so it's no big deal; it's just a matter of changing them. As bawang said, a gain of 3 or 4 would allow a 500mv signal to drive the Leach to full output, so i beleive that would fit your requirements.

The exact details for this mod escape me (i haven't built either... yet atleast), but i'm sure they're explained on their respective web pages.

BTW, bawang, how would you compare both preamps sonically? I'm curious, having to build a preamp in the near future...
 
Comparison of components

Lisandro, I may be blasted off the earth for saying this, I am a true believer of double-blind AB comparison where you keep all other parameters (or devices, including volume level) constant, changing ONLY the component under test, and trying to identify which component is being used. That said, it is a bitch trying to keep all else constant, especially the volume. A decibel meter and a pink noise generator will help tremendously, but I have neither.

What you can't hear won't hurt you (or your wallet!), this is the final judge. In all my years of indulging in HI-FI (or HI-FIey, if you will), the component that really stands out in the double-blind AB comparison test, assuming all other components are competently designed, manufactured and operating within their designed limits, are the loudspeakers. But of course, each one of us have our own preferences in the quest for the perfect sound (for our own ears).

What is perfect for one may be lousy for another. As long as you're happy with it, so be it! Enjoy it for as long as you can, until you decided to change. But of course, the art of tweaking is always a pleasure...........
 
Well considering the fact that all the ESP projects I've undertaken have turned out wonderfully (unfortunately I haven't built the DoZ though) I can say that Rod does an amaizing job and will answer your questions too (and I didn't even buy any boards from him). Although I hear that the BoZ is really good as well. But when it comes down to it, how you build your pre-amp and what components you use will probably matter more then which of these two projects you choose to embark on, since they're both apparently excellent...
 
Re: Comparison of components

bawang said:
(...)

What is perfect for one may be lousy for another. As long as you're happy with it, so be it! Enjoy it for as long as you can, until you decided to change. But of course, the art of tweaking is always a pleasure...........

Of course... i just wanted to know how they sounded to YOU. Anyway, i haven't built neither as i said before, but i am sure they both perform excellent.
On the subject of preamps, "Surf, Sun & Sound" recently pointed me to a series of simple, discrete preamps by John Linsey Hood that look quite promising too, so i'm still trying to make up my mind on that :D
 
BOZ Clipping

I have completed the BOZ, and have made the same observation with regard to its clipping the negative portion of the signal as it approaches 2 volts at the input. I have followed the various threads and am a bit confused as to why one would want to change the bias point verses using a voltage divider at the input or some other means of attenuation. It is my understanding that the hot bias is what makes the BOZ sound good and measure well. My logic says that we want the device to be biased up to a point of most linear operation. How would it make any difference when driving a ZEN or some variation of a more conventional, but less musical current gain device? If it clips as result of being over driven it matters not what it is driving. Or am I missing something? Thanks in advance for your replies.

:confused:
 
Hello,

I too am planning to build a preamp. I've already decided on the DOZ but would like to use +/- 15V rather than the +30V for which it is designed. At the ESP site, Mr. Elliot says that this is possible but not trivial and alludes to circuit changes required but does not define them. Could someone knowledgeable in this area tell me what modifications are needed?

Thank you.

Mike L.
 

Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
Re: BOZ Clipping

gpsmithii said:
I have completed the BOZ, and have made the same observation with regard to its clipping the negative portion of the signal as it approaches 2 volts at the input. I have followed the various threads and am a bit confused as to why one would want to change the bias point verses using a voltage divider at the input or some other means of attenuation. It is my understanding that the hot bias is what makes the BOZ sound good and measure well. My logic says that we want the device to be biased up to a point of most linear operation. How would it make any difference when driving a ZEN or some variation of a more conventional, but less musical current gain device? If it clips as result of being over driven it matters not what it is driving. Or am I missing something? Thanks in advance for your replies.
:confused:
The attenuator is before the input coupling cap, and does not
alter the bias.
 
Mike L. said:
Hello,

I too am planning to build a preamp. I've already decided on the DOZ but would like to use +/- 15V rather than the +30V for which it is designed. At the ESP site, Mr. Elliot says that this is possible but not trivial and alludes to circuit changes required but does not define them. Could someone knowledgeable in this area tell me what modifications are needed?

Thank you.

Mike L.

Rod's DoZ preamp is a typical single supply circuit. It's common point (ground, reference) is at emitter of Q3, which is also a point of single-polarity supply 0V voltage. Output from the DoZ preamp is between collectors of Q3 (second stage transistor) and Q2 (constant current source) is at half of power supply voltage, that's why it needs output cap. It is really not good idea to try to convert this circuit into non-capacitor output one with 2 power supplies. Despite that this could be done by connecting +Vs to R7/D1 point, -Vs to emitter of Q3, input signal should be connected between C1 and 0V of +/-Vs supplies (center point), output would be against 0V (center point). VR1 trim would set 0V at the output (collectors of Q2/Q3). I suppose that output dc offset would be unstable, as it is a very simple circuit. Probably better to connect 2 of them as differential DoZ, but the best to keep it as it is with output capacitor. You do not need great value and electrolytic type, this depends on input impedance of the following amp.
 
Hello

About the Bride of Zen clipping.

Since the input signal can clip asymmetrically with high input signals, you need to set the bias current using an oscilloscope for a symmetrical clipping, or use a distortion analyser or a fft software and set the bias current for the minimum distortions.

In the Bride of Zen, If you place the volume potentiometer before the input coupling cap, due to the gate capacitance of the MOSfets, the volume potentiometer will formed a lowpass filter. In my simulation image R11-R8 are a the input potentiometer, and to reduce the loss in high frequencies you need to use no more than 25 K ohm for the input potentiometer. Look at my freq response graph image for the circuit image I included in my post.

I've change the value of the 1K 3W resistor in the BoZ to 200 ohm give a gain of 2.

I've ad C5 for a better stability on a square wave.

Anybody compared the the Bride of Zen sound to some high-end preamp or to the Pass Lab B1 ?

Bye

Gaetan
 

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