Pass Bride of Zen preamp

Systems

This is my second iteration of this classic pre having built one back in 95 .I now use the first unit in my PC rig , it was built using the PC board designed by Nelson for the original Audio Amateur article.(see pic1).
With one exception it was build as per the article using reasonably hi quality parts like Holco resitors,Alps black beauty pot and Panasonic film coupling caps.

The beauty of this circuit is its simplicity as it only has one active device in the gain stage,an IRF 610 mosfet.It is a pure single ended, single transistor Class A design and IMO a very good sounding one.
I don't use balanced sources or I might have built the balanced version called The Son of the Bride of Zen.The Pass Labs Aleph P and Adcom GFP 750 preamp's are based on this version.Being single ended the total harmonic distortion is mostly 2nd order but the fully balanced version will cancel much of this making it the more neutral of the two.

For the second unit I used perf board's for the the gain stage and regulators and etched custom boards for the raw DC power supply.(shown in pics 2-4).
I deviated from the original mainly in the power supply and regulator areas,not because I think I can improve on NP's design but for expierimental reasons.

The main differences are.

The original has 1000uf of filter capactiance before the regulators,the second has 32 x 470uf =15000uf before the regulators.This is overkill but I had a bag of these caps laying around so I figured I would put them to use.

Aswell I added a coil to the supply to form a CLC for improved filtration.

Voltage regulation in the original was via a stack of veners suppliing 60 volts to both channels.For the second unit I gave each channel their own regulator,a high voltage adjustable type the LM783.

Nelson recommends using the pot at the output of the circuit as this will attenuate noise,but in the first unit I had to place the pot at the input or the source periodically overloaded the gain stage and caused distortion.
For the second unit I have used individual 25k pots at the input to prevent overload and used a nice NOBLE 10K at the output for volume adjustment.In the future I may replace the NOBLE with a stepped attenuator.

Input and output coupling caps are Wima MKC4 polyesters.

Rectifier diodes are MUR810 fast recovery types.

The transformer will be housed in its own chassis outboard.

ben62670

Dude I would have had boards made for this if you asked. I shall be watching. I want to make a big board with the active XO (3way EQ'ed), pre, buffer for the DAC, phono, PS regulation, and passive pre. I am getting ready to get R done.
Take care.
Ben

nikolas812

Thats some of the nicest DIY work I've seen. VERY clean.








Nick

nikolas812

In the future I may replace the NOBLE with a stepped attenuator.

Why?



Just curious..





nick

Systems

ben62670 wrote: »

Dude I would have had boards made for this if you asked.

Thanks but this has been in the works for awhile and was simple enough for perf board and home PC board etching.

I want to make a big board with the active XO (3way EQ'ed), pre, buffer for the DAC, phono, PS regulation, and passive pre.

That will be a busy board but very versatile,I can't wait to see the end result.
I downloaded that PC board design program but have not spent much time with it yet.

nikolas812 wrote: »

Thats some of the nicest DIY work I've seen. VERY clean.

Thanks Nick.

nikolas812 wrote: »

Why?...Just curious..

With the stepped attenuator there will be perfect tracking between channels and the signal will only be going through a single 1% metal film resistor (and switch contacts) whereas with the pot it will be going through a conductive plastic substrate.The resistance values of two sections of a pot can vary as much as 10-20% from each other causing a balance mismatch between channels.

Face

Great job Fred!

feel like building another...?

nikolas812

With the stepped attenuator there will be perfect tracking between channels and the signal will only be going through a single 1% metal film resistor (and switch contacts) whereas with the pot it will be going through a conductive plastic substrate.The resistance values of two sections of a pot can vary as much as 10-20% from each other causing a balance mismatch between channels.

Thanks you.:)







Nick

Systems

Face wrote: »

Great job Fred!

Thanks Mike

feel like building another...?

I could send you the original to try and see if you even like how it sounds but shipping cross border wouldn't be cheap.

ben62670

Stepped attenuators is the way to go unless you get into the lightspeed attenuator that I am working on. No switches, and very clean. GV youi help with the board as in I design it, and you tell me where I am off we will get it done. You get a board on the house;) I do like Nelson passes work. I think he is the one who did the GFA-545 and it's sound is a beautiful thing. Very straight forward with no caps in the way. LMK if you want the schematic.
Ben

Edit: Face it is time you go active on the XO's. Colorless. Caps in passives cost way too much. I am still studying tube buffers that would have the ability of being bypassed. We should put our heads together on this. Time to get real serious on going all out with many options.

Systems

ben62670 wrote: »

..you help with the board

Sure

I do like Nelson Pass's work.

Yeah especially his generosity sharing great sounding, simple to build projects with us DIYers.

LMK if you want the schematic.

for your board or the 545?

Face it is time you go active on the XO's.

Yes he should.;)I suggested that to him before but he was apprehesive.OK so you need a few more channels of amplification and pairs of Ben's IC's but it's worth it.Once you go active you'll never go back, the veil will have been lifted.:)

ben62670

Yes the 545 diagram if interested. Very staright forward. Great sounding amp:)

Face

You guys are killing me... 6 channels of tube amplification isn't cheap.

I do happen to have this sitting around though: http://mcc.berners.ch/power-amplifiers/MC126.pdf

zingo

That'll do it for you better than most. That is my problem with an active XO; the multiple amps thing... bleh.

heiney9

Very, very nice Fred.............I'm so jealous.....in a good way. I need to check this section out more often. You can't go wrong with this NP design. Simple, simple and it sounds so good. A classic.

H9

Systems

heiney9 wrote: »

very nice

Thanks,I can't afford a GFP750 so I have to settle for a roll my own Pass design.

btw.tubes don't rule.