Which pre-amp to build?

Hello all, i've spent a few months searching the net for a high quality pre-amp schematic for me to build. I started off wanting to build an op-amp based one and have now wound up here asking for opinions on which class-A design would be better.

The designs in question are the ever so popular Bride of Son of Zen and this one: http://www.geocities.com/capecanaveral/galaxy/6623/preamp.html

Your opinions and experiences are greatly appreciated.
 
Bride of Zen is awfully hard to beat

I can unhesitatingly reccomend Nelson Pass's Bride of Zen preamp. I built mine 3 years ago using run of the mill parts and my jaw dropped to the floor when I first heard Pink Floyd playing in my living room. Yes,it sounded like they were in the room with me. I had never thought a preamp could make that much difference.
If you build it though, don't use the 500 ma. transformer reccomended. Use a 3-4 amp torroidal Avel Lindberg, with 30+30 secondarys. Makes a huge difference in sound improvement. Also fast/soft recovery diodes in the power supply circuit are worthwhile.
Just one opinion though.
mg16
 
BOZ PROJECT

At the time, 3 years ago, I was using a Quicksilver GLA tube amp. I am now using Doc Bottleheads 2a3 Paramours, with full upgrades. The Boz circuit board includes on board regulation. Yoy can buy Avel Lindberg transformers online. Do a search using Avel Lindberg, and you'll get the web site link. Pick from the 400 series transformers at there site. Use one with dual primarys of 115v, and dual secondarys of 30+30 at 3 amps minimum. Also try the soft recovery/fast recovery diodes. I got mine from Mouser for about $1.00 each.
I used holco 1/2 watt resistors. Panasonic tsu series elec. caps. Caddock t0-220 package 1k drain resistors, and MIT input and output coupling caps. Use 5k or 10k,(max), Clarostat pots at the output of the preamp.
Best of Luck
mg16
 
Simulation of circuit

HooRide said:
Hello all, i've spent a few months searching the net for a high quality pre-amp schematic for me to build. I started off wanting to build an op-amp based one and have now wound up here asking for opinions on which class-A design would be better.

The designs in question are the ever so popular Bride of Son of Zen and this one: http://www.geocities.com/capecanaveral/galaxy/6623/preamp.html

Your opinions and experiences are greatly appreciated.


HooRide,

I had a few spare moments and plugged the circuit you linked into Multisim 2001 Pro.

My simulated currents were a little higher than the numbers listed on the diagram. Mine were around 75 Ma per device.

At normal listening levels with .25 Vrms input to input level the output voltage will be about .444 Vrms out on each output when loaded with a light load of 10 Kohms.

The distortion will be primarily second harmonic at at level of about .01% at 10 Khz.

In terms of DB down the second harmonic 100hz may be -113DB, at 1 Khz -100.2 DB, 10Khz -81.15 DB and at 20 Khz -76.75 DB. This with .25 Vrms in from input to input.

At 1 Vrms input to input the 2nd harmonic should be close to .2% and perhaps .5% at 20 Khz. This level provides about 1.79 Vrms on each output at 1Khz.

Distortion figures are now expected to be, -89 DB at 100hz, -76 DB at 1Khz, -57 DB at 10 Khz and -52.6 DB at 20 Khz. The third harmonic should still be down to around -96 DB at 20 Khz at the 1 Vrms input to input level.

I ran out of time to do more. Perhaps someone can build it and provide actual measurement data.

I did notice that the voltage rating of the of the output capacitors as mentioned on the circuit diagram is to low. They should be able to withstand the full supply voltage.

John Fassotte
Alaskan Audio

[Edited by alaskanaudio on 12-12-2001 at 10:07 AM]
 

Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
This circuit is essentially a cascoded version
of the SBOZ and will work somewhat better at the
cost of a bit more complexity.

A cautionary note about the zener diodes at the
input. My experience is that a good number of
sources will oscillate when presented with bare
zener protection diodes, and I suggest some
additional resistance at the input before them.
 
Mr Pass,

Thanks for the zener diode tip.

I based my design on the SBOZ and a few others which used a similar topology. I have seen this topology implemented with J-FETs and tubes as well as MOSFETs but never with cascode. So I decided to give it a try.

HooRide,

Here is another one you could consider building - http://www.geocities.com/d_broadhurst/sepre97.jpg This was e-mailed to me a couple of years back. I wouldn't know how to contact the designer. It is simpler but features constant current sources.
What about the Aleph P1.7 ?
 
Wow, thanks for all your replies and thank you alaskanaudio for taking the time to enter that schematic into your program.

I've searched far and wide for a quality potentiometer and i've come up with this one: http://www.allelectronics.com/cgi-bin/category.cgi?category=470010&item=MPOT-10K&type=store

I know alps makes decent pots, it is motorized, and it's only $4!!! Any warnings about using this certain one? I origionally was going to get a high quality Noble or Alps from partsconnection.on.ca but they don't stock the 10k versions.

Also, would it be worth using Holco H2's over the H4's in the signal path?

Dave,

Thanks for the link, but i've decided to stick with the BoSoZ, the main reason is simplicity, that and http://www.audioxpress.com sells the PCBoards, saving me time.

[Edited by HooRide on 12-12-2001 at 04:47 PM]
 
I built a supply with MUR1620CT and it had a lot of nasty noise on the rails. I think these diodes are fast, but not soft. Their datasheet does not characterize reverse recovery. I replaced them with IRF HFA08TA60C and the same power supply had no problems.

As for the Hammond 182-series transformer, I used those a few times and can recommend them. Their size is absurd for a preamp, but whatever :)
 
ToB,

I don't think HEXFREDs would work out well as zener diodes. I use plain-jane IN4739 9.1 V zeners and have had no complaints.

The HEXFREDs do work well as rectifiers, of course. I've used them in my own BoZ-based lineamp. There's more soldering to do with discrete rectifiers vs. a pre-packaged bridge. Of course if you dig soldering, no problem there. ;-)

Hope that helps,
Erik
 
Um... Hello and welcome to last year :confused:
BTW, thanks to all that have helped me with the questions. My BoSoZ has been plugged in almost 24/7 (power switch? who needs that?) for the past 8 months. Excellent design, not a single problem, i'm very happy with it.

Next upgrade: looking for a better pot, Alps Blue maybe a black beauty if i can hunt one down