From: andrew@alice.att.com (Andrew Hume)
Subject: Re: Corey's Buffered Preamp
Summary: here is one man's story
Originator: tjk@csd4.csd.uwm.edu
Article-I.d.: alice.23639
Organization: AT&T Bell Laboratories, Murray Hill NJ
Date: Tue, 8 Sep 1992 21:26:32 GMT

In article <9209032131.AA15103@csd4.csd.uwm.edu>, ST801804@BROWNVM.brown.edu writes:
> 
> Has anyone had any experience with the buffered preamp outlined in
> Stereophile a while back using the BUF-03 buffers?  What's the
> approximate total costs?
> 
> Specifically, I'm interested in knowing whether it's worth the effort:
> is it better than something like a PS audio preamp? Is it expensive?
> I've basically got no electrical construction expereince behind me, so
> I'm sure it will be a considerable hassle to build the power supply
> outlined in stereophile.
> 
> thanks,
> steve


	i have built the greenberg preamp but have not yet
satisfactorily auditioned it yet. it passes sanity checks (that is,
the preamp is inaudible heard through my NAD receiver).
note also that the nov 92 stereophile is scheduled to have
an update on the preamp.

	i built the preamp including power supply using the parts
listed below. my design was a rack wide 1U high box (17x8x1.75 in)
for the preamp. The preamp takes 2x18V unregulated DC which is supplied
by a small box containing the transformer, switch and 1/4 of the power supply
(the bridge and small caps). The other 3/4 of teh power supply,
including all the regulation, is in the preamp proper.
the power supply is easy if you get the PC board (or kit) from old colony.
(i cut my board in two. i had to get different big capacitors than those
recommended for teh power supply; the recommended ones were too tall for
teh 1U high enclosure. I used a home made cable and a locking DIN plug
for the power connector - 5 18ga conductors.)

	the preamp has 5 inputs, two outputs (only one set of outputs
is attenuated/buffered, the other is REC OUT for my cassette deck).
the front has a volume knob, an input selector and two toggle switches.
one is SRC/MON for tape monitoring and the other is REC OUT enable.

	the parts and costs are

needed      UC       TC     part                       desc
_________________________________________________________________________________________
 1        6.78       6.78   Allied #663-7020           Power Cord 6' 18AWG
 2        7.94      15.88   Allied #676-3145           SW2: C&K 7203P3YZQE
 1        7.60       7.6    Allied #736-1112(BLK?)     Plastibox (black)
 1        2.06       2.06   Allied #759-1190           volume knob (AUGAT KLN-900B-1/4)
 1        4.07       4.07   Allied #759-1305           selector knob (AUGAT KPN-900B-1/4)
 2         .55       1.1    Allied 619-0040            buf heatsink
 1       46.27      46.27   Avel 4030                  2x18V, 4.4A
 1        9.00       9      Brice & Barclay #77-0099   SW1: Electroswitch 900A
 5(2)      .27/5     0.27   Digikey #1KH               Rx,y: 1K
10(6)      .84/10    0.84   Digikey #1N4002Gl          D5-10: 1N4002
 2        1.07       2.14   Digikey #3386C-502-ND      VR2,3: 5K
 2         .35       0.7    Digikey #HS111             heatsink
 4         .76       3.04   Digikey #P4537             C19-22: 1uF(50V)
 8         .18       1.44   Digikey #P4713             C4-7,11-14: .01uF, 400V polypro
 2         .17       0.34   Digikey #P6239             C2,9: 100uF, 25V electro
 4        3.16      12.64   Digikey #P6788             C15-18: 470uF(35V)
 1        3.23       3.23   Digikey #V1042-ND          Vectorboard (4.5x6.5 FBG)
 1       63.88      63.88   Gray Box                   Enclosure: 19inx8inx1U
 1        3.80       3.8    Marshall LT1033CT          LT1033CT
 1        4.75       4.75   Marshall LT1085CT          LT1085CT
 4        2.02       8.08   Mouser #140-XR35V4700      C1,3,8,10: 4700uF, 35V electro
 1        4.19       4.19   Mouser #164-2522           5 pin DIN receptacle
 1        3.90       3.9    Mouser #174-2512           5 pin DIN plug
 5(2)      .60/5     0.6    Mouser #29MF500-10.5K      R2,4: 10.5K 1% MF
 5(2)      .60/5     0.6    Mouser #29MF500-1K         R1,3: 1k, 1% MF
 2        2.59       5.18   Mouser #333-RS602          BR1,2: 6A 100PIV
 1        3.33       3.33   Newark #87F2635            SW1: Arrow Hart 2500A11E (amber)
 2       21.64      43.28   Newark #BUF-03EJ           BUF1,2: BUF-03EJ
 1       15.00      15      Old Colony G-5             PC board
 1        1.99       1.99   Radio Shack #271-1732      VR1: 100K
 7        6.95      48.65   Sound Connection CM1F      gold,insulated RCA pair
_________________________________________________________________________________________
total: $324.63 (amp=$67.69, sw/conn=$79.66, encl=$63.88, pwr=$113.40)


	no doubt, you might find some parts for cheaper. the enclosure
really looks nice; highly recommended although if i did it again, i'd
get a 10in deep. this was my first electronics construction project
from scratch so i believe its not a difficult one. i followed the
advice in the stereophile article.

	$324 sounds a lot to me; i was surprised at how much it came to
(naive, i guess). on the other hand, greenberg noted that some person
was selling preamps with exactly this circuit (but different, secret, physical
layout) in a professional looking unit for $2400. if cost is critical, you
could economise by getting a non-toroidal transformer, a BUD box, cheap nickel
RCA jacks, single enclosure, and the A series BUF-03s; this would save you
about $160 (30+40+50+15+25). Of course, this will affect the overall
sound and quality of the result. (how much? I don't know.)


		andrew hume
		andrew@research.att.com

Newsgroups: rec.audio.high-end