From: dplatt@snulbug.mtview.ca.us (Dave Platt)
Newsgroups: rec.audio,sci.electronics
Subject: Group purchase: Burr-Brown OPA604, OPA2604 op-amps
Date: 15 Aug 92 19:16:41 GMT
Reply-To: dplatt@snulbug.mtview.ca.us
Distribution: usa
Organization: Snulbug Software
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I've been interested for some time in buying and trying out some of the
Burr-Brown OPA2604 dual op amps.  They're fast, have low noise and
distortion, and have robust input and output stages.  These op amps
have been designed specifically for high-quality-audio applications...
both high-end consumer and professional.  Burr-Brown is pricing them
quite competitively... apparently in order to gain a foothold in this
market (I think they're trying to supplant the NE5532/NE5534 family).

On paper, they look ideal for upgrades to CD players, mixing consoles,
DAT recorders, active filters and crossovers, and any other sort of
component which uses audio op-amps. The OPA2604 has received favorable
mention in a couple of letters to Audio Amateur, in applications as
sensitive as a phono preamplifier. Julian Vrieslander has posted
articles in rec.audio in which he's reported good results using the
OPA2604 to replace the commonly-used NE5532 dual.

I haven't found any retail dealers or distributors who sell them in
small quantities.  When I spoke to Burr-Brown last year I was told
they had a $75 minimum order, and that they didn't yet have a single-
op-amp equivalent for the OPA2604.  So, I shelved the idea.

Things have changed for the better.  Burr-Brown now accepts charge-card
orders for a minimum of $25, and they're shipping the OPA604 single op
amp as well as the OPA2604 dual.  I'm going to order some, and I'm
willing to order extra and distribute them to other hobbyists who'd like
to try them out.  If at least 25 chips of one type are ordered, we'd get
a substantial price break.

The actual price-to-the-buyer will depend on the size of our order.
The OPA2604 dual op amps list for $2.75 each in onesies, $1.95 each in
batches of 25 to 99, and $1.45 in batches of 100 or more.  The OPA604
singles are $1.83/$1.30/$.97 in those quantities.  For comparison:
DigiKey charges $2.26 for the NE5532 dual, and $1.46 for the NE5534
single (quantity 1 to 100).

The "delivered" price will also depend to some extent on how hard I
have to work ;-}. Anybody who's willing to include a hefty (reinforced
kraft-paper or Tyvek) self-addressed stamped shipping envelope with
their payment will pay the quantity-part price for however much we
order, plus a pro-rated portion of whatever shipping charges and tax I
pay. In other words, I break even, and I don't have much to do - I
re-pack the order into individual antistatic tubes, wrap in
bubble-pack, seal in the provided envelope, and drop in the mailbox.

Anybody who doesn't include a suitable self-addressed stamped shipping
envelope will have to pay the onesies price regardless of quantity
ordered, plus a couple of dollars for postage and handling and the taste
of stamp-gum on my tongue.

If you're interested in participating in this purchase:  send me email,
and commit to a specified quantity of OPA604 singles and/or OPA2604
duals. I'll collect requests for a week or so, total up the chip count,
and phone in an order to Burr-Brown.  Delivery should be in 1-2 weeks,
I was told.  Once I know the total order cost including shipping and
tax, I'll send you email and let you know what your cost will be.  Do
NOT send any money now, please... wait until we know what the actual
prices are.

Summary of op amp specifications:

The OPA2604 has 20 MHz gain-bandwidth product and slews at 25 volts per
microsecond (symmetrical).  JFET inputs.  Input offset voltage is
laser-trimmed to +/- .1 mV typical, +/- 3 mV worst case.  Input bias
and offset currents are 100 and +/- 4 pA. Noise density (up to 10 kHz)
is 10 nV per root Hertz; voltage noise over 20 Hz - 20 kHz bandwidth is
1.5 microvolts, peak-peak.  Current noise over .1 Hz - 20 kHz is 6 fA
per root Hertz. THD+noise (G=1, f=1 kHz, Vo=3.5 Vrms, Rload = 1k ohm)
is .0003%;  the curves seem to show that THD+noise increases linearly
with gain (e.g. .03% at 1kHz for G=100).  The output stage will drive a
600-ohm load to +/- 12 volts (typical) when powered from +/- 15 volts,
and can source and sink 35 mA.  Open-loop output resistance is 25 ohms.
The output stage has a special bias circuit which keeps the output
drivers from cutting off; I was told there's "no crossover distortion".
Internally compensated for unity gain stability.  8-pin plastic DIP
with industry-standard dual-op-amp pinouts.  Unlike many older
JFET-input parts, they won't suffer from output phase reversal if you
accidentally overdrive the inputs below the negative power-supply rail.

I don't have the spec sheet for the OPA604 yet, so I don't know the
details of the trimming and compensation pinouts.  Most of its
specifications are identical to those of the OPA2604.  Substituting the
OPA604 for older single op-amps such as the NE5534 may require minor
changes to the offset-nulling circuitry (if used, in the existing
circuit) or to the compensation capacitor (the OPA604 is internally
compensated for unity-gain stability;  the NE5534 is not unity-gain
stable and must be externally compensated in low-gain circuits).
---
Dave Platt
    dplatt@snulbug.mtview.ca.us       (domain/MX)
or  apple!snulbug!dplatt              (uucp path)
or  dplatt%snulbug.uucp@apple.com     (non-MX Internet)
Newsgroups: rec.audio