381 John Kay Electronics

[wmthor]

What's the feasibility of installing the electronics of a 381JK into a 360?

[jingle_jangle]

Anything's possible; if the type numbers of the three transistors (U1) on the diagram could be discovered, it would make the task easier. Any competent electronics guy experienced in solid state circuits (not me ) could build the circuit.

[ryan.jones]

those are generic op amps, not transistors. at these moderate impedances and audio frequencies, any general purpose fifty-cent op amp will do, as long as it is near the right gain value. possibly within a g=20 to g=120 range or less. the only unknown is the gain value of the audio op amp. could be as little as g=10 for all we know...

[ryan.jones]

if you know anyone with a real JK, just get them to post all the little silver numbers off the top of the two little black squares (integrated circuits) on the internal circuit board under the PG. then again, it could be packaged as two separate four-pin op amps within one eight pin IC package on the circuit board.

we build this kind of stuff every day at work.

[kennyhowes]

The original circuit was done on a board, FWIW.

[jingle_jangle]

Thanks, Ryan. Electronics are just opening up to me, so I'm sorely lacking in ability in that arena!

[johnhall]

Back when this circuit was designed, most OP amps were noisy as could be. The units we used . . . and I don't remember what we used . . . were carefully selected to be very low noise. No doubt low noise components now exist today, like you say at $0.50 each. that we probably paid $10 for back then.

[johnallg]

Back when this circuit was designed, most OP amps were noisy as could be. The units we used . . . and I don't remember what we used . . . were carefully selected to be very low noise. No doubt low noise components now exist today, like you say at $0.50 each. that we probably paid $10 for back then.

Ain't it the truth! Like computers and the new HDTVs....

Using an AD824 (http://www.analog.com/en/amplifiers-and ... oduct.html) would do the trick with a 9V battery source.

http://search.digikey.com/scripts/DkSea ... 4ARZ-14-ND

[ryan.jones]

Back when this circuit was designed, most OP amps were noisy as could be. The units we used . . . and I don't remember what we used . . . were carefully selected to be very low noise. No doubt low noise components now exist today, like you say at $0.50 each. that we probably paid $10 for back then.

(08/03/2007 0:39 PM EDT)

Dallas, Tex. — Texas Instruments Inc. has introduced a single-supply operational amplifier with e-Trim precision and very low noise. The OPA376 combines a low offset voltage of 25 microamps (μA) (maximum) and a wide bandwidth of 5.5 MHz in micro-packages.

In addition, the OPA376 op amp offers low noise density of 7.5 nV/sq rt Hz and a quiescent current of 950 μA (maximum), which enable this device to meet requirements for both AC and DC specifications for filtering, data acquisition and single-supply processing systems. Applications include sensor and signal conditioning, wireless communications, medical instrumentation, handheld test equipment and consumer audio equipment.

The OPA376 device is also said to offer very low noise in relation to the quiescent current of less than 1 mA and excellent temperature drift characteristics of 1 μV/C (maximum). Dual and quad versions will be available in third quarter 2007. All versions are specified for operation over the temperature range of -40°C to +125°C and provide identical specifications.

Companion products of the OPA376 for portable medical and industrial applications include the OPA333, OPA340, ADS123x, MSP430 and REF50xx. For consumer audio applications, the OPA376 complements the OPA363/4, DAC557x, and audio Codec products.

Pricing: Suggested resale pricing for the OPA376 is $0.65 in quantities of 1,000. The dual version, OPA2376, will be priced at $1.00 and the quad version, OPA4376, will be priced at $1.40, both in quantities of 1,000.
Availability: The OPA376, offered in the micro-size SC70, SO-8 and SOT23-5, is available now. The dual-version OPA2376, in the MSOP-8 and SO-8 packages, and the quad version, OPA4376, in the TSSOP-14 package, will be available at the end of 3Q 2007.
Data sheet: OPA376
Product information: analog design support

Texas Instruments Inc., 1-800-477-8924, www.ti.com

[ryan.jones]

John Hall is right, back then it was a much pricier affair to get low noise and practical voltages for a guitar onboard preamp, I suppose. Today, the OPA-376 is a good device at the 50-cent price point, readily available mail-order, and it uses a single supply voltage between 2.2 vdc and 5.5 vdc. That means it will run off two AA batteries, or a 5vdc phantom line down the center pin of a jack DC-tapped off the amp with an adapter box. No need for a 9vdc battery or for voltage-shifter chips to turn whatever your 9-volt battery produces into double-ended 15 vdc (meaning two supply rails, one -15 vdc to ground and the other +15 vdc to ground).e the fact th The drawback of the Analog Devices chips is that they cost five times as much, but don;t let that stop you if you are building a one-off circuit board. They are a good chip, you just won't notice the noise difference in real-life playing scenarios most likely.

There are lots of other good op amps of course these days, we just use a lot of the OPA-376 and its sister chips in our own preamp designs.