Author Topic: What OpAmp is used in the 5-pin preamp?  (Read 1111 times)

Offline sean

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What OpAmp is used in the 5-pin preamp?
« on: May 27, 2017, 12:30:25 AM »


Can somebody look inside their 5-pin preamp with sliders and tell me what dual Op Amp chips were used?
See http://www.fenderrhodes.com/org/ch11/fig11-1.jpg
The service manual doesn't say.  They only identify it as Rhodes part number 013528.

Was it LF353, TL082, NE5532, or lowly uA/LM1458?
And what is the assembly and part number printed on your circuit board (015244/015245 or 013487/__)?

Just curious,

Sean

P.S. - I have a 5-pin preamp, but it is the model with five knobs.  It uses four single-channel op amps for the audio paths, and two dual-channel op amps for the tremolo oscillator and LDR drivers: four NE5534 chips and two RC4558 chips.




Offline Jenzz

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Re: What OpAmp is used in the 5-pin preamp?
« Reply #1 on: May 29, 2017, 03:31:52 PM »
Hi .-)

Audio path: 2x 4558
Tremolo LFO: 1x 1458

Jenzz

Offline Krischu

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Re: What OpAmp is used in the 5-pin preamp?
« Reply #2 on: February 14, 2020, 11:02:43 AM »
While being at this 5pin  amp and although this thread is two years old, I‘m asking it here:

I have  this amp here for inspection. Don‘t have the power supply here. Can I assume that the supply is +-15V?


Christoph
P.S.The amp has two slide pots for treble and bass,Vibrato Intensity/Speed knobs,Volume knob,
Accessory 1and2, which seems to serve as an effects loop in/out, if I interpret the above  circuit diagram correctly.
U1, U3 are RC4558P
U2 is CA1458G to answer the O.P‘s question.



« Last Edit: February 15, 2020, 04:52:33 AM by Krischu »

Offline sean

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Re: What OpAmp is used in the 5-pin preamp?
« Reply #3 on: February 14, 2020, 01:36:01 PM »

Christoph,

Yep, the preamp you have on your bench in intended to run on a +/-15V DC supply.  (For testing, this preamp will run just fine on a pair of 9V batteries.)

Preamps with sliders (instead of knobs) are one of these two circuits:
Schematic for Janus preamp with sliders: http://www.fenderrhodes.com/org/ch11/fig11-1.jpg
Schematic for Janus preamp with sliders, version 2: http://www.fenderrhodes.com/pdf/late-mark1-suitcase-janus1.pdf

I think PC boards marked 015245 became 015244 when stuffed with parts and soldered, and this matches up with the figure 11-1 drawing that is marked 015243. 

In the two schematics above, notice the slight routing difference in the oscillator at the lower left, and the difference in the LDR circuits top right.  You should be able to tell if you have the later design circuit by the presence of capacitors C8 and C20 near the LDRs.

If you want ugly detail on building a new power supply for this preamp, see https://ep-forum.com/smf/index.php?topic=9657.0 and
https://ep-forum.com/smf/index.php?topic=9706.0

Sean
« Last Edit: February 14, 2020, 01:40:35 PM by sean »

Offline Krischu

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Re: What OpAmp is used in the 5-pin preamp?
« Reply #4 on: February 15, 2020, 04:43:52 AM »
Thanks, Sean. I could identify the second circuit diagram being close (but not identical) to the PCB layout I have (see uploaded photo in the other thread). I may be blinded but I cannot figure out R39 in that 015243 schematics either. Mine is P/N 105244.


Oops! Found it. Going from junction of CR1/CR2 to pin 7 of U2B/R26.
Ok. Now I can be sure to have the right schematics.

--
Christoph
« Last Edit: February 15, 2020, 05:11:10 AM by Krischu »