It appears to be in a non-inverting x82 gain configuration judging by the feedback network R135/R139. DC bias is set by R136.
I'd suggest an opamp non-inverting stage, using 180k||22pF and 2k2+470uF feedback network (ac gain x80, DC unity gain). Hold the input at mid-rail with a pair of 100k resistors, capacitively couple input and output as in the above circuit.
You'll need a high bandwidth opamp for a single gain stage of x80 ideally.
I'd suggest an opamp non-inverting stage, using 180k||22pF and 2k2+470uF feedback network (ac gain x80, DC unity gain). Hold the input at mid-rail with a pair of 100k resistors, capacitively couple input and output as in the above circuit.
You'll need a high bandwidth opamp for a single gain stage of x80 ideally.
@Mark Tillotson: many thanks for the suggestion. Please see if the attached is what you had in mind. I can use a FET input opamp like OPA134 with bandwidth of 8 MHz.
@JonSnell Electronic: thanks for the information. I may want to try with modern opamps using an 8-pin IC socket and a "homemade" 8 to 7 pin adapter and do some tests to find out which one is best for my ears.
@JonSnell Electronic: thanks for the information. I may want to try with modern opamps using an 8-pin IC socket and a "homemade" 8 to 7 pin adapter and do some tests to find out which one is best for my ears.
Attachments
Yup, that's the circuit - although it might benefit from decoupling the middle of the top resistor in the potential divider, otherwise it will be sensitive to rail noise with no input or high-impedance input.
@franzm: thanks for the information. The solution I am looking for is for a good cassette deck from 1978, a JVC KD-85, which can play/rec 20-18000 Hz, so I am looking for a good solution with a modern opamp.
The original uPC1024 of one channel seems to have problems --- I troubleshot it with an oscilloscope. Per attached this uPC1024 is in a circuit that includes the play/rec head.
@Mark Tillotson: thanks for the reply. I have upgraded X601+Zener, etc. in the power supply (attached) with an LM338 solution and new Nichicon caps (actually I recapped the whole equipment). It is supplying precise 22 VDC on the left of the R605 resistor (8R2, 2 W) and 21.7 VDC at the uPC1024. But I think I can connect a 100uF capacitor for instance near the new opamp, per attached. Also the original JVC circuit has a 3.3uF+1k8 on each extreme of the uPC1024 (per picture). ((I think this uPC1024 was a cheap idea back then... I have JVC cassette decks from 1979 and they started using uPC4558 (8-pin dual opamp) for instance)).
I was wonder if anybody else here ever replaced a uPC1024 with a modern opamp solution, apparently not. So I hope this solution can help someone in the future.
The original uPC1024 of one channel seems to have problems --- I troubleshot it with an oscilloscope. Per attached this uPC1024 is in a circuit that includes the play/rec head.
@Mark Tillotson: thanks for the reply. I have upgraded X601+Zener, etc. in the power supply (attached) with an LM338 solution and new Nichicon caps (actually I recapped the whole equipment). It is supplying precise 22 VDC on the left of the R605 resistor (8R2, 2 W) and 21.7 VDC at the uPC1024. But I think I can connect a 100uF capacitor for instance near the new opamp, per attached. Also the original JVC circuit has a 3.3uF+1k8 on each extreme of the uPC1024 (per picture). ((I think this uPC1024 was a cheap idea back then... I have JVC cassette decks from 1979 and they started using uPC4558 (8-pin dual opamp) for instance)).
I was wonder if anybody else here ever replaced a uPC1024 with a modern opamp solution, apparently not. So I hope this solution can help someone in the future.
