How far can one go? KA-3750

[petehall347]

quick look says one for dc offset other for bias .. if they are in tolerance leave well alone ..just adding more to go wrong ..simple is best if it works .
i cant make out them transistor id numbers .. guessing it is diff pair

 

[Blue Shadow]

KA-3700 is the silver KA-3750.

 

[Kontrabaß]

Hi Rob, loved your thread on this old amp. I have one on the way as well, which I got with the KD-1033 turntable, KX-503 tape deck AND KT-5550 tuner for £80, flipping bargain.

Anyway I’m going to recap it as well, but I was surprised to see you replacing the resistors in the phono amp. What was your reason for this? My understanding was that resistors don’t perish often and if they don’t maintain the right value, it’ll be pretty obvious when you listen, if you can!

Also, did you come to explore the vacant trimmer pot options on the main board?

Thanks, Josh

 

[Gazzcap]

I know that this is an old thread, But a good one at that, I just wanted to point out that in post #3 there is a typo to anyone using this thread to upgrade their own KA-3700 - KA-3750, The NE5534 is a Single Op Amp, The NE5532 is the Dual Version.

 

[gibber]

Well spotted! I tried a bit of OpAmp rolling and find the upgrade worthwhile. Not all are stable. A really fast and stable and good-sounding choice is LT1364. You need to put two bypass caps in. Soldered Wima 5mm pitch MKP directly to pins 4/8 on lower side of board (100nF/100V in my case). Nice ground available, just scratch a 2mm patch free of lacquer per cap). Moved the two pop-killer lytics to underside, too. Then large 3.3uF/400V MKP4s into that space. RIAA ceramics measured 23.4 and 29.1 nF, respectively. Put in Wima FKP2 in 100V, 22nF on top and 4,7 nF bottom. Smaller value for larger of the two RIAA caps than the target 27nF should result in a slight bass boost, if in feedback loop, right?
The phono change to my ears is more rewarding than an all-lytics change to Pana FC (big ones 10mF/35V Nichi Gold Tune). Doesn‘t help on CD or tuner...
I spent € 30 on all parts, 70 on the amp. A lot for this little cutie. But believe it‘s money well spent
— Ralph