Op-Amp for Kenwood KA-5500

Spenser

AK Subscriber
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Hello there. Can you take a look at this?

Original op-amp on the KA-5500 was the in-line, TA7136P -- a long time ago "...when op-amps were still young." (Echowars) Far better op-amps are made today.

So what I am wondering...

Would an op-amp upgrade improve performance enough to justify?

Which reasonably priced, readily available op-amp (ideally Mouser-stocked), would be a good choice?

What other modifications would be needed?

Some weeks ago Hopjohn (THANKS), suggested to me -- IF one were to switch out the op-amp -- possibly go with 595-OPA2132PA. He added caveats. One, 'op-amp rolling' is not his specialty. Two, there is give and take, from what he understands. Three, it would be advisable to seek counsel from others.

In 2002 Echowars posted a thread on an op-amp upgrade he did on his KA-5500; said performance enhancement was significant. He noted that improved performance also was attributable in-part to electrolytic capacitor upgrades. In any event the op-amp Echowars selected was the now, no longer available / outdated (Burr-Brown - later Texax Instruments), OPA604AP with a .18uF stacked film cap soldered directly to the leg of an IC socket to deal with "supply voltage outrageous by opamp standards (+/- 19V)." The OPA604AP was an eight-pin DIP. To adapt he had fashioned a small PC board which he wired to the Kenwood PC board; incorporating a a gold DIP socket, in case someone came up with another op-amp that might be fun to try.

Edit: I think I left out that he may also have adjusted resistors, as follows: "... the preamp supply voltage resistors are dropping the supply voltage from +/- 19V to about +/- 17.5V. I was prepared for this, and changed the resistors to get the supplies back up to 19V."

Tin pin gold DIP socket 575-11043308?
 
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how about the BB/TI OPA2604. 8pin dip dual.
Definate sound imprvement in my sony CDP302 output stages compared to sony origs..
If all specs match with the 604 it should work ok.
 

Hey Beau Geste, That was very nice reading you suggested. The op-amp NE5532 mentioned in the article was part of the exploration in year 2002 on the preamp section we are talking about here in a Kenwood KA-5500. It was tried but ruled out due to its greater input current demands.

Your comments and suggestion made me think to go back and add an edit to my original post:

how the power supply resistors for the preamp section (where the IC is), got adjusted to get the voltage back up from its decrease to +/-17.5 (due to the more modern IC), to where it belonged by specifcations +/-19V.

It is pretty involved this matter of op-amp rolling. Well beyond my current analytical and engineering abilities on my own.

How about the OPA2134 mentioned in the article? (Hopjohn see initial post offered perhaps look into OPA2132).
 
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I understand. At the same time judging from the article I would not want something like the OPA 627. Overkill on performance for the type of amplifier we are talking about here, and way too expensive for me.

The OPA 1642 is perhaps more in range (at least in terms of price). Only comes in the SMT/SMD mounting format on Mouser.

Back to the OPA 2134. While not the latest and greatest, would it nonetheless be a significant performance improvement over the original factory IC (remember we are talking here replacement of circa mid-1970s TA7136P)?

IF looking at OPA 2134 or the OPA 2132, which would be the better choice of the two?
 
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I do not think that you will notice any differences. have to make sure that you do not exceed the supply ratings and that you may get oscillations/instability as these faster devices are more sensitive to supply decoupling. The best is to use 100n MLCC cap as close to the supply leads as possible and short ground connections.
 
OK.
have to make sure that you do not exceed the supply ratings and that you may get oscillations/instability as these faster devices are more sensitive to supply decoupling. The best is to use 100n MLCC cap as close to the supply leads as possible and short ground connections.
This is good. I will look at datasheets; might get a couple different ones to try; these specific tips are helpful. Thank you!
 
This was a great idea. I want to look into it.
I do not think that you will notice any differences. have to make sure that you do not exceed the supply ratings and that you may get oscillations/instability as these faster devices are more sensitive to supply decoupling. The best is to use 100n MLCC cap as close to the supply leads as possible and short ground connections.

Looking back, I see that I got confused and totally goofed up this thread beginning at Post #1. I apologize.

First I mistakenly stated that Echowars went with OPA604. It was actually an OPA2604.

Two, I mistakienly stated that the OPA604 is today unavailable. Again, wrong. The OPA604 is still around.

It is the OPA2604 that is unobtainium.

A Kenwood KA-5500 amplifier has in its control amplifier two TA7136P IC's. These are 70's vintage single channel op amps. One for each channel. OPA604 IC's also are single channel op amps.

I believe Echowars originally planned to try two OPA604 IC's. I believe instead he went straight to designing and wiring a small, supplemental circuit board with single socket so he could try the dual op amp NE5532 (which was troublesome), and the OPA2604 (which worked), and then he would have the socket there in-place for possible trial of future dual op amp IC's.

I would like to carry out Echowars's original plan and see if the OPA604 IC's would work. I should start by investigating relative current demands; possible effect on voltages; and at what voltage the OPA604 likes to live. While it's max as I recall is fairly high, it probably prefers +/- 15V. The .1 or .18uF MLCC is probably still important.

I'm interested in trying the 7pin p/n 111002 TA7136AP Upgrade Adapter BrownDog linked in Post #3. There might be space for these, and sockets.

https://audiokarma.org/forums/index.php?threads/kenwood-mod-city.3248/#post-26303
 
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Been a while, sorry I lost track, but I did flag this post so we continue.
I know of one that prefers his Marantz 2385 over his Pioneer SX-1980. The 2385 uses TA7136 as the pre-amp part, so it ain't that bad a part, but compared to today's offering well it is 70's tech for sure.
There is nothing wrong with a NJM2068 imo, still in production, I'd have to look at your KA-5500 again to see what you are up against.
I think you are okay with OPA604 in that circuit voltage supply wise, stability wise, you have to find out by trying but for other types, you will need the +/- 15-17V, They use a dropping R so that can be changed as well to drop the +/-24V supply
Looking at that design, I think changing the TA7136 will not make much noticeable difference. I say this in that if you go through all this change and do not notice any difference will you be happy? You have to look at the whole design, the power amp design is lets say a warm design in the 0.1-0.3% THD league because of the way it was done. Low powered amps usually did not use more advanced deign techniques, it is too bad, since many do not need powerful amps just clean, good sounding ones.
I was thinking of doing up an adapter pcb, with a whole bunch of dip to smt options, so I will include TA7136 which was well used. Brown dog makes adapters iirc.
 
Spenser, I'd take a look at the C1 resto sticky. leestereo used a NJM2068DD with PS updates (16v zener). If you lived closer I'd give you one to try. I used these in a C2 resto.
 
rcs16, thank you for jumping back in here. I set this Kenwood KA 5500 aside for a bit.

Love the TA7136 story.

Good points you make.

So I'm doing a NAD 3150 integrated, too. Anticipating a similar result.

Good learning opportunities. I will be happy and love the outcomes either way.

I need to work on my understanding of pre-amp and power amp circuit architecture. Bob Cordell's power amp book has 100 watts as the minimum floor where you start getting into good designs.
 
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