Upgrade TA7136P1 in Phono and Tone board

Well, I have two 750s, both with TA7136 ICs.
So I farmed the tone control from the one in the garage and finished the work on this one.
I was not respectful of the original cherry veneer, I just think darker veneer makes a better contrast with the brushed aluminum and the whole thing less tacky.
IMG_20201006_221842.jpg

This is the niche where the SX750 will be enthronized and that old faithful SX535 sitting there is going for a full revision and will find a new home.
IMG_20201006_222104.jpg

I may still insist on the OPAs on the other 750 that is now waiting for recap.

@zebulon1 thanks for the tips, I now assume you may have removed those components following the instruction to disconnect anything that would connect to pins 1 and 5 of the OPA. I have ordered the adapters but they are backordered and won't arrive for 3 or 4 weeks.
I am now looking for other options, which includes to find a TA7136 somewhere or buy an adapter from some other supplier.

M
 
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Unfortunately, three weeks goes fast these days.
You could fashion up a set using some perforated board but I would wait and enjoy the operational one in the meantime.
Nice job.
 
Hey folks, I just wanted to share that I have converted all 4 TA7136 to 4 LM358P op amps.
I have used Monte Allums adapter board.

This adapter allows you to disable the dual feature of the IC.
In fact they come "disabled" by default and if you want to enable it, you have to solder the two terminals displayed on the right picture.
upload_2020-10-20_15-17-45.png

When testing the modification with the scope I noticed a lot of noise, not sure what is was going on there or perhaps I wasn't testing it properly.
I injected an audio signal in sine waveform in the phono inputs and connected the scope to the audio out.
The sine wave was dirty and shaky.
Although when I connected to an actual turntable the magic was done.
Sound was just crystal clear.

I am very happy with the results of the mod...
...and very frustrated with my desolderting pump, it seems it is discharging some current against the IC pins and I ended up loosing two of these amplifiers in the process.

M
 
Why did you choose a LM358? I am sorry to say it is not a very good sub for a TA7136. compare the specs and learn what they mean. Lm358 was never designed for high performance audio. It is a general purpose op-amp.
As I said before, a Marantz 2385 uses them and I have never heard anyone complain about them other than they are obsolete but still in supply if you can trust the suppliers of them. If not just use the proven opa2604. There is nothing wrong with a ne5532a either if you can keep the supply down to its max supply v.
The new kid on the block is the TI opa1656.
 
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A few factors...
Including other thread on this same forum that suggested so.
I decided based on my limited knowledge. Not a good answer, but honest.
Perhaps my next step will be to upgrade them.
But first I have to find a desoldering pump that does not toast them.
 
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Wow someone suggested a LM358 to replace a TA7136. But this thread is talking about the OP604 replacing the TA7136
The SX-750 allows you to change the voltages the phono and pre amps op-amps run at, there is the 560ohm/1W dropping resistors and the 19V2 zeners

I had one of these for eons
https://www.mouser.ca/ProductDetail/Jonard-Industries/DP-200?qs=OoIWmhSwP62LNdFPNEnWnQ==
That and some solder wick and your off to the races.
Just do not press the iron tip into the pad with the solder sucker tip or you can damage pads. Practice makes perfect.
 
@rcs16

Here is a snippet of the SX 750 phono amp section.
Supply foir the TA7136 is 20.1v


upload_2020-10-21_21-10-57.png

I was looking at OPA604 datasheet and it says from +- 4.5 to +-24v
Perhaps this was never a problem after all, or am I missing something?

M
 
D12 and D13 set the op V
I was mentioning them because many opa's want to see +/-15V, a few select others like the OPA604 can go up to 24 so they were the obvious choice since one does not need to fiddle with the supplies.
One of my first phono pre-amps used a NE5534A, sounded good back in 78, never imagined they would still be in production today.
 
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Ok, I need a little help here...

Here is what I encountered about TA7136P pin configuration:
TA7136P pins:
1. frequency comp
2. non-inverting input (+ input)
3. inverting input (- input)
4. V-
5. voltage comp
6. outout
7. V+

Here is what OPA604PA datasheet says:

upload_2020-10-27_12-52-27.png


I've perfboarded an adapter that maps 1:1, except for pins 2 and 3 which are reversed.

TA7136P = OPA604AP
1 = 1
2 = 3
3 = 2
4 = 4
5 = 5
6 = 6
7 = 7
= 8 no connection


Reminder: this is a Pioneer SX 750 (let me know if I should create my own thread).

M
 
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mgrisoli
"...and very frustrated with my desolderting pump, it seems it is discharging some current against the IC pins and I ended up loosing two of these amplifiers in the process."

Is your 604 a SMD device; or through hole?

I did not fully document my SA-6800 modification; I used a LME49870MA SMD, VS the OPA as earlier suggested.

I did destroy one of my SMD's with too mush heat.

Quick on\off is the key with a pre-tinned perfboard, and a touch of rosin paste.

BTW, we are local it seems based on your profile. Welcome to AK.

rcs16. "Imo, there is really nothing wrong with the TA7136. I have a customer who has a Marantz 2385, it uses the TA7136 in the pre-amp. He says the 2385 sounds better stock than the serviced Pioneer SX-1980 that he has. One persons opinion, not necessarily mine."

after replacing the TA7136, my noise floor went from slight rice crispies to dead silent. All of my Marantz have a much warmer sound than my late 70's pioneers...... and you are very correct, YMMV. ( And, its a hobby:) )

I searched through my image backup, but have yet to locate my modification images.... with digital images from 1997 to today, 2 terrabytes of data gets "cumbersome" to manage. I need to de-dupe again..
 
elvi said:
mgrisoli
"...and very frustrated with my desolderting pump, it seems it is discharging some current against the IC pins and I ended up loosing two of these amplifiers in the process."

Is your 604 a SMD device; or through hole?

I did not fully document my SA-6800 modification; I used a LME49870MA SMD, VS the OPA as earlier suggested.

I did destroy one of my SMD's with too mush heat.

Quick on\off is the key with a pre-tinned perfboard, and a touch of rosin paste.

BTW, we are local it seems based on your profile. Welcome to AK.
.
Click to expand...

Howdy!

It is a through hole.
I measured the voltage between the desoldering pump and the receiver (unplugged from the power outlet) and I got a reading of 60VAC.
Perhaps shorting from unloaded capacitors.
So, I don't think the problem was the heat but the electrical insulation of the desoldering pump hot tip.
I've grounded it and it is now fine on that aspect. I also bought an used PACE MBT station that I am eager to try.
 
Tried that T-MODS board for the TA7136, and the OPA604AP doesn't work without a few mods to the board. Pins 2 & 3 are reversed like they should be, but pin 7 on the adapter board goes to pin 8 on the chip. So you have to jumper from pin 8 to pin 7 to get you positive voltage rail going. Then if you want output from pin 6 you better connect it to that little pad so it actually makes it out of the adapter board. Then they have pin 6 connected also to pin 1 so cut a slice in the trace to stop that. They also have pin 2 going to pin 6 with a trace on the back of the board as well pin 3 Going to pin 5. Not sure why so cut a Grove in those two traces and now the board works as it should with the OPA604AP. This was done on a pioneer SA-608 which has the same preamplifier as the SA-6800 and sorta follows this thread. Hope this helps.
 

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I ended up perfboarding, just thought that if I was to spend money onto an adapter that I would still have to... adapt for my purpose, I would rather make one.

I know, it doesn't look super neat, but it is not so bad at all.
upload_2020-10-31_10-0-23.png


I could have reversed the connector to the "bottom" side and made the IC to be on top, it would look neater and at least the soldering and wiring would be out of sight...
upload_2020-10-31_10-0-41.png

On the receiver board, I installed also a female pin connector and used small sections of hookup wires as pins.
The reason for that is simple... I am terrible on soldering male pins onto boards.
upload_2020-10-31_10-2-56.png

Btw, they work and sound very good.
 
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As long as it sounds good that's what matters. I just thought those boards were drop in replacements, and just pop in your chip and your off to the races. Nope. It's alright though just wanted to let folks know you can use the T-mods board as long as you mod the board a little more. Maybe a little later tonight I can listen to the amp instead of looking at sign waves.
 
Here is my attempt at trying to clean these boards up. In some of the pictures the .1uf cap is under the header riser. You might be able to see where I cut the traces.
 

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