Tascam 32 Fix found.

First results Hiss comes from headphone amp.

First results back tonight indicate that the headphone amp hiss in intrinsic to the IC power amp. Shorting the summing input to ground does not change the hiss level. Plus the hiss is much the same in both channels.

I suspect that the IC amp has always been this hissy as a design "feature". Rather than as an aging of the device. (I have one more test to do on this amp so all is not lost yet)

For me the next step is to take a look at replacing the headphone amp. Possably with a CMoy amp or other headphone amp. Target headphones would be Koss pro4aat (150 ohm headphones)

As a side note in the process of tracking down the hiss I have noted that the record and playback circuits are quite quiet. This is limited to the headphone amp.

Regards
 
Data sheet

For what its worth, this is the datasheet (at least the only one I could find) on the amp IC.

I'm guessing that any number of alternatives could be used - even something cheap like the TDA2822M (NZ$3.17) would be lower noise than the 32 I borrowed last week!
 

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Try this first
I know I'm about 20 years late to this party, but I do find the headphones hiss a very interesting topic. Unlike everyone else that has posted on this topic, I bought my Tascam 32 brand new from the dealer in the late '80s. I used it as a master mix down tape deck, and for the life of me I can't ever remember the headphone hiss when reviewing my mixes with the headphones. It was never an issue. After 5 or 6 years I didn't really use it too much although I have changed the capstan belt twice.
A month or so ago I got it up and running again and sure enough the headphone hiss was horrendous. I thought where did that come from? Also the right channel output was gone. That was caused by a cold solder joint, and thanks to this user's group it was a quick fix to get it up and running again.
As for the headphone hiss, I don't think it's a design flaw, rather the IC power amp just degraded as a result of use and age. To test this, I've ordered a brand new original Toshiba 7230 IC chip off of eBay, two for $9, and when I get some time I'll remove the old one and install the new chip. Should be an easy swap.
If these 7230s are only good for 15 or 20 years, no wonder everyone else has tons of hiss. My tascam 32 is at least 35 years old. Either way I'll post my results when I get them.
 
Well disassembling the Tascam 32 to get to this chip was a little bit of work. Really important not to get the screws mixed up because there are different lengths and styles and there are tons of them. Have to take all the stuff off the back to be able to remove the bottom cover to slip the board out.
After all that I did replace the old TA7230p chip with a date code of 1990 June, with a brand new one I bought off eBay but with the date code of 1994 January.

I have to admit I was disappointed that the new chip did not appreciably reduce the headphone hiss. Oh well now we know. The 7230 is one hissy chip.

You could try the NTE1387 chip since it is a pin for pin compatible IC, but it has exactly the same specs and I wonder if it was made by Toshiba and they simply put the NTE logo on it.
Fortunately the headphone hiss doesn't find its way onto the recorded tapes and is really just a (minor?) irritation.
 
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