Improving SNR of old school Pioneer SX-780

[OVerLoRDI]

This is a shot in the dark, but here it goes.

I have an old Pioneer SX-780 stereo amp, and it works and sounds fantastic for speakers. However, through my headphones the noise floor is way too high, there is quite a noticeable amount of "hissing" going on in the background on them. While it isn't unbearable by any means, I was hoping to find a way to maybe lower it.

On an old receiver like this it is quite easy to open up and swap parts out, so I was hoping someone with some expertise could offer some opinions on what parts in the amp are the culprits here. Thanks

 

[Howard]

Probably not worth your time, unless you're going to try to fix it for fun.

 

[A5]

Yeah. Unless someone has made a guide for that model, you'd risk frying it doing the trial and error to make it better.

If you consider yourself a soldering expert, you could maybe try replacing the op-amps with modern parts or replacing the capacitors on the output path with modern high-end parts.

I say this is an expert project because you would likely be converting any replaced op-amps from through-hole to surface-mount and you would probably have to run short wires to re-establish the connections since the new op-amps will likely be much smaller than the originals.

If you consider the value of your time to do the work, you'd probably get better performance/dollar from a modern low-end stereo amp.

 

[darkswordsman17]

OP, have you tried just cleaning it (I think it was DeoxIt? There's a common cleaner that gets recommended for cleaning up vintage gear like this)? That could help wonders.

As mentioned you'd need a schematic/guide, some capability and knowhow, but if the amp is functioning well, I'm not sure that you're gonna be able to improve it like you want, or you might be able to improve that but will end up with impedance mismatch.

If you're not confident in your own abilities, you could also check and see if there's a local shop or someone that can do cleanup/repair. It might cost a fair amount, but could be worth it, especially if its a good shop.

What headphones are you using with it?

Yeah. Unless someone has made a guide for that model, you'd risk frying it doing the trial and error to make it better.

If you consider yourself a soldering expert, you could maybe try replacing the op-amps with modern parts or replacing the capacitors on the output path with modern high-end parts.

I say this is an expert project because you would likely be converting any replaced op-amps from through-hole to surface-mount and you would probably have to run short wires to re-establish the connections since the new op-amps will likely be much smaller than the originals.

If you consider the value of your time to do the work, you'd probably get better performance/dollar from a modern low-end stereo amp.

I doubt it uses opamps. Most integrateds just use resistors to step down the main amp for the headphone out.

 

[OVerLoRDI]

I figured the response I might get would be, better to buy a new amp. Likely true. This project would be for fun as I love taking things apart, figuring out how they work, and improving them.

My soldering skills are decent, and the only reason I'd consider this project is most of the stuff on the inside of this amp looks like it was hand soldered to begin with. Realize this amp is from the late 70s, everything is pretty big and accessible.

I'll tear it down later this week and try to determine if it is using resisters to step down or opamps for the headphones. Also I'll post some pics.

To darkswordsman17, I'm using Sennheiser HD650s.

 

[OVerLoRDI]

Found a very detailed service manual. So this project has potential of happening.

 

[NutBucket]

A common source of noise in older units are leaky/failed/failing electrolytic caps. I haven't done a real comparison as the last unit I recapped wasn't working when I got it so i recapped and repaired it at the same time.

 

[darkswordsman17]

I figured the response I might get would be, better to buy a new amp. Likely true. This project would be for fun as I love taking things apart, figuring out how they work, and improving them.

My soldering skills are decent, and the only reason I'd consider this project is most of the stuff on the inside of this amp looks like it was hand soldered to begin with. Realize this amp is from the late 70s, everything is pretty big and accessible.

I'll tear it down later this week and try to determine if it is using resisters to step down or opamps for the headphones. Also I'll post some pics.

To darkswordsman17, I'm using Sennheiser HD650s.

Ok, so impedance mismatch isn't likely to be a big issue (my concern was that the headphones you're using were low impedance and/or really sensitive and it wouldn't be something that even a cleaned up and properly functioning amp could overcome).

Found a very detailed service manual. So this project has potential of happening.

Go for it! Just be careful and test things before plugging anything into it. Would hate to see you fry your headphones or something. Actually that'd be a good thing that could help you diagnose problems is measuring it first.

If you can get some pics and maybe a log of what you try and how well it works.

 

[slashbinslashbash]

If you can get some pics and maybe a log of what you try and how well it works.

Yes. OP, please provide pics so that I may live vicariouslylearn more about this interesting project

 

[A5]

Well if you have a service manual and decent skills, then I'd recommend starting with a re-cap. Just be careful to match the values as exactly as you can so that it doesn't change the performance in an unexpected way.

 

[SithSolo1]

http://www.audiokarma.org/ is a good place to find help with retro gear, they even have a forum dedicated to older Pioneer stuff.

 

[mmntech]

I've got a Pioneer SX-626. Those old models from the 1970s are some of the best analogue receivers ever made. When I replaced it with a Pioneer VSX-819H, I was quite surprised to find this modern receiver wasn't nearly as good. Very weak bass without the sub turned on. The SX-626 pumps bass out like its going out of style.

They do tend to hiss though. Mine does too. I think its probably the old caps that do it, though I don't know enough about electronics to be sure. It's a minor quirk though. Try cleaning the contacts first and see if that does anything.

 

[Plugers]

As far as op amps go, just put in a socket, You can always get boards to put SMD op amps on and plug them in the socket.

 

[NutBucket]

I wouldn't mess with any of the transistors unless they are defective. It will alter the sound of the unit...probably not in a good way.

Also, it is very unlikely you will even FIND any op-amps in receivers from that era. All the ones I've worked with use discrete transistors.

 

[bigsnyder]

Any update to this project? You didn't mention which sound card. This hiss may be from the computer.

 

[sdifox]

waste of time. get a headphone amp (or build a diy one) and take the signal from tape monitor. I doubt it will reduce the noise floor though.

 

[Charlie98]

Sounds like a fun project. My brother's first stereo was a Pioneer SX (lower-end, like a 330 or something) back in 1976. He recently bought one similar to yours (I don't remember the model number) that sounds pretty good but I don't think he has listened to it through headphones.

It's also my understanding on the old analog pots for the adjustment knobs (volume, etc) create noise. Darkswordsman was on the right track with some sort of de-oxidizer for those.

Once you get it squared away, you need to get a tube amp to go with it!

 

[chucky2]

http://www.audiokarma.org/ is a good place to find help with retro gear, they even have a forum dedicated to older Pioneer stuff.

This x infinity.

AudioKarma.org Pioneer Audio

Register there like you had to here, and then you are all set. Everything you could possibly ask or want to done to your receiver will be known there.

That is a great site and a great forum...

Chuck

 

[mikeford]

waste of time. get a headphone amp (or build a diy one) and take the signal from tape monitor. I doubt it will reduce the noise floor though.

Best idea, the headphone drive in most consumer gear is an after thought, best to skip it entirely and go with a circuit made create good sound with modern headphones.

 

[Howard]

waste of time. get a headphone amp (or build a diy one) and take the signal from tape monitor. I doubt it will reduce the noise floor though.

Why not get the signal from the source directly?

 

[mikeford]

Why not get the signal from the source directly?

Depends on the source, if its FM or more than one choice the receiver switches to, not a lot of option unless you like to do a lot plugging and unplugging.

On some receivers, the tape out may actually be unbuffered, no active circuit between it and source, just a switch mechanism. Ironically this purer signal tends to be in cheaper units as a cost savings.

I wish I had a chance to listen to the OP's system, tracking down and removing noise is fun, and there really should be no hiss on the headphone output with a clean source.

 

[bigsnyder]

The old Pioneers and other similar receivers from the late 1970s are not your "normal" consumer gear.

Best idea, the headphone drive in most consumer gear is an after thought, best to skip it entirely and go with a circuit made create good sound with modern headphones.

 

[mikeford]

I figured the response I might get would be, better to buy a new amp. Likely true. This project would be for fun as I love taking things apart, figuring out how they work, and improving them.

My soldering skills are decent, and the only reason I'd consider this project is most of the stuff on the inside of this amp looks like it was hand soldered to begin with. Realize this amp is from the late 70s, everything is pretty big and accessible.

I'll tear it down later this week and try to determine if it is using resisters to step down or opamps for the headphones. Also I'll post some pics.

To darkswordsman17, I'm using Sennheiser HD650s.

Didn't notice this at first, the HD650 absolutely needs a real headphone amp, with current drive not some op amp and a limiting resistor, like the old Pioneer almost certainly has.

Use plenty of caution and common sense, and its possible to get a taste of the sound of a real amp by hooking up a headphone socket to a speaker level output with LOW volume.