Hiss reduction? Any ideas? GF555

Perrin21 · Jun 23, 2017

I have a GF555 and there is the typical background hiss as the volume is increased. Has anyone found a way to reduce this? I'm sure it isn't faulty i just wondered if there was a tip or trick to drop this noise and increase the S/N ratio. Could Ferrite cores be used on any internal wiring etc?

ralrein1 · Jun 23, 2017

I don't know much about the technical stuff. What I can tell you is to reduce the treble when listening to FM radio. If your box has a Dolby noise reduction for cassette playback,us that too. Also I believe I read that you used Deoxit on all the sliders?? If you haven't then try that as well. Also its a good idea to get a spray electronics "wash" to get all of the dust and whatnot. That dust can build up on printed circuit boards and cause problems. That's all I know,I hope it helps you out.â˜ºâ˜ºâ˜º

HRmeteohub · Jun 24, 2017

Hi!

Well, the noise can originate from tranistors, diodes, and in some rarer circumstances - any other component. While you can get the replacements or even original (NOS) transistors and diodes, there is very slim chance that there is a replacement for IC. As it was brought before on this forum, IC's are often designed for specific task, sometimes even for specific box.
I would first take the schematic and instruments. Measure the hiss (noise with no other signal or weak signal (e.g. sine 1kHz) ) from the speaker all the way up to the source of the signal. This is by no means easy and straightforward, and takes time.
On the othr hand, there are some components that are known to go bad and produce problems. You could also try searching the 'net using the component list, even before you open the box. Perhaps that could help, or lead you to waste hours and hours searching for the gost in the machine... or Gremlins, as my friend would say.

Perrin21 · Jun 25, 2017

HRmeteohub said:
Hi!

Well, the noise can originate from tranistors, diodes, and in some rarer circumstances - any other component. While you can get the replacements or even original (NOS) transistors and diodes, there is very slim chance that there is a replacement for IC. As it was brought before on this forum, IC's are often designed for specific task, sometimes even for specific box.
I would first take the schematic and instruments. Measure the hiss (noise with no other signal or weak signal (e.g. sine 1kHz) ) from the speaker all the way up to the source of the signal. This is by no means easy and straightforward, and takes time.
On the othr hand, there are some components that are known to go bad and produce problems. You could also try searching the 'net using the component list, even before you open the box. Perhaps that could help, or lead you to waste hours and hours searching for the gost in the machine... or Gremlins, as my friend would say.

I don't think its a gremlin as such, more a characteristic of the era. I just wondered if anyone had tried ferrite beads internally or some shielding? As you say a ghost in the machine. I will probably leave it as it is.

ralrein1 · Jun 25, 2017

So what have you decided to do? Have ya cleaned the insides out and or done all that cool technical stuff HR suggested? Enquiring minds want to know.

HRmeteohub · Jun 26, 2017

Perrin21 said:
I don't think its a gremlin as such, more a characteristic of the era. I just wondered if anyone had tried ferrite beads internally or some shielding?

Well, if that is so, then you basically ask for replacement of the internal parts in order to get less noise out. Meaning, buying/making/designing modules for e.g. tape deck. Ferrite beads are hardly going to be helpful as the most of the noise comes from the components itself, not from outside interference. You can't change internal characteristics of the transistors, chips and other stuff.

Easiest way is just to buy a good (read: low noise) module with op.amp and tweak it for tape playback. It helps if you know what are characteristics of the modules that are inside. Power amp is even easier to get on ebay/aliexpress/whatever. Sounds better?

hopey · Jun 28, 2017

I would change the power supply as the laminations can vibrate overtime and produce background noise.

Perrin21 · Jun 29, 2017

hopey said:
I would change the power supply as the laminations can vibrate overtime and produce background noise.

is that an easy swap?

Superduper · Jun 29, 2017

Perrin21 said:
I would change the power supply as the laminations can vibrate overtime and produce background noise.

Click to expand...

is that an easy swap?

I don't suggest you do that. It would make zero difference for you. Lamination noise is more of a mechanical noise (think hum or imagine transformer noise). Transformers don't make hiss. That's more likely attributed to system topology, or component junction noise. Is your background noise excessive as if something is wrong, or are you simply trying to turn a low fi into hifi?

Perrin21 · Jun 29, 2017

Superduper said:
I would change the power supply as the laminations can vibrate overtime and produce background noise.

Click to expand...

is that an easy swap?

I don't suggest you do that. It would make zero difference for you. Lamination noise is more of a mechanical noise (think hum or imagine transformer noise). Transformers don't make hiss. That's more likely attributed to system topology, or component junction noise. Is your background noise excessive as if something is wrong, or are you simply trying to turn a low fi into hifi?

The latter if I'm honest lol. Sounds like more effort than its worth.

Superduper · Jun 29, 2017

Well, then since we are being honest, it's easier to build a new system than it would be to do what you contemplated. I mean ask yourself this question: if a manufacturer could, by virtue of simply adding a few ferrite beads or thin sheets of shielding, for pennies, why wouldn't they already have done so, instead of settling for lower and inferior S/N ratio specs in an era when the most minute difference in specifications could result in bragging rights or king of the hill status?

hopey · Jun 29, 2017

Superduper said:
I would change the power supply as the laminations can vibrate overtime and produce background noise.

Click to expand...

is that an easy swap?

I don't suggest you do that. It would make zero difference for you. Lamination noise is more of a mechanical noise (think hum or imagine transformer noise). Transformers don't make hiss. That's more likely attributed to system topology, or component junction noise. Is your background noise excessive as if something is wrong, or are you simply trying to turn a low fi into hifi?

One mans Hiss is another mans Hum. Doesn't look like we are going to resolve this thread problem however I have swapped power supplies before which reduced back ground noise ( what ever you want to call it). After all this signal is then amplified along with the noise and ripple from the power supply.

Superduper · Jun 29, 2017

A transformer is not a power supply, it is A component in the power supply and has nothing to do with ripple which is smoothed by the filter caps, but the reason you suggested for replacement was laminations which is a design component of the transformer. Furthermore lamination issues can manifest but only at 60hz, WHICH DOES NOT hiss, hiss being higher frequency. Also lamination noise is mechanical and stays the same volume, but the OP has stated that it varies with volume.

Perrin21 · Jun 30, 2017

Superduper said:
A transformer is not a power supply, it is A component in the power supply and has nothing to do with ripple which is smoothed by the filter caps, but the reason you suggested for replacement was laminations which is a design component of the transformer. Furthermore lamination issues can manifest but only at 60hz, WHICH DOES NOT hiss, hiss being higher frequency. Also lamination noise is mechanical and stays the same volume, but the OP has stated that it varies with volume.

its just a symptom of old cheap components and design I'm guessing. Feed it no signal and turn the volume to max it makes a hiss. Im sure all do.

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Hiss reduction? Any ideas? GF555

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