SH-101 Mains Hum

[steevio]

you dont necessarily need a Boss adapter, i use a universal adapter on both of my SH101 s with no problems,

in fact i get a hum when i use a Boss adapter ( it used to be fine, but started humming a few years ago, - the adapter not the synth. )

could you take the PS back to Maplins ? it may be faulty, that would be my first move.

you probably need a 500 mA (6VA) minimum universal adapter but make sure the polarity is set right ( as mentioned in my first post ) sometimes they have a switch, sometimes you have to put the jack end on the opposite way round (there are small symbols on the plastic sleeve of the jack)

(but saying all this, it just wouldnt work at all if you had it the wrong way round.)

it could well be a fault with the SH101.
are you sure you dont have any LFO going to anything? - filter / VCO etc. have you tried wiggling all the sliders down at the end of their travel incase theres a dodgy slider ?

[oblioblioblio]

@Lem, you're right, the first thing to check is almost certainly the power supply.

in an audio circuit the power provides a lot of the voltages from which all other voltages are derived from. If the power supply is sh!t then it can have a lot of knock on effects.

[lem]

in an audio circuit the power provides a lot of the voltages from which all other voltages are derived from. If the power supply is sh!t then it can have a lot of knock on effects.

This is why it seems odd that it says 9v - 12v? It must have some internal regulation, which you get in some oscillator design. Irregularities on the power rails normally result in terrible tracking.

[steevio]

just out of interest could you post a link to the PSU you bought ?

these days most PSUs seem to be 'switching PSUs', which are really small and light compared to the old style heavy transformer types, my electronics mate reckons they are sh!t...

like Lem says try it with batteries, that will eliminate a PSU problem straight away.

[lem]

these days most PSUs seem to be 'switching PSUs', which are really small and light compared to the old style heavy transformer types, my electronics mate reckons they are sh!t...

Your mate is correct. Switch mode power supplies are more efficient but much lower quality than a Linear supply. The power supplies in modular synths are linear.
Altough I have heard that switching technology is coming on strong, with switching getting so fast that it is hardly noticable, I would still exclusively use a linear supply on analogue designs. Maybe i find security in the weight of the things
Also I know that laptop supplies (switched) are known to die, and power supplies in minimoog (Linear) are still going strong.

I don't think I have ever seen a Linear 'brick' 'wallwart' type power supply. I can normally identify them by the type of power connector they have going into them. Most linear power supplies have a IEC 'Kettle plug' or that 'Figure of 8' plug. It also depend on the type of circuit. I could be way off the mark tho, it's just my findings.

It has been ages since I looked at the prices of D (for the sh101? - correct me if I am wrong) Batteries. But it could be the same price to buy a new power supply?
Also by using batteries you could be bypassing the internal rectification circuit, which could also be the culprit.

I would take it to a music shop and try out some of their power supplies, ring em first! Be sure you know what kind of power supply you are looking for, don't break it on account of a stupid shop assistant.

[steevio]

It has been ages since I looked at the prices of D (for the sh101? - correct me if I am wrong) Batteries. But it could be the same price to buy a new power supply?
Also by using batteries you could be bypassing the internal rectification circuit, which could also be the culprit.

in the UK carboot sales are the best source of cheap batteries

[lem]

It has been ages since I looked at the prices of D (for the sh101? - correct me if I am wrong) Batteries. But it could be the same price to buy a new power supply?
Also by using batteries you could be bypassing the internal rectification circuit, which could also be the culprit.

in the UK carboot sales are the best source of cheap batteries

I wish there were still decent ones in cornwall. Or I wouldn't be sat here on forums!

[oblioblioblio]

This is why it seems odd that it says 9v - 12v? It must have some internal regulation, which you get in some oscillator design. Irregularities on the power rails normally result in terrible tracking.

Lots of audio chips work fine at different voltages. You can run lots of modules designed for +/-15v at +/-12v and not damage anything, but it can fck with the calibration and other stuff.

But yeah, I think poor PSUs can easily introduce noise and instabilities.