MIC amplifier

[mrtinb]

The power packs you mentioned should be stabilised/regulated ones as un-stabilised/unregulated ones induce a bad hum in pre-amps of this type at any voltage.

Any markings on a power adapter to see whether it is stabilised or not?

[Moggy]

The power packs you mentioned should be stabilised/regulated ones as un-stabilised/unregulated ones induce a bad hum in pre-amps of this type at any voltage.

Any markings on a power adapter to see whether it is stabilised or not?

All the power packs I use just say stabilised or regulated on the label.

Just measure the out-put at any selected voltage with a multi meter.

Stabilised power packs will show give or take a few volts the voltage you have selected.
Unstabilised power packs will show a slight rise under no load conditions.

IE stabilised 12 volts selected= 12 volts to within a volt or so measured at the output plug.
Unstabilised 12 volts selected anything between 14-18 volts measured at the output plug.

The same method applies to all the other voltages.

Unstabilised supplies rely on increased current consumption by the electrical load to pull the working voltage down to the required level, which is fine for power audio amplifiers but not so good for audio pre-amps.

[mrtinb]

Stabilised power packs will show give or take a few volts the voltage you have selected.
Unstabilised power packs will show a slight rise under no load conditions.

IE stabilised 12 volts selected= 12 volts measured at the plug.
Unstabilised 12 volts selected 14 volts plus measured at the plug.

Thank you for helping me

[Moggy]

Stabilised power packs will show give or take a few volts the voltage you have selected.
Unstabilised power packs will show a slight rise under no load conditions.

IE stabilised 12 volts selected= 12 volts measured at the plug.
Unstabilised 12 volts selected 14 volts plus measured at the plug.

Thank you for helping me

No worries I look forward to seeing the end result.

[1024MAK]

If the mains adaptor/ power supply is a bought item (as opposed to one that came with an item of equipment), they normally say on the label, or the packaging "Regulated" or "stabilised".

If there is no mention of either of these two words, it is very likely a unregulated type.

Regulated or stabilised types normally regulate the output voltage to within +/-5% of the rated output voltage at all normal load currents.

Unregulated types, when not suppling the rated maximum normal output current, will have a greater than rated output voltage. With no load, often as much as 1.5 X the rated output voltage.

Mark

[Moggy]

This confirms my earlier post Martin, but the important thing here is that a stabilised supply is needed otherwise the output wave will have a lot of hum attached to it which the zeddy might not reject.

[Paul]

Just my comment on the power supply.
I use a 9V battery to power my Chinese mic amp. It introduces no noise.
kind regards Paul

[1024MAK]

To amplify the MIC output signal from a ZX81, try this circuit:

ZX Mic to PC Amp _20160630 50.png (24.78 KiB) Viewed 2738 times

Mark

[gammaray]

From another post:

"Thought to [be] honest such pre-amps are now so inexpensive to buy ready made it's not worth building yourself".

Unless you want to learn somefin'.

[mrtinb]

I'm still having problems with saving files that can be read again.

I've built Velleman Kit K1803 and used this psu which I think is regulated, but the recordings are still with noise.

image.jpeg (15.27 KiB) Viewed 2660 times

https://www.dropbox.com/s/xl68e1v7qe3ni ... 2.m4a?dl=0