Sinclair ZX80 / ZX81 / Z88 Forums

google is your friend, it would take me ten minutes to draw one up, but ten seconds to google for one.

http://forum.allaboutcircuits.com/threa ... fier.4348/
This circuit should also work with 5V, and the gain should be changeable to say 30 times (10mV to 300mV)

good luck.

I understand the need to want build something yourself and therefore learn something in the process but if all you want is a solution then as mentioned earlier just buy this and problem solved.

It's 40db boost is more than adequate for the job.

http://cpc.farnell.com/velleman-kit/k18 ... dp/HK00619

If not from Farnell then someone more nearer to you, Vellemen kits are sold worldwide.


Here's the manual.

Moggy wrote:I understand the need to want build something yourself and therefore learn something in the process but if all you want is a solution then as mentioned earlier just buy this and problem solved.

I've been talked to reason. Velleman Kit K1803 has been ordered now. Thank you for your patience so far.

Hope it works for you mrtinb and I too also thank all the posters here because I have learnt quite a lot myself from this thread.

Moggy wrote:http://cpc.farnell.com/velleman-kit/k18 ... dp/HK00619
...
Here's the manual.

Looking at the manual it seems this circuit needs 12V and not 5V.

Any idea if it will work with 5V, but just give a lower amplification?

Yes the 741 chip fitted works down to 4.5 volts.

I have successfully used it as a mic/guitar pre amp at voltages from 5-30 volts depending on application.

But why the 5v limitation?

Moggy wrote:Yes the 741 chip fitted works down to 4.5 volts.

I have successfully used it as a mic/guitar pre amp at voltages from 5-30 volts depending on application.

Something's just dawned on me.

When mentioning voltages I assumed (perhaps wrongly) that you were referring to +- 5V split rail making 0-10v single rail. If that's the case then at least 6-7 volts single rail is the minimum that this pre-amp will run at without introducing some hum.

Moggy wrote:Something's just dawned on me.

When mentioning voltages I assumed (perhaps wrongly) that you were referring to +- 5V split rail making 0-10v single rail. If that's the case then at least 6-7 volts single rail is the minimum that this pre-amp will run at without introducing some hum.

I was hoping to use a standard iPhone power adapter with 5V DC 5W.

Apart from that I have a power adapter that can give 3V DC 4.5V DC 9V DC and 12V DC, but I have no power adapter that can give -12V and +12V. They are all DC.

mrtinb wrote:

Moggy wrote:Something's just dawned on me.

When mentioning voltages I assumed (perhaps wrongly) that you were referring to +- 5V split rail making 0-10v single rail. If that's the case then at least 6-7 volts single rail is the minimum that this pre-amp will run at without introducing some hum.

I was hoping to use a standard iPhone power adapter with 5V DC 5W.

Apart from that I have a power adapter that can give 3V DC 4.5V DC 9V DC and 12V DC, but I have no power adapter that can give -12V and +12V. They are all DC.

Hi Martin as I possibly gave erroneous information I thought it only fair I do some testing on your behalf.

I connected the pre-amp power lines to the ZX81 regulator just for fun and can now confirm that it will run at single rail 5 volts with no hum. ( I assumed wrongly again that you were using the zeddy regulator) and at even at this reduced voltage you should get the required out put.

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.