Search found 1257 matches

by mrtinb
Mon Jun 27, 2016 8:59 am
Forum: Hardware
Topic: Creating Wilf Rigter's ZXKBD v3
Replies: 52
Views: 14261

Re: Creating Wilf Rigter's ZXKBD v3

This weekend has been used to solder a pcb connector on the backside of the keyboard controller, so a RAM expansion can be connected. Before I had to choose between keyboard or 16K RAM. (hard choice) I had made a custom doublesided board to get the pcb connector. You can see the lanes has holes in t...
by mrtinb
Sat Jun 25, 2016 12:06 pm
Forum: Sinclair Misc
Topic: UK Voted to Leave the EU
Replies: 12
Views: 4209

Re: UK Voted to Leave the EU

This forum should not turn into politics. My personal opinion is that Denmark (where I live) should join Britain and leave as well.
by mrtinb
Thu Jun 23, 2016 9:49 am
Forum: WANTED
Topic: ZX81 folding Reference card
Replies: 9
Views: 4695

Re: ZX81 folding Reference card

dessony wrote:Here is a PDF version of this card! :-)
Reference card.pdf
Is it possible to scan at a higher resolution? Some of the small printing cannot be read.
by mrtinb
Wed Jun 22, 2016 2:42 pm
Forum: Hardware
Topic: MIC amplifier
Replies: 71
Views: 14084

Re: MIC amplifier

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. Than...
by mrtinb
Wed Jun 22, 2016 2:24 pm
Forum: Hardware
Topic: MIC amplifier
Replies: 71
Views: 14084

Re: MIC amplifier

Moggy wrote: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?
by mrtinb
Wed Jun 22, 2016 1:54 pm
Forum: Hardware
Topic: MIC amplifier
Replies: 71
Views: 14084

Re: MIC amplifier

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...
by mrtinb
Wed Jun 22, 2016 1:13 pm
Forum: Hardware
Topic: MIC amplifier
Replies: 71
Views: 14084

Re: MIC amplifier

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.
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by mrtinb
Wed Jun 22, 2016 12:43 pm
Forum: Hardware
Topic: MIC amplifier
Replies: 71
Views: 14084

Re: MIC amplifier

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?
by mrtinb
Wed Jun 22, 2016 12:14 pm
Forum: Hardware
Topic: MIC amplifier
Replies: 71
Views: 14084

Re: MIC amplifier

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. :D
by mrtinb
Tue Jun 21, 2016 12:20 pm
Forum: Hardware
Topic: MIC amplifier
Replies: 71
Views: 14084

Re: MIC amplifier

No the output is 5V, because its fed into a 5V logic device that needs 5V logic, this is not simply a preamplifier its a circuit designed to take audio levels from the sound played from a laptop, and convert them so that they will become ideal Transistor Transistor logic levels inside the ZX81. No ...