Homemade Audio Mixer - UK Vintage Radio Repair and Restoration Discussion Forum

Michael Maurice · 18th Feb 2009, 12:41 pm

Recently got out of the loft and offered on this site for free and going to Graham (Ilama)

I thought I'd post pictures on here and link it to the sets offered section and vice versa.

Mods if this is against the rules please delete and let me know.

I built this mixer back in 1977/1978, I was still in college at the time.

It was once used as a mixer for turntables before i built my own disco unit in 1982 and was also used for sound at a couple of amateur plays.

I'm afraid I don't have any circuits or notes for this, but will endeavor to answer any questions.

I have taken a few photo's as its going to be my last memory of it before it goes to Graham who hopefully will be able to do something with it.

These are pictures of the top of the mixer.

At the time there was an electronics shop in London's Edgware Road called HL Smith, anyone remember them?

In the early days (long before my time) they supplied chassis and valve amplifier kits, and in my days that cut and shaped aluminum to size and shape.

You can take the top cover off but you have to undo every knob first!!

More pictures of the underneath to follow.

Here is a link to my thread in sets offered: https://www.vintage-radio.net/forum/...ad.php?t=37446

Michael Maurice · 18th Feb 2009, 12:49 pm

And here are some pictures of the underside.

All boards and modules were designed by myself, at first using one of those etching pens, drawing directly onto the copper clad board which was then etched.

Then at college we used the black tape and black circles which were bought from Maplin.

I think the power supply went through a revision the original transformer wasn't a toroidal.

Michael Maurice · 18th Feb 2009, 12:51 pm

The last picture is the back of the unit which shows the smaller VU meter drive circuits on their plug in boards, each board carried the drive for 2 meters and led's.

Now can anyone guess what inspired that design?

yestertech · 18th Feb 2009, 4:49 pm

Wow - that's one hell of an impressive home made item...
Well done that man !
Yes, I recall HL Smith - you could take in some measurments spend 1/2 hour pottering around the rest of the Edgware rd shops and come back and collect your new chassis from them - what a service !
The last time I saw their shop was in the late 90's - still there, all boarded up with assorted vegitation growing out of the gaps .
Very sad !
As ever, supply and demand.

Andy

Welsh Anorak · 18th Feb 2009, 5:32 pm

Hi
That's quite a machine! You could have kept quiet and said it was a commercial unit in a home-made case and we wouldn't have been any the wiser.
Were you a fan of the A77 by any chance? The layout of those presets looks quite familiar, except yours won't spring apart as soon as you look at them....
Glyn

arjoll · 19th Feb 2009, 10:32 am

Nicely done! My dad made a mixer in the late 70's, nowhere near as complex though. His was based on the ETI (Australia) "Master Mixer" which used the LM382 preamp chip, one per two channels, and metal can 741's. All on Veroboard, connected with looms of hookup wire all laced together!

He had 6 channels, grouped to three sliders, so he could pan left/right and use one fader for a stereo pair.

How is your EQ done? Dad never built the ETI one, it used custom wound inductors.

The casework is nice. He never did manage to get the hang of drilling holes in a straight line. I seemed to have inherited that trait

Michael Maurice · 19th Feb 2009, 10:39 am

Hi Arjoll,

I think I used a version of the ETI design, I seem to remember using an LM380 or LM381.

The EQ was done using home made wound coils, i cant remember how effective it was, my disco that i built much later used an 'electronic' coil based around some op amps.

I also couldn't drill in straight lines, if you look at the knobs they've all got skirts on them!

I was making provision for a compander as well which is why there are eight holes with nothing in them.

I also put in an audio limiter which was based on my college project and was also my first project to be published in Practical Wireless June 1980.

Later I'll start another thread on this.

18th Feb 2009, 12:41 pm	#1
Michael Maurice Moderator Join Date: Feb 2006 Location: Wembley, Middlesex Posts: 7,224	Homemade Audio Mixer Recently got out of the loft and offered on this site for free and going to Graham (Ilama) I thought I'd post pictures on here and link it to the sets offered section and vice versa. Mods if this is against the rules please delete and let me know. I built this mixer back in 1977/1978, I was still in college at the time. It was once used as a mixer for turntables before i built my own disco unit in 1982 and was also used for sound at a couple of amateur plays. I'm afraid I don't have any circuits or notes for this, but will endeavor to answer any questions. I have taken a few photo's as its going to be my last memory of it before it goes to Graham who hopefully will be able to do something with it. These are pictures of the top of the mixer. At the time there was an electronics shop in London's Edgware Road called HL Smith, anyone remember them? In the early days (long before my time) they supplied chassis and valve amplifier kits, and in my days that cut and shaped aluminum to size and shape. You can take the top cover off but you have to undo every knob first!! More pictures of the underneath to follow. Here is a link to my thread in sets offered: https://www.vintage-radio.net/forum/...ad.php?t=37446 Attached Thumbnails

18th Feb 2009, 12:49 pm	#2
Michael Maurice Moderator Join Date: Feb 2006 Location: Wembley, Middlesex Posts: 7,224	Re: Homemade Audio Mixer And here are some pictures of the underside. All boards and modules were designed by myself, at first using one of those etching pens, drawing directly onto the copper clad board which was then etched. Then at college we used the black tape and black circles which were bought from Maplin. I think the power supply went through a revision the original transformer wasn't a toroidal. Attached Thumbnails

18th Feb 2009, 12:51 pm	#3
Michael Maurice Moderator Join Date: Feb 2006 Location: Wembley, Middlesex Posts: 7,224	Re: Homemade Audio Mixer The last picture is the back of the unit which shows the smaller VU meter drive circuits on their plug in boards, each board carried the drive for 2 meters and led's. Now can anyone guess what inspired that design? Attached Thumbnails

18th Feb 2009, 4:49 pm	#4
yestertech Nonode Join Date: Dec 2002 Location: Coulsdon, Surrey, UK. Posts: 2,130	Re: Homemade Audio Mixer Wow - that's one hell of an impressive home made item... Well done that man ! Yes, I recall HL Smith - you could take in some measurments spend 1/2 hour pottering around the rest of the Edgware rd shops and come back and collect your new chassis from them - what a service ! The last time I saw their shop was in the late 90's - still there, all boarded up with assorted vegitation growing out of the gaps . Very sad ! As ever, supply and demand. Andy

18th Feb 2009, 5:32 pm	#5
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,918	Re: Homemade Audio Mixer Hi That's quite a machine! You could have kept quiet and said it was a commercial unit in a home-made case and we wouldn't have been any the wiser. Were you a fan of the A77 by any chance? The layout of those presets looks quite familiar, except yours won't spring apart as soon as you look at them.... Glyn

19th Feb 2009, 10:32 am	#6
arjoll Dekatron Join Date: May 2006 Location: Invercargill, New Zealand Posts: 3,457	Re: Homemade Audio Mixer Nicely done! My dad made a mixer in the late 70's, nowhere near as complex though. His was based on the ETI (Australia) "Master Mixer" which used the LM382 preamp chip, one per two channels, and metal can 741's. All on Veroboard, connected with looms of hookup wire all laced together! He had 6 channels, grouped to three sliders, so he could pan left/right and use one fader for a stereo pair. How is your EQ done? Dad never built the ETI one, it used custom wound inductors. The casework is nice. He never did manage to get the hang of drilling holes in a straight line. I seemed to have inherited that trait

19th Feb 2009, 10:39 am	#7
Michael Maurice Moderator Join Date: Feb 2006 Location: Wembley, Middlesex Posts: 7,224	Re: Homemade Audio Mixer Hi Arjoll, I think I used a version of the ETI design, I seem to remember using an LM380 or LM381. The EQ was done using home made wound coils, i cant remember how effective it was, my disco that i built much later used an 'electronic' coil based around some op amps. I also couldn't drill in straight lines, if you look at the knobs they've all got skirts on them! I was making provision for a compander as well which is why there are eight holes with nothing in them. I also put in an audio limiter which was based on my college project and was also my first project to be published in Practical Wireless June 1980. Later I'll start another thread on this.