Why I haven't been building bikes this year

[Mark Kelly]

First one.jpg

One unit

Build in parts.jpg

Ten units in bits

Main_board.jpg

The heart of the matter



This project has consumed all available resources. It finishes tomorrow.

For those who are wondering, they are specialised motor drives designed to run the ancient Garrard 301 turntable.

[devlin]

So would you be able to build guitar amps as well? Nice by the way.

[Mark Kelly]

So would you be able to build guitar amps as well? Nice by the way.

I would, but the subjunctive is appropriate. I don't and won't, not my field.

[summilux]

Good lord. Are you the Mark Kelly of the LP12 board? I've got one of those languishing because I've been spending too much time on my bikes. My next project is going to be a Lenco anyway. Never thought there'd be someone from diyaudio here.

[Britishbane]

Good lord. Are you the Mark Kelly of the LP12 board? I've got one of those languishing because I've been spending too much time on my bikes. My next project is going to be a Lenco anyway. Never thought there'd be someone from diyaudio here.

It is. The one and only.

[Mark Kelly]

Are you the Mark Kelly of the LP12 board? I've got one of those languishing because I've been spending too much time on my bikes.

The board in pic three above retains several design elements from that synch board. The microcontroller at bottom right now does the frequency division of the quartz clock instead of the clunky counter chip version I first used but the logic that generates the stepped waveform is the same.

Voltage setting now uses a bandgap reference chip and digital pots so it can be adjusted from the front panel. The filter now uses a tracking PLL to set F0.

The analogue section is similar except this is a single phase so the second "channel" is used for feedback. The big change is that this signal is passed to a 12AU7 driving a pair of KT88s, the OPTX on the KT88s is effectively just an isolation transformer (1:1 winding ratio plus feedback coil).

[summilux]

The big change is that this signal is passed to a 12AU7 driving a pair of KT88s

Dammit, you've ruined my evening. Now I'm going to have to pull the schematic and figure this out. And I've got a Crumpton to build.

[Britishbane]

I assume ancient isn't quite correct, right? I've no doubt you've built a new plinth, rejuvenated or replaced bearings, etc. What tone arm(s) are you using? Cart? Details man, details.

[Paul]

Yes, let's see more.
That's a lovely piece of work!

[Mark Kelly]

I assume ancient isn't quite correct, right? I've no doubt you've built a new plinth, rejuvenated or replaced bearings, etc. What tone arm(s) are you using? Cart? Details man, details.

Well the one I have is my age, so it probably feels ancient at the moment.

Yes, it's a homemade plinth as is usual with these things but I'm about to replace it with one laminated from veneer leaf the way I do my frames. Less usually, I made the tonearm too, and am in the process of constructing a new one which is a pivoting linear tracker (think Burne Jones, but this actually works).

Cart at the moment is a Grace F9 but I'm talking to the people at Garrott Bros. about making me a special version of their P77 with one "channel" responding to horizontal modulation and the other to vertical. It looks like a goer, but I have to rebuild the tonearm to suit.