DIY Transistor Amp Using NVA Boards

[Cressy Snr]

This was me last night:

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Relaxed and off the upgrade treadmill.

[steve s]

Nice one Steve. Looks good !
I remember putting a pair of sansui speakers (still have them ) in the lounge for a couple of months, quite enjoyed them but I eventually went back to my diy stuff.

I keep thinking I should set my old quad corner speakers back up too.. although I should really sell them on

[Daniel Quinn]

If your appetite can be sated by bog standard commercial speakers then I think you need to try harder with your diy not give it up

[Cressy Snr]

If your appetite can be sated by bog standard commercial speakers then I think you need to try harder with your diy not give it up

I'm happy, so there is no reason to continue.

[ed]

what are you doing with your fane 12-250s Steve?
Blue Aran seem to have gone to ground and I'm still waiting for a response from Fane.

[Cressy Snr]

what are you doing with your fane 12-250s Steve?
Blue Aran seem to have gone to ground and I'm still waiting for a response from Fane.

Ed,
You have Email.

[Mike H]

This was me last night:
D5A449DD-99F4-4D86-B70E-310C7CC812BD.jpeg
Relaxed and off the upgrade treadmill.

-

[Cressy Snr]

I’ve just changed my speaker cable to some stuff from B&Q at £1.75 per metre. Not made a blind bit of difference or blown up the amp, but I was sick of the existing cable dangling because it wasn’t long enough to reach up to the Mission speaker terminals and stay down on the floor.

[Cressy Snr]

Back on topic,
Over the last few days, the amp has had a bit of an internal and external facelift. I retrieved my old Khozmo 10K shunt stepper and an Elma 3 position rotary switch from our Ant’s place and did an internal refresh, incorporating the attenuator, and switch onto the front panel and moving the phono board to the internal side wall. Regulator for the phono board sits between the two amp boards:

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Reworked the front panel to take two control knobs and moved the LED on indicator to the other end of the panel. Gave the front a re-wax and There you go.

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From a distance with Pat Metheny Group on the turntable:

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[Cressy Snr]

The stepped attenuator has certainly improved the amp’s performance, but anything would have been an improvement on the crappy carbon pot I had in there. Just shows the importance of the quality of the volume pot and selector switch, in the scheme of things.
I also flipped up the amp boards and put the feedback resistors back in their allotted places. The inside had become an utter rat’s nest and totally offended my aesthetic sensibilities, hence the moving of the phono board and the resistor relocation. It turned out that I was out of 18K resistors, but I did have a few 15K values.
Managing to find a pair that matched, these were installed: one in each board, so strictly speaking, the boards are no longer Richard’s intended design and I’m sure I would have got a right bollocking if he was still here and I had been stupid enough to let him find out. But unlike when I put 10K in the feedback position, in an attempt to lose a bit of gain when I had the Fanes, 15K has not produced dry, dead, sterility, so I’m happy with the results.

Three weeks I lasted before the DIY bug hit again.

[Dave the bass]

You can check out....but you can't leave!

[Cressy Snr]

You can check out....but you can't leave!

[Mike H]

Very good Steve.

[Cressy Snr]

[Cressy Snr]

OK so I've finished up the amp properly now.
I fitted bleed resistors to both power supplies: a) to discharge the caps safely, and b) to provide at least a little bit of regulation.
I also fitted polypropylene film PSU bypass caps, right where the power connects to the boards.
Those last couple of jobs had a far bigger effect on the sound amp than I thought they would. To be perfectly honest I'm gobsmacked. It's absolutely fantastic.

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Below are the two PSUs.
Transformer voltages are different because that is what I had to hand when I originally doubled up the power supplies that's all:

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