Stereo 35w + 35w hybrid valve/tda7376b audio power amplifier

[nigelwright7557]

35w + 35w into 4 ohms.
Have a couple going spare.
Requires valve (12au7 or 12ax7), heat sink and +/-18v power supply.
£19.99 each + p+p
p+p is £4-20 to UK and £12.99 Europe and £17 rest of world.

 

[mctavish]

I would be interested in a pair. Do you have a schematic also available?

 

[nigelwright7557]

When you say "pair" do you mean one stereo pcb or two stereo pcb's ?
If you buy I will include circuit diagram.
Regards Nigel

 

[mctavish]

2 Stereo pcb's. Ok, great, I will send you a pm. Thanks!!

-Mac

 

[nigelwright7557]

I would be interested in a pair. Do you have a schematic also available?

I also have 2 mono pcb's if you would prefer.

Circuit is pretty basic, cathode follower valve stage into TDA7376B stereo chip amp. It uses negative supply and positive supply for valve B+.
Heaters are dropped off positive supply.
Requires +/-18VDC at 100VA.
Heatsink for TDA is also required.

 

[mctavish]

Is the mono version just a bridged stereo?

or a different circuit altogether?

 

[nigelwright7557]

The mono version is just a single channel TDA7294 chip amp.
Uses just one half of valve.

The stereo version uses a stereo TDA7376B chip amp.
Uses both sides of valve in stereo mode.

 

[mctavish]

Ok, thanks. I think the stereo will suit my needs better, I will respond to the PM.

Thanks!

 

[ollyboyd]

Hey Nigel, any recommendation on a suitable (preferably low cost) power supply for your board?

 

[nigelwright7557]

Use a traditional transformer, bridge and smoothing capacitors.
It has two 1000uF caps on the pcb plus valve heater so a SMPS tends to complain as power up surge can be quite high.
0-12 0-12VAC 100Va transformer should be fine to get +/-18VDC.

 

[nigelwright7557]

Hey Nigel, any recommendation on a suitable (preferably low cost) power supply for your board?

I dont think you can get low cost power supplies now.
Transformers are expensive and SMPS isnt so cheap either.

On my JLH1996 I used a £10 20 watt SMPS and that works fine.

The hybrid valve amps I have designed seem to upset SMPS.
When I tried the 20 watt SMPS with my TDA7376B hybrid amp the power rails bounced a few times on power up. Even with a separate supply for heater it still clicked a few times through the speaker.
The 1000uF caps on the amp upset the SMPS and the valve heaters are low Z on power up so dont help.

 

[mctavish]

Would a 22v. power supply be too much for these?

thanks

 

[nigelwright7557]

Yes The TDA7376B max supply voltage is 18 volts.
The pcb needs +/-18vdc, the -ve rail is used by the valve.
Regards Nigel

 

[nigelwright7557]

Built up another couple today on my spare pcb's.

 

[nigelwright7557]

Only 2 left.