convenient little amplifiers

[Opcom]

These things turned up in a search on MCM Electronics. Wouldn't they be interesting to put in a small or bookshelf speaker enclosure for listening with certain BA gear that does not have a speaker output?

http://www.mcmelectronics.com/product/KEMO-ELECTRONIC-M031N-/28-6400

[W2PFY]

Perhaps these could be used to drive a class B amp? On the first page I see amps that go up to 18 watts and one looks to have a RCA plug on it. Al you would need is an audio transformer hooked in reverse to drive the grids. I haven't looked at the spec's yet and who knows if they are RF proof but it was a good find!

This looks very interesting for the above.

http://www.mcmelectronics.com/product/28-6411&cid=prodCrossSell

 

[steve_qix]

3.5 watts into 4 ohms.  Still, very interesting!

Thanks for the link!

[Opcom]

They also sell a 4 ohm to 70V transformer rated 100W and a several smaller ones. For a line to speaker transformer, the lower the wattage rating the higher the turns ratio. How much peak volts needed for the modulator?  I have driven 6146's in AB2 with a line to VC transformer very well with a 12W 4 Ohm amp for the source. The voltage ratio was what was needed, not much power.

turns ratios for a 4 ohm to 70V trans. of various wattage ratings:

watts rating - voltage ratio - turns ratio
100W - 20V to 70V - 1:3.5
50W - 14V to 70V - 1:5
20W - 8.9V to 70V - 1:7.8

The 70V sides don't seem to be tapped on them, but a voltage divider for a CT might work if it had a low resistance compared to the grid-grid load.

[steve_qix]

Now you're into a transformer, and anything except AB1 or A presents a nonlinear load to the driver    Going through a transformer into a nonlinear load, unless the transformer secondary is HEAVILY loaded, will cause the usual distortion in the grid waveform.

[W2PFY]

3.5 watts into 4 ohms.  Still, very interesting!

Thanks for the link!

The review on this amp aid it was very distorted on all frequencies below 300 Hz.

[Opcom]

Possibly a smallish output cap. Unknown test conditions but who is to argue? I did not find the real specs on that one but 3.5W is very loud through a 4" speaker.

[W4AAB]

I saw another amp with 40 watts single-ended output, and for no much more than the 18 watt unit. Cheap modulator, maybe?

[Opcom]

That was my point. Not very costly and a module is always convenient. The subwoofer amp made me look at the plywood ottoman I bought last week at wally world. (American made). The thing has rather thin padding but is OK. The top comes off for storage but it would not be hard to screw it on, and the furniture has little 1/2" feet. An 8" sub mounted downward in there might improve the PC speaker situation. I was thinking of upgrading the PC speakers to a real stereo setup anyway.