Gainclone is done

[fourspeed]

I finally got everything together. How does it sound? I don't know yet, because I have only tested it with my cheapo surround speakers. There is no hum, no pops.

The surround speakers are 8 ohm, and the actual speakers that the amp will drive are 4 ohm.

I measure DC offset of .3mv and .5mv with no source connected and the 8ohm speakers hooked up. I do not have an appropriate resistor on hand to use as a load. I hope the speaker is an acceptable load ????

Soon, I'll connect it to my Heresy II's and see how they like the amp. Then I'll bypass one speaker protection circuit and disconnect it from the power supply to compare the sound using a mono source.

Thanks to all who helped with my questions along the way.

Here are the obligatory photos. I didn't clean the case, what looks like scratches rubs off the anodized surface. Not to worry. Yes, that is heater hose. That's what happens when a car guy ventures into electronics!

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

 

[Greg Erskine]

I measure DC offset of .3mv and .5mv with no source connected and the 8ohm speakers hooked up. I do not have an appropriate resistor on hand to use as a load. I hope the speaker is an acceptable load ????

hi 4speed,

DC offset should be measured with nothing on the output and the input shorted. Normal LM chipamps without a DC offset nulling servo, will typically be 10 to 100 mV.

Nice build.

regards

 

[fourspeed]

Ok, preliminary test says: It sounds good, overall. A slight hum when connected to the Klipsch's. That MIGHT be coming from my Nakamichi surround receiver, which has begun to do some strange things. It's not going to be around long. So the preamp may be a factor. I'll investigate this.

Tested with some Nora Jones and Allison Krauss. When played loud, there is some occasional harshness in the vocals and higher piano notes. I realize this could be due to a whole raft of factors, though. Plus, the amp is not really "burned in" yet.

As far as bass, I think it's great! I've always leaned toward tight, controlled bass, though. I'm not a thump-thump fan.

Tomorrow I'll test with some old standbys like Money For Nothing. The wife and kid are asleep so I'll have to wait!

Oh, yeah, this is funny: On the Nora Jones CD, the acoustic bass caused a buzzing. I was kind of worried, but I looked for the source and ruled out the speakers. It turned out to be the amplifier case. The front panel vibrates against the frame. That was a relief. A bead of RTV will fix that right up.

Mark

 

[AndrewT]

Hi,
I echo Greg's advice.
Test the output offset with the input shorted and no load on the output terminals.
Then couple your source and remeasure offset with the source switched off.
Then remeasure the offset with the source switched on.
If all three of these conditions pass the maximum offset you are prepared to tolerate, then connect your speakers.

 

[frank1]

Hi and nice job.
It is really nice to see the heat-sink OUTSIDE the box where it should be.
It makes me cringe every time I see countless, otherwise well-made amps with huge heat-sinks INSIDE the enclosure.

Frank