[mfaughn]

I just received a second-hand EF1 modded with a kit from Hi-Flight. The essential aspect of this mod is really just replacing the stock opamp with a brown dog type adapter holding dual AD743. I notice a definite and audible distortion (crackily and fizzy on peaks). Each channel seems to be producing distortion in the other channel. To test/discover this I used an EQ to input only to one channel or the other. When I EQ out the left channel so that only the right channel is being fed a signal and then crank up the volume a bit it clips in the left channel. It also does not seem to produce distortion in the right channel (the one actually playing music). It does it the other way (left to right) also. So, when I run both channels I get clipping in both channels but in each channel it is caused by the other channel...make sense? More volume results in more distortion. The distortion manifests well below volume levels that would be considered unsafe listening volumes.

I thought at first that it was subsiding as the amp warmed up but now I'm not so sure. There is enough distortion to be REALLY noticeable and unpleasant.

I tried this while both feeding the amp a low signal and cranking its gain and also feeding it a high level signal and using the amps gain set low -- problem exists both ways.

The problem is also more noticeable/prevelant with DT150 than with HD650. A bit surprising as this is just 250ohms vs. 300ohms. Haven't tried it with anything else yet.

I've tried swapping tubes to no avail. I'm going to try putting the stock opamp back in and see how that goes. Any other ideas for diagnosis etc..? If I can't get this resolved the amp will be unusable as far as I am concerned.

Thanks,
Michael

 

[Tridacnid]

Your EF1 uses a double triode tube, correct? Do you have any tubes to switch it out with? You may be getting some crosstalk between channels in what may be a faulty tube.

OR

You may have a bad solder job on the mod.

 

[AmanGeorge]

If I'm being dense and vastly underestimating your intelligence, I apologize, but I had some distortion issues when I first got my EF1 and freaked out for 15 minutes or so before I realized I just hadn't gotten the tube securely in and just needed to push and jiggle it a little harder.

 

[mfaughn]

Well, thanks for the suggestion. I have tried two different tubes, twice each. I am pretty darned sure that I didn't have them poorly seated four times in a row. The tube in there now is seated as good as it is going to get. I just left it playing for a couple hours to see if it got better after getting good and warm. No change, still sounds bad.

-Michael

 

[mfaughn]

update: swapped in the stock opamp and distortion is gone. problem is that stock opamp doesn't sound anywhere near as good as the ad743 pair (excepting the clipping/distortion).

Anyone else ever have issues with this cross channel distortion?

update 2: hmmm, i edited once and wrote this already but it didn't show up...so, again the run-down. tried different circuits in the house, different sources. no luck. removed and reseated the adapter with AD743. the adapter hadn't been seating well so I piggy backed it on an additional dip socket. no luck there either. swapped in an LM4562, again problem disappeared. So, with the dual AD743 I get problems, with either the stock opamp or the LM4562 there is no problem. Next to try a new brown dog and/or two new AD743. Kindof a bummer because this isn't exactly cheap or easy to source AD743.

-Michael