Seventh Circle Audio

Okay... i finished the J99 and the power supply and everything measured out bang on with my DMM. Installed the op-amps and revved it up... still great... sounds super...

The only anomoly that i am getting is that there is a signifigant gain reduction when i flip the phase switch. The sound is good... just reduced in volume.

Any thoughts?

thanks,
greg

PS since i very rarely use the phase reverse on any of my preamps i am tempted to leave this bug as a 'feature' and just call it a pad switch... nevertheless i am curious as to what is going on.

Headphones?

http://seventhcirclestudios.com/SCA/phpBB/viewtopic.php?t=627&highlight=phase+headphones

hmmm...

interesting Randyman... thanks. i will try actually recording the output with the switch in both positions and see if what i am experiencing is this 'headphone' effect.

I did observe this while wearing headphones and singing.

This seems to make more sense as i could not understand why the phase switch should have any effect on the rest of the circuit as i assume it just flips the poles.

cheers,
greg

nope...

just checked it out and there is an actual descrepency between the regular output and the output with the polarity flipped.

any other thoughts?

I have the exact same problem with a newly built J99 as teleharmonic describes on this thread. Was there ever a resolution? It sounds great otherwise, but the volume drop when flipping the phase switch to the right is dramatic.

Thanks,

-Scott

Minimize the signal path, use a test signal and meters, not an open mike and headphones. We have never been able to duplicate this symptom here, and our AP shows any difference amplitude to be so close to 0dB as to make no difference. If you find a difference in amplitude in a controlled test, let us know.

I have a problem with phase flip as well, on 2 different preamps. I have 2 A12s and a J99. the J99 and one A12 have a significant volume boost when i flip phase to the right. This just happened suddenly. I built them about a week ago and phase flip worked fine, it just started acting funky today

Can you describe the signal path that produces the symptom?

Over the years, I am noticing that my pre's are getting more and more 'hissy'.

Going thru each pre to isolate any one that may be injecting psu noise, I started playing with my J99's. When I flipped the phase a HUGE drop in background noise occurred! Amazing! And to think for years I've been using these pair for makeup gain for a passive mix bus. Hundreds of song mix downs, and had I inverted phase switch I would have seen a reduction in noise. It's made me pretty sad and astonished.

Both J99's have the same effect. I tested each of them in mono with and w/o headphones.

Has anyone figured out what could be causing this? Thanks.

Can you describe the signal path that produces the symptom?

Mic Pre In: nothing
Mic Pre out: XLR to Mains

Mic Pre In: nothing

You must terminate the inputs with a low impedance (<=150 ohms) to make a meaningful measurement.

I actually have experienced a noise or hum, or buzz on my N72, that was resolved with a flip of the phase switch....

Just thought that this could be related to what you guys are talking about, even though it's a different module, of course.