Turn-off Pop in class-d amps

[KT]

OK, so the pop doesn't happen when I turn the Charlize or SI off. Rather, I get this pop when I turn off the tube preamp that's right in front of my class-d amps.

Oddly, I only get the pop when I use bypass caps tied to the output caps in my tube pre. Right now I have a 3.3uF Auricap paralleled with a .22uF VTV Ultratone per channel as output caps. When I experimented with just running the Auricaps with no bypass, there was absolutely no turn-off pop. Anyone know why this happens?

Incidentally, the turn-off pop sounds identical to the loud pop that you hear when you power up a Charlize. Or a SI that has a bigger input cap installed, for that matter.

Also, I'm assuming that if I have these output caps on my preamp, I can do away with the input cap on the SI.

I've actually tried it, running the signal from the SI's RCAs into a 22k ohm Riken (normally there would be a 2uF cap in front of the Riken) which then goes to the input of the chip. Sounds good after a day of play. The tube pre really mellows out the slightly strident quality of the SI and adds body.

I had basically given up on the SI after the Charlize came out, but with the tube pre the SI sounds smooth but still has a fast, quick, clear, and surprising quality that's a nice alternative to the more balanced sound of the Charlize. I'm going to burn in the SI further to see if it's worthy to stay in the system. Could be that the captivating quickness and clarity of the modded SI will become tiring - we'll see.

Thanks,
KT

[bachiano]

Turn the preamp first and let it charge up two minutes - then turn on Charlize or SI.
Reverse the order when turning off - Charlize first then the Preamp.

Bachiano

[KT]

Thanks, Bachiano.

I've been using my amps with a battery supply that has a built-in monitor/charger that charges the battery when it needs it automatically. Because of this, I set up my amp to be on all the time. It's worked fine, so far, but now that this popping issue has come up I've added an on/off switch to the DC power line. I think this will solve the pop issue.

Best,
KT

[phase_accurate]

This problem isn't class-d related indeed. It would happen with every power amp that is on all the time.
Instead of switching the power supply you could also short the input to ground (maybe you should take care about what is considered ground in this case) i.e. something like a standby switch.

Regards

Charles

[KT]

Hi Charles,

The thing that has me flusters is that I don't get this turn-off pop when I drive a Gaincard (powered up all the time) or Chord power amp with the same preamp. Don't know why.

Also, when I use just the 3.3uF Auricaps as output caps in the preamp there is no turn-off pop. I only hear it when I also have .22uF bypass caps attatched to the 3.3uF Auricaps. I've tried VTV Ultratones, Jupiter beeswax, and Dynamicaps in the bypass position and use of any results in the turn-off pop.

I have no issue with preamp turn-on noise as the pre has a relay that connects the circuit only after the tubes have been on for about 30 seconds or so.

I don't think it's a fault of of the class-d amps - maybe just a grounding issue between the two components or something?

It's not really a big deal, but just something that I've never observed in my system before. Thanks for your advice.

Thanks,
KT