Amp Syncing Issue

[mgriggs]

What would cause an amp to all of a sudden start sending a signal at a higher pitch and a faster speed?

 

The System: Base System Dell PC w/ SFX 5.60 build 24 -> echo gina 24/96 -> a&h wz14:4:2+ --- Amps ---> mackie fr series m1200 -> 2 ev sx300's

---> mackie fr series m800 -> 2 apogee acs-1's

---> DBX 1231 Graphic EQ (functioning as a gate above 100hz) -> tapco j1400 -> JBL SR4725

Everything has worked just fine. I played an effect that comes through all 5 speakers and it sounded fine. I stopped it, adjusted volumes in SFX, then replayed and the sound was out of sync. After a lot of system testing, the mackie m1200 seems to be sending the signal at a faster rate and at a higher pitch than the others. This literally happened out of nowhere without anyone touching the amps or system configuration.

 

Any insight into what is happening would be wonderful. Thanks.

 

[Bobbsy]

Er, probably nothing. Speed/pitch issues are generally caused by a mismatch in terms of sample rate, for example playing tracks recorded at 48kHz at 96kHz.

 

I'd be checking farther upstream in the computer/sound card area.

 

Bob

[tolley1466]

This happened to me when I was recording once, either the desk or the multi-track recorder was set to a higher bit rate and I got a faster and higher pitched song. Was only a shift from 44.1kHz to 48kHz but it was noticable.

 

Or (a long shot) could it be anything to do with power and the frequency??

[cedd]

Or (a long shot) could it be anything to do with power and the frequency??

Very long shot! Nope it couldn't! Amps are DC beasties, hence the huge torroidal transfromers in most analogue ones.

 

I'd doubt very strongly that this problem has anything to do with the amplifiers at all. Check your sample rates.

[J Pearce]

OT, but whats a torroidal transformer got to do with dc? Bridge rectifier and smoothing caps are the magic ac-dc devices.

[cedd]

Yeah alright alright!

So the torroidal actually just gives a lower AC voltage and then the rectifier and smoothing gives you DC. BUT what I was driving at is that the power supply as a whole is a big lump which makes the amp heavy (I'm not even going to start on the light weight switchmodes and how they work!).

The point is this, that big lump (including transformer, bridge rectifier and smoothing caps) is there for the express purpose of giving you DC, so mains frequency won't be an issue.

[J Pearce]

Pedant satisfied :P

 

I concur with everyone else, this frequency fault is almost certainly coming from the playback device. However, just check you don't have any effects unit in circuit that could be running a phaser or pitch shift effect.