rascalseven

I'm racking a bunch of PM1000 channelstrips and am wondering what to do (if anything) with the 0.47uF tants that couple the preamp stage to the eq and the output of the channel fader into the line amp that drives the busses/routing.  I haven't yet recapped the channels, which I plan to do, but I've wired up a few, and I've noticed that the LF could use a bit of improvement, which perhaps the recap alone will help.  But I can't help feeling that 0.47u seems a rather small value for these two caps, no?  I was wondering if there is a reason NOT to change these to something like 10 or 22uF instead?  I'm new to the PM1000 circuit, so I'm wondering if there is something obvious that I'm missing here.

Here's a schem:



FWIW, I already changed the line output cap (c37) from 33uF to 220uF to drive a 600:600 output transformer, and still the LF is lacking a bit.  Thoughts??

Thanks, and peace,

JC
« Last Edit: August 16, 2009, 08:27:21 PM by rascalseven »
"If you dig the gig, do it. -But listen to the signal, not the person talking."  -Keef


MartyMart

Re: Yamaha PM1000 channelstrips..... tantalum caps -- increase value?
« Reply #1 on: August 17, 2009, 06:06:56 AM »
It depends on the whole R/C network, for example a 0.1uf ( 100n ) cap with 100K ohm input impedance
gives a 3 dB attenuation at approx 16Hz and 9 dB at 8 Hz !
So your 0.47uf ( 470n ) cap is not looking very small. ( depending on what's in front and behind it )
I'm sure that the Yamaha techs are not idiots and have chosen those caps for a reason.
You may well induce "motorboating" or other nasty artifacts if you go towards the 10uf area !

I'm not a genius and perhaps some will "chime in" but why not try just doubling the value to 1uf
and see what happens within this circuit ?

Peace,

Marty.


"Success is the ability to go from one failure to another with no loss of enthusiasm"

RuudNL

Re: Yamaha PM1000 channelstrips..... tantalum caps -- increase value?
« Reply #2 on: August 17, 2009, 07:43:40 AM »
As long as the input impedance of the stage following the 0.47 uF capacitor is high enough, I don't see a real problem.
Increasing the value of this capacitor may have a disadvantage: it will take longer for the capacitor to charge, resulting in a longer time before the following stage is correctly biased.
There is a solution for every problem!

http://www.vansteenisaudio.nl

rodabod

Re: Yamaha PM1000 channelstrips..... tantalum caps -- increase value?
« Reply #3 on: August 17, 2009, 10:41:07 AM »
What sort of -3dB point are you getting, and how steep is the roll-off?
Quote from: tv
punchy fat bastard chip

rascalseven

Re: Yamaha PM1000 channelstrips..... tantalum caps -- increase value?
« Reply #4 on: August 17, 2009, 01:25:07 PM »
I'll recap the modules first (leaving the interstage tants alone for now) and do some listening and measurement tests.  Will report back after this.

Thanks, guys,

JC
"If you dig the gig, do it. -But listen to the signal, not the person talking."  -Keef


 

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