strangeandbouncy

reduce noise with more modern transistors?
« on: July 13, 2008, 06:11:54 PM »
My Pye TVT console is SERIOUSLY noisey.(mix bus noise of -44dB with 18 channels open, unity gain!) It uses BC108b and bc148 transistors. Might it be possible to lower the noise with, say bc548/550 or 2n4401 as BC108b replacement? Is there something suitable for bc148 replacement? i am way out of my depth here . . . . .

  Pye noise is NICE noise though, and "liveable with" if necessary, since desk is SO impossibly fat!


  Any advice will be most greatfully welcomed!



       Kindest Regards,


    ANdyP
. . . . RUH ROH . . . . .


reduce noise with more modern transistors?
« Reply #1 on: July 14, 2008, 05:47:19 AM »
Reason for the noise must be something else but the transistors. You should investigate it with a level meter to find out where it comes from.

strangeandbouncy

reduce noise with more modern transistors?
« Reply #2 on: July 14, 2008, 05:56:59 AM »
Hi,

   thanks! I will - eventually . . . .


    KIndest regards,


       ANdyP
. . . . RUH ROH . . . . .

strangeandbouncy

reduce noise with more modern transistors?
« Reply #3 on: July 14, 2008, 06:15:39 AM »
Actually I think that the noise might be endemic, due to enornmous amount of gain. Line is attenuated 40 dB, and then shoved through the mic amp, needing a further 25dB of attenuation from full gain, which i guess is about 65dBish . . . . So i am looking to try to reduce this. i don't think thaT anything is wrong, just noisy!
. . . . RUH ROH . . . . .

keefaz

reduce noise with more modern transistors?
« Reply #4 on: July 14, 2008, 09:09:11 AM »
Have you a link to console schematics ?
If you have inserts, did you try them as line input ?

strangeandbouncy

reduce noise with more modern transistors?
« Reply #5 on: July 14, 2008, 09:20:41 AM »
I would KILL for the circuit diagrams . . . . ! Inserts both pre and post fade are seriously low level, @ -20dB, though i haven't measured them. An SM8 owner i know told me that he tried pre sends, and when boosted to apropriate levels, they were very noisy too. Mix bus noise with all channels open [email protected] below digitaL zero on  -15fsd Protools. Mix bus noise with all channel faders pulled down is @-60dB below digital zero on  +15fsd Protools. mix bus noise with master faders down is @-70dB below zero on -15fsd Protools.

       Hisssssssssssss . . . . . !
. . . . RUH ROH . . . . .

strangeandbouncy

reduce noise with more modern transistors?
« Reply #6 on: July 14, 2008, 09:22:54 AM »
Inserts are prefade. ie post preamp and eq as far as I can tell, so not a lot of use as line ins . . .
. . . . RUH ROH . . . . .

JohnRoberts

reduce noise with more modern transistors?
« Reply #7 on: July 14, 2008, 09:33:31 AM »
To characterize mix bus noise, you need to measue with channels muted or full attenuated.

With 18 channels at unity you are hearing the channel or input noise too.

18 channels combined incoherently will increase the noise of just one channel a little more than 12 dB, so your mix bus appears quieter than your inputs.

You might want to focus on input electronics first. If inputs have very high gain, that will contribute to noise, so noise measurements should be normalized for gain.

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

strangeandbouncy

reduce noise with more modern transistors?
« Reply #8 on: July 14, 2008, 09:44:17 AM »
Thanks,

   i was just trying to illustrate the large amount of noise from the channels when you open up the faderz . . . .


    Kindest regards,


   ANdyP
. . . . RUH ROH . . . . .

PRR

reduce noise with more modern transistors?
« Reply #9 on: July 15, 2008, 01:53:52 AM »
If one channel is noisy, it could be a bad transistor. If they are all the same, and has mike transformers, the noise level is surely already within a few dB of the best a perfect amplifier could do, no swap is going to make a big difference.

I think you are just using it wrong.

> illustrate the large amount of noise from the channels when you open up the faderz . . . .

If it hurts, don't do that.

It probably was NOT meant to be run "all up".

My JBL sure as hell could never be worked all-up.

Put all the knobs DOWN. Put a high gain monitor amp on the main outputs and note the output stage noise. Now bring up the masters until noise barely rises. Nail it there! Now bring up one channel until the noise just rises. Put it down and bring up 4 channels together until the noise just rises. Mark those two settings: 1-ch and 4-ch noise rise.

When mixing, your highest faders should be in this range.

And with the masters set lowish, your insert levels are probably more rational.

Such mixers have a ton of gain for when you need it, but 99.9% of the time you do not need it. They normally work with lots of pot loss and unused gain.

> Line is attenuated 40 dB, and then shoved through the mic amp

That was very common. It does suggest that input overload is lower than a large condenser in a loud sound field.


strangeandbouncy

DOH!
« Reply #10 on: July 15, 2008, 06:16:17 AM »
Dear PRR,


    I didn't consider that the faders might be "holding" 10dB . . . .i took 0db at thr top of the fader literally. Doh! With channel and master faders holding 10dB each, Desk is as quiet as a mouse. - well a 35year-old mouse anyway! Doesn't sound quite as dynamic, but so sweeeeeet!  and no HISSSSSSSSSSSSSSSSSS!

     Thank you so much!


     Kindest regards,

 
        ANdyP
. . . . RUH ROH . . . . .

cannikin

reduce noise with more modern transistors?
« Reply #11 on: July 15, 2008, 12:36:13 PM »
Be careful and go slow.  I had the same issues with my raindirk 1973 console, more specifically the buss noise and hiss.  It was cumulative, one fader up, still usable -- two faders up, noticeable -- 3 or more faders up, poop.   In the end it was the a combination of old caps, bad grounding, oscillating ICs, dirty faders, not well regulated power supply and probably some things I know nothing about.   I couldn't fix it and so I had to be sent to a seasoned tech who could.

my suggestion start with the Power supply.

If you run into a scratch your head situation..... Give Cyril a call at Raindirk.  The nicest man and so knowledgeable -- sh*t he'll probably give a bunch of old parts for fun
Tube limiters..yum!

strangeandbouncy

reduce noise with more modern transistors?
« Reply #12 on: July 15, 2008, 07:30:41 PM »
Dear Cannikin,


   All's well now, thanks to PRR. I took 0dB on the faders too literally. Quiet(ish!) - Fine for a 35 year-old console anyway. I've used Neve's and Helios'es that were MUCH noisier. I am going to get it to a tech friend who seriously knows his stuff. As it is down @1dB at 30Hz and 16kHz, it may need some recapping. He sometimes replaces bc108s in Neves of similar vintage to reduce noise a bit, so I might not be too far off course after all!


     Over and out,



    ANdyP
. . . . RUH ROH . . . . .

pstamler

reduce noise with more modern transistors?
« Reply #13 on: July 15, 2008, 08:26:56 PM »
Also...many, perhaps most mic inputs are a lot noisier when nothing is plugged into them than when they have 150 ohms at the input.

Peace,
Paul


 

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