AWA Vari-mu limiter

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squib

Well-known member
Joined
Jun 5, 2004
Messages
244
Location
Australia
I've just finished this restoration job and thought some might be interested in checking out this project.
http://www.proharmonic.com/awa.htm
 
I have the orginal schemo, but will ammend with the circuit changes I made and post in due course!
 
You are talking about polypropilene caps....i wonder what was before...hope not "ugly" paper-oil :wink:
 
There was an interesting post over at Turtlerock mastering a while ago regarding AWA limiters.

http://iggy.triode.net.au/forum/read.php?f=11&i=34&t=34

How does yors fit in with this info, Squib?

Peter
 
what a big project, contrats!
this is the 1st time I see a feedforward varimu design...
I´m very curious how it sounds...

steff
 
not sure why you are having trouble logging into my web site...try again, let me know if the problem continues.
So far i've only listened to it in the workshop with my test disc of raw drums, bass, vocals etc. It sounds pretty fat and can limit very hard whilst having a level of transparency about it. This afternoon i'll lug it up to the studio and see how it shapes up on a few sessions.
I'll report back!!

The approx transformer ratios are as follows T1 1:1, T2 1:100, T3 2.5:1, T3 10:1. Didn't measure T5!

The feed forward is interesting and the "hardness" of the limiting is affected by both the input level control and the threshold control, which determines the gain of the side-chain amplifier.
I should do some dynamic tests to show this....stay tuned!
 
not sure why you can't get the website?

Sorry guys lack of sleep has lead to a screw-up of those turns ratios!!

Try again ..... T1 1:1, T2 1:3.16, T3 1.25:1, T4 1.4:1 ie 0dB, +20dB, -4dB, -10dB

I've posted some pics of the Attack and Release performance
 
sorry guys...can someone educate me about expressing turns ratios of transformers? I thought that the ratio was expressed as the square root of the voltage gain ie +20dB = gain of 10, so ratio is square root of 10.
Back to electronics 101
I took the AWA into the studio yesterday where an album was being mixed and we put the AWA over the main vocals, replacing the combined 1176 and Distressor that was being used, a quick tweak of the knobs and the producer said "This is it...I like it" and continued mixing. It seems to slam the level very hard, whilst still retaining some dynamic feel ?? Does that make sense? More reports to follow!!
 
Turns ratio is equal to voltage ratio.

Voltage ratio (and therefore turns ratio) is the root of the impedance ratio.

Easier to express/determine the voltage/turns ratio then square it to get the impedance ratio...

Keith
 
Just power down unit.
Pull the tubes
drive the low z side with a audio generator.
Set it for 1Khz
measure the audio level at the transformer
measure the level on the other side
record both the numbers.
Divide one into the other.
That is your ratio.
 
The other switch positions measure the plate current through each valve.
This isn't essential, but harks back to it's broadcast origins and decided to keep this feature for funk value. It does have a use in balancing the vari-mu tubes V1 and V2 for lowest distortion.
I'll check out the specs of T5 when it comes back....if it comes back!!
 

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