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Old 4th February 2011, 12:10 AM   #1
wdcw is offline wdcw  Australia
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Default Valve Compressor Circuit

Could someone help with a relatively simple Valve Compressor Circuit-Schematic, It's for Guitar.
I have done a bit of a search but didn't have much luck.

I would like to try one.

Thank You
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Old 4th February 2011, 01:31 AM   #2
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Here's one. It's a conventional AGC-type circuit. To make it work really well will probably require a remote cutoff pentode, but there are a lot to choose from, and they're not audiophool expensive either.
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Old 4th February 2011, 03:40 AM   #3
wdcw is offline wdcw  Australia
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Thanks Miles,

I think I have just got something to work with a small Pentode, I have attached a picture of a simulation signal that is the same as I get on my O-scope with a sinewave at the input.

Is this what is refered to as a compressed signal with the peaks compressed a little?

Or is this just symetrical clipping or are they one & the same thing?


Thanks
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Last edited by wdcw; 4th February 2011 at 03:54 AM.
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Old 4th February 2011, 03:53 AM   #4
RTF671 is offline RTF671  United States
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Yes, but that's a very little amount. You will need more than that to be able to compress the signal more before the effect is even noticeable.
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Old 4th February 2011, 03:57 AM   #5
wdcw is offline wdcw  Australia
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Thanks RTF671,

I see what you mean, so the idea is to compress it more but without clipping the signal is that correct or is ok to have some clipping as well.

If I have it right when the signal is clipped the peaks are sort of flattened out--correct?


I had it compressed a lot more but convinced myself that it was clipping the signal & wasn't sure if that is what is required?

Last edited by wdcw; 4th February 2011 at 04:01 AM.
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Old 4th February 2011, 04:07 AM   #6
wdcw is offline wdcw  Australia
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More like this?
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Old 4th February 2011, 04:19 AM   #7
RTF671 is offline RTF671  United States
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Yes that is more like it

What is that running on?
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Old 4th February 2011, 04:55 AM   #8
wdcw is offline wdcw  Australia
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Thanks RTF671,

Now I get the Idea

I use LTspice, I find it very close to what I get when I build the Circuits, I designed & built a fantastic little pentode frequency doubler as well that sounds fantastic with no adverse effects to date.

Thanks for the help once again.

Cheers.
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Old 5th February 2011, 12:15 AM   #9
jjman is offline jjman  United States
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Compression and clipping are not the same thing to me. Compression would not cause clipping. However, clipping causes compression.

Compression is where increasing the input by X% increases the output by less than X%. It's represented by this type of graph. The 1:1 is not compressed whereas the others are compressed.

Click the image to open in full size.
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Old 6th February 2011, 03:06 PM   #10
DF96 is offline DF96  England
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Yes, my understanding is that clipping and compression are quite different. Clipping distorts the peaks, compression does not. If I show you a clipped sine wave you can see the effect. A compressed sine wave looks exactly the same as an uncompressed sine wave, only smaller. To see the effect of compression you have to look at the whole music waveform - then you see that the volume peaks are smaller and the quiet bits are louder.

Clipping chops the top and bottom off the signal. Compression is like an invisible hand riding the volume control slider up and down.
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