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Old 26th March 2012, 03:37 PM   #1
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Question Onboard Bass compressor?

Hi!
I'm looking for a Compressor that can run off a single 9 volt battery, sounds really good with bass, and does not use any (hard to get or expensive) ICs only opamps and transistors and has a variable attack /release.
Something simple, low parts count would be the best because i don't have much space in my guitar, there is already an active EQ an a balanced line driver inside.

I understand the basic principles of different compression methods(FET as variable resistors and LDRs), but i'm no engineer to design my own

Any help or tip are very much appreciated !
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Old 28th March 2012, 06:13 AM   #2
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anyone?
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Old 28th March 2012, 11:57 AM   #3
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Would something that utilizes an optocoupler be out of the question for you?

If you find john hollis's flatline compressor, you have all you need! It just so happens that I am working with it on the breadboard right now, so I'm familiar with it.

IF you make the op amp a CMOS type that can swing rail to rail (for max headroom) such as the 2272...and if you make the gain stage invertering, rather than non-inverting, you can get the compressor to ATTENUATE on peak transients, as well as amplify a decaying signal. Wire as stock, it's still good, but it will only be able to drop to 'unity gain' on peak transients, meaning less headroom leeway. Depends how much squash and headroom you want.

The original schematic calls for a LED/LDR combo, but that's just the DIY approach to optical component fabrication. Available LDRs are quite slow in response to effectively attenuate a guitar's attack, let alone a bass. That might work well if you want something with very subtle compression - borderline no compression.

As a counterpoint, the VTL5C6 or VTL5C6 are expensive parts but work fantastic in this scenerio. the Silonex NSL-32SR3 is another part that has specs which suggest it would do quite well here - and has the added benefits of being far more compact than the Vactrol type as well as more affordable. I have two on hand and have been meaning to see how they perform in the circuit; I've heard good things but can't offer direct experience.

But oh yeah, it doesnt have attack-release times. What you're asking for is a tall order - easy to do in a stombox, but onboard, a real tought thing to do. If you'll have nothing but the best, power a THAT 4301 chip with bipolar rails and away you go...the carl martin compressor uses it as do $$$$ rack units, that are all mostly just duplicating the datasheet/appnote circuit and tweaking component values here and there.
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Old 28th March 2012, 09:18 PM   #4
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Join Date: May 2010
Hi

Thanks for the answer
I indeed find the "flatline compressor", but a lot of comments said that it doesn't sound very good on low frequencies on a guitar.
And I have a 5 string bass , it goes down to almost 30hz.

The problem is that i can't get any of those opto isolators here
I don't need any lower gain than unity, i use single coil pickups and they have a very weak output
I would like something that is very fast, because i want to use it mostly for slapping parts
I have been looking at this one:
Fast Audio Peak Limiter (Figure 2 )
It possible to set attack and decay time with this one ( just a switch to toggle between fast mode for slapping and slow mode for finger style)
But with lower voltage and single supply, and i don't really know what needs to be changed.

Quote:
Originally Posted by Liquids View Post
Would something that utilizes an optocoupler be out of the question for you?

If you find john hollis's flatline compressor, you have all you need! It just so happens that I am working with it on the breadboard right now, so I'm familiar with it.

IF you make the op amp a CMOS type that can swing rail to rail (for max headroom) such as the 2272...and if you make the gain stage invertering, rather than non-inverting, you can get the compressor to ATTENUATE on peak transients, as well as amplify a decaying signal. Wire as stock, it's still good, but it will only be able to drop to 'unity gain' on peak transients, meaning less headroom leeway. Depends how much squash and headroom you want.

The original schematic calls for a LED/LDR combo, but that's just the DIY approach to optical component fabrication. Available LDRs are quite slow in response to effectively attenuate a guitar's attack, let alone a bass. That might work well if you want something with very subtle compression - borderline no compression.

As a counterpoint, the VTL5C6 or VTL5C6 are expensive parts but work fantastic in this scenerio. the Silonex NSL-32SR3 is another part that has specs which suggest it would do quite well here - and has the added benefits of being far more compact than the Vactrol type as well as more affordable. I have two on hand and have been meaning to see how they perform in the circuit; I've heard good things but can't offer direct experience.

But oh yeah, it doesnt have attack-release times. What you're asking for is a tall order - easy to do in a stombox, but onboard, a real tought thing to do. If you'll have nothing but the best, power a THAT 4301 chip with bipolar rails and away you go...the carl martin compressor uses it as do $$$$ rack units, that are all mostly just duplicating the datasheet/appnote circuit and tweaking component values here and there.
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