Anyone make a preamp / compressor combo unit?

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mayfly
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Joined: Thu May 19, 2011 1:35 am

Anyone make a preamp / compressor combo unit?

Post by mayfly »

Hi Folks,

I'm new, so please take it easy on me. I am interested in taking some of the fine JLM modules and creating a single RU preamp / compressor combo unit. That is, I'm looking for one good channel. Intended use is recording female voice and violin, likely with a Neumann TLM 102 mic. The signal path that I'm considering is:

Neumann -> preamp -> compressor -> apogee digital interface -> Mac running logic.

The compressor would naturally be the MAC, but the preamp I need advice on the best for the application. BTW, a past recording of the subjects can be found at this link:

http://www.cornflowerbluemusic.com/Seco ... %20Lot.mp3

Is this something that has been done?

Thanks and best regards,

Trevor

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Joe Malone
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Re: Anyone make a preamp / compressor combo unit?

Post by Joe Malone »

mayfly wrote:Hi Folks,

I'm new, so please take it easy on me. I am interested in taking some of the fine JLM modules and creating a single RU preamp / compressor combo unit. That is, I'm looking for one good channel. Intended use is recording female voice and violin, likely with a Neumann TLM 102 mic. The signal path that I'm considering is:

Neumann -> preamp -> compressor -> apogee digital interface -> Mac running logic.

The compressor would naturally be the MAC, but the preamp I need advice on the best for the application. BTW, a past recording of the subjects can be found at this link:

http://www.cornflowerbluemusic.com/Seco ... %20Lot.mp3

Is this something that has been done?

Thanks and best regards,

Trevor
Since the female vocal has good solid body (low mid) to it, the best would be BAD built as Dual99v (OEP/VTX with 2 x JLM99v) but it you do not need the 75dB Gain then the BA with OEP/VTX and 1 x JLM99v. Both I would build with variable impedance so the high airy bright part of the vocal can be balanced with the body (low mid) without any other EQ. Also this would be a great mic pre for most acoustic instruments and general all rounder with the variable impedance.

I have seen several home grown BA BAD and MAC combo's now but if there is enough interest we could run some rack cases and/or front panels with the Dual99v or BA mic pre on the left of a rack and the MAC on the right of the case fairly easily.
Joe :-)
JLM Audio
Capturing Audio without Injury

mayfly
Posts: 2
Joined: Thu May 19, 2011 1:35 am

Re: Anyone make a preamp / compressor combo unit?

Post by mayfly »

Hi Joe,

Thanks very much for your reply. Regarding front panels for this configuration, please consider me as an interested party! In the mean time, my intention is to order a front panel cut for two BAs and then modify the right hand side as appropriate for the MAC. Do you see any issues with this plan?

Trevor

awguitars
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Joined: Sun May 23, 2010 8:05 pm

Re: Anyone make a preamp / compressor combo unit?

Post by awguitars »

Hi joe.

I was thinking the exact same thing. Only i was thinking of building a dual BA/MAC into a single rack unit.

My main question is how to power the unit.
I was considering buying a larger SMPS and building it into the unit. If this works how do i setup the power supplies to the 4 units?

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Holger
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Re: Anyone make a preamp / compressor combo unit?

Post by Holger »

Q: Anyone make a preamp / compressor combo unit?
A: Yes, me. Built it for a local musician for his home studio. He wanted a dual pre/compressor unit, I left out the first PreAmp because he decided to buy a tube preamp for his voice channel, so this is a one PreAmp/two compressor unit with an option for a second PreAmp. Panel is white powder coated. BA with Lundahl and 2604, no O/P transformer, compressor with Joe's 1:1:1 transformer wired for second parallel output.

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Joe Malone
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Re: Anyone make a preamp / compressor combo unit?

Post by Joe Malone »

awguitars wrote:Hi joe.

I was thinking the exact same thing. Only i was thinking of building a dual BA/MAC into a single rack unit.

My main question is how to power the unit.
I was considering buying a larger SMPS and building it into the unit. If this works how do i setup the power supplies to the 4 units?
2 x MAC and BA could work running on a 48v SMPS but would be confusing and for advanced builder only. Easiest and probably the best is to do it as Holger has done with a AC/DC kit .

Great looking layout Holger :-)
Joe :-)
JLM Audio
Capturing Audio without Injury

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Holger
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Re: Anyone make a preamp / compressor combo unit?

Post by Holger »

Thanks Joe.
I've recently went to a local EE audio company to get some test results for the combo unit.
The BabyAnimal has an EIN of -117 dBU at max gain, 20-20000 Hz, 150 Ohm terminated. This is, IIRC, 10 dBu worse than the theoretical possible EIN of -127 dBu.

Here's the AP plot for the BA (Lundahl 1538 jumpered 1:2,5 (IIRC), 2604, no output transformer) at 34 dB gain.

Image

Here at 56 dB (full) gain:

Image

Here's a plot for one of the compressors at uni gain, no GR, 2 x 2604, Joe's 1:1:1 output transformer. Maybe Joe has an explanation for the THD+N curve.

Image

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Joe Malone
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Re: Anyone make a preamp / compressor combo unit?

Post by Joe Malone »

Holger wrote:Thanks Joe.

Here's a plot for one of the compressors at uni gain, no GR, 2 x 2604, Joe's 1:1:1 output transformer. Maybe Joe has an explanation for the THD+N curve.

Image
Yes that is why we do not recommend driving JLM111DC (or any output transformer) with anything other than a discrete opamp or hybrid or our V8 that can drive 50R to 75R. As the low output impedance and drive current is needed with the correct output resistor to minimize and control the saturation of the output transformer to as low a frequency as possible. Using the a dual opamp in the dingo will double this effect as differential OPA2604AP outputs can only drive 1200ohm load. Plus the 2 x 51R output resistors which is 2 high for the JLM111DC to be controlled. So the THD lift will start higher. Using a 990 footprint opamp and output resistor between 22R and 51R the rise point for the THD should be able to be reduced down to starting to rise at 100Hz to 200Hz. This rise is output level dependent so will get better with lower level and worse with higher level. Also in music this level is lowest as it is not being constantly saturated by a pure tone.

The THD rise will look like the one in the first graph of the BA where the THD rises due to the 1538 core saturating due to the higher input level at the input due to the low gain setting.

Douglas self has some great examples in his reference books of dip type opamps driving sowter and other brand transformers that look exactly as your graph above for same reasons as I explain above.

There is another THD that will also happen if the opto has done some gain reduction in the last 60 seconds (even when gain reduction is now off) but this will show as THD in the higher frequencies.
Joe :-)
JLM Audio
Capturing Audio without Injury

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Holger
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Re: Anyone make a preamp / compressor combo unit?

Post by Holger »

Thanks for the explanation. It was my first assumption that the plot is a result of using an 2604 here. Will exchange them with DOAs.

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