Which preamps to build?

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Paul
Posts: 30
Joined: Sat Mar 24, 2007 5:16 pm

Which preamps to build?

Post by Paul »

Hello all,

Ive built my first jlm baby animal pre amp and have it running and I am very pleased with the results (understatement).

The initial pre i built used the OPA2604 & JLM14 combination. Now I'd like to build a few more. The pres are to be used for the standard reqordings - drums, guitars, bass and voice. For drums I will be building 2 matched pres.

Any comments on which opsamp/transformer combos for certain applications and their characteristics would be great.

Can anyone let me know what the advantages of using the jlm input transformers are?

What does variable impendance give when using a pre?

For the time being I will be concentrating on only building baby animals, however down the line i'd love to try out the 99v and and the 1290 so any comments on these is also welcome.

thanks

paul

chrisp
Posts: 184
Joined: Sun Mar 04, 2007 11:46 am
Location: Sydney, Australia

Post by chrisp »

Lots o'questions - I'll just report on the variable preamp side.

The sonic effect of variable impedance, in very broad terms, is that higher impedance passes more high frequency sound but less signal level (I think I got that the right way around).

Whether or not this effect is worthwhile (or even noticable) depends on the mic and the preamp configuration. I have it on my 1:4/99V BA's and yes, for most mics (but not all to the same extent) the variable Z can act as a sort of low pass shelving EQ filter. In fact I have a vari-Z switch on a couple of my tube mics as well (nod nod wink wink and thanks to JLM for the MC03 mod).

For some mics, the effect is very musical and useful: you get more functionality out of the one mic. For other mics, the impact is simply not that great. However, it is SO easy to implement on the BA that I can't think of any great reason not to do it unless you are really sure you'll never need it.

HOWEVER, the impact also varies depending on the input tranny: I think I recall Joe saying the vari-Z impact was best through the JLM14 and less impressive through some other input trannys

Good luck with the projects
Chris P
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I do lots of things. I believe eclectic skills are best.

Paul
Posts: 30
Joined: Sat Mar 24, 2007 5:16 pm

Post by Paul »

thanks chris. makes some sense to me now.

To get the ball rolling on the mic pres, im looking at building a matched pair for overhead mics to use with drums. Anyone using baby animals for overheads and do they have an opinion on the opamp/transformer combo they recommend?

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