Topic: DIY preamp for Edirol R-44

[nOrD]

Hi all,

I would like to extend my gear with a good quality preamp but do not have enough money to buy a Sound Device, for instance. I have some knowledge in electronics, mainly analogue audio and has built some amps, circuits before.

What I would like to realize is a quiet linear portable amp with two balanced I/O, switchable phantom power. Rather minimal design but quality parts. I have a little stock of caps, resistors, wires, etc at home.

Does somebody could help me with circuit and PCB design to think of? Cheap kits are also very welcomed

Thank you,
nOrD

[nOrD]

Fixed or variable gain?  Battery power?  Size requirement?

Fixed gain (I think about 30-40dB), battery power by RB-270 (9VDC/5400 mAh), size depends on the covering box required, but something about 200x100x50 (in mm) would be perfect, I guess.

I forget to mention that I have a lot of tubes, from tiny nixies to larger types though DC/AC power conversion throw me away to think about anyway loved tubes for this project.

[DSatz]

The preamps in the R-44 are very good; why do you want to replace them?

I mean, I use an outboard Grace V3 for channels 1 and 2 most of the time, but that's because I find the metering on the V3 much clearer and I can select the low-cut frequency. It's not because the R-44 has bad mike preamps by any means. I've used them and gotten very good results.

I'm just asking. You might really have a reason.

--best regards

[nOrD]

The preamps in the R-44 are very good; why do you want to replace them?

I mean, I use an outboard Grace V3 for channels 1 and 2 most of the time, but that's because I find the metering on the V3 much clearer and I can select the low-cut frequency. It's not because the R-44 has bad mike preamps by any means. I've used them and gotten very good results.

I'm just asking. You might really have a reason.

--best regards

Hi DSatz,
Sure, I do agree with that R-44 has great preamps. The main reason behind my wish to add a preamp is that when I use my shootgun mic (AT815b) I need some more gain. I know that this is because of the relative low sensivity of this type of mic (actually -39dB with PP) and I would like to regain that "loss" by using a good preamp.....

or a stepped attenuator with transformer or with a series of resistors:

http://www.iagaudio.com/steppedattenuator.htm
http://www.sowter.co.uk/acatalog/SOWTER_TRANSFORMERS_ATTENUATORS_13.html
http://www.sacthailand.com/Transformer_Attenuator.html

I used similar transformer attenuator between my CDP, turntable and power amp, and can tell you, it has make rounds of many expensive high-end preamps. Only impedance matching would be considered with such an attenuator, and voila: we get a unit that needs NO battery, can fit in your pocket, has NO electronics - just to mention first coming arguments.

I wonder if somebody runs their recorder with attenuator as preamp? I am very interested.

Greets,
nOrD

[DSatz]

An AT815b has ~12 mV/Pa sensitivity, which is certainly not low; Schoeps "Colette" series mikes have very similar sensitivity, and my R-44's mike preamps have well more than enough gain for them. So I just don't see your problem.

--best regards