battery powered ±15 48 V PSU for Micpre Project

Hi all,
I'd love to  have a good portable Preamp to go with my tascam dr-100. The main problem is going to be the PSU
anybody has an idea where to start ? ... This is going to e my first project.

nicholas

I'd start by looking at a THAT1510/1512 powered by, say, a dozen AA batteries, with five 9V batteries for Phantom power. Simple, and no specialized batteries so you can get fresh ones anytime and anywhere. Not as small as your Tascam, but definitely portable.

One of my portable pres consists of Rod Elliott's Project 66, similarly powered by sixteen AA cells and five 9V batteries. You could power everything off 9V batteries to reduce logistical/stocking issues, but I find that the AA/9V combo offers reasonably balanced runtime between pre and phantom.

If you have to ask, I would urge you to stay away from switching power supplies aka DC-DC converters. Really.

More interesting reading:
http://www.groupdiy.com/index.php?topic=24334.0
http://www.groupdiy.com/index.php?topic=34097.0
http://www.groupdiy.com/index.php?topic=21933.0
http://www.groupdiy.com/index.php?topic=16909.0

JDB.

thanks

you gave me a nice reading time. I anyway thought about the that 1510, and the battery solution was also on my mind.
The thing is, I checked out a funk-tonstudiotechnik PSU and they are incredible clean and small and they are switchers.

maybe I drop by Mr Funk and ask him a few questions

nicholas

e.oelberg said:

The thing is, I checked out a funk-tonstudiotechnik PSU and they are incredible clean and small and they are switchers.

Click to expand...

Up to you, of course.

Switchers can be attractive. Switchers are nice if you are already married to a certain voltage for your main system supply and need something that's higher or lower. Switchers are handy if you go commercial, as customers find it cumbersome to change or charge more than a few batteries. Switchers can help you keep a constant output voltage for a varying input voltage. The majority of the designs I come up with in my day job have at least one switcher.

However, for DIY or small series work with qualified operators switchers have one major downside. Forget about noise for a moment. Thing is, no switcher is 100% efficient. That sounds obvious, but for portable systems it's a big thing. A really good single-purpose switcher might have 95+ percent efficiency. This goes down for varying output currents, especially low currents. Need to support varying input voltages? Lose a few %. Want low noise? Then you have to turn your FETs on and off more slowly, and you can't use most variable-frequency schemes, and that'll cost you. A switcher that is good for audio work with battery input will likely be between 65-75% efficient, 80% if you're really lucky.

Now think about this:
- how much extra battery capacity do you need for equivalent run time to compensate for switcher losses?
- how much batteries could you have stuffed in the space(/weight) that your switcher takes?
- if you use a switcher only for one of the voltages (Phantom would be obvious), how long would it take before the switcher has paid for itself? Consider that 5 9V batteries can supply Phantom power for 20-40 hours continuous.

Alkaline cells have a terminal voltage of 1.5-1.6V when full, 0.9V when considered empty. With a dozen AA cells a THAT15xx will keep operating fine until the batteries are empty, still driving the -10dBV inputs that that Tascam probably has without clipping.

JD 'right tool for the job' B.

> a dozen AA cells
> -10dBV inputs

Think outside the box.

Since this is 2.8V peak, there's no reason to be married to +/-15V supply. A gain-controlled preamp running on one 9V battery will do the job, and down near 7V if you use a near-rail-to-rail output stage.

Likewise many-many Phantom mikes are quite happy at 18V. If you are very brave, some run at 9V internally, so you can hack in and not waste any power in studio-style convenience powering schemes.

Then again.... a 12V lawn-tractor battery and a cigar-lighter 120V inverter can (perhaps badly) power massive preampery for an hour or two, for $80 investment (re-usable) and 2 minutes of "building".

PRR said:

> a dozen AA cells
> -10dBV inputs

Click to expand...

(I'd suggest arranging the dozen as six per rail, or +/-9V nominal, +/-5.4 at end-of-life, just within spec of the THAT15xx -- not a dozen per rail. I see I could have stated that more explicitly. And of course a lower-voltage solution with a newer op-amp would work fine into -10dBV inputs, but that THAT chip is just so dang convenient for the level of performance it offers)

PRR said:

Likewise many-many Phantom mikes are quite happy at 18V. If you are very brave, some run at 9V internally, so you can hack in and not waste any power in studio-style convenience powering schemes.

Click to expand...

You could even go all formal and make it P12-compliant. You just have to be sure that you (or your less-than-stellar assistant) never forget that your Phantom isn't real Phantom, and don't try to plug in just any mic in the heat of the moment.

JDB.
[Many of those cheap Chinese condensers sold at the likes of Banjo Center would appear to use the phantom voltage directly for capsule polarization; with those you're SOL with too-low Phantom voltages]

I know how some of my mics sound with 18V phantom, thats why I'm investigating a 48V solution. I think I'll put me a pair of jlm baby animals in a box with 5 x 9Volt blocks. baby animals run on 48volt, with an OPA2604 they shouldn't suck so much power.

nicholas

LM3524D.15V to 48V.300kHz chop.
Passing cloud London at drawing moment.
10Kx2-180Kx2.

e.oelberg said:

I'd love to  have a good portable Preamp to go with my tascam dr-100.

Click to expand...

Since the DR-100 already has a mic preamp with 48V phantom I wonder what problem you are trying to solve? Have you found a fault with the existing preamp?

Not that I have anything against a project like this...the thing that got me into audio DIY was owning a Panasonic SV-255 DAT. No phantom power on that baby, so I built a Jensen preamp powered by a string of batteries like JDB has suggested when all I really needed was a phantom adapter. The SV-255 had audio problems that had nothing to do with the pres.

mnats said:

Since the DR-100 already has a mic preamp with 48V phantom I wonder what problem you are trying to solve? Have you found a fault with the existing preamp?

Click to expand...

the tascam pre's are very noisy, no problem to record a rock concert with them, they sound fine, but I'd like to do field recordings with a pair af bruel & kljaer 4011. I pondered to use the phantom power from the tascam to get the 48V. But then I thought I might get the noise again I try to get rid off. I think the baby animal solution could be great actually.

nicholas.