Fron battery to preamp, what´s the best way?

[lagoausente]

Consider a comercial mic preamp with 220 V input.

In my mind I think about this posibilities to run from NIMH battery.

1) just a 12 to 220 V pure sine wave inverter. It´s logical but I think it will waste much energy converting from DC to 220 AC, and then again to +/- DC. Think on the heat will waste just the preamp transfomer..

2) The preamp has inside +/- 18 v. Could take 15 batteries of 1.2 volt and 2600 mah for the +18 and another 15 for the -18. Here my doubt is that when full charged, they batteries have 1.4 volt each, so I would have then 1,4x 15= 21V. And so +/- 21 volt. I don´t know if the preamp stabilization would allow this variation from +/-18 to +/-21..

3) Take a inverter, but instead of going to 220 AC, modify it to give me 18AC, and so go directly to the rectifier section avoiding the main transformer of the preamp. Maybe could waste less energy this way?
I would like to know your opinions.

 

[mzzj]

If you have +-18v dc now, you would need apprx 14VAC so that it is 18v dc after rectification and filtering


#2 is best option. I guess you have +-15v after regulation? With fully charged batteries regulators have to work bit harder, but mic preamp is probably so low current anyways that power loss is tolerable. Can you measure or guesstimate current needed?

 

[lagoausente]

If you have +-18v dc now, you would need apprx 14VAC so that it is 18v dc after rectification and filtering


#2 is best option. I guess you have +-15v after regulation? With fully charged batteries regulators have to work bit harder, but mic preamp is probably so low current anyways that power loss is tolerable. Can you measure or guesstimate current needed?

I have meaured voltages.
The Sec of the transformer gives 2 x 24 VAC for the preamp.
After the rectifier, just on the filter caps, I have +29,3 and -29.3 VDC.
Also have around 54VDC for phantom.
After filtering, stabilization seems made by two transistor for the preamp and another one for the phatom.
After them have the finally +/- 18 V for preamp and the 48 for phantom.

So if I´m on the correct conclusion I have enough regulation margin from 29,3 V to 18 V. Isn´t?
If I go for the batteries, maybe could be ok with 4 12V batteries to get +/- 24v before regulation?
If I´m correct, the full charged 12V battery would be near 13.5 or 14V, and so would be 2x 28V max, and when discharging get down to around +/- 24V?

Regarding the current, I didn´t find easy to desolder a component to measure, but I think could be deduced. Resistence between +18V and ground points is 176 ohm, and between -18 and ground , the same. So 18/176= 0,102 amp.
The phantom section are 48v/ 890 ohm= 0,050 amp.
So I think consumtion would be around 102+102+ 50= 254 ma.
Let me know if I had errors on my conclusions, and about the posible best solution/s.