15vdc/6A to 12vac/850mA inverter

[ninonpas]

hello

inside a modular sound synth system that has its own regulator circuit to give 12vdc i would like to include a piece of equipment that needs 12vac/830mA

my three questions are:

do anyone please have some complete circuit i can follow to build the smallest adaptor possible ?

is there normally a voltage drop when converting dc to ac?
if so maybe i should take the voltage directly from the external transformer which gives 15v/6A so i would have 3v extra to compensate the possible loss?

as this is for audio aplication i guess i will need a perfect sinus...
wouldn't using a direct pwm conversion probably introduce noises in my audio signal ?

[tatus1969]

can you provide some detail about the circuit that you want to power? It may be well possible that you can supply it 12VDC and do not need an inverter. For example, most low-wattage electronic PSUs, like for example USB chargers, do work very well when fed with 100 ~ 400V DC. And you want at least high frequency interference in an audio system, so you have one problem less when not having to use a PWM based inverter. Maybe it does not work with DC but accepts 50Hz square wave.

[Ian.M]

The peak voltage of a 12V RMS sinewave is 12*sqrt(2) = 17V, so you are likely to be screwed without a transformer or a boost circuit.   

A 10VA transformer + linear drive circuit + heatsink isn't going to to be particularly small.  A switched mode or PWMed solution is likely to be noisy unless the switching frequency is much greater than 30KHz,  the control loop response doesn't permit subharmonics in the audio band, and it has adequate screening and filtering.

Probably the best option would be to investigate modding the 12vac/830mA piece of equipment for DC input.  It probably uses AC input + two half wave rectifiers to get positive and negative DC rails for OPAMPs etc.   Generating a steady DC rail from a small switching regulator module without excessive noise is a *LOT* easier than generating clean 50Hz or 60Hz AC @ approx 1A.

[ninonpas]

thank you very much for your responses

the piece of equipment i'd like to include in my modular is an old Marian ADCON audio to adat/adat to audio conversor http://www.marian.de/en/products/adcon

i want to get rid of the case and the big jacks to fit the circuit inside my modular's box and add 16 minijacks on a small front panel

i have searched for schematics on the net but there is none.
i will contact the company to ask if they can provide me with one

i will try to make some hi-def pictures of the actual circuit, maybe it will show if it's possible to power it with dc

the modular itself has a good regulator (TPS80) giving 80w of +12vdc -12vdc and 5vdc
https://intellijel.com/other-products/

of course a simple solution is to go with its own separated external power suply but i try to get rid of it if possible

[tatus1969]

if you already have +-12v I bet there is a good chance to use that directly. Just post some pictures and we'll see.

[Ian.M]

The Marian ADCON has a phantom power option on its microphone inputs, and that probably relies on the supply being AC, so if you need to retain that, its probably going to be a little more complex . . . .

[ninonpas]

i won't use the phantom power anymore nor the preamps neither,
i just want to use the 8 line I/Os to and from ADAT

and basically only for audio

i know about the possibility to send cv controls thru those I/Os using Expert Sleeper's Silent Way but that is not even my priority (if i end up being able to use it, OK, but mostly want multiple audio I/Os)

[Zero999]

It probably just converts the 12VAC into a bipolar PSU using a rectifier. It may work perfectly fine from a 15V square wave.

Here's the simplest circuit inverter know of which doesn't use a transformer. It was originally designed for 24V but will work off 15V. The main disadvantage is it's noisy and does draw some high current pulses in between cycles but the power dissipation won't be too high as long as the frequency is low.