Balanced input PCB for use with power amplifier etc.

[Igor]

There are many amps which can be used with studio monitors, Adcom, Yamaha, etc in 100-300W range,
but most of them are unbalanced.

Another case - when I needed cheap solution for amplifying NS-10's, clean enough, but with good damping factor,
I used for this purpose bit tweaked up IRAUDAMP7s (google). Yes, no tubes for monitoring

I use digital amp for my home system (subs).

All these goodies needed balanced input. IRAUDAMP7s I used on subs btw had reversed phase on both channels ref. input (was easy to fix).

After making some friend's and customer's studio monitor's amplifiers balanced with breadboard, copper foil (ground),
wires and patience, I decided to make once and for some years respective board.

This board have basic voltage regulator dropping amp's power supply voltage (+/-30 to 70V usually) down to +/-13...18V (depending on Zeners).
Pair of balanced line receivers and some parts.... done. 30-40 min to convert amp inputs to balanced including drilling 2 holes at back panel.

Another important point. The level of most amps to reach full output is about 1.75V RMS.
The D/A output can go as high as +18..22db, so... using -6db balanced line receiver
with passive balanced (relays, yes )attenuator always improving the monitor's resolution, compared to
standard mixer's crm outputs, and... not to be mentioned here.... Small Knobs and other funny stuff,
where signal passing  4-5 opamps, 5-10 electrolitycs, cracky pot, ceramic caps at feedback etc etc till get to amplifier tired and lossy.

So... The balanced -6db tweak always worked for me and customers fine, especially with passive relay-based CRM.

Have fun and enjoy!

Some pictures:

Photobucket album with more pics:

http://s251.beta.photobucket.com/user/diy33609/library/Balanced_inp_amp_pcb

If interested - will add to store, the price for this board should be within $13-15.

 

[straypacket]

+1 interested

 

[Winetree]

+3 boards.
Got 3 Adcoms. GFA-555,545,535.

 

[grubbyliver]

I could use a few of these.

 

[Sylvain D.]

Exellent idea Igor!
Perhaps a "balanced out" counterpart also? :

And might I ask what you mean by "bit tweaked up IRAUDAMP7s"?

 

[abechap024]

One of our adcoms is down slightly like 1db on one channel, would there be a simple resistor we could tweak on this to compensate? Good stuff!

 

[Brian Roth]

I agree....EXCELLENT idea.  Just one suggestion ...    sometimes a -6 dB drop is insufficient, depending upon the amp, in order to maintain the optimal S/N of a system.  Perhaps the addition of pads for two resistors (one each from the "output sides" of R1 and R5 to AGND, as shown in your photobucket schemo) would allow some tweaking...which could also give Abechap his requested tweaking feature.

Bri