DA amp

[shooter]

I want to build a quick, low thought, Distribution Amp to feed the source audio (~line level) to 4 separate amps, still at line level adjustable +/- some.
Googlin wasn’t much help for kits, if someone’s got a KIT link, that helps the quick – low thought design part 

Here’s the stuff I lifted so far, I like the headphone buffer amp but I’ll need to get it to like line level in.

The other route a 1 transistor amp + 1 transistor buffer.  Downside it’s 2 transistors X 2 X 4
Ideas n help always welcome

Dave

[PRR]

The first has a low input impedance; perhaps lower than four line-ins just paralleled.

The second has an absurdly low input impedance.

Line Level *may* need more than 12V supply. Is such a thing available?

_I_ would just power a unity-gain opamp with 24V, run four 470 Ohm output resistors so if one load gets shorted (shorts happen) the show goes on with the other three loads. (I used to record live public concerts so it was essential that one fault did not ruin all the recordings.)

[shooter]

low input impedance

I've been putting off learning those calculations, think it's time to grasp it again 

That's the problem now, the input gets loaded down and each amp/speaker's audible loudness is effected.
like you, the humidity/temp has been so bad my brain just quits n looses all motivation.  It broke today so hopefully you feel it soon 

thanks as always for your help
 

[shooter]

more web'n found fully assembled @ ~$50 for 6 ch, but sorely lacking in docs/specs
went barn scrounging n found boards from a gutted traynor yvm-4 (pdf in Doug's library)
here's a snippit form that.  Cutting along blue line, my audio PS has a 13.2vac tap, close enough for test.
the red line n X I'm guessing is ok 

I should be able to tweak for "centered swing" at 1VacRms in

[shooter]

Line Level *may* need more than 12V supply. Is such a thing available?

images below show exactly that!  Now I gotta go off n re-learn why/how that works 
17.68vdc is all my bench supply could make, but looks like it's good enough.
I gutted the TS, used the output stage of the mix board as-is, which looks pretty good, some compression on the positive lobe.
NOTE: I only changed the B+ to get Out_12vdc and Out_17vdc

[glass54]

Hi Shooter,
I'm sorry for the late reply. I just saw this and I have interests and experience on this topic. Do you still need ideas or are you done?
Kind Regards
Mirek

[shooter]

done for now, I did get the 4 channel mix board from an out SS amp working, but in the end my "issue" for my specific needs wasn't input signal size or loading.

I do have 3-4 of the old boards if you want a start down your own rabbit hole 

[glass54]

Thanks Shooter.
Was happy to help as I just finished a ruggedised (is that a word  ) Low Impedance Buffer Amp for the Solomon Islands and tested it fully on the Audio Precision APx525. One of those projects I enjoyed.
Thanks for my PM.
Kind regards
Mirek

[PRR]

> I just finished a ruggedised (is that a word  ) ....for the Solomon Islands

You are correct. In 120V land we write ruggedized; but SI is 230V land so you write ruggedised. (My browser spellchecker does not like either word, so much for that.)

https://www.lexico.com/en/definition/ruggedized
https://www.dictionary.com/browse/ruggedised
https://en.wiktionary.org/wiki/ruggedize#English
https://en.wikipedia.org/wiki/Rugged_computer

REAL Rugged: "MIL-S-901: .....Qualification testing is performed on a barge floating in a pond where TNT is detonated at various distances and depths in the pond to impart shock to the barges." https://en.wikipedia.org/wiki/MIL-S-901 Video

[shooter]

 
I ruggedized a few jeeps in ponds n rocks n.....