EMI TG Summing Amp

Hello,
Following on from my post here:
http://www.groupdiy.com/index.php?topic=23161

I just prototyped (rats nest style) the EMI TG output amp configured as a summing amplifier and since it appears to work rather well thought Id post in The Lab.

There does seem to be a practical limit to the gain that can be utilzed in the amp which also limits the number of channels that can be connected of course but 16 channels works well and up to 32 are possible without too much change in amplifier characteristics.
Basic schematic is here:
http://picasaweb.google.com/PROAUDIO.DIY/SonicScrewdriver/photo#5080276959877391890

BTW I used a trifilar wound Cinemag output transformer with half steel and half nickel lams,

Cheers all

Little hard to see the schematics junctionpoints. R9 and R13 goes to ground for exemple?
R12 and R15 sets the voltage? ( like in the TG1 )
How do you set the gain?

I've built the outputstage using BD139/BD140, workin' just fine driving a LO2567. BD140 acting as a current source.

BC184 / BC214 is also workin' fine.

Any more EMI schematics hidden in the closet?

[quote author="Tekay"]Little hard to see the schematics junctionpoints. R9 and R13 goes to ground for exemple?
R12 and R15 sets the voltage? ( like in the TG1 )
How do you set the gain?

I've built the outputstage using BD139/BD140, workin' just fine driving a LO2567. BD140 acting as a current source.

BC184 / BC214 is also workin' fine.

Any more EMI schematics hidden in the closet?[/quote]

Yeh sorry about the schem being a bit hard to read!

R9 and R13 do go to ground yes


R12 and R15 can indeed be adjusted for the input stage voltage set

Gain is set by R17 but remember there is gain in the output trannie too

I see no reason why BD139/BD140 and BC184 / BC214 could not be used if that is what you have

LO2567 in a 200:600 config is a good one

Nothing hidden in the closet, everything within arms reach

Thanks

I tested it with the outputtransformer as 50:600 ohm config, gives you around 10dB of extra gain.
TG CHannel uses a Carnhill VTB2012 and IIRC TG1 uses (used) VTB9057 = LO2567. Both with the primary windings in parallell.

About the closet! I was just curious about if you have any EMI mic pre info.

[quote author="Tekay"]I tested it with the outputtransformer as 50:600 ohm config, gives you around 10dB of extra gain.
TG CHannel uses a Carnhill VTB2012 and IIRC TG1 uses (used) VTB9057 = LO2567. Both with the primary windings in parallell.[/quote]

Tekay
Thanks for your responses : )
Strapping the output at 50:600 ohm is not necessary and possibly deleterious

The original "TDS" transformers used in the EMI desks were nowhere near that ratio for what it's worth :wink:

ps: forgot to mention and it may not be clear from the schematic I posted but since the amp is inverting you should flip the secondary windings on the output to maintain absolute polarity
If another inverting stage (as in the TG limiter) is used beforehand then this is not necessary