neophyte questions

[Roly-M]

Hi folks

First, I would like to thank the guy who sent me a schematic for a McCurdy PE 1000 mixer. I'm sorry, I don't recall his name.

Next, I want to thank Joe Malone for doing a wonderful job of racking up two AM-16s.

I have two more AM-16s that I had planned to send to Joe for racking.

Things have gone for a crap financially  and I have no choice but to rack up the AM-16s and sell them.

Here's my questions....will in line pads on the input bugger up the frequency response of the preamps?

Is it possible to put a pot in line with the input that will keep the load that the preamp sees consistent? Instead of an inline pad.

Does it matter?

Same questions for the output.

Looks like I can make the input impedance switchable between 150 and 600 ohms with a DPDT switch. Is that a good idea?

I repair, service and hand build tube guitar amps. That's the extent of my depth in audio land.

Thanks for your help.

cheers
Roly

 

[Roly-M]

I fear I have somehow offended you folks.

If that's the case....I'm sorry.

Thanks
Roly

 

[PRR]

Much of this stuff CAN be figured out on your own.

"bugger up"... how bugger is bugger? Every broadcast tech threw pads in front of mike preamps as needed to get the signal on the air. Of course you need some sense of impedance level. And in a Bridging interface (how we usually like mikes) any low-loss pad is sure to show too-low-Z to mike or too-high-Z to preamp. How low is low, how high is high, is 0.1dB too much, is 3dB close enough?

A SPST switch can throw 200r across 600r and give 150r. I don't know where 150r and 600r targets came from. (They are long-line impedances, not necessarily mike impedances, though 150/600 may simplify things.)

Padding the output for true-600 interfacing faces the same concerns. But in modern practice, all loads are >10K and semi-ignorable. Put 1.5K fixed and 1K pot across the output, that's your pad. If you don't tell anybody the output is not "perfectly balanced", they will never know until they try to drive 10 miles of good line. Lo-Z studio-length lines can run a floating L-pad without harm.

 

[Roly-M]

Hi PRR

Thanks for your help.

I'm in love with my JLM Audio racked AM-16s.
I hate having to sell my other pair.

cheers