API output attenuators

[Gus]

A friend asked me about making output attenuators for API 512s going to Motu A/D.

A couple of questions anyone care to share the input R of motu A/D line in? I looked at the site but did not want to sign up to get the information.

The first idea that came to mind was a simple U attenuator. I would make a first guess at two matched 100 Ohm resistors and a 1K pot and maybe a fixed resistor to start. The Pot and series fixed resistor between the 100 ohms API to the 100 ohm side and to the Motu from the ends of the pot and fixed series resistor. API is 75 ohm out?

API 512, Motu 896 and 828mk2

 

[Gus]

Roger
Thank you

 

[therecordingart]

[quote author="Gus"]A friend asked me about making output attenuators for API 512s going to Motu A/D.

A couple of questions anyone care to share the input R of motu A/D line in? I looked at the site but did not want to sign up to get the information.

The first idea that came to mind was a simple U attenuator. I would make a first guess at two matched 100 Ohm resistors and a 1K pot and maybe a fixed resistor to start. The Pot and series fixed resistor between the 100 ohms API to the 100 ohm side and to the Motu from the ends of the pot and fixed series resistor. API is 75 ohm out?

API 512, Motu 896 and 828mk2[/quote]

How did you end up building the attenuator? I'm currently in the same boat...my 312s are way too hot for my 002.

 

[skipwave]

[quote author="RogerFoote"]Why don't you go unbalanced?
Then use a single 10K pot for each channel's trim.[/quote]

Why not use that 10k as a rheostat in the shunt leg of a balanced attenuator? New York Dave posted an example of that.


[quote author="RogerFoote"]All things being equal (or not) and assuming there are no ground noise issues where balanced would be better, an unbalanced connection should sound better.[/quote]

I see how the receiving stage of the following device has more to do (whether it be a transformer or active debalancer) than a simple unbalanced input, which is typically direct to the first device with maybe a single capacitor intervening.

I remember PRR posting the schematic of a 1k pot lashed onto a balanced output. He didn't claim it was better than the balanced attenuator, but just as good when the unbalanced run doesn't introduce issues.

 

[CJ]

Hard to knock down 75 without consequences on the freq chart vs R.

 

[vertiges]

what about this ? :

 

[vertiges]

(removed - double post)

 

[therecordingart]

[quote author="vertiges"]what about this ? :

[/quote]


I'm trying to make this make sense in my head, but I'm not able to figure out how I would lay out these resistors on the rotary switch.

 

[vertiges]

[quote author="therecordingart"]

I'm trying to make this make sense in my head, but I'm not able to figure out how I would lay out these resistors on the rotary switch.[/quote]

You need to use a "multideck switch".
3 decks : 1 pole / 6 positions per deck.

Could someone confirm that 600 Ohm is the right value ?

eD)))

 

[therecordingart]

[quote author="vertiges"][quote author="therecordingart"]

I'm trying to make this make sense in my head, but I'm not able to figure out how I would lay out these resistors on the rotary switch.[/quote]

You need to use a "multideck switch".
3 decks : 1 pole / 6 positions per deck.

Could someone confirm that 600 Ohm is the right value ?

eD)))[/quote]

Now I got it. Thank you.