12 Position Stepped Attenuator

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

RSRecords

Well-known member
Joined
Jun 8, 2009
Messages
320
I know this has been talked about in various incarnations but I am planning a simple stepped attenuator project.

--2 Channels
--Balanced
--0-6dB total so .5db Steps
--12 positions

Am I right in thinking I need a 4-pole 12 position switch?
For now it is 600 ohm to 600 ohm. That might change.

Anybody have any good plans for calculating the r values?


 
Here's a chart. Pretty handy.

Ftuy3Ag.jpg

 
rackmonkey said:
Here's a chart. Pretty handy.

awesome thanks!

To further clarify what I'm looking for is a linear attenuator with .5dB steps for lacquer cutting.
Basically a stereo level attenuator before the lathe.

Would I be better served by a series attenuator?
or a more complex ladder style or shunt style?




 
RSRecords said:
Would I be better served by a series attenuator?
or a more complex ladder style or shunt style?
You said you wanted 600 ohms in, 600 ohms out, so it's gotta be a T-pad or H-pad. H-pad requires 3 wafers instead of 2.
However, I doubt very much the 600 ohms in. There are very few 600 ohms sources today. And I'm not so confident in the 600 ohms out either.
What are the source and the load, namely?
 
abbey road d enfer said:
You said you wanted 600 ohms in, 600 ohms out, so it's gotta be a T-pad or H-pad. H-pad requires 3 wafers instead of 2.
However, I doubt very much the 600 ohms in. There are very few 600 ohms sources today. And I'm not so confident in the 600 ohms out either.
What are the source and the load, namely?

600 is indeed just a guess at the moment. Its for attenuating the 2 bus console mix to a cutting lathe.  Anyone know off hand the input impedance of a Neumann VMS70 lathe?  ;)I can take measurements.


 
RSRecords said:
600 is indeed just a guess at the moment. Its for attenuating the 2 bus console mix to a cutting lathe.  Anyone know off hand the input impedance of a Neumann VMS70 lathe?  ;)I can take measurements.

A VMS 70 has three inputs for the lathe automation.

VMS 70 tells you nothing about the drive electronics. You will need a four channel attenuator if you plan on using the automation.
 
Gold said:
A VMS 70 has three inputs for the lathe automation.

VMS 70 tells you nothing about the drive electronics. You will need a four channel attenuator if you plan on using the automation.

Good point. I believe the amplifier is an Neumann VG 74b.  Unfortunately I am not intimately familiar with lathes. This will be fed from a source impedance below 50 ohms. The Attenuator will live between the amp input and the output of a bus compressor.
 
Right that was my thinking. I was going to build 2 balanced attenuators so 4 gang switches.

The All of the outputs are less than 50 ohms, still working on load impedances.
 
abbey road d enfer said:
Well it's an awfully long time since I put my hands in a lathe so there'll be one signal from the play head and one from the preview head; what is the other?

It needs Preview Left and Right along with Left Modulation so it knows where the  next  revolution  is.

The drive electronics are most likely a SAL74B. If the B conversion was done completely it has opamp input with a 10K input impedance. It could have a transformer input if the conversion wasn't done completely.

If you are supposed to be setting this up with no manual and no experience the only advice I can offer is stop now.
 
Gold said:
It needs Preview Left and Right along with Left Modulation so it knows where the  next  revolution  is.
OK, I misunderstood you, I thought you meant three sets of stereo signals. I've never seen using only the Left channel of preview. We always had 2 channels PB and 2 channels Preview. With some mixes (fake stereo) you may lose significant LF information by not using both preview channels, unless the preview uses a mono head...?

If you are supposed to be setting this up with no manual and no experience the only advice I can offer is stop now.
I'm not the OP, and as far as I know, he just want to put an additional level control, not realign his set-up.
 
abbey road d enfer said:
I'm not the OP, and as far as I know, he just want to put an additional level control, not realign his set-up.

That's correct and  I appreciate all the input. Interestingly enough GOLD, your name came up whilst discussing cutter amps. I know you know your stuff!
 
abbey road d enfer said:
OK, I misunderstood you, I thought you meant three sets of stereo signals. I've never seen using only the Left channel of preview.

The VMS66/ 70 automation system uses both Left -and  Right Preview and Left Modulation. If it wasn't set up that way it was set up wrong. A Zuma or other aftermarket automation system only needs a stereo Preview input. A VMS 80 only needs a stereo Preview input.
 
To the OP. You want to attenuate  both Modulation and Preview paths so the level to the automation is the same. If you are using the internal automation passive is not the way to go. As Abbey caught the load differs between Modulation Left and Modulation Right.

You could even out any level differences with calibration points but I wouldn't do it.
 
Gold said:
The VMS66/ 70 automation system uses both Left -and  Right Preview and Left Modulation. If it wasn't set up that way it was set up wrong. A Zuma or other aftermarket automation system only needs a stereo Preview input. A VMS 80 only needs a stereo Preview input.
I'm sure the three set-ups I knew (one particularly well, being in charge of its maintenance) used stereo preview; they must have been VMS80 then. It was in 1979. I remember we had the first SM74 in France.
The paucity of on-line information about these systems is appalling, Neumann themselves seem to have obscured this part of their history.
 
abbey road d enfer said:
I'm sure the three set-ups I knew (one particularly well, being in charge of its maintenance) used stereo preview; they must have been VMS80 then. It was in 1979. I remember we had the first SM74 in France.
The paucity of on-line information about these systems is appalling, Neumann themselves seem to have obscured this part of their history.

The VMS80 was brown. The VMS70 was white and grey. The  VMS66 was green hammertone.

The information is available to those who need it. It's not online.  On purpose. Not all information needs to be freely available.

Neumann has no information. It all went in a dumpster when AKG acquired them.
 
Gold said:
Neumann has no information. It all went in a dumpster when AKG acquired them.
I remember AKG having a bout of acquisition fever in the late 80's, acquiring dbx and Ursa Major, but Neumann? I didn't know that. I thought they were independant until being acquired by Sennheiser.
 
abbey road d enfer said:
I remember AKG having a bout of acquisition fever in the late 80's, acquiring dbx and Ursa Major, but Neumann? I didn't know that. I thought they were independant until being acquired by Sennheiser.

Sorry, Sennheiser. All Austrians look the same to me:)
 

Latest posts

Back
Top