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Gain Structure help, Mcintosh D100 to Primalune tube amp

Need to adjust the gain structure, D100 (used as DAC and pre) outputs 0-8V and Primaluna has 1.2V input sensitivity.

I can adjust the source input gain (PC via USB to the D100) which will allow me to use the D100 volume control at more than 50%, but I have heard this is not the best way.

Or should I try some attenuators (12db - Harrison Labs) on the output of the D100 going into the Primaluna amp.

Thanks
128x128johnziomas
georgehifi's avatar
georgehifi
10,312 posts
 

Yes you can still use the remote variable out of the D100, but preset the Schitt so the maximum out of the D100 is the loudest you ever want to go. In other-words the Schitt becomes a fixed attenuator, and you still have the remote volume of the D100 to use.

The whole idea is to be able use the D100 variable output in it’s top 1/4 of the range so you don’t run the risk of "bit stripping"

I’ll try to explain:

The reason to use the Schitt, is that we know it’s a 10kohm passive which is still a perfect impedance match with your D100 (150ohm) and Primaluna amp (100kohm). Where inline attentuators like Rothwells and the one you mention can have impedance mismatches as we don’t know what series shunt resistors have been used inside them.


Cheers George

johnziomas's avatar
johnziomas OP
41 posts
 
Thanks George,

the interesting thing is that all of the Mcintosh preamps have the same output V range 8v unbalanced and 16v balanced.  And some of their amps have low input sensitivity (I think the tube 275 is at 1.8V.)  Theoretically you wouldn't need to do anything gain wise to plug one of their preamps into their amps, wonder how that works.
georgehifi's avatar
georgehifi
10,312 posts
 

Mac do do some crazy things in my view, like putting output transformers on solid state amps. But I loved some of their old stuff from the 60,s 70,s.


Cheers George 

johnziomas's avatar
johnziomas OP
41 posts
 
Hi George,

I spoke with Ron at Mcintosh, and he said they are using an analog volume control and there is no bit stripping or any advantage to try to attenuate the output of the unit.  Essentially my range is up to 50-55% (hard to tell with the Primaluna amp if it is clipping at that point or what, but it is plenty loud) which I can live with.  Unit/system does sound amazing even at low levels (20% or whatever) just wanted to make sure I am not leaving anything on the table.

any thoughts?
georgehifi's avatar
georgehifi
10,312 posts
 

You maybe right, because the manual I looked at said

"0 to -60db digital volume control"

Maybe I looked at another model by accident. If this is correct then you have no trouble going direct no mater how low the volume is.

Here are some pics

This one shows the VC on the right, connected to the digital side of things

http://www.avmagazine.com.hk/common/createthumb.asp?w=640&h=480&p=/image/content/personal/D100_640.jpg

This one shows the analog output board and analog outputs on the left with the selector switch attached to it.

http://www.audio-activity.com/uploads/1/3/0/9/13098779/_9628528_orig.jpg

The only pot that goes to this board is a selector switch, if the VC is analog it should go to this board, not the digital board. Makes me wonder now. I guess they know??

Cheers George

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