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.

6423b01c a746 44d6 aedc 25e6da9fe9c2johnziomas

You have way too much gain. And the volume control in the D100 is digital domain, so anything below 3/4 and you run the risk of "bit stripping" the music

Your Primaluna input sens is about normal, and high impedance. If you use the fixed outputs of the D100, they are 1/4 the level of the variable.

You could then use a $49 Shitt sys and run the fixed output of the D100 and use the Schitt's level control. 

Or using the variable out you could turn it up full, then for the loudest you want to hear and adjust the Shitt to that level, then you can still lower the remote level up and down but you’ll be using it the top 1/4 of full. So no "bit stripping"

Don’t bother with those inline attenuators, I’ve haven’t heard any that sound good.

Cheers George

Thanks George,

using the variable out is almost a must as this is the only way to control the volume remotely with the D100 remote (looks like the schiit unit does not have remote volume control capability.)

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

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.

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 

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?

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

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

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

Hi John, just found this out for you, looks as though the front right panel knob is digital in the way it send the coding onto the analog side of things. "maybe"

Quote from "The Ear" review

"Mostly the output mode is chosen with the use of DIP-switches or through software. Volume control takes place in the analogue domain within a special chip driven by impulses from the front panel rotary knob."

Maybe you can set this front panel vc low for your max you want (preset), then use the remotes vc as the master vc, if indeed it is analog??

Like I said before Mac can do some crazy things.

Cheers George

What Mark Levinson and Wadia did in their great R2R Multibit dacs/cdp of yesteryear, was to use a digital domain VC, which is the best if you don’t "bit strip"

But they allowed and instructed the user to get the best sound was to set with bridges across small two pin connectors the amount of gain the analog output stage had 10 different levels from 1 to 5v each channel. So then you could use the digital VC at or down to 1/4 below full output.

Very smart they knew about "Bit Stripping" before it was even named

Cheers George

Thanks so much George,

this is interesting, I'll test tonight.  I'm almost certain though that the remote's VC and the knob act the same, just by judging at the percentage of volume shown.

I'll check it out and thanks again. 
Looks like they both perform the same function.  If I set the volume with the knob at 30%, then use the remote to reduce it to 20%, then go back at the knob the volume is at 20%.

unless I misunderstood, it seems to me both knob and remote do the same thing with the volume.

Another info that I found, but I am not following;

The more astute of you may be thinking as you read that, ‘hang on, this sounds more than a little like a Cambridge Audio DacMagic Plus and the last time I checked, that was a good deal less than three grand.’ This much is true. The functionality of the D100 is replicated on a number of devices that cost quite a bit less than the McIntosh does but the bald feature list doesn’t completely describe what the D100 can do. The first is that unlike most other digital preamps, the D100 has a preamp circuit that is completely separate from the digital board.

McIntosh D100 Design
The reasons for doing this are fairly compelling. If you are acting directly on the digital signal of a DAC you have two options about how to adjust volume. The first is bit reduction which physically reduces the size of the signal the DAC handles. As the name suggests, physically clipping the amount of data in the signal isn’t a great way to maintain quality so this is not ideal and certainly not for McIntosh. The second way is to use DSP to adjust the volume level in the digital domain without actually losing any information. This is much more effective at retaining the overall quality of the recording but it does tend to make adjustment a little slow and unwieldy.

By fitting a conventional preamp to the D100 - albeit one on a rotary encoder rather than a classic volume ‘pot’, the D100 feels like a normal preamp. If you rapidly twist the volume control on the D100, the volume climbs or descends at a ‘proper’ speed rather than coming to terms with the world around it and slowly ‘ramping.’ Furthermore, with an encoder in place, the D100 has a full remote control that means it is possible to use it at rather more than arm’s length although the remote itself is certainly in the running for the ‘most buttons that have no actual bearing on the operation of the product’ award.

The other benefit of implementing a preamp this way is that it also doesn’t have to be part of the signal path. As well as the variable outputs, there are fixed level ones too that ensure that the D100 can be used as a completely normal DAC into one of McIntosh’s preamps and integrated amps (of which there are many). The preamp isn’t deactivated in this instance, it is completely absent from the circuit.