Does a DAC need a pre-amp

[Summit]

A stand-alone pre amp, everything else held equal, has to be “superior built” and use better components etc than the DAC’s analogue amplifying stage to sound better IMO. Less is more in an analogue chain.

 

If most DAC’s amplifying stage, VC, chassis shielding and PSU really is as good as a good standalone pre amp is another story, as is impedance matching and which power amp it's going to be used with.

[Panelhead]

9 hours ago, sandyk said:

 

 Basically, it's usually Current Output capabilities, and more often than  not, a discrete output stage using higher supply voltage rails with the Preamp. Your average DAC would be lucky to have  + and -15V supply rails using a generic opamp for their output, sometimes even using a Dual opamp, and most likely also using 100 ohms series output resistors,(or higher)  as many I.C.s don't like driving capacitive loads of >100pF as with some Interconnect designs. 

Some better DACs MAY also use an output Buffer I.C. which makes them less sensitive to Interconnect vagaries.

 Many discrete Preamps have > + and - 20V supply rails and a markedly more sophisticated PSU, most likely not SMPS as with many DACs either. Neither do they usually need to share power supplies with a Digital area either.

With my own DIY Class A Preamp, you will see it is of a dual mono construction with separate sophisticated PSUs for each channel, and it is fed low voltage A.C. by 2 separate external transformers. This Dual Mono type construction also results in a considerable improvement in channel separation, especially in the HF area.

(Click twice on the image for a much larger image.)

 

   Very nice design. One item that MAY improve it is using shaft extenders and moving all the switches and pots to the back. If the chassis is tall enough the shafts can pass over the top of the circuit board. 

  This also allows moving the power supply to the front and placing the amplifying circuits next to the inputs and outputs.

  I find this is an audible improvement. This way the signal wires can be a few inches in length. 

  

[sandyk]

8 hours ago, 4est said:

It has been said that one of the issues is that analog engineers are not always the best digital engineers and vice versa.

 

+1 

[sandyk]

6 hours ago, Panelhead said:

 

   Very nice design. One item that MAY improve it is using shaft extenders and moving all the switches and pots to the back. If the chassis is tall enough the shafts can pass over the top of the circuit board. 

  This also allows moving the power supply to the front and placing the amplifying circuits next to the inputs and outputs.

  I find this is an audible improvement. This way the signal wires can be a few inches in length. 

  

 The Chassis  is a 1U rack case. This makes implementation of the shorter signal paths harder to implement.

Yes, I did consider that possibility originally.

However, I have not noticed any audible degradation using the existing layout.

The PSU lead lengths have a much greater impact,  when they are optimised as I mentioned., especially equalising the  0 volt PSU lead resistances !

 I also have a larger, beautifully made ceramic selector switch that unfortunately, I can't use.

I have compensated for the different lengths of PSU leads by using thicker gauge wire for the + and -  of the more distant PCB, and doubling up of the o volts leads on this as well ( 2 green wires)

I could have used relay switching at the RCA input sockets, but didn't want to draw current from just one PSU PCB. The copper traces of the Relay Switching PCB may also degrade HF channel separation!

I use a different layout for my headphone amplifier which uses the same channel PCBs which were designed to my requirements by collaboration among members from another forum.

 The H.A. version now also uses a DACT2 Attenuator.

Incidentally, the width of the main PCBs makes it difficult to further optimise the layout when using this 1U rack case.

[mansr]

8 hours ago, 4est said:

It has been said that one of the issues is that analog engineers are not always the best digital engineers and vice versa.

So get an expert in each and let them build a DAC together.

[sandyk]

5 minutes ago, mansr said:

So get an expert in each and let them build a DAC together.

 

 Perhaps you should collaborate with Marc ?

No, I am not being facetious !

I don't doubt that either of you have vast experience in your individual areas of specialisation.

[gmgraves]

23 hours ago, mansr said:

So get an expert in each and let them build a DAC together.

 

At Schiit it's Mike Moffat for the digital stuff and Jason Stoddard for the analog designs. Both are legendary in their fields. Maybe that's the reason their stuff consistently seems to outperform it's price points. 

[mansr]

21 minutes ago, gmgraves said:

At Schiit it's Mike Moffat for the digital stuff and Jason Stoddard for the analog designs. Both are legendary in their fields. Maybe that's the reason their stuff consistently seems to outperform it's price points. 

I've only had limited interactions with them, but they seem to know their schiit.

[GUTB]

I asked in the Head-Fi thread why Schiit seemed to be against torodial transformers. The legendary Jason Stoddard responded with an attack on torodials in audio...and then was corrected on several inaccuracies in his statements by some other other members.

 

It's  true that Mike Moffat was a name back when Theta was in the limelight. What ever happened to them?

[gmgraves]

9 minutes ago, GUTB said:

I asked in the Head-Fi thread why Schiit seemed to be against torodial transformers. The legendary Jason Stoddard responded with an attack on torodials in audio...and then was corrected on several inaccuracies in his statements by some other other members.

 

It's  true that Mike Moffat was a name back when Theta was in the limelight. What ever happened to them?

 

Mike might be like a number of entrepreneurs, the "fun" and the challenge is in starting a new company and coming-up with innovative new products, not operating a company on a day-to-day basis, and I put the emphasis on MIGHT. 'Cuz I don't know one way or another. I do know that back in the 90's Moffat built a DAC for Theta called the Generation VII, that was so good that people who bought them still have them and won't sell them. Whether or not the Yggy is built upon concepts first explored in that $15K Theta design or not, I don't know either. I'd love to see somebody contrast a Theta Gen VII with the latest Yggy. Now that would be interesting.....