design a mastering mixer

[buschfsu]

i have a mastering room that is getting busier so i want to go out of the box with some of my hardware (w492, poorman670, varimu..)  problem is that i only have an apogee duet.  it has 2 line inputs and 2 monitor outputs.  i assume the monitor outs are -10.  i think what i need is a box that i can run the monitor outs into that will bypass into the poweramp (bryston b2)  or will go into an amp stage to boost to +4 with mastering fidelity.  then go out to my hardware and back into the duet line input.

long winded way to ask what the most neutral mastering quality amp for -10 to +4 conversion.  only two channels so i can spend a bit.

thanks

 

[Gold]

The slang for what you are describing is a "bump box". A simple opamp circuit with at least 14dB of gain will work. Just make sure the input impedance is high enough for a -10dBv source. You could impedance balance the output. I think that qualifies as minimalist.

Gains Audio makes good ones if you just want to buy something.

 

[buschfsu]

thanks!

id use high quality switches for bypass but what would be considered high enough fidelity in an amp for mastering.  standard opa2134 type chips?

 

[Gold]

I have OPA 134's in my Neumann mastering console. They replaced the LF356's. So far no one has complained.

 

[buschfsu]

thanks!  one last thing... looking at node 1 would there be any problem running the active monitors AND the duet +4 line inputs off of the output of the rack?  last piece would probably transformer balanced varimu comp.

 

[Gold]

If you go for the single opamp I'd try something that is better in a non-inverting configuration like an AD797. Or use a line driver like a THAT 1646 to flip the polarity back if you use an inverting configuration.

 

[buschfsu]

thanks using the 797 datasheet for noninverting impendance balanced with a 600R on the output and on pin 3 to ground. 

any thoughts on node 1 above?

 

[mjk]

thanks!  one last thing... looking at node 1 would there be any problem running the active monitors AND the duet +4 line inputs off of the output of the rack?  last piece would probably transformer balanced varimu comp.

Except converting from -10 dbV to +4 dbu is not a voltage gain of +14db. Note that the -10dbV level is referenced to 1V RMS ( -10 dbV=.316V RMS) and the +4dbu level is referenced to the old 1mW into 600ohm level of 0.775V RMS (+4 dbu=1.228V RMS). So the actual gain you need is from 1.228/0.316 or about 12db.

Cheers,

Michael

 

[Gold]

Note that the -10dbV level is referenced to 1V RMS ( -10 dbV=.316V RMS) and the +4dbu level is referenced to the old 1mW into 600ohm level of 0.775V RMS (+4 dbu=1.228V RMS). So the actual gain you need is from 1.228/0.316 or about 12db.

I think you want a little wiggle room with the gain.

Just make sure the input impedance is high enough for a -10dBv source.

And I even used the correct lower case v. And upper case B.

 

[mjk]

And I even used the correct lower case v. And upper case B.

Thanks!

I was getting sloppy  :-[

 

[Flundran]

Good explanation mjk. (Do not care bout grumpy replies.)

/F

 

[buschfsu]

ok so any issue with hanging the monitor outs and the duet line ins off of the node 1 as pictured.  i may also add a cmoy headphone amp.  this would all be ok as long as they are each a couple k ohm input impedance?

 

[Gold]

That looks fine to me as long as the Rack Out can drive the load. If you put a passive attenuator before the monitors you should make sure the impedance of the attenuator works. This is a nice simple setup. I like it.

 

[Bill Wilson]

If you want highest quality amplification use analog devices AD744. Has wide bandwidth slew rate of 75 uv. It is fast but not too fast for high quality audio, can be operated in pure class A config. It will put the burr browns in the shade, hands down. AD797 is a great chip but you do not need the low noise input as you are dealing with -10db signal levels. The ability tyo operate in class A gives you additional sonic benefits.

 

[abbey road d enfer]

If you want highest quality amplification use analog devices AD744. Has wide bandwidth slew rate of 75 uv. The ability tyo operate in class A gives you additional sonic benefits.

I haven't seen anything on the spec sheet mentioning this possibility. Do you mean adding a resistor or ccs at the output?

 

[ruairioflaherty]

Hi Buschfu,

I could be missing something obvious but why are you trying to make do with a single stereo pair of D/A?  I think you will be limiting yourself enormously.  A good mastering quality D/A can be had for a good price these days, I used a Benchmark DAC-1 for years before I got my Cranesong and I've seen them go for $550.  You'll also get good quality headphone outs.

Just my 2c and I've been doing the mastering thing a while.

Cheers,
Ruairi

P.S. for Paul Gold - joined the Maselec club this week and got me an MEA-2!

 

[Gold]

I could be missing something obvious but why are you trying to make do with a single stereo pair of D/A? 

P.S. for Paul Gold - joined the Maselec club this week and got me an MEA-2!

I agree with Ruari. A dedicated monitor DAC so you can listen post AD capture is the right way to do it. If the reason is financial it's not a bad compromise. A good AD doesn't change the sound that much. You could always backtrack if there is a surprise.

Ruari,
I've been using an MEA-2 for about 15 years now. I still like it. Well designed and unglamorous. I'm sure you'll get many years of trouble free service. Leif knows his customers by name and is very on top of any service related issues. He knows you make your living with it.

My favorite part of the EQ is the precision of the low mids. Getting that right separates the men from the boys. All bands being able to shelve is also very handy.

 

[buschfsu]

so your suggesting more than one set of dacs in different devices (one in my apogee and one in the benchmark?) i dont think i can clock those together?  interested in what options i have.  the duet is 2 in 2 out with no digitial ins or outs.  if i dump it and get the benchmark i still have to build a switcher for my rack vs staying in the box correct?

 

[Gold]

You want to be able to have one DAC feed the processing chain and another DAC to monitor the DAW output post AD capture. This may be an expensive proposition depending on your setup. You would listen to the DAC that feeds the process chain for "before" and the second one for "after". With the way you have it now you can't monitor the signal post AD. Not to mention the easy potential for a feedback loop if you forget to switch the software from input to playback.

 

[buschfsu]

ok so if i get another dac i dont actually need them synced they are not running together they are monitoring different sources.  would an apogee mini dac be on par with a benchmark.  i think i can get one of those.
thanks