Another summing bus op amp comparison

[living sounds]

Here's one more comparison of op amps in the mix bus position of my highly modified Soundcraft console. It's part of an entire mix summed in the console with live outboard compression and added FX, so null tests don't work.  24 channels (FX returns counting) are being summed.

Summing happens on a CAPI ACA board with resistor and feedback cap values adjusted to the boards summing resistor values. The console is powered by a discrete high end PSU, great care has been taken to optimize grounding and decoupling. After the summing op amp the signal travels through a transformer, the fader, the booster amp (CAPI hybrid op amp using 80s Signetics NE5534), another transformer and then straight to the converter. Only significant processing applied afterwards is sample rate conversion via FinalCD from 48khz to 44,1 khz.

Mixing was done using CAPI hybrid Signetics NE5534 in the summing position, so it has an advantage here.

All op amps used:

APP992
Whistle Rock Audio ML2520
CAPI gar1731
Signetics NE5534 (NOS)
TI NE5534 (current model)

This is a blind test, so the files are not necessarily in the above order.

https://www.dropbox.com/s/r0dxb08rtdhfxb5/5.wav?dl=1
https://www.dropbox.com/s/o4985wurzsl0lb6/4.wav?dl=1
https://www.dropbox.com/s/ye3w00a4mkpgrji/3.wav?dl=1
https://www.dropbox.com/s/0kpmn5lg71jzp1z/2.wav?dl=1
https://www.dropbox.com/s/3i38dwvdjipdqdz/1.wav?dl=1


What do you think?

 

[scott2000]

I need to figure out how to switch between all 5.....can only do two at a time.....but after scanning through them........

I like the 2nd one from the top....... (4)  followed by (2)

for now.......

 

[JohnRoberts]

I think a null test and empirical data would be more useful, but do whatever floats your boat.

JR

PS: the stress on a sum bus amp is mainly from operating at high noise gain. Besides the obvious noise floor, errors can express as phase shift (from the dominant pole compensation), distortion and response errors from insufficient loop gain margin.

 

[living sounds]

I need to figure out how to switch between all 5.....can only do two at a time.....but after scanning through them........

I like the 2nd one from the top....... (4)  followed by (2)

for now.......

Interesting!

 

[living sounds]

I think a null test and empirical data would be more useful, but do whatever floats your boat.

JR

PS: the stress on a sum bus amp is mainly from operating at high noise gain. Besides the obvious noise floor, errors can express as phase shift (from the dominant pole compensation), distortion and response errors from insufficient loop gain margin.

A null test would not much use here, since the signal travels through a few transformers and coupling caps, so what comes out of the console deviates from the source significantly in any way. I've done relative null tests (comparing op amps to each other) a lot before (on this mixbus and in other places) and they can be interesting, but this is about picking what sounds the best, not what is the clostest to neutral. There would be no need for the kind of transformer coupled mix bus I have if neutral were the goal.

 

[scott2000]

I sometimes like to use the left channel of one track and the right of another to hear what affect that has too ...... Floating boats...lol

I really think it'll be interesting to listen more and really try to hear what these differences may be.....

Are we talking about how the summing of different tracks is handled by certain amps??? So, more dense sections would be more telling of some things?????
Pretty interesting......

 

[living sounds]

Are we talking about how the summing of different tracks is handled by certain amps??? So, more dense sections would be more telling of some things?????
Pretty interesting......

I usually hear the same or a similar "color" regardless of position with (these and other) op amps. No matter if they're used as summing amps, fader buffers, mic preamp stage, DAC buffers, whatever. The least offensive ones are usually certain types of NE5534/NE5532. It would be interesting to know what's going on.

 

[scott2000]

Yes I wouldn't doubt if I like some extra stuff maybe even offensive as I'm sure my hearing isn't even what it used to be..... .....on my good ear...lol

I'm pretty sure I hear some more something on (4) that's missing on the others although (1) has it too...... Very subjective stuff....

( a kind of extra space/noise/something that's easier to pick out when there are less things going on) Could be my imagination.....

I Like some of the punch in the mix.....Got a nice  tight pound to it...... I Put it on with some sub......

If nothing else it's a good nod to the 5534 if there was any doubt I suppose........

I yanked a bunch of 5533 duals from something recently and wondered if they'd be of any use down the road. They're Signetics too....Not sure what to make of the talk of the different makes but, I know I like the sound of the 5534......

Good Luck!

 

[Bo Deadly]

A null test would not much use here, since the signal travels through a few transformers and coupling caps,  ....  but this is about picking what sounds the best, not what is the clostest to neutral.

Sorry in advance for being a judgmental pedantic science puke but for a thread titled "summing bus op amp comparison", you're not being particularly objective. If you want to compare op amps, then compare op amps and not channel strips. Take the DOA out of it's socket, run a null test next to a 5532 and post some numbers. Yeah, it should be very uninteresting but then again, it might not be. Compare level vs THD up to 1% and post spectra. Look at noise. That should yield some differences that might support claims that something "sounds the best".

 

[iampoor1]

If Im being honest, I dont really hear any differences. 

 

[scott2000]

Yeah it's really really subtle and tiny stuff I'm actually trying  to hear now..... .....
......... There's  some  spatial and slight panning differences going on between them with certain notes from what I can tell .... .....  but overall in the context of the whole mix they sound a lot alike...... but I am certain hear differences when trying to find them.....

To mention what squarewave pointed out .....

Are we most likely to be hearing different channel strips? This must be the reason for any noticeable differences....especially notes wandering in the pan field/spacial stuff????? just weird it seems like certain notes only.....but I just started listening again....

Edit////I guess I missed the point of this. Of course there are supposed to be differences??? But it's supposed to be which one we think sounds best overall???  I guess I'd go with my first instinct still ......But I like what's happening in different ways in all of them... So I'd experiment with them all at the same time probably like I mentioned earlier......... I think it can add some weird something sometimes when using different op amps for left and right and especially in this case with some of the obvious differences.... Not too much unlike disabling a stereo link...??? That's crazy???

Or splice/comp every favorite part from each one.....

 

[living sounds]

No, you're not hearing different channelstrips. This is a real time mixdown of 24 channels, with compressors, reverb, delay etc. I simply turned off the console, took out the two summing op amps and replaced them with a different pair. Turned on the console again, let it warm up a little, recorded and repeated the process with different op amps.

The audible differences are representative for the differences I have recognized with the respective op amps in other test setups. 

 

[scott2000]

That's pretty interesting. I've heard some pretty big differences in various op amps before when listening to one piece of gear more or less but, I just figured it was due to the various conditions of the circuit and the loads, newer amp characteristics vs older ones,oscillations maybe ,etc.....

These things in your tracks I'm hearing aren't as easily noticeable as what I'm able to pick out in my above example which is really surprising to me because of the number of pieces being used but, they are pretty significant in what they do differently and it makes me really want to revisit some other things I've listened to to see if there are spacial or other characteristics in the sounds that are standing out because of a certain amps behavior in a piece or chain.

It seems to me that , in these examples, everything in the chain can't act the same exact way every time? Maybe especially the delays/reverbs>>>////some phasing?? It's pretty wild because they , the tracks, are so close in many ways , identical "sounding" to me even,yet, the differences aren't small when they appear and then are singled out.

Thanks for posting these. It's opened up some more thinking for me for sure.

Maybe you could make two passes with the same op amp or, turn of the test chain, then turn it on again and run the same op amp just to see if these differences can be picked out again which would verify that the chain itself or some piece in it  is actually behaving differently at random.....

If not, then that would be pretty wild......

 

[abbey road d enfer]

All op amps used:

APP992
Whistle Rock Audio ML2520
CAPI gar1731
Signetics NE5534 (NOS)
TI NE5534 (current model)

I wouldn't expect much difference, since they all are very similar.
I would rather try the differences between a 5534, a VLN opamp such as LT1115 and a current-feedback type such as AD811.
There would be objective (measurable) differences, the VLN opamp resulting in lower bus noise, which may or may not be an advantage because of the dithering effect of noise, the current-FB would result in much higher BW/lower phase-shift at HF.
I think the topology using a bipolar front end coupled to an opamp, with current-FB to the transistor's emitter, such as used by Soundcraft (Doug Self design, IIRC) has not been significantly bettered, combining very low EIN and extended BW.
IMO that's how transparent analog summing can be; for those who want "colour", look elsewhere.