bushwick wrote on Thu, 06 January 2011 13:29 |
Do any of y'all have S/N specs on large format boards with all channels summed to the L/R buss. It came up in conversation today and I am very curious. Something north of 40 channels and along the lines of a 72 ch SSL, or 72 ch of 8078, or a legacy. Thanks, josh |
Jim Williams wrote on Mon, 10 January 2011 11:56 |
It all depends on what your reference point is. If +4 dbu analog tape, not so great. If you use elevated levels as found from some DAC's, it improves quite a bit. If your signal levels reside at +12 dbu or more, you can improve the S/N by the same amount, 8 db. Take 8+ db of buss noise off the mix and complaints go away. |
Jim Williams wrote on Tue, 11 January 2011 09:38 |
I'm talking buss and console noise contributions, not source noise from the storage device. By elevating the signal levels throughout the console, the console's noise contribution is lowered. Signal levels throughout my analog console reside at around +14~16 dbu. It clips at +28 dbu. That still offers enough headroom to be able to boost EQ without overloading the system. The opamps I use also sound best at higher levels. The buss noise does degrade with common digital reverbs, exception being the Bricasti M7. Noise problems were solved many years ago here. It's not something I ever hear anymore. With a console loaded with .9 nv/hz/sq noise opamps, it's below the 16 bit theoretical noise floor so noise is not encoded to CD's. |
John Roberts {JR} wrote on Tue, 11 January 2011 08:48 | ||
Agreed, not noise, but phase shift and linearity still count. JR |
Jim Williams wrote on Tue, 11 January 2011 23:33 |
Your buss noise should be pretty low. If you unassign all the mix buss resistors, it really goes down. That noise adds up from both the buss resistor's thermal and current noise plus the electronic hiss from the input channels. The resistors are fixed but the electronic hiss contribution can be lowered. There are some very low noise fet input opamps that do very well lowering noise in older designs that used larger value resistors. |
bruno putzeys wrote on Fri, 14 January 2011 13:12 |
The curious thing is that when one keeps perfecting the console and the converters in this manner, you start approaching the sound quality you can get by not leaving the digital domain at all. |
John Roberts {JR} wrote on Wed, 19 January 2011 08:15 |
Back in 1980 I wrote an article on console design for RE/P where I described a way to bus numerous channels together without the N+1 noise gain of a virtual earth summing amp (replace the resistors with current sources). |
Bob Schwenkler wrote on Sun, 23 January 2011 13:51 | ||
Is there available or do you have a copy of this article? |
dcollins wrote on Sun, 23 January 2011 22:22 |
Has anyone read this!? http://collinsaudio.com/Muth_Summing/ DC |
dcollins wrote on Sun, 23 January 2011 21:22 |
Has anyone read this!? http://collinsaudio.com/Muth_Summing/ DC |
ssltech wrote on Mon, 24 January 2011 11:38 |
Back when that paper was current, I voiced similar comments, and Chris Muth registered and posted some rebuttals... Several people whom I respect all dig Chris's work, and I've used some of his product before and it's certainly been very well made. -I wouldn't wish for a second to impugn his abilities or his product. |
dcollins wrote on Tue, 25 January 2011 17:44 | ||
That doesn't mean the gear won't sound great, but I was just surprised that both the analog and digital conclusions were off the mark. Was the paper ever revised? DC |
Geoff_T wrote on Wed, 12 January 2011 18:47 |
Hi Vintage Neve consoles had signal to noise measured in three stages. 1. The output noise with the 4T fader at minimum... usually up around high 90's 2. The output fader up and a single channel assigned to the 4T bus 3. A channel at 80dB gain assigned to the same path with 20 to 20KHz filter on all these measurements and the input terminated 200 ohms. That last test gave figures better than -45dB = EIN better than 125. But note, they did not assign all the channels to a bus... just one channel. All these tests are clearly listed at the rear of the technical handbooks along with a polaroid photo of the square wave response. Plus all vintage Neve tests were referenced to 0dBu, not +4dBu and the noise was not subtracted from the maximum output like digital measurements these days and power amps. Hence their wonderful figures! |
JGreenslade wrote on Thu, 27 January 2011 17:04 | ||
This reminds me of a chat I had a while back with a certain pipe-smoker who looks after a gaggle of vintage Neves here in the UK. A client had remarked that, whilst their facility could live with the console's noise floor, they were interested in bringing it below that of the new-fangled hard disk recording devices. Said engineer decided to try an experiment, by equipping a selection of bus amp cards with uber-low noise Japanese epitaxial types (the type developed in the eighties for low noise MC cartridge preamps), putting these in place of the original cards that contained BC184s and seeing what difference this made to the broadband noise trace on the FFT... ...suffice to say, there was no difference at all. The transistors themselves are by far one of the least dominant noise sources - as I'm sure the Neve stalwarts here will be fully aware. I just thought it would make an interesting interjection to relay the tale. I guess he wished in his heart that he could walk away from the studio feeling smug that he'd taken 12dB off the console's floor... No cigar that day! Justin |
JGreenslade wrote on Fri, 28 January 2011 07:05 |
There were a handful of transistors supposedly made specifically for MC carts - I believe up until the early eighties, but you might be right (the audiophile boom seemed to peak around the late '70s from what I've seen). Sanyo and Hitachi both offered devices that were claimed to be developed for this purpose. IIRC, Mackie used the Sanyo parts in one of their consoles. Well, say what you want about Mackie, but their consoles have never been noisy! There's a Self-designed MC preamp that parallels the SB737 at the front end. 2SA872 - I seem to remember that off top of head. Justin |
JGreenslade wrote on Thu, 27 January 2011 15:04 |
This reminds me of a chat I had a while back with a certain pipe-smoker who looks after a gaggle of vintage Neves here in the UK. A client had remarked that, whilst their facility could live with the console's noise floor, they were interested in bringing it below that of the new-fangled hard disk recording devices. Said engineer decided to try an experiment, by equipping a selection of bus amp cards with uber-low noise Japanese epitaxial types (the type developed in the eighties for low noise MC cartridge preamps), putting these in place of the original cards that contained BC184s and seeing what difference this made to the broadband noise trace on the FFT... ...suffice to say, there was no difference at all. The transistors themselves are by far one of the least dominant noise sources - as I'm sure the Neve stalwarts here will be fully aware. I just thought it would make an interesting interjection to relay the tale. I guess he wished in his heart that he could walk away from the studio feeling smug that he'd taken 12dB off the console's floor... No cigar that day! Justin |
Jim Williams wrote on Fri, 28 January 2011 10:18 |
The 2SB and 2SD devices were the slow stuff, the 2SA and 2SC are the fast ones. Besides those slower parts, there were/are faster varients of them. The Hitachi 2SA1083 and 2SC2545 series were the quicker parts. Toshiba also makes similar parts, the 2SA1316 and 2SC3329. Renesas also now makes the 2SA1084. |
bruno putzeys wrote on Fri, 28 January 2011 12:23 |
Yes, but even lower than that. I've not yet managed to make a transformerless pre for a ribbon with sufficiently low noise. |
Geoff Emerick de Fake wrote on Fri, 28 January 2011 15:46 |
A ribbon has a typical impedance of about 1/10th of an ohm. The necessary transformer uses a few turns of large-gauge wire at the primary. Even with these precautions, most of the reflected impedance at the secondary is resistive. |
Geoff Emerick de Fake wrote on Fri, 28 January 2011 17:09 |
As Bruno mentioned, there have been some experiments. The essence of the problem is that, in order to achieve a good ratio of En to In, the input transistor compound would have to operate at several amps quiescent. |
Jim Williams wrote on Sat, 29 January 2011 11:14 |
Actually less of them if you use the right parts. There are very low noise jfets available. Linear Systems makes the selected low noise 1 nv 2SK170. NXP (Phillips) makes the BF862 at .7 nv voltage noise and minimal current noise. That part does work well in mic preamp front ends without the noise trade-off of most other jfets. That also allows one to set the input impedance very high to minimize loading. It also allows you to reduce the value of the input blocking caps letting you select quality film caps in place of traditional electrolytic caps to block 48 volts. |
Jim Williams wrote on Sat, 29 January 2011 11:14 |
Actually less of them if you use the right parts. There are very low noise jfets available. Linear Systems makes the selected low noise 1 nv 2SK170. |
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NXP (Phillips) makes the BF862 at .7 nv voltage noise and minimal current noise. |
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That also allows one to set the input impedance very high to minimize loading. |
Geoff Emerick de Fake wrote on Mon, 31 January 2011 10:58 | ||||||
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Jim Williams wrote on Wed, 02 February 2011 09:54 |
Which is still not high impedance like you can do with the jfets, I'm talking meg ohms here. |
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100k bias resistors used alone with a LM394 will cause a lot more resistor source noise than that part is designed for, a low input impedance to match it's noise and current noise specs. |
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Once the 6.81k phantom resistors are fitted, that sets it low again anyway. With a phantom switching scheme that switches out the phantom resistors and input blocking caps you can raise that input impedance pretty high with the jfets without source impedance noise problems that occur with bipolar transistors. |
Jim Williams wrote on Fri, 04 February 2011 10:30 |
No concern, it's just another way to skin a cat. Sonically an all jfet low noise high input impedance mic preamp design does sound different. As I mentioned before, the higher input impedance allows the designer to use smaller value, higher quality film caps to block 48 volts in place of common larger valued electrolytic capacitors. It does allow one to inject high impedance sources without a DI box, but that's not even needed. Besides an all jfet design, I also have some with all transimpedance amplifiers, those are very fast and once again, different sounding. They run at over 100 mhz and sound very good. Which ever topology I use, they all sound a lot better to me than the commercial stuff you can buy. |