abbey road d enfer

Re: Direct output from Neve channel switching unit
« Reply #20 on: June 27, 2019, 09:48:20 AM »
Abbey, I wouldn't know how to set up the 1646 for more than 6dB gain. It seems fixed, at least according to the documentation. Is there some trick?
  You need to add another opamp with 4dB gain. That's all.

Quote
The Tech Info Sheets are pretty clear on not running an opamp at less than 10dB gain...
  What? Many opamps are unity-gain stable.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.


Re: Direct output from Neve channel switching unit
« Reply #21 on: June 27, 2019, 12:45:09 PM »
  You need to add another opamp with 4dB gain. That's all.

Too many stages I think.

  What? Many opamps are unity-gain stable.

Not the 340 / 440 /640. Unsure why though, just that the 406 was the only one approved as a buffer. These are all non-inverting, and unable to take a diff input for reasons that I’m unable to grok.

abbey road d enfer

Re: Direct output from Neve channel switching unit
« Reply #22 on: June 27, 2019, 02:38:20 PM »
Too many stages I think.
Minimalism is an obstacle to free thinking.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

Re: Direct output from Neve channel switching unit
« Reply #23 on: June 27, 2019, 07:14:07 PM »
Minimalism is an obstacle to free thinking.

 ;D

ruffrecords

Re: Direct output from Neve channel switching unit
« Reply #24 on: June 28, 2019, 03:18:30 AM »
Most of the early Neve amps are not unity gain stable because, unlike most op amps, they don't take a sledge hammer to stability by adding a pole at a few Hz. This means you don;t get the 20dB/decade rise in distortion that op amps give you. Maybe that is part of why they sound so good.

If yo really want to retain the transformer them use a BA283 with an appropriate pad in front of it,

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Re: Direct output from Neve channel switching unit
« Reply #25 on: June 28, 2019, 03:34:01 AM »
If yo really want to retain the transformer them use a BA283 with an appropriate pad in front of it,

I'll look at that, cheers.

Re: Direct output from Neve channel switching unit
« Reply #26 on: July 16, 2019, 04:34:40 PM »
I'll look at that, cheers.
Won't you have to use the inductor too since your trans. are ungapped?   What about a 440 style amp or that BBC specific one?  Someone makes a version you can buy I'm sure. 

Re: Direct output from Neve channel switching unit
« Reply #27 on: July 16, 2019, 04:42:02 PM »
Won't you have to use the inductor too since your trans. are ungapped?   What about a 440 style amp or that BBC specific one?  Someone makes a version you can buy I'm sure.

That’s the issue, they are ungapped and nobody’s even making a PCB for a 340, 440, or 512. The Eisen 512s are really cool but I’d have to rail split. I wish a board and heatsink existed for the original 512 design, it would be the perfect thing. I actually have one that could be reverse engineered but I’m not excited about taking it apart.

There are many solutions involving things that run on bipolar 15-18V, but it would be really nice to leave it single 24V. I’m quite a bit more up to speed on this than when I started the thread. In the land of “affordable,” and mucking about with power supply not originally spec’d, it’s basically the the CAPI BB2521, or the JLM Hybrid.
« Last Edit: July 16, 2019, 04:56:15 PM by atavacron »

Re: Direct output from Neve channel switching unit
« Reply #28 on: July 16, 2019, 05:10:15 PM »
Would it have to be the same footprint of the 512 or 440?   Or would you be happy with, say 8 amps on one board? 
There's also the Neve 640 BBC amp which is just a 5534 and a couple of transistors.

Edit,. I think you said you want this inside each module so 8 amps on one board is out.   Why not just a 440 on a little PCB that is just secured inside and hard wired?
« Last Edit: July 16, 2019, 05:13:55 PM by Winston O'Boogie »

Re: Direct output from Neve channel switching unit
« Reply #29 on: July 16, 2019, 05:26:39 PM »
Would it have to be the same footprint of the 512 or 440?   Or would you be happy with, say 8 amps on one board? 
There's also the Neve 640 BBC amp which is just a 5534 and a couple of transistors.

Edit,. I think you said you want this inside each module so 8 amps on one board is out.   Why not just a 440 on a little PCB that is just secured inside and hard wired?

Good questions.

I believe the appropriate placement for these is as close to the 33752 modules as possible. The “direct output” wiring runs from there to another area of the desk, where the LO2567s are clustered without convenient power. So to accommodate both existing  wiring and impedance rules, the ideal solution is a 420mm wide board that mounts up under the channel switching units.

The 640 is not really worth cloning if one is going to the trouble of a custom solution. The 440 would be great. For those who are in the know, the 512 is perfect. A 420mm board would have the opamp layout x 12, with resistors and capacitors according to the BA489 spec onboard. All in one solution.

Then that same layout could work for folks who are not interested in paying $150 a pop for untested vintage 440s on eBay and Reverb. What a rip.


Re: Direct output from Neve channel switching unit
« Reply #30 on: July 16, 2019, 05:59:05 PM »
OK then I would do that.  I agree that the 640 isn't worth the hassle.  To drive the 200 ohms of your transformers I think just using 3 X 5532 chips in parallel would sound better than a 640. 
Isn't the 512 basically just an output protected version of a 340/440?  It isn't gonna be a full class A into 200 ohms with that output stage so is there any benefit of it sonically Vs a 340/440?
 
I don't mind laying out a 440 amp if you can't do it.  I haven't got a pc with the usual software I'm used to but I can get something that'll work on my MacBook Pro.

Lemme know, shouldn't be hard or take long, famous last words...

Re: Direct output from Neve channel switching unit
« Reply #31 on: July 16, 2019, 07:52:56 PM »
BA440

https://drive.google.com/open?id=1LdvKK5EKboJ7RZkHSXE0xIPrwYEUy8zQ

BA512

https://drive.google.com/open?id=12E6kBQZzdEWJMiU26TTVRA0xzoX4-01E

I’m out of town but I can take pics of a 440 and a 512 when I get back. There’s no trace layout in either doc but I could put ‘em in a scanner and do something in Photoshop  to make ‘em usable. I doubt anyone would have a problem with a faithful layout and part substitution only to accommodate an easy Mouser  BOM. I don’t believe the part equivalents are terribly unusual.

I do need to scan the BA489  schematic and call out the correct supporting components for each amp. There are some significant value differences across types.

This is all class A/B, there were no Class A output amps in the broadcast desks AFAIK. The best application example of a 340/440 into an LO2567 is of course the 1081, albeit into 50 ohms parallel series. The common application example of a 340/440 into a LO1173 is the 3405 line amp. This desk has 33415 and 33416 line amps, which output with 440s into the TO129, which is like a LO1173 with a tertiary winding for NFB.

3415: https://drive.google.com/open?id=1rIBRKHPKbknvcBvmehG9iuU2oyn3ZYNA

3405 schematic attached.

With a DIY BA440 solution, a 12-channel board could run the amps inverted at a gain of 2 (+6dB) into the transformers at 200:600. It is my understanding from the Tech Info Sheets that they are not stable below 10dB of gain non-inverting, though I suppose one could clone the pad from the 3405 and just eat the extra 4dB. The 33752 would not mind seeing another 5K-10K trimmer on its unbalanced output, as it already has four aux sends at 4k76 and eight groups at something like 8k each that it feeds off of the same, so if these ran non-inverting, one could basically just clone the output of the 3405 and trim to suit. The trim on the 3415 is in the front half of the amp, by the way, so it’s a little less straight ahead. Klett’s online EDO is the best trafo ref.

I don’t know if they are unity gain stable when inverted, but regardless, it feels like a stretch to ask them to do unity gain inverted just to be able to run the trafo parallel/series for its 10dB of free gain — also it would really be a lot of current draw. But they certainly will drive 50 ohms all day!

It really would make my whole dang Summer to see an appropriate amp birthed as a result of this topic, and I’ll bet a lot of other folks would dig it too. I am supremely lucky to have a spare power supply with this desk...
« Last Edit: July 16, 2019, 08:24:48 PM by atavacron »

Re: Direct output from Neve channel switching unit
« Reply #32 on: July 16, 2019, 08:50:11 PM »
OK cool.  I remembered wrong on the BA512, its input being a CCS fed diff amp rather than the single transistor with  low z inverting input on the 340/440. 
Up to you, but I would run them into a series connected 200 ohm primary on your transformer rather than into 50ohms.    I think an input trim into the amp would be an appropriate way to lose a couple of dB and line up the whole driver circuit to whatever standard you're working to.   
Possible that an inverting input is lower distortion but maybe nothing in it over going non-inverting.
Maybe I would think about using the trimmer arrangement from the 340 to set the bias spreader TR5 and output current rather than the "select on test" R16 on here.   It's a bit easier to dial in, but then maybe not as long-term reliable.   Either/whichever way, I think it's worth your effort using a Neve amp stage since you already have the output iron.

Re: Direct output from Neve channel switching unit
« Reply #33 on: July 17, 2019, 03:19:46 AM »
I'm gonna attempt to have an intelligent conversation about the BA440 vs the BA512 and potential directions for a reproduction, but I'll be missing some key terminology due to not knowing as much about how opamps work.  (What's CCS?) For reference, this console's setup level is +4dBu. Everything on the patchbay is that...except for these -2dBu weirdos.

The BA512 is spec'd a bit more carefully than the 440, 7 to 17dB for lowest distortion (I would assume to please the client), whereas the BA440 is spec'd generally up to 20dB. The BA512's .1uF output load spec is interesting, I wonder what the capacitance of 1 meter of Canford FST going into the series primary of an LO2567 would be. Probably way lower.

Do I need to do a listen test? I kinda feel like taking the last opamp of the broadcast series and improving it slightly for DIY is probably the best call. And with people nowadays having plenty of BA283/LO1166 options, I'm gonna guess that the BA512 would be considered a slightly more hifi / snappier transient starting point for line amps and low-channel-count summing amps and other output sections. Might also appeal to people who would otherwise default to ICs, but do need to drive a transformer.

On the other hand, doesn't the BA512 split the rail, and isn't that what I'm trying to avoid?

If either amp will let me do 7dB of gain non-inverting, I would run it that way with a little input trim, or just ignore the extra 1dB.  I do wonder if the BA440 is as stable as the BA512 at that low level. The Tech Info Sheets list the "not less than 10dB gain" rule for all opamps other than the BA406 in a very prominent list of Don'ts, but this was before the BA512 came along (with its diff input as you mention).

I think a trimmer in place of R16 would be a good call...a side adjust 3/8" or smaller, so you could get to it without taking off the heatsink. 2K 25-turn I presume, if the goal is always in the neighborhood of 1K. Or are you saying wholesale import the 5K arrangement from the 340? Seems more reliable to just change one resistor than two at a time.

Why not just integrate the supporting parts from the 1081 or 3405 into the board itself? It would make everyone's life easier (except for folks who need a drop in replacement). In this arrangement, I'd put decoupling and smoothing below or above the core amp layout, to keep the total width less than the broadcast module size of 35mm. 24V, 0V, IN+, IN-, OUT could all just be on a .100" header at one edge, or separate the power and the output by .100 off the inputs.

Last but not least, maybe there's a way to lay this thing out so that some beefy clip-on heatsinks could be used (see for example how the 33752 mimics the BA640 but without the top plate). Having to have a custom plate milled just adds cost...they do get hot but not crazy hot.


« Last Edit: July 17, 2019, 04:49:28 AM by atavacron »

Re: Direct output from Neve channel switching unit
« Reply #34 on: July 17, 2019, 05:55:48 AM »
What's CCS?

Constant current source.


 The BA512's .1uF output load spec is interesting, I wonder what the capacitance of 1 meter of Canford FST going into the series primary of an LO2567 would be. Probably way lower.


Yes, much lower than .1uF (which is 100,000pF).  A metre might be 150pF or so.  A small value output isolator resistor or inductor combo at the amp output wouldn't hurt though, it'll isolate the cable from the amp feedback loop.


Do I need to do a listen test?


It's always good to do that if you can I think


I think a trimmer in place of R16 would be a good call...a side adjust 3/8" or smaller, so you could get to it without taking off the heatsink. 2K 25-turn I presume, if the goal is always in the neighborhood of 1K. Or are you saying wholesale import the 5K arrangement from the 340? Seems more reliable to just change one resistor than two at a time.


I just think that it'll make your life easier when biasing them up for the first time.  Another option is to put in a higher than needed value in R16, say 2k, and have an empty spot for another R in parallel with it.  Then use a regular pot clipped across it to determine the bias.  Then remove the pot, measure the value and solder in the nearest value resistor.


On that note, why not just integrate the supporting parts from the 1081 or 3405 into the board itself? It would make everyone's life easier (except for folks who need a drop in replacement). In this arrangement, I'd put supporting parts below and above the amp, to keep the total width less than the broadcast module size of 35mm.

One board with everything on it will cost less and be less work than building a mother/daughter board dealie.   Laying out a separate BA512 daughter card is easy enough for folks that want or need that.


Last but not least, maybe there's a way to lay this thing out so that some beefy clip-on heatsinks could be used (see for example how the 33752 mimics the BA640 but without the top plate). Having to have a custom plate milled just adds cost.

I thought about that myself and believe it should be fine.  Thermally coupling the pair of out transistors is nice and all that, but a couple of strategic LEDs would protect against thermal runaway, and it's not like we're looking to get a low DC offset at the output since it sits at 12V.  Whatever heatsinks work, are nice and cheap, but look sexy are where it's at.


Re: Direct output from Neve channel switching unit
« Reply #35 on: July 17, 2019, 06:50:06 AM »
Righto. Well I don’t know the BA512 well but I do know the 3405 and 33415 schematics, so here is an idea specifically for the BA440, attached.

Having the pads for the trimmable pad, the feedback resistor/cap, and the gain resistor labeled generically would be smart. I believe this would work with any step up transformer. The primary shunt might want to go on the board though.

The more I am thinking about this, the more I am thinking BA440. It’s better supported in Neve literature and is more native to the systems people would be aping (including this desk, which is all 3114 / 3415 / 3416). The one BA512 I have came from a 33422, which is from that weird era where Marinair was ditched for Belclere but the module size remained 35mm.
« Last Edit: July 17, 2019, 07:04:45 AM by atavacron »

ruffrecords

Re: Direct output from Neve channel switching unit
« Reply #36 on: July 17, 2019, 07:33:34 AM »
Won't you have to use the inductor too since your trans. are ungapped?   What about a 440 style amp or that BBC specific one?  Someone makes a version you can buy I'm sure.

Yes you would which seems rather wasteful of iron especially as the inductor need to be gapped anyway. Simpler to spring for the gapped Carnhill transformers and be done with.

Cheers

ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

ruffrecords

Re: Direct output from Neve channel switching unit
« Reply #37 on: July 17, 2019, 07:36:26 AM »
Righto. Well I don’t know the BA512 well but I do know the 3405 and 33415 schematics, so here is an idea specifically for the BA440, attached.

You don't need the 150 ohms across the transformer primary do you?

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Re: Direct output from Neve channel switching unit
« Reply #38 on: July 17, 2019, 07:44:41 AM »
Yep, I can see that a 440 or 340 would be a more appropriate fit.  The 512 is a pretty standard op-amp architecture, albeit not used as. DC op-amp.  Maybe it was the transition idea towards using the 5534 op-amp 640 card?  Who knows specifically why the BBC wanted it?


One thing, and this addresses Ian's observant 150 ohm question: 
That 150 ohm primary terminating resistor you show on the last drawing isn't appropriate for your transformers wired 200:600.   Those resistors were there to put a somewhat light load on the transformer in case it wasn't loaded externally by anything close to 600 ohms.  It helps with ringing not caught by the zobel.
So: the 150 ohms you show is for a transformer with a 70 ohm primary.   You will also see a 100 ohm resistor used on a 1081 when that transformer is strapped for 50 ohms.
If you follow so far, you might grasp that these light loads are approx.  twice the usual load.
Lots of desks (thinking about an 8066 and a couple other 8000 series I've slaved over)  had a 1200 ohm strapped externally across the secondary 600 ohm side.  And at the patch bay point rather than on the transformer itself.  Thats what I would do with your transformers, shove a 1k2 on the secondary as well as the zobel.  Or, do what everyone does now when they build or rack modules, leave it unterminated other than the zobel to ring away.  Folks have now adjusted to what they think is the correct Neve sound.
« Last Edit: July 17, 2019, 08:05:49 AM by Winston O'Boogie »

Re: Direct output from Neve channel switching unit
« Reply #39 on: July 17, 2019, 07:53:40 AM »
P.S.  I also wasn't completely comfortable with what the 512 amp was doing regarding its dominant pole compensation and then just using the external feedback networks of the 340 or 440.  I'd want to shove it in the simulator to check stability etc.
Using the straight 440 scheme or 340 which is basically identical is a safer bet without doing any real design work


 

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