Build Thread:MS76
« on: June 13, 2015, 03:43:45 AM »
I am not done finding applications for the small MS circuit, and I figured, I could use it for linking two 1176 and get rid of any L/R tracking errors (would be M/S tracing errors, which I find to be less critical). I realise this introduces other challenges, but I think its a neat trick. Theres also every mod I could think of/find implemented.

Rev 2 boads for sale.
Documents in the bottom.

https://pcbgrinder.com/index.php?route=product/product&path=59_69&product_id=205

This is a new project, so there is no FAQ and maybe some possible issues I haven't even thought about, but Ill do my best to help out if you have any questions, or if some error I did not catch shows up. This is how these things usually work....

Gustav
« Last Edit: August 22, 2015, 08:06:17 AM by Gustav »


XAXAU

Re: MS76
« Reply #1 on: June 15, 2015, 08:00:38 AM »
I'm loving this! MS is so useful in this comp and also if you have a bunch of mono units and your MS Matrice!:)

Please don't skimp out on the mojo in this unit! :P

Re: MS76
« Reply #2 on: June 15, 2015, 01:25:43 PM »
I'm loving this! MS is so useful in this comp and also if you have a bunch of mono units and your MS Matrice!:)

Please don't skimp out on the mojo in this unit! :P

Thanks!

For starters, I would be ecstatic to get it working. The circuit is the same as the usual 1176,  so the sound of it should be a given :)

I went through the boards with the layout gurus at Printline today, and after correcting an issue or ten,  Will have board before the end of the week if all goes well.

Gustav

XAXAU

Re: MS76
« Reply #3 on: June 15, 2015, 04:41:27 PM »
Sorry for asking but is it a rev. F sort of or?

Re: MS76
« Reply #4 on: June 17, 2015, 01:48:14 AM »
Sorry for asking but is it a rev. F sort of or?

I can't say I know, but arent the differences after revision A just in the transformers (A being class A, later revisions being class AB)?

In that case, its not really any specific revision, since the whole input and output stage is changed in this, adding the THAT circuits for input and output, and/or optional Lundahl footprint on the output.

The schematic Ive been working from was drawn up from the G1176.

Gustav

XAXAU

Re: MS76
« Reply #5 on: June 20, 2015, 11:17:13 AM »
Rev F uses AB output transformer and in rev G they ditched the input transformer.

http://www.uaudio.com/blog/1176-la2a-hardware-revision-history

Would it be possible to make a footprint for lundahl trafo on the input as well or is it too much work? Trafo = mojo!:)

Re: MS76
« Reply #6 on: June 20, 2015, 12:35:54 PM »
Would it be possible to make a footprint for lundahl trafo on the input as well or is it too much work? Trafo = mojo!:)

I may have gotten a batch with the mojo missing, but I never found the input trafo added anything significant on the G1176. If your findings have been different, you can hardwire a trafo easily.

I made sure to add a layer of mojo to the PCB layer 3, though (you should be able to see it on the board layout), so I can assure you, it was not skimped on for the slightest.  :)

Gustav

Re: MS76
« Reply #7 on: June 23, 2015, 04:36:23 AM »
Small update.

Went over the boards a few more times, and finally started production. Factory is closed Wednesday, so hopefully I'll have them thursday.

Gustav

tata

Re: MS76
« Reply #8 on: July 05, 2015, 02:15:18 AM »
Gustav, can you pls shed some light on the signal route / phase when Blend is engaged and M/S processing is fully OFF?

so far what i think : signal is "in phase" at the out of the debalancer stage, but then it flips at the CLEAN-L(/R), right? (after the buffer / inverting stage). then it flips back at "BLEND-L(R)" and stays the same at the balancing stage / output.

the "DIRTY" signal is "in phase" at LM-OUT, but then it flips at "BLEND-L(R)" and stays flipped?

thanks


Re: MS76
« Reply #9 on: July 05, 2015, 01:19:06 PM »
Gustav, can you pls shed some light on the signal route / phase when Blend is engaged and M/S processing is fully OFF?

so far what i think : signal is "in phase" at the out of the debalancer stage, but then it flips at the CLEAN-L(/R), right? (after the buffer / inverting stage). then it flips back at "BLEND-L(R)" and stays the same at the balancing stage / output.

the "DIRTY" signal is "in phase" at LM-OUT, but then it flips at "BLEND-L(R)" and stays flipped?

thanks

Note that the buffer tapping the clean blend is non-inverted.

And sorry, I dont understand the observation you made on "dirty" tap. It just reroutes the signal to one pin of the blend circuit, same place is comes back.  Make sure you see that the MS is switched in two locations as well (I am just taking a guess it might be relevant).

Honestly, I am not 100% sure I nailed the blend (Its actually #1 on my "check if you screwed this up" list. #2 is my implementation, using a doubler to provide 30V, so I could use a 2x15V trafo). I went through it quite a few times, sometimes thinking I had it, but then changing the phase on the buffer back again, and again. I had a unit in for service to compare some issues to, but I gave it back before I checked the blend phase/realised I am a bit lost understanding how the signal is inverted (or if its not) in the AB stage, and I actually had an opamp providing the 12dB of gain at some point as well in the schematic, which would've been easier to see for me.

Theres always errors on a first rev board, so in the spirit of moving ahead, my plan ended up being - Measure the phase on the blend, hack and correct the board, make any needed changes to a second revision board. Factory is closed for the holidays ,so this way I have something to work with, make needed revisions, make a new board after the holidays.

If it weren't for the German postal workers, I would have had it fired up by now!

Gustav
« Last Edit: July 05, 2015, 01:34:11 PM by Gustav »


Re: MS76
« Reply #10 on: July 05, 2015, 01:37:11 PM »
Current status...

I am a few trimmers, transistors and a 7910 short of placing all components.

Gustav

tata

Re: MS76
« Reply #11 on: July 05, 2015, 02:53:08 PM »

Note that the buffer tapping the clean blend is non-inverted.


Gustav

right.. my bad. learning every day.
thanks

but signal is polarity flipped after the Blend stage, right?

german post sucks these weeks, 30+ days and i still didnt get my pack.. :(  (normally 4 days)
« Last Edit: July 05, 2015, 03:06:37 PM by tata »

tata

Re: MS76
« Reply #12 on: July 05, 2015, 02:57:30 PM »
btw if you're still refining your PCB - don't you think adding multipads for diff. sized (electrolytic) capacitors and for 3/8" trimmers is a good idea?

Re: MS76
« Reply #13 on: July 06, 2015, 02:19:20 AM »

Note that the buffer tapping the clean blend is non-inverted.


Gustav

right.. my bad. learning every day.
thanks

but signal is polarity flipped after the Blend stage, right?


There is an inverting opamp after the blend. Please refer back to my last post for a longer answer on the phase relations through the blend. I could start going over it again, and I probably messed it up, but I think going into the details is a waste of time, when the method for testing and correcting is so simple.

I just experienced working with someone who checked these things 100 times on schematic level, but still ended up with these "wrap your head around it" errors. Its easy for me to shoot out a board, check it, and correct it, since I work at a PCB manufacturing plant.

I dont see it as beneficial to add multipads to my board designs, sorry.

Gustav
« Last Edit: July 06, 2015, 04:46:08 AM by Gustav »

tata

Re: MS76
« Reply #14 on: July 06, 2015, 04:55:34 AM »
i refer back to your last post, but i read you are uncertain..

i see the inverting opamp in the Blend stage, and then signal goes to the out trafo / 1646 - noninverting, right?

so the final out is flipped?  (M/S off)

Re: MS76
« Reply #15 on: July 06, 2015, 05:42:59 AM »
i refer back to your last post, but i read you are uncertain..

Exactly!

"Honestly, I am not 100% sure I nailed the blend (Its actually #1 on my "check if you screwed this up" list. "

"Theres always errors on a first rev board, so in the spirit of moving ahead, my plan ended up being - Measure the phase on the blend, hack and correct the board, make any needed changes to a second revision board. Factory is closed for the holidays ,so this way I have something to work with, make needed revisions, make a new board after the holidays. "

The loop back you mention, yes, you are correct.


Gustav

« Last Edit: July 06, 2015, 06:14:13 AM by Gustav »

tata

Re: MS76
« Reply #16 on: July 06, 2015, 06:39:27 AM »
so a blend circuit that keeps the phase consists of : 2x (noninverting) input buffers, an inverting summing amp and an inverting buffer? is this right?

if yes, how about designing a separate PCB like this, so we could add it to any gears? (a FET Grinder and a Phat Phet are waiting for it here :) )
« Last Edit: July 06, 2015, 06:56:24 AM by tata »

Re: MS76
« Reply #17 on: July 06, 2015, 08:13:33 AM »
so a blend circuit that keeps the phase consists of : 2x (noninverting) input buffers, an inverting summing amp and an inverting buffer? is this right?

For this circuit, its obvious I have something to check, and 99.99999% certain I have something to correct, but I feel like I have replied to that a number of times now. I may be confused because I am not concerned about it other than measuring and correcting for this circuit, while you may be interested in using it elsewhere!?

For any implementation, it would depend on the phase relation where you draw the clean/dirty signals and where you feed back the blend, of course.

if yes, how about designing a separate PCB like this, so we could add it to any gears? (a FET Grinder and a Phat Phet are waiting for it here :) )

If you want to do it in a stand-alone unit, I would recommend a line receiver to the blend pot to summing amp to a line driver.  However you invert/non-invert any or each stage doesnt really matter as long as it adds up correctly.

In that case, you are drawing the signal at the balanced input and output of your hardware and sending it out.

Someone already did a project like that. Try searching "crush n blend".

Hope that helps!

Gustav

Re: MS76
« Reply #18 on: July 07, 2015, 02:01:45 PM »
One mistake when drawing up the PSU schematic, one cut trace, one jumper.

Had to stack a few capacitors on the 30V rail, because I only had 25V i in the drawers

I am sure this PSU will need to be refined, but I have the voltages I need.

Hope to have transistors before end of the week, so I can smoke test the main board.

Gustav

Re: MS76
« Reply #19 on: July 09, 2015, 07:39:53 AM »

Honestly, I am not 100% sure I nailed the blend (Its actually #1 on my "check if you screwed this up" list. #2 is my implementation, using a doubler to provide 30V, so I could use a 2x15V trafo).

Any comments on this spur of the moment doubler I decided to try? There are an awful lot of transistors in there dependent on the 30V supply, and I have a little cold feet powering it up after reading up on it a little.

When I did it, I thought the only implication would be doubling the current draw, but after reading this - http://www.electronics-tutorials.ws/blog/voltage-multiplier-circuit.html I have no real sense what the implications would be if the supply is starved.

If its just a matter of ripple, I dont really care. For now, checking functionality and correcting the schematic is good and fine, and when thats established, I can work on a  better supply for rev 2. Im more worried about frying something than usual, though.

Its ready for me to hit the power button, so feedback would be appreciated. Otherwise, Ill play it safe and breadboard a supply without the doubler using a 2x24V transformer.

Edit:Tried adding the doubler as is. Voltages stable, no smoke.

Gustav
« Last Edit: July 10, 2015, 11:01:20 AM by Gustav »