Sontec: hardware bypass, balanced THAT I/O, MS, power supply - at one PCB!

[dandeurloo]

DOA's are in now I just need time!

 

[dandeurloo]

Feed signal to left channel; short right to ground (no signal);
ms is in; adjust the pot for minimum signal at right output.

Igor would it work to not feed the right channel any input instead of grounding the signal?  If not where is a good place to ground the right channel to ground?

Also, one of my bands on 1 eq does nothing?  Its the MF2 band.  I reflowed everything and checked components and all seems well.  I replaced IC's in that position as well and still nothing. Any thoughts on where to look?

 

[duantro]

Feed signal to left channel; short right to ground (no signal);
ms is in; adjust the pot for minimum signal at right output.

Igor would it work to not feed the right channel any input instead of grounding the signal?  If not where is a good place to ground the right channel to ground?

Also, one of my bands on 1 eq does nothing?  Its the MF2 band.  I reflowed everything and checked components and all seems well.  I replaced IC's in that position as well and still nothing. Any thoughts on where to look?

Hey Dan,
I just fed signal to one channel, instead of shorting. Not entirely sure though.
I also had a high filter that was intermittant, and I did the same thing- rensoldered a number of pins to no avail. Then I exposed a little metal on the front panel, at the filter pot nut, and it worked. I'm assuming they need to connect to panel ground?

 

[dandeurloo]

good tip on the front panel.  I believe it was working on my proto panel which was not painted and now it doesn't work.  I will try that more and see if it fixes it!

 

[dandeurloo]

Well that didn't fix it.  Hmm it is strange that everything but the MF2 band works.  Any ideas where to look?

 

[Majestic12]

Well that didn't fix it.  Hmm it is strange that everything but the MF2 band works.  Any ideas where to look?

I'm at work and can't check the circuit, but I remember that one of the caps in the MF band is labeled somehow confusing. When I remember correctly it's a 150N cap that can be confused with 150pf. It's one of the caps that sits directly behind one of the pots

Triple check your caps again, maybe that's where the problem is.

 

[dandeurloo]

Well, I built a stereo unit and one channel works great.  So its just something strange with this one channel and one band?  I just bought a scope but I am waiting on leads/probes to show up so I can see if I can figure it out.  The schematic is a little strange to read as well.  Or at least I don't understand it 100%.  The band that doesn't work is just the same if I take the IC out.  So I can't tell if its that the signal isn't getting into the band or if is not getting out of that band. 

I did trace all the connections and points in that band with my MM for continuity.  Everything looked good.  I'm very puzzled but hopefully once I can get it on the scope I can figure it out. 

BTW, thanks everyone for your help.

EDIT:  I had a bad 50k pot so I am now getting a replacement sent to me.  That should fix it.

 

[Bhudie]

Hi guys,

I'm currently trying to put a BOM together for this build and am struggling with a few things. 

Firstly, please forgive my newbness.  I would still consider myself new to DIY despite being engaged in it for a few years.  I've built some SCA stuff, and am nearly finished wiring 2 of mnats 1176's.  (although, I've been reading for years, and I feel like i've spent many months of cumulative time reading on this forum... I'm only now beginning to come out of my lurking mode and start to post )  I have learned so much already and feel like my understanding of audio circuits has significantly improved from when I started, but there are still large holes, and some of them are fundamental.  I really want to take the step from paint by numbers to real self sufficient DIYer and am using this project to force me to learn what I still don't know.

For the record, while knowing which parts I need to get going on this build is cool and welcome, I am not as interested in which part I should choose as much as how I should be able to go about figuring that out for myself.

So with that said, I'll start with this question. 

Here goes:

How do I work out what the max voltage is for these caps on the filter boards?


Electrolytic Caps
220U CPOL-EUE5-10.5
33U CPOL-EUE5-6

Ceramic Caps
0.1U 5MM PITCH CERAMIC POWER SUPPLY BYPASS

Poly Caps
0.15U C-10-15/6
0.47U C-10-15/6
1U C-10-15/6
2U2 C-10-15/6
4u7 C-10-15/6
** C-10-15/6

Silver Mica or Poly Caps
3n3 C-7-10/5
2n70 C-7-10/5
100P C7.5/3
330P C7.5/3

Silver Mica or COG caps
5p C2.5/2



Theoretically, I believe that I need to figure out what the voltage is that's being fed to the cap and then maybe add a buffer, and maybe I also need to figure out what the max voltage could potentially be in the event of a failure somewhere in the circuit and ensure I'm above that.  If that's the case, do I just start at the power source on the schematic and work through the circuit part by part to calculate the voltage drop until I get to the part I want?  Is this correct? (if so, it'll take me some more studying before I can actually do it but at least I know I'm barking up the right tree)  Or is there another way that I am overlooking? 

Feel free to tell me that I need to do more studying (I know this to be true...), even so a gentle nudge in the right direction would be greatly appreciated.

Thanks,
Aaron

 

[Harpo]

I believe that I need to figure out what the voltage is that's being fed to the cap and then maybe add a buffer, and maybe I also need to figure out what the max voltage could potentially be in the event of a failure somewhere in the circuit and ensure I'm above that.

The (AC or DC) voltage difference across the cap (and you will have a hard time finding a poly or cer cap with a lower than needed voltage rating for this project). Caps pin spacing that matches the pcb will make it an easier fit.

 

[Bhudie]

Thanks for the clarification Harpo.  That makes sense to me now. 

So my second question is similar for the regulators LM317 and LM337:

I look at Mouser and can find the regulators that match the footprint, but they come with an Input Voltage Max of -4.2v and -50v.  My thinking is that they need to be the -50v version because my transformer will be putting out 2x25v.  Is this conclusion correct?

 

[Harpo]

So my second question is similar for the regulators LM317 and LM337:

I look at Mouser and can find the regulators that match the footprint, but they come with an Input Voltage Max of -4.2v and -50v.

They don't (and BTW the LM317 is a positive, the LM337 a negative voltage regulator). Typos happen or you looked up a wrong part.

My thinking is that they need to be the -50v version because my transformer will be putting out 2x25v.  Is this conclusion correct?

No. They regulate down a raw DC voltage in in front of the regulator to a DC voltage out, set by the ratio of two resistors and this input/output differential voltage must not exceed 40V for this type of regulator. This voltage differential times current drawn is also the generated heat this part has to dissipate, for usual by help of a heatsink. Your transformer puts out 2* 25V AC at rated load (+/-10%, depending on location or time of day. AC mains isn't a constant.) that gets rectified and smoothed to about +35V and -35V raw DC with 0V reference voltage in between.

 

[Bhudie]

Typos happen or you looked up a wrong part.

Indeed... busted.  I actually looked up the 337 twice.  So embarrassed. :-[

No. They regulate down a raw DC voltage in in front of the regulator to a DC voltage out, set by the ratio of two resistors and this input/output differential voltage must not exceed 40V for this type of regulator. This voltage differential times current drawn is also the generated heat this part has to dissipate, for usual by help of a heatsink. Your transformer puts out 2* 25V AC at rated load (+/-10%, depending on location or time of day. AC mains isn't a constant.) that gets rectified and smoothed to about +35V and -35V raw DC with 0V reference voltage in between.

OK, this took me a long time to digest.  I now know I clearly have larger holes in my understanding than I previously thought.  I've gone back and done some reading, and I think I now understand the full wave rectification, and the purpose of the voltage regulator.  I just want to make sure that I understand fully what you wrote, Harpo...

As I understand it out of the transformer the AC is rectified to a pulsing DC of about + and - 35V.  The positive gets fed to the 2 LM317s which are then regulated to +24V and +18V.  This is 11V and 17V of regulation so with a heatsink I have no concerns of overheating.  So in the end if I choose an LM317 with an input max of 40V I should be fine. 

The negative gets fed to the 2 LM337s and are then regulated to -24V and -18V.  This is also 11V and 17V of regulation so I'm fine for overheating, and if I select a part with a max input voltage greater than -35V I should be fine.  Please let me know if I've got this wrong, and I'll get back to studying. 


Now, the last thing that confuses me slightly is how max voltage is decided for negative voltage?  Is it a matter of amplitude or just which number is higher?  What I mean is -35 is less than -4.2, so In my case I have -50V, -40V, and -4.2V, so I would choose the -4.2V part as the others don't allow for the maximum.
But if it's a matter of amplitude, a sine wave that goes to -35V is larger in amplitude than a wave that goes to -4.2 so the maximum input voltage should be below -35.
Apologies again for another stupid question... I hope I explained myself properly.

And Harpo, thank you so much for your help. 

-Aaron

 

[Harpo]

As I understand it out of the transformer the AC is rectified to a pulsing DC of about + and - 35V.  The positive gets fed to the 2 LM317s which are then regulated to +24V and +18V.  This is 11V and 17V of regulation so with a heatsink I have no concerns of overheating.  So in the end if I choose an LM317 with an input max of 40V I should be fine.
The negative gets fed to the 2 LM337s and are then regulated to -24V and -18V.  This is also 11V and 17V of regulation so I'm fine for overheating, and if I select a part with a max input voltage greater than -35V I should be fine.  Please let me know if I've got this wrong, and I'll get back to studying. 

There is no talk about 'input max of 40V'. As long as you don't exceed the i/o 40V voltage differential, you could feed this type of regulator with a much higher voltage. (a clamping <40V zener across i/o would be a little insurance to stay within these parts limits tough, just in case there might be a short connected between reg.output and reference voltage, IE broken part or caps take too long to charge)

Now, the last thing that confuses me slightly is how max voltage is decided for negative voltage?  Is it a matter of amplitude or just which number is higher?

The higher number, IE ABS(voltage).

.., so In my case I have -50V, -40V, and -4.2V, so I would choose the -4.2V part as the others don't allow for the maximum.

With your -50V, -40V and -4.2V numbers, whatever and in what respect these might be, I have no other idea then you did not connect your 2* 25V transformer secondaries in series to substitute a 50V center tapped secondary mains transformer, this series junction being the center tap for the 0V reference voltage.

 

[Aleguitarpro]

Hi.
I've a problem with my sontec upgraded!

I built 2 regular Sontec and then I decided to build one upgraded.

The filters works correcly: I measured the boost/cut and frequencies with Waves Q-capture(Q-clone) plugins and it displays all the correct things.

The problem I have regards a loss of 20dbs in both m/s and in l/r modes.
In mid/side mode also I have a problem of balancing the two output channels: my right channel is about 15-20 db less high than left channel, so I think there is a mistake anywhere.... but where??

I've checked switching system and all the things works correctly:

1) bypass mode: the relays near the XLR connectors (BYP-L1 and BYP-L/BYP-R1 and BYP-R) are normally closed to bypass the signal and obiouvsly  I've the same amount of db I put in the EQ

2) m/s mode: the bypass relays are now feeded with the correct Vs (11,5 V circa) and the MS-PRE/POST relays are powered, too.

3) l/r mode: bypass relays are powered and the MS-PRE&POST are normally closed to bypass the signal through filters and DOAs.

I've used in the filters NE5532 instead of OP275 that I used in my previous built SONTECs, but I don't think this is a problem!
The filters are powered with +/-18V.

I've used as DOA a IC-to-DOA adapter built in protoboard but it works with OPA604.
I think the problem is somewhere in audio path in the M/S decoded-encoder, but it's strange to measure a loss of 20dbs also in l/r mode...
And in m/s mode the big unbalance between L and R channels in output (about 15/20dbs) is so strange...

Any idea?

Thanks!
Ale

 

[druu]

Tried adjusting the M/S BAL trimmer?

 

[Aleguitarpro]

Tried adjusting the M/S BAL trimmer?

Solved...Simply a bad THAT chip in M/S decoder/encoder.

Now all it's ok!

 

[Screamer]

Hi everyone!

Does anyone have a "RED sontec stereo PCB" to sell for me? Or only the filter boards?

I bought the "Sontec/MS/hardware bypass/power supply upgrade board" but I didn't buy the "RED Sontec Stereo PCB Set"... The Igor's store is close now...
I can't finish my Sontec EQ... 

Thanks,
ScreameR

 

[DOMC Mastering]

Hi everyone!

Does anyone have a "RED sontec stereo PCB" to sell for me? Or only the filter boards?

I bought the "Sontec/MS/hardware bypass/power supply upgrade board" but I didn't buy the "RED Sontec Stereo PCB Set"... The Igor's store is close now...
I can't finish my Sontec EQ... 

Thanks,
ScreameR

Ill buy the ms board off you if you don't need it. I need one

 

[Trench Recordings]

Anyone have the docs for this still ? Link is down

Thanks,
Dave

 

[duantro]

I probably have docs at home, pm me an addy and I can send them if I do.
@screamer- I think I have a red stereo board also. I bought the m/s boards and think I have the unused stereo one still. Let me know if you still are looking.