Barry Porter "Net EQ"

[frazzman]

Gustav sells finished PCBs, why bother with Gerbers?

Because I fabricate boards for a living and it's easier for me to just make them.

Even this one ? It's a whopper in size and double sided

 

[druu]

https://www.sendspace.com/file/55klo1

 

[therecordingart]

I bought two of these boards from Gustav, and they are populated with the exception of the pots. I want to replace the pots with rotary switches, but I can't figure out the math for the life of me to select the correct resistors. Can any of you folks help me out or point me in the right direction? I feel like an idiot, but can't seem to get my head around the schematic. Even the math for the gain isn't coming to me even though I know that the db formula for an inverting opamp is 20*LOG(Rf/Ri)...but for some reason I can't get the numbers to pan out and make sense.

I would be super grateful if one or more of you can school me on this.

 

[Gustav]

I bought two of these boards from Gustav, and they are populated with the exception of the pots. I want to replace the pots with rotary switches, but I can't figure out the math for the life of me to select the correct resistors. Can any of you folks help me out or point me in the right direction? I feel like an idiot, but can't seem to get my head around the schematic. Even the math for the gain isn't coming to me even though I know that the db formula for an inverting opamp is 20*LOG(Rf/Ri)...but for some reason I can't get the numbers to pan out and make sense.

I would be super grateful if one or more of you can school me on this.

Harpo posted some great cheat sheets in this thread.

Gustav

 

[p0ulp]

Hello, just ordered those board from gustav,  gathering part etc ... bref

I ll start it with pot and make it run first, but I m looking for stepped switch at last ... the thing is , it look like a pain to make, and a real source of disfunction for a bad solder( how do you call a guy soldering ? )  like me ...

Can someone guide me to make modular pcb for 24 position switch, 12 position switch etc, thanks to Harpo for his calculation sheet,  I m really new to eagle so I need some input ... then  of course I would publish the PCB (selft etch friendly) for those wanting to etch their board

Would like to use Electrotech C4 switch, but hopefully whole those 24p switch have the same footprint and those pcb could be used with some other.

If that's a stupid idea for whatever reason, please let me know

 

[therecordingart]

Harpo posted some great cheat sheets in this thread.

Gustav

I found the one for freq, but how do I go about calculating the resistors for stepped gain?

 

[Gustav]

Harpo posted some great cheat sheets in this thread.

Gustav

I found the one for freq, but how do I go about calculating the resistors for stepped gain?

Harpo posted some great cheat sheets in this thread.

http://groupdiy.com/index.php?topic=33256.msg611681#msg611681

Gustav

 

[p0ulp]

Working on this unit too, and starting to order the "special" component for this build, and after whatching carefully the BOM and component overlay (thank you guys !)  I am still unable to find proper part reference for the 30uH self .. I ve found another one which is twice bigger and won't fit properly on the board.

( http://fr.rs-online.com/web/p/inductances-traversantes/6694197P/ )

I ve tried to find inside view of other people barry porter to catch any info but this component is in the top corner of the pcb and have no chance to even see how does the package should be like.

Also I m not sure about the variable (adjustable ?) capacitor , on the pcb track document , C36 is only relied by one pin I don't have the board but I suppose the two other pins are relied to GND plan of the board , please correct me if I m wrong ?  also C41 seems to have 2 pins, I don't find variale capacitor with 3 pins, my choice would be this one , which is in a good range , but only 2 pin ...

http://fr.rs-online.com/web/p/condensateurs-ajustables/2470423/

Please confirm me that it is the way that board have been designed, I have the same question about the trimmer P1 also ...

Please also note that poly capacitor package are mixed (5mm and 7.5mm) ... wouhou so fun

thank you

 

[Gustav]

Working on this unit too, and starting to order the "special" component for this build, and after whatching carefully the BOM and component overlay (thank you guys !)  I am still unable to find proper part reference for the 30uH self .. I ve found another one which is twice bigger and won't fit properly on the board.

( http://fr.rs-online.com/web/p/inductances-traversantes/6694197P/ )

I ve tried to find inside view of other people barry porter to catch any info but this component is in the top corner of the pcb and have no chance to even see how does the package should be like.

Also I m not sure about the variable (adjustable ?) capacitor , on the pcb track document , C36 is only relied by one pin I don't have the board but I suppose the two other pins are relied to GND plan of the board , please correct me if I m wrong ?  also C41 seems to have 2 pins, I don't find variale capacitor with 3 pins, my choice would be this one , which is in a good range , but only 2 pin ...

http://fr.rs-online.com/web/p/condensateurs-ajustables/2470423/

Please confirm me that it is the way that board have been designed, I have the same question about the trimmer P1 also ...

Please also note that poly capacitor package are mixed (5mm and 7.5mm) ... wouhou so fun

thank you

I think most people just jump the inductors on the input instead of mounting them.

I can't remember what I did for the variable inductor, but board is set up for a standard 3 terminal, variable trimpot.

Gustav

 

[p0ulp]

Ok just to update , if everythings fit to the board I will rearrange the board that biasrock provided earlier, for now I ve ordered :

C86/C89  -  470n  -  5mm  Code commande RS 312-1481  / Code commande RS 191-991 / Code commande RS 108-2744 (Wima)
C56/C82  -  220n  -  5mm  Code commande RS 108-2722
C80              -  680n  -  5mm  Code commande RS 875-1983
C83/C59  -    47n - 7,5mm  Code commande RS 668-9993
C61/C84  -    10n - 7,5mm  Code commande RS 622-4634 Panasonic
C85/C63  -  2n2  -  7,5mm ebay
C77            -  6n8    -  7,5mm ebay
C81            -    1n      -  7,5mm ebay
Cxx            -    100n  -  5mm


I supposed that every capacitor in the nF range is polyester ( depends on the value the voltage specification can goes up to 400v  ... )  and pF is ceramic (multi/simple layer ?? )I have simple in stock but also ordered multi anyway , I ll make some research about what is better for this application if there is any difference .

 

[rafafredd]

You can use Polyester, but generally polypropylene will perform better. Other types of film caps may also work great, like Polycarbonate, Polyethylene naphthalate, Polyphenylene sulfide, Polytetrafluoroethylene, etc may also work great.

For the smaller caps, use Film and Foil, or maybe Polystirene or MICA if you can find it.

If you have to go Ceramics, make sure you use only COG / NPO types (but I think you won't find it in the values needed). Anything else ceramics will be bad for this.

 

[frazzman]

Hi folks,

Having finally completed my dual mono build  - I stupidly agreed to building a stereo build for a friend. Yesterday I powered up the first channel. First test was with no ICs present - measured voltages on the sockets and all good voltages there.

Next step - I populated all the opamps and powered on. I Immediately got a plume of smoke around U2. It almost looked like it was coming from the 1000uf /6.3v BP caps. I couldn't tell for sure, however they all look ok and they certainly didn't leak.

Needless to say I pulled the power plug promptly. I noticed that my 10R/3W - R18 and R19 heated up and now look a tiny bit scorched but measure ok.

I removed all opamps and powered on again - all voltages checked out on opamp sockets. I progressively added in each IC one at a time and test powered on at each stage thinking that I would replicate the first scenario, but that didn't happen.

So now I'm in a situation where all opamps are present, no smoke now... Voltages look ok on the opamps. So in the absence of any other apparent issue, I wired up the XLRs and ran in a sine wave. It passed audio but the signal was relatively low - however there are no switches/pots connected except for a bypass switch.

Given the low output - I Can't help but think something is fried or maybe this is normal behaviour in the absence of any switches/pots ? Also I am puzzled about the root cause of the plume of smoke.

Maybe a duff opamp but It seems like a pretty drastic response. The second channel is ready to power up but I am reluctant to power it on until I come to some conclusion on the first channel.

Seeking any guidance/thoughts on this one.

Many thanks

 

[p0ulp]

I ve partially receive my component once again ( more to come, it's a never ending story) ... and would like to know if the decoupling capacitor on each opamp could be multi-layer ceramic ... I m running out of money for those fancy Wima 2,5mm pitchn and don't want to bend my regular 100nF 5mm to fit the pcb, also if there is no point (cause no audio path)  I ll skip high quality component on this one.

thank you

 

[frazzman]

I ve partially receive my component once again ( more to come, it's a never ending story) ... and would like to know if the decoupling capacitor on each opamp could be multi-layer ceramic ... I m running out of money for those fancy Wima 2,5mm pitchn and don't want to bend my regular 100nF 5mm to fit the pcb, also if there is no point (cause no audio path)  I ll skip high quality component on this one.

thank you

Hi poulp - I used multi layer ceramics in those positions on my first build without any issue, doesn't seem to be any compromise in terms of fidelity and what not.

 

[frazzman]

Hi folks,

Having finally completed my dual mono build  - I stupidly agreed to building a stereo build for a friend. Yesterday I powered up the first channel. First test was with no ICs present - measured voltages on the sockets and all good voltages there.

Next step - I populated all the opamps and powered on. I Immediately got a plume of smoke around U2. It almost looked like it was coming from the 1000uf /6.3v BP caps. I couldn't tell for sure, however they all look ok and they certainly didn't leak.

Needless to say I pulled the power plug promptly. I noticed that my 10R/3W - R18 and R19 heated up and now look a tiny bit scorched but measure ok.

I removed all opamps and powered on again - all voltages checked out on opamp sockets. I progressively added in each IC one at a time and test powered on at each stage thinking that I would replicate the first scenario, but that didn't happen.

So now I'm in a situation where all opamps are present, no smoke now... Voltages look ok on the opamps. So in the absence of any other apparent issue, I wired up the XLRs and ran in a sine wave. It passed audio but the signal was relatively low - however there are no switches/pots connected except for a bypass switch.

Given the low output - I Can't help but think something is fried or maybe this is normal behaviour in the absence of any switches/pots ? Also I am puzzled about the root cause of the plume of smoke.

Maybe a duff opamp but It seems like a pretty drastic response. The second channel is ready to power up but I am reluctant to power it on until I come to some conclusion on the first channel.

Seeking any guidance/thoughts on this one.

Many thanks

Just a second thought to my rather long winded post.
I guess if I could ascertain whether a level drop in the absence of pots/switches connected is "normal" then maybe my "issue" may be a non issue.

It's just that with the initial plume of smoke with all opamps in place, you can't help but wonder what's going on.

In saying that - with all new opamps in the sockets, no sign of smokes signals... Level drop is about -12db.
-/+ 18v reading on opamp pins are correct

 

[ruairioflaherty]

Why are you powering up with no switches/pots? 

If I absolutely had to power up without the above I'd be simulating them with resistors.  You could try to understand how the circuit will work without pots connected but it would be much quicker to simulate using dummies.

 

[frazzman]

Why are you powering up with no switches/pots? 

If I absolutely had to power up without the above I'd be simulating them with resistors.  You could try to understand how the circuit will work without pots connected but it would be much quicker to simulate using dummies.

Only powering up as a diagnostic process I suppose, I haven't built my stepped switches yet - I just wanted to make sure my main boards are operating as expected before diving into  the switches.

I did the same on my previous build and I'm pretty sure it passed a full output signal with all the pots omitted. I've just got the bypass led and toggle switch wired up.

Anyway, I can't replicate it on my working unit as the switches are hard wired.

Cheers

 

[druu]

Just perform the voltage checks only for now. Don't bother testing with audio until completion.

 

[frazzman]

I know man.... But my backwards logic is that I don't want to bust my chops on these monster 6 pole switches if the main board is cooked

I've checked all the -/+ 18v on the opamp sockets... Can you recall if there any other docs that reference other voltages on the board ? Otherwise I might have to unrack my dual mono unit and start comparing.

 

[Gustav]

I know man.... But my backwards logic is that I don't want to bust my chops on these monster 6 pole switches if the main board is cooked

I've checked all the -/+ 18v on the opamp sockets... Can you recall if there any other docs that reference other voltages on the board ? Otherwise I might have to unrack my dual mono unit and start comparing.

With no switches and pots, you have open input pins on quite a few opamps. I would have made sure to analyse the circuit or at put in dummy loads if it was beyond my capability. If nothing else, just to make sure I wouldn't be driving an opamp death somewhere

Looking at the schematic on the bands, I am having a hard time figuring out how  you are passing audio at all with no switches or pots installed, but I am not a wizard

Your safe bet is to apply the dummy resistors as Ruairi suggested, if you want to see how it behaves before wasting time doing switches and pots.


Gustav