[BUILD] 1176 Rev A - Back to the beginning...

[hymentoptera]

Concerning capacitor C22, 0.22uF film type;

Does anyone have insight as to why a Kemet is used at C22 in this revision, when WIMAs are uses at other .22uF positions, as well as at C22 on other revisions?

I'm thinking of using a NOS mylar made by Sprague here, but I don't understand what this capacitor is doing. It seems to sit between Pad 7 and GND.

 

[rainton]

May I ask where you got your LED or a part number? I'm planning to do the same, and I'm overwhelmed at the number of different LEDs and bezels to choose from. I'd like to try one that's known to work with a given resistor and voltage.

Thanks!

Just a quick heads-up regarding the dropping resistor for the LED: I now use a 750 Ohms (3W) resistor and now I get 11.5V at the anode of the LED
which is pretty much exactly what I wanted 

BUT - another little problem appeared - nothing to do with the LED but still I'm hoping for some help:

I originally built my Rev A with metal resistors everywhere like suggested in the BOM but I kept reading that even though it increases the noise level, it would give the comp more mojo using carbon comp resistors in the preamp and line amp section. So after reading a lot of details about the differences - today I went for it and swapped all metal resistors in the preamp and line amp section for 1/2W carbon comp resistors...

...now went through calibration again - and it all went fine - and I have to say I really love the difference in sound - it really has more mojo!!  ;D
I'm lovin it!

So long story short - now the little problem. When turning the Output pot  beyond "6" - I hear a a "pop" and the VU-meter jumps to the far right when in +4 or +8 mode (and also the input of my console to which the 1176 is connected hits the red). backing down the output knob below "6" - everything back to normal. This also happens when there's no XLRs connected to the comp.

Apart from that the comp is working perfectly! No hum or distortion or whatever.

Could it be a FET in the "Line-Amp" section is acting weird? Any ideas?
Thanks!!

 

[hymentoptera]

May I ask where you got your LED or a part number? I'm planning to do the same, and I'm overwhelmed at the number of different LEDs and bezels to choose from. I'd like to try one that's known to work with a given resistor and voltage.

Thanks!

Just a quick heads-up regarding the dropping resistor for the LED: I now use a 750 Ohms (3W) resistor and now I get 11.5V at the anode of the LED
which is pretty much exactly what I wanted 

thanks for the headsup. I've already ordered the 470 ohm 5 watters, but i'll go order some 750 ohm ones instead.

... today I went for it and swapped all metal resistors in the preamp and line amp section for 1/2W carbon comp resistors...

...now went through calibration again - and it all went fine - and I have to say I really love the difference in sound - it really has more mojo!!  ;D
I'm lovin it!

So long story short - now the little problem. When turning the Output pot  beyond "6" - I hear a a "pop" and the VU-meter jumps to the far right when in +4 or +8 mode (and also the input of my console to which the 1176 is connected hits the red). backing down the output knob below "6" - everything back to normal. This also happens when there's no XLRs connected to the comp.

Apart from that the comp is working perfectly! No hum or distortion or whatever.

Could it be a FET in the "Line-Amp" section is acting weird? Any ideas?
Thanks!!

I wish I could be more help here, but it sounds a bit like when you have a poor contact somewhere, and the signal is really quiet and distorted until suddenly at a certain gain the signal breaks through and sounds fine. Common with pressure contacts like in 1/4" jacks, etc. This is usually fixed by making a better connection. But, this isn't what you're experiencing, is it? You're getting a pop when you crank the output almost all the way up? I'm not sure that it's normal (I haven't built my kit yet, still waiting on a few parts), because most users describe an especially loud output at almost any setting past about 12 o'clock or so.

I have a Q for you, though, if you don't mind: I'm replacing some resistors with carbon comps too, and I've ordered more than 20 different values shown in the signal and line amps, 10 or 20 of each depending on how many are found in the schematic, but many are so far off from nominal or failing to show pairs close enough to each other (I'm building a pair w/ stereo link boards if funds allow), that I'm afraid I need to buy more resistors to make pairs match up closely to each other AND as close to nominal as realistically possible. I don't want to spend a small fortune here, as I've already got more than US$200 into vintage parts for these things...

So my question is which resistors did you swap to carbon comp? Just the handful directly in the signal path, or did you swap the nearby ones too? Any tips would be greatly appreciated!

 

[rainton]

So my question is which resistors did you swap to carbon comp? Just the handful directly in the signal path, or did you swap the nearby ones too? Any tips would be greatly appreciated!

I basically now have 1/2W carbon comps in the entire "signal preamp" and "signal line amp" section.
And since I want to build a second Rev A later I also ordered more of the relevant parts -  i.e. if I needed 1 resistor of a certain value I ordered 4 of them and then chose the 2 that were measuring closest together.

Well regarding the "pop" when turning the output knob beyond "6" I went through the thread and found some other people experiencing something similar - most of them wrote they would hear that "pop" when turning the output knob beyond "9" and then an extreme increase in white noise...
So mine actually pops a little later...
...anyway - all of those that were having this issue were asking wether it was normal or not and if not what to look for - BUT I haven't found a single answer to it.
SO I try again hoping one of those that know this comp inside out might chime in  :
1. Is it normal?
2. What could it be?

I'm not sure but I think I didn't have this issue before swapping the resistors...
And I know that I will most likely never use the 1176 at these extreme output settings but it is still bugging me

any ideas would be highly appreciated!!

P.S.: I highly recommend using carbon comps in the above said sections! I sent some samples through the unit before the swap just to
have something to compare it to - and now did the same thing after - and the difference is clearly audible! It sounds warmer - more vibe!
Love it!  ;D

 

[hymentoptera]

I basically now have 1/2W carbon comps in the entire "signal preamp" and "signal line amp" section.
And since I want to build a second Rev A later I also ordered more of the relevant parts -  i.e. if I needed 1 resistor of a certain value I ordered 4 of them and then chose the 2 that were measuring closest together.

...

P.S.: I highly recommend using carbon comps in the above said sections! I sent some samples through the unit before the swap just to
have something to compare it to - and now did the same thing after - and the difference is clearly audible! It sounds warmer - more vibe!
Love it!  ;D

wish I could help more with the popping. if i encounter any hints in my journeys I'll post back.

I was curious how you felt about the inevitable "aging-up" of carbon comp resistors, and did the higher values concern you, did you find some that were pretty close to nominal, and did you feel that only a 4:1 ratio purchased (i bought 10:1 and still don't have many good matches) was enough? What I mean by that last part, is do you wish you'd bought more?

I realize it's not so much a big deal with the voltage divider resistors, since the ratios between them remain pretty much the same as they age-up, but as for resistors directly in the signal path I'm concerned that if I don't match up pairs for my two units, and choose pairs that are as close to nominal value as possible, I'm not going to have a very good sounding pair of Rev A's. With 10, 20 an even 30 of some values, I still feel like there's much to be desired from the actual measured resistance values I'm coming up with.

 

[hymentoptera]

I believe evilcat build a pair using carbon comps in the signal path, carbon film everywhere else in the signal/line amps, and metl film everywhere else, but i'm not sure what page or post he talks about it. but I think he ultimately built a third unit using metal films because he didn't like how noisy the carbon compositions were

 

[evilcat]

Hi guys!

This is where I talked about the "carbon comp" ones :
http://www.groupdiy.com/index.php?topic=40154.msg504629#msg504629

And the "metal film" one :
http://www.groupdiy.com/index.php?topic=40154.msg504629#msg504629

Indeed, I've made the "metal film" version in order to have a quieter unit, as I need it to record radio commercial speech with it. But for recording and mixing music the noise of the "carbon comp" ones is not a problem, it's all about good vibe!!! I've never made a comparaison between the 2 versions, it could be fun to see if there really is a "vibe" difference or if it's just in our heads , but even if it is, I don't care ;D. I'll try to have time for this.
Best,

Ben

 

[rainton]

I realize it's not so much a big deal with the voltage divider resistors, since the ratios between them remain pretty much the same as they age-up, but as for resistors directly in the signal path I'm concerned that if I don't match up pairs for my two units, and choose pairs that are as close to nominal value as possible, I'm not going to have a very good sounding pair of Rev A's. With 10, 20 an even 30 of some values, I still feel like there's much to be desired from the actual measured resistance values I'm coming up with.

Well, I think of course the chances you find a pair that's really close to each other is better when ordering more resistors of the same value but I with the ones I ordered were pretty close...
...I think if you buy them off the same batch you'll find a good pair in a 4:1 ratio.

And I'm sure it will sound VERY good!

I'm super happy with mine here and not all the parts that are in the box are exactly the nominal value - but close enough.

BTW Hey evilcat! Good to see you around - you don't know but you were actually the one that got me intrigued on the entire carbon comp thing in the first place
I read your thread a while back, haha! And I made a comparison - before and after - it is only with some crappy samples that came with Logic but still - other people that were here that didn't know what was what could tell which one had more vibe - it was always the Carbon Comp one

And I can confirm the "noise" level is really ok - like even more than ok it is actually really good! But I can imagine if you're doing voice overs or something like that.

Actually I like the difference in sound so much that I also swapped all the resistors in my LA2A for carbon comps  ;D

 

[rainton]

And BTW:

bump on the "popping" questions - anyone?

Well regarding the "pop" when turning the output knob beyond "6" I went through the thread and found some other people experiencing something similar - most of them wrote they would hear that "pop" when turning the output knob beyond "9" and then an extreme increase in white noise...
So mine actually pops a little later...
...anyway - all of those that were having this issue were asking wether it was normal or not and if not what to look for - BUT I haven't found a single answer to it.
SO I try again hoping one of those that know this comp inside out might chime in  :
1. Is it normal?
2. What could it be?

I'm not sure but I think I didn't have this issue before swapping the resistors...
And I know that I will most likely never use the 1176 at these extreme output settings but it is still bugging me

any ideas would be highly appreciated!!

 

[mnats]

And BTW:

bump on the "popping" questions - anyone?

Well regarding the "pop" when turning the output knob beyond "6" I went through the thread and found some other people experiencing something similar - most of them wrote they would hear that "pop" when turning the output knob beyond "9" and then an extreme increase in white noise...
So mine actually pops a little later...
...anyway - all of those that were having this issue were asking wether it was normal or not and if not what to look for - BUT I haven't found a single answer to it.
SO I try again hoping one of those that know this comp inside out might chime in  :
1. Is it normal?
2. What could it be?

I'm not sure but I think I didn't have this issue before swapping the resistors...
And I know that I will most likely never use the 1176 at these extreme output settings but it is still bugging me

any ideas would be highly appreciated!!

Believe it or not this has been answered before either in this or the Rev D thread. Look at the output on an oscilloscope and tell us what you see when the noise increases.

 

[hymentoptera]

I have another question/concern about C22, a 220nF film cap that sits between the FET control voltage (pad 7) and ground, as the Kemet EVOX capacitor currently in the Mouser cart has a 7.5mm lead spacing, while the PCB (v1.2.5) expects 5mm spacing. The WIMA recommended in the Rev A BOM has the correct 5mm spacing, as does the part (same one?) in the Rev F Mouser cart, which I also bought a pile of those too.

Correct part?

I supposed it's possible to bend the tiny leads with needle nose pliers and get them to fit. I'd like to know more about what this capacitor is doing in the circuit to assist with me choosing a replacement, and I'd like to know what others have done here, i.e. is everyone just bending their leads, or did I somehow end up with the wrong part?

 

[rainton]

Believe it or not this has been answered before either in this or the Rev D thread. Look at the output on an oscilloscope and tell us what you see when the noise increases.

Thanks Mako - but I don't own an oscilloscope yet - guess it is about time right - sooner or later I'll need one anyway if I keep on DIYing

But is there anything I can do in the meantime? I'm not at the studio until friday but I did some measurement a couple of days ago and found out that if I measure DC voltage to ground at any particular spot in the "line amp" section I  constantly have the same reading  no matter how much I turn up the output knob between "-∞" and "6" but as soon as I turn up the output knob any further the voltage drops by about 50% - this is when the VU-meter peaks instantly when in "+4" mode...

I'll try to get an oscilloscope asap but it might take a while - in the meantime I'm grateful for any help!

 

[Echo North]

I have another question/concern about C22, a 220nF film cap that sits between the FET control voltage (pad 7) and ground, as the Kemet EVOX capacitor currently in the Mouser cart has a 7.5mm lead spacing, while the PCB (v1.2.5) expects 5mm spacing. The WIMA recommended in the Rev A BOM has the correct 5mm spacing, as does the part (same one?) in the Rev F Mouser cart, which I also bought a pile of those too.

Correct part?

I supposed it's possible to bend the tiny leads with needle nose pliers and get them to fit. I'd like to know more about what this capacitor is doing in the circuit to assist with me choosing a replacement, and I'd like to know what others have done here, i.e. is everyone just bending their leads, or did I somehow end up with the wrong part?

I need to update that for proper spacing.  505-MKS2.22/100/10 is 5mm and in stock.

C22 is a big deal in the 1176.  It smooths the rectified control voltage and also does the actual attacking (time for it to charge) and releasing (time for it to discharge) based on the those controls.

Probably doesn't need to be a wima (no audio going through it), jut a decent film cap.

Mike

 

[Echo North]

Believe it or not this has been answered before either in this or the Rev D thread. Look at the output on an oscilloscope and tell us what you see when the noise increases.

Thanks Mako - but I don't own an oscilloscope yet - guess it is about time right - sooner or later I'll need one anyway if I keep on DIYing

But is there anything I can do in the meantime? I'm not at the studio until friday but I did some measurement a couple of days ago and found out that if I measure DC voltage to ground at any particular spot in the "line amp" section I  constantly have the same reading  no matter how much I turn up the output knob between "-∞" and "6" but as soon as I turn up the output knob any further the voltage drops by about 50% - this is when the VU-meter peaks instantly when in "+4" mode...

I'll try to get an oscilloscope asap but it might take a while - in the meantime I'm grateful for any help!

I don't recall this issue...try back here:

-----------
Title: Re: [BUILD] 1176 Rev A - Back to the beginning...
Post by: dmp on March 06, 2012, 11:09:12 AM
Quote
Does anybody have problems with Rev A oscillating if the output pot is set close to maximum? Mine goes crazy and stops only when I touch the "7" point. Looks like a sidechain thing... Anybody?

I had this problem and it took me forever to figure out what was going on. I finally installed the ground wire from the pcb ground to the chassis start point, and the oscillations stopped immediately!
Also check the shielding for the wires to the output pot.
If you pull the FETs you will be able to tell if it is the sidechain.-
-------

Also make sure your wires from the meter to the XLR are far away from the PCB.

Mike

 

[hymentoptera]

...
C22 is a big deal in the 1176.  It smooths the rectified control voltage and also does the actual attacking (time for it to charge) and releasing (time for it to discharge) based on the those controls...

Are you sure you aren't thinking of C27 (10nF, 12nF or 22nF in later revisions) , the cap directly soldered to the attack pot? I'm sure you're right, I just want to be certain I understand. And if you do mean C22 (220nF), then what is the purpose of nearby R7 and C6 network?

Thanks!

 

[Echo North]

...
C22 is a big deal in the 1176.  It smooths the rectified control voltage and also does the actual attacking (time for it to charge) and releasing (time for it to discharge) based on the those controls...

Are you sure you aren't thinking of C27 (10nF, 12nF or 22nF in later revisions) , the cap directly soldered to the attack pot? I'm sure you're right, I just want to be certain I understand. And if you do mean C22 (220nF), then what is the purpose of nearby R7 and C6 network?

Thanks!

Definitely C22.  They talk about it in the manual.

Not sure what's going on with R7/C6.  I'm not an expert on every component in the circuit.  Come kind of divider/coupling/lowpass filter thing with C1 and R6? 

Now I gotta know....off to do some research.

Mike

 

[evilcat]

BTW Hey evilcat! Good to see you around - you don't know but you were actually the one that got me intrigued on the entire carbon comp thing in the first place
I read your thread a while back, haha! And I made a comparison - before and after - it is only with some crappy samples that came with Logic but still - other people that were here that didn't know what was what could tell which one had more vibe - it was always the Carbon Comp one

And I can confirm the "noise" level is really ok - like even more than ok it is actually really good! But I can imagine if you're doing voice overs or something like that.

Actually I like the difference in sound so much that I also swapped all the resistors in my LA2A for carbon comps  ;D

Hi Rainton,
I'm flattered to have inspired you on this one! And now I really wanna make this "carboncomp Vs metalfilm" blind test too !!!
Have you listened to my comparaison files between 5088 and 3708 transistors? What have put in yours?

 

[rainton]

I don't recall this issue...try back here:

-----------
Title: Re: [BUILD] 1176 Rev A - Back to the beginning...
Post by: dmp on March 06, 2012, 11:09:12 AM
Quote
Does anybody have problems with Rev A oscillating if the output pot is set close to maximum? Mine goes crazy and stops only when I touch the "7" point. Looks like a sidechain thing... Anybody?

I had this problem and it took me forever to figure out what was going on. I finally installed the ground wire from the pcb ground to the chassis start point, and the oscillations stopped immediately!
Also check the shielding for the wires to the output pot.
If you pull the FETs you will be able to tell if it is the sidechain.-
-------

Also make sure your wires from the meter to the XLR are far away from the PCB.

Mike

Thanks Mike - I will check it when I'm back at the studio tomorrow - but I'm pretty sure the wires from the meter to the XLR are routed along the rails
and thus also pretty close to the pcb - I'll let you know how it goes! Thanks a bunch!

Hi Rainton,
I'm flattered to have inspired you on this one! And now I really wanna make this "carboncomp Vs metalfilm" blind test too !!!
Have you listened to my comparaison files between 5088 and 3708 transistors? What have put in yours?

Hi evilcat Unfortunately I didn't have the chance to listen to them because they're not available anymore - I tried to download them but the link didn't work...but I followed what other people said about your test and from there I tried to find out more...until I ended up just trying it myself

I have 3708s installed - I heard people on this forum saying the unit sounds a little brighter with 5088s? But soundfiles to compare would be nice for sure!

 

[hymentoptera]

Definitely C22.  They talk about it in the manual.

Not sure what's going on with R7/C6.  I'm not an expert on every component in the circuit.  Come kind of divider/coupling/lowpass filter thing with C1 and R6? 

Now I gotta know....off to do some research.

Mike

LOL! I know what you mean! 6 months ago I knew jack about electronics, but this project has sent me reeling headlong into the matter. I can't thank you (and everyone else here!!) enough for this journey I'm on.

I just noticed a 0.015uF WIMA in the Mouser cart today. Is this the new C27 (on attack pot) ??? How will a different value affect the performance? Immeasurably slower attack? or...? I'm planning on using a NOS 0.012uF Sprague mylar axial here and if 0.015uF is a better choice I might try to find one in the new value instead.

 

[Echo North]

Definitely C22.  They talk about it in the manual.

Not sure what's going on with R7/C6.  I'm not an expert on every component in the circuit.  Come kind of divider/coupling/lowpass filter thing with C1 and R6? 

Now I gotta know....off to do some research.

Mike

LOL! I know what you mean! 6 months ago I knew jack about electronics, but this project has sent me reeling headlong into the matter. I can't thank you (and everyone else here!!) enough for this journey I'm on.

I just noticed a 0.015uF WIMA in the Mouser cart today. Is this the new C27 (on attack pot) ??? How will a different value affect the performance? Immeasurably slower attack? or...? I'm planning on using a NOS 0.012uF Sprague mylar axial here and if 0.015uF is a better choice I might try to find one in the new value instead.

Most likely a change in "standard values" between the 60's and today.  I see a lot of it in caps.  I schem will quote a cap value you can't find anywhere because the new standard value has changed.  I doubt you could even find a measurable difference between 0.015 and 0.012.

Mike