Purple MC76 P2P problems - SOLVED !

[Purusha]

Finally I got my first SCOPE !!!!!

Now I just have to learn how to use it. :green:

OK, Keith, I am ready for your help to guide me through the troubleshooting :grin:

Sintech told me the problem must be in the area around the R59 as this trimmer
doesn't effect the output in any way. I must say I am lost without your help.

 

[sintech]

Hey Purusha,

I'm here with my RAF scope! (four feet deep) and working Mc76's if you need any cross reference of any kind.

The Qbias Adjustment should work all the time, and it seems you have no kind of response at all.

Your sidechain seemed to be fine, as we traced it from input through to the GR FET, with the soft scope.

Main thing is the Point to point is 100% right and tested.

good hunting!

 

[Purusha]

Thanks Andy :thumb:

I just tested my scope and it works fine. I think I am ready to use it. The 1KHz tone was shown nicely on both channels.

Waiting for Keith now :wink:

 

[Purusha]

BUMP

Has anyone seen Keith lately? :grin:

 

[SSLtech]

..only the unlucky ones!!!

Right, step by step we'll have to go gradually, and I'll have to 'predict' what I'd expect to see, since all the 1176's here are in use in studios...

Keith

 

[Purusha]

Hey Keith, I am really happy you stopped by :grin:

We have also Sintech on the line who bought the scope recently so we can compare mine with his if needed :thumb:

OK, waiting for your instructions.

 

[Purusha]

Right, step by step we'll have to go gradually, and I'll have to 'predict' what I'd expect to see, since all the 1176's here are in use in studios...

Keith

When do you think you will find the time? Not that I want to rush you but I am really
hoping to be able to use them soon on the incoming mixing session.

 

[radiance]

[quote author="Purusha"]

Waiting for Keith now :wink:[/quote]

[quote author="Purusha"]BUMP

Has anyone seen Keith lately? :grin:[/quote]

[quote author="Purusha"]

OK, waiting for your instructions.[/quote]

[quote author="Purusha"]
When do you think you will find the time? Not that I want to rush you but I am really
hoping to be able to use them soon on the incoming mixing session.[/quote]

:shock:

 

[Purusha]

OK, I see some are :shock: when reading my posts. Let me explain, a few pages back Keith offered
his help to guide me through the troubleshooting provided that I have the scope. This was two months
back when I didn't have the scope yet. Anyway I am still stuck with the problem that my two Purples don't
compress although we tried to solve this problem with Sintech... since the problem is the same in both units
it must be something wrong with either one element or P2P wiring. I checked what I can but no luck so far.

My knowledge is just not up to this situation yet so I depend on the mercy of someone who can guide me
through now when I finally bought the scope just for this purpose.

 

[Purusha]

BUMP

 

[Purusha]

Hello,

just wanted to confirm that my P2P wiring on the photo below works 100% OK.

 

[Purusha]

THE PROBLEM IS SOLVED!!!

I was using the FETs for the G1176 version which should be installed backwards in the Purple to work at all :shock:
... so they were replaced with right ones and the problem is gone thanks to Sintech who discovered the error!!!

The Purple MC76 is a very transparent compressor capable of compress a lot and you can't tell until you hit the bypass :grin:

 

[radiance]

:thumb:

 

[Rob Flinn]

Purusha

I am looking at your hook up diagram. The 0.22u cap across the 470R resistor in your diagram is 0.022u on the Purple diagram !!!

By the way the diagram has been very useful ! Thanks !

 

[Purusha]

Thanks Rob :thumb:

Will correct this ASAP. I have to check what I used in my unit as well :roll: :grin:

 

[Rob Flinn]

I seem to be having a problem understanding the calibration procedure, can someone (Ed SSLtech) clarify it for me.

I'm reading the MC77 & MC76 manual & it has 2 steps which are puzzling me:

7. Set attack control full CCW (off position). Set input control for +10dB as read on external meter
8. Turn the attack control OFF (CCW) & readjust the output level control for 0 If necessary.

Both these steps appear to have the unit bypassed ????

I have adjusted the null successfully, & done the fet -1dB adjustment, but seem to be having problems getting the meter to show the correct gain reduction.

 

[thestudio]

I have a MC76IIIV15 pcb and would like to know the info on C1000, R1001, S1000 I have the value for R1000 :?:

 

[mnats]

[quote author="Rob Flinn"]I seem to be having a problem understanding the calibration procedure, can someone (Ed SSLtech) clarify it for me.[/quote]
I'm neither of the people you asked for, so you can take my advice with a grain of salt. Since the MC76/77 is essentially an 1176, try the calibration instructions in section 5.3.3 of the UREI manual. R54 in the commonly circulated manual refers to R44 - the fixed, selected resistor in the Rev C/D/E and MC76 schematic, but other than that I don't think there is a more lucid, comprehensive explanation of the calibration process that has ever been written.

FWIW

 

[edanderson]

[quote author="thestudio"]I have a MC76IIIV15 pcb and would like to know the info on C1000, R1001, S1000 I have the value for R1000 :?:[/quote]

look in the MC76 manual.

http://purpleaudio.com/pdflib/PurpleMC76.pdf

ed

 

[edanderson]

[quote author="mnats"][quote author="Rob Flinn"]I seem to be having a problem understanding the calibration procedure, can someone (Ed SSLtech) clarify it for me.[/quote]
I'm neither of the people you asked for, so you can take my advice with a grain of salt. Since the MC76/77 is essentially an 1176, try the calibration instructions in section 5.3.3 of the UREI manual. R54 in the commonly circulated manual refers to R44 - the fixed, selected resistor in the Rev C/D/E and MC76 schematic, but other than that I don't think there is a more lucid, comprehensive explanation of the calibration process that has ever been written.

FWIW[/quote]

i am one of the people you asked for, and i agree with mnats. if the calibration procedure in the MC76/77 manual doesn't make sense to you (and i agree it is confusing), just use the cal instructions in the 1176 manual.

r44 on the more recent MC77 PCBs is a resistor, trimpot, and jumper in series. this is so you can use a 100r resistor (so that the composite value is never 0 ohms) in series with a 2kohm trimpot to dial in the value of r44. the jumper is there so that you don't have to remove the resistor during cal.

ed

ed