U73b (drip) - 3 questions

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hugo

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Hi mates,
I finished a drip U73b, and I have this issue that I can not understand.
The 2 first release times  (fastest ) are working well, but when I use 3rd, 4th and 5th release times, the signal got compressed by default like 15db, and the needle stay at this point..like no attack time  (needle stays at -15 on the meter even with no sound passing the unit) and no release (the needle never go back to 0) same issue on 2 channels, so it does not seems to be a short or a bad connection.. any idea ? Does anybody have the same issue ?

My second question concerns the calibration. Is there any starting point for all these trimmers and even for the threshold )

Last question : when looking at the documentation, I saw that the limit mode is about -10db than the compressor mode, no comparison can be done between the 2 modes. Is it a problem if I use the « cathode » trimmer to obtain the same level on output ?

If you have any info on any of this, thank you very much

Hugo
 

gyraf

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Hi Hugo,

I'd say that these are very much questions that should be directed to drip - they are surely the ones with the best first-hand knowledge on these their commercialized DIY-projects.

And I think they owe their customers some support

/Jakob E.
 

Michael Tibes

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+1 to what Jacob said.

Nevertheless, the first issue could be missing discharge resistors. The fact that it happens on 2 channels could point to  some misunderstanding during the build process  ;)

The calibration has been discussed here before, you should be able to find that.

The third issue is design-based, that's how the unit is supposed to work originally if I remember right. You'd have to modify the circuit to change that. What documentation are you refering to?

Michael
 

axl85

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hugo said:
Hi mates,
I finished a drip U73b, and I have this issue that I can not understand.
The 2 first release times  (fastest ) are working well, but when I use 3rd, 4th and 5th release times, the signal got compressed by default like 15db, and the needle stay at this point..like no attack time  (needle stays at -15 on the meter even with no sound passing the unit) and no release (the needle never go back to 0) same issue on 2 channels, so it does not seems to be a short or a bad connection.. any idea ? Does anybody have the same issue ?

My second question concerns the calibration. Is there any starting point for all these trimmers and even for the threshold )

Last question : when looking at the documentation, I saw that the limit mode is about -10db than the compressor mode, no comparison can be done between the 2 modes. Is it a problem if I use the « cathode » trimmer to obtain the same level on output ?

If you have any info on any of this, thank you very much

Hugo


Hi,
just came across your post.  Did you check the Errata note with the 220k resistor across + and - in the ftc time constant?
Maybe that's why you have the release time problem? Just a guess...
I also finished the unit but still have some problems here and there.
For exemple if i put a +6db signal to the input i get asymetrical distortion at the output.
Witch shouldn't be the case according to the schematic  (if i'm not mistaken).
I was wondering if the Sowter 1275e is the right OT for this unit as it seems to have a different ratio (2:1). The original OTs are 10:1.
Do i get something wrong here?
I also figured (with some help from Impulsstudio) that the plate choke (Sowter 9375) is also not the right one for this unit.
I really would appreciate some help from all you smart guys here!
This project is unfortunately not good documented and i'm not expecting some support from the Drip people...

 

Impulsstudio

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Joined
Apr 26, 2018
Messages
13
hugo said:
Hi mates,
I finished a drip U73b, and I have this issue that I can not understand.
The 2 first release times  (fastest ) are working well, but when I use 3rd, 4th and 5th release times, the signal got compressed by default like 15db, and the needle stay at this point..like no attack time  (needle stays at -15 on the meter even with no sound passing the unit) and no release (the needle never go back to 0) same issue on 2 channels, so it does not seems to be a short or a bad connection.. any idea ? Does anybody have the same issue ?

My second question concerns the calibration. Is there any starting point for all these trimmers and even for the threshold )

Last question : when looking at the documentation, I saw that the limit mode is about -10db than the compressor mode, no comparison can be done between the 2 modes. Is it a problem if I use the « cathode » trimmer to obtain the same level on output ?

If you have any info on any of this, thank you very much

Hugo

Hi,
1. sounds like it´s the 220k resistor between plus and minus (got problems there too, misplaced the 220k in the beginning, now it´s ok (will change to the original one )...got a jpg that shows where to place...not sure if i want to publish this stuff here...it´s from greogory and so,,.(may message?)

2. Also got a paper for calibration (in German, attsched)...so far: input and output attenuator full cw, threshold full ccw the rest isn´t so that important. May put the Bias full cw.

3. don´t know.

good luck

 

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  • Abgleich U73b_dbU (1).pdf
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Sc

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Hi Hugo

Regarding your question 3 - I'm quite shure you will mess up calibration in both modes by turning the cathode trimmer (R 67 ??). But in case you have the output attenuator, you might turn it by 10db to compare ? Or do I get your idea wrong ?

Regards Walter
 

hugo

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gyraf said:
Hi Hugo,

I'd say that these are very much questions that should be directed to drip - they are surely the ones with the best first-hand knowledge on these their commercialized DIY-projects.

And I think they owe their customers some support

/Jakob E.

Unfortunately, i even have difficulties to obtain some build documents from them, even if i ordered the pcb...
 

hugo

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Feb 26, 2016
Messages
501
Location
Paris
axl85 said:
Hi,
just came across your post.  Did you check the Errata note with the 220k resistor across + and - in the ftc time constant?
Maybe that's why you have the release time problem? Just a guess...
I also finished the unit but still have some problems here and there.
For exemple if i put a +6db signal to the input i get asymetrical distortion at the output.
Witch shouldn't be the case according to the schematic  (if i'm not mistaken).
I was wondering if the Sowter 1275e is the right OT for this unit as it seems to have a different ratio (2:1). The original OTs are 10:1.
Do i get something wrong here?
I also figured (with some help from Impulsstudio) that the plate choke (Sowter 9375) is also not the right one for this unit.
I really would appreciate some help from all you smart guys here!
This project is unfortunately not good documented and i'm not expecting some support from the Drip people...

THANK YOU SO MUCH !!
 

hugo

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Feb 26, 2016
Messages
501
Location
Paris
Impulsstudio said:
Hi,
1. sounds like it´s the 220k resistor between plus and minus (got problems there too, misplaced the 220k in the beginning, now it´s ok (will change to the original one )...got a jpg that shows where to place...not sure if i want to publish this stuff here...it´s from greogory and so,,.(may message?)

2. Also got a paper for calibration (in German, attsched)...so far: input and output attenuator full cw, threshold full ccw the rest isn´t so that important. May put the Bias full cw.

3. don´t know.

good luck

would you have the picture ? I dont see any reason for greg to not showing it, i think there is no pb...
 

Impulsstudio

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Messages
13
hugo said:
would you have the picture ? I dont see any reason for greg to not showing it, i think there is no pb...
Here is the pic, the orange painting in the pic is where you should place the resistor.
 

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  • 220k Insert.jpg
    220k Insert.jpg
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Impulsstudio

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hugo said:
would you have the picture ? I dont see any reason for greg to not showing it, i think there is no pb...
Just in case your boards have the same bug, flipped lim and cmp at the relay, here´s a pic that shows where you should cross the contacts.

PS. again, thanks Walter!
 

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  • Relais_Lim_K (1).jpg
    Relais_Lim_K (1).jpg
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hugo

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Impulsstudio said:
Just in case your boards have the same bug, flipped lim and cmp at the relay, here´s a pic that shows where you should cross the contacts.

PS. again, thanks Walter!
Which bug was it ?
 

hugo

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Messages
501
Location
Paris
Impulsstudio said:
Hi,
1. sounds like it´s the 220k resistor between plus and minus (got problems there too, misplaced the 220k in the beginning, now it´s ok (will change to the original one )...got a jpg that shows where to place...not sure if i want to publish this stuff here...it´s from greogory and so,,.(may message?)

2. Also got a paper for calibration (in German, attsched)...so far: input and output attenuator full cw, threshold full ccw the rest isn´t so that important. May put the Bias full cw.

3. don´t know.

good luck

thank you for your support
 

Impulsstudio

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Messages
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hugo said:
Which bug was it ?
„ The relay issue - only on the first Edition 2018 board - the switch lim/comp acts wrong on the R79 cathode bypass – R79 is open in comp mode instead of bypassed to ground. You can fix it by crossing two pins on the relay.“ (from Walters post). This bug makes it impossible to calibrate lim.

So your Time constant is working now? Nice.

 

hugo

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Impulsstudio said:
„ The relay issue - only on the first Edition 2018 board - the switch lim/comp acts wrong on the R79 cathode bypass – R79 is open in comp mode instead of bypassed to ground. You can fix it by crossing two pins on the relay.“ (from Walters post). This bug makes it impossible to calibrate lim.

So your Time constant is working now? Nice.

Hi, how to check if i have a recent board or not ?... I purchased it last year so probably corrected, i didnt see anything on the docs.
Regarding constant times, yes, just like a real fairchild hehehe.

I would like to add a hpf sidechain if possible, does somebody know how to proceed ?

Thx
 

Sc

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Hi

there is a copyright print left of the transformers - it says 2018 or 2019. 2018 has this bug.

Regards
Walter
 

hugo

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Impulsstudio said:
„ The relay issue - only on the first Edition 2018 board - the switch lim/comp acts wrong on the R79 cathode bypass – R79 is open in comp mode instead of bypassed to ground. You can fix it by crossing two pins on the relay.“ (from Walters post). This bug makes it impossible to calibrate lim.

So your Time constant is working now? Nice.

I ordered few months ago but it seems the boards are still defective here . I think they all have this issue.
 

hugo

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Messages
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Location
Paris
Impulsstudio said:
Just in case your boards have the same bug, flipped lim and cmp at the relay, here´s a pic that shows where you should cross the contacts.

PS. again, thanks Walter!

Hi again, could you tell how did you proceed to cross this ?
Thank you
 

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