Retired:Symmetrical FET

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Aah yes, that makes sense now.

For judging and setting balances, it's often best at full-clockwise settings, as this point is the only not suffering from pot unbalance.

When building my stereo units, I buy 1000 stereo pots and select the 50-75 that is good enough for stereo - and then I use the rest as mono pots or for non-critical functions...

Jakob E.
 
Hell, this is a neverending story...

Left channels distorts heavily, especially and much mode in gr. Voltage peaks, don't know where they comming from. Input is fine +-15,4 exactly, no peaks.

In gr, left Meter is jumping as crazy with the peaks, changed the 22pf and the 470. no change. Without NPD everythings fine.

Suggestions?
 
Okay, sorted it out, had something to do with the bias-settings.

I tried to calibrate it with several methods I found, but there is still an unbalance, changing with setting, ie. ratio, attack, release.

My last try will be to match some bf245a and test it, if this doesn't change the stereo image, I will let it be and use it as a mono device :)
 
Hey Jakob,

thanks for your interest.

I do not think that this has something to do with gain reduction at all.

When I remove the npd, there is still an unbalance. When I move the input, the balance changes from about 1-5 db difference, sometimes at the same level different. Also the outpu knob changes this difference. That should not be an gain reduction problem, I suppose.

This is strange, and again, may the pots are the problem. Do you agree?

 
I have to say, whilst most dual-gang potentiometers are not perfect, I've never had one 5dB out! I feel like something else is a miss here.

Out of curiosity, the NPD5566 you used, is it a real one, or a slightly more suspicious one from eBay?



mike76 said:
Hey Jakob,

thanks for your interest.

I do not think that this has something to do with gain reduction at all.

When I remove the npd, there is still an unbalance. When I move the input, the balance changes from about 1-5 db difference, sometimes at the same level different. Also the outpu knob changes this difference. That should not be an gain reduction problem, I suppose.

This is strange, and again, may the pots are the problem. Do you agree?
 
Hi Nick,

it is indeed from eBay, China.

But, as I posted above, even if I remove the NPD and turn the input/output knobs, the difference is there and changes. Not always 5db, most 1-2. but this changes, randomly.

I am not sure, if this is caused by the pots or anywhere else my circuit.

I have only basic understanding of the schematics. Therefore I decided to put it back in my rack until this changes or I found someone, who is more experienced than myself :)
 
Is there any issues with using a pair of single pots instead of the dual gang units? (getting hard to source)
 
Gustav said:
gt_jumper said:
Can i use n4007 in the place of Z10? I have a large bag of N4007s.

I am not really sure when the 10V breakdown voltage becomes relevant (22dBu?), so it could be interesting to hear from someone smarter than me.

I would use the zener :)

Gustav

Someone smarter than me....

Harpo said:
There is no/nada/niente zener diode in the 1178 (IIRC the Urei house numbers Y10 were 1N914 or 1N4148).
Your 10V zeners at the audio rectifier might cause unexpected behaviour when driven harder.
As always YMMV.
 
Gustav said:
Gustav said:
gt_jumper said:
Can i use n4007 in the place of Z10? I have a large bag of N4007s.

I am not really sure when the 10V breakdown voltage becomes relevant (22dBu?), so it could be interesting to hear from someone smarter than me.

I would use the zener :)

Gustav

Someone smarter than me....

Harpo said:
There is no/nada/niente zener diode in the 1178 (IIRC the Urei house numbers Y10 were 1N914 or 1N4148).
Your 10V zeners at the audio rectifier might cause unexpected behaviour when driven harder.
As always YMMV.

Thanks Gustav :) I went with the Zener i linked you to.
 
So how close do the voltages have to be at the designated check points? I have +15.08Vdc and -14.7Vdc on each. Is that close enough to move ahead? Or shall i swap out the program resistor to get them closer to 15Vdc?
 
gt_jumper said:
So how close do the voltages have to be at the designated check points? I have +15.08Vdc and -14.7Vdc on each. Is that close enough to move ahead? Or shall i swap out the program resistor to get them closer to 15Vdc?

A little off, but close enough to move ahead Id say.

I would probably tweak the negative rail.

Gustav
 
Gustav said:
gt_jumper said:
So how close do the voltages have to be at the designated check points? I have +15.08Vdc and -14.7Vdc on each. Is that close enough to move ahead? Or shall i swap out the program resistor to get them closer to 15Vdc?

A little off, but close enough to move ahead Id say.

I would probably tweak the negative rail.

Gustav

Thankyou Gastav :)

Here is a progress shot with rainbows!

20150710_115302_zpsjwnd5zjg.jpg
 
Harpo said:
There is no/nada/niente zener diode in the 1178 (IIRC the Urei house numbers Y10 were 1N914 or 1N4148).
Your 10V zeners at the audio rectifier might cause unexpected behaviour when driven harder.
As always YMMV.
Thanks Gustav :) I went with the Zener i linked you to.

Sorry, bit confused, are you now saying install 1418s? BOM on first page says zener. Should this not be updated if so?

Cheers
 
Paradigm X said:
Sorry, bit confused, are you now saying install 1418s? BOM on first page says zener. Should this not be updated if so?

I will assume you mean the 4148, and if so, yes - install those.

Since I made the MS76, the project is no longer available, so I haven't been updating the documents. Following quote should also clarify how hard you would have to drive it to matter.

gt_jumper said:
Gustav said:
Gustav said:
gt_jumper said:
Can i use n4007 in the place of Z10? I have a large bag of N4007s.

I am not really sure when the 10V breakdown voltage becomes relevant (22dBu?), so it could be interesting to hear from someone smarter than me.

I would use the zener :)

Gustav

Someone smarter than me....

Harpo said:
There is no/nada/niente zener diode in the 1178 (IIRC the Urei house numbers Y10 were 1N914 or 1N4148).
Your 10V zeners at the audio rectifier might cause unexpected behaviour when driven harder.
As always YMMV.

Thanks Gustav :) I went with the Zener i linked you to.
 
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