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Old 3rd March 2003, 01:44 PM   #1
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Default A new fashion tube design!

Hi folks!

See the schematic of this chinese tube amplifier!

http://www.audioasylum.com/forums/tu...ges/26058.html

A volume pot inside a overall feedback loop!!!!

I think that we must going on designing ours owner amplifiers

as the French say "en est jamais mieux servie,que par soi meme"

Any coments?

Cheers

Jorge Santos
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Old 3rd March 2003, 02:04 PM   #2
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Default CHINESE?

Hi,

First of all it is a German amplifier, not a Chinese one.
Second, I do see a global feedback loop but no volume pot in it.

Cheers,
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Old 3rd March 2003, 02:14 PM   #3
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Default Chinese or not chinese!

Hi fedgrove!

If you see the post under the schematic the owner said that it is chinese.. i presume that is one more case of a chinese product sell in west with a western name...but that i don't know!

Regarding the volume pot is conected to C2 . C3 ...a 100KOhms pot!

Regards

Jorge Santos
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Old 3rd March 2003, 02:22 PM   #4
Joel is offline Joel  United States
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Jorge,

It's just the volume pot. Am I missing something interesting?
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Old 3rd March 2003, 02:27 PM   #5
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Default The volume pot!!

Hi Joel!

I will past the folowup of the answer that i give to the guy!

Hi Foes!
The schematic of this chinese amplifier is seriousely wrong!!

First of all the junction point of R10,R11,R12 must be conected to ground!

Second and more important the volume control is inside the overall feedback loop...so when you turn the volume control the feedback try to compensate and the gain will be changed...because the feedback will see the variation of the volume control as a error!

A very much flowed design!

Regards

Jorge santos
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Old 3rd March 2003, 02:47 PM   #6
Joel is offline Joel  United States
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Default Re: The volume pot!!

Quote:
Originally posted by Tube_Dude
First of all the junction point of R10,R11,R12 must be conected to ground!
You are right. The ground connection is missing.

I don't have a problem with the volume control placement though.
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Old 3rd March 2003, 03:25 PM   #7
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Default Volume pot!

Joel Says! " i don't have a problem with the volume control placement though"


But the feedback loop have a problem!


Imagine when the operator turn the volume pot a little down...the feedback loop see this as a reduction of gain,and it try to compensate with a encrease of open loop gain...in the previous stages.

Resuming the open loop gain will be not defined but it changes with the volume pot position!Not a good designe pratice!

Regards

Jorge Santos

PS: In the link you can see the complaint of the owner saying that the amp is saturating!
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Old 3rd March 2003, 06:12 PM   #8
EC8010 is offline EC8010  United Kingdom
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Default Bizarre

Yup. Looks like a volume control inside a feedback loop to me too.
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Old 3rd March 2003, 06:23 PM   #9
dhaen is offline dhaen  Europe
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Hi,

Another odd thing is the volume control's "W" taper.
Who knows, maybe with the feedback fighting back, it's necessary...

Cheers,
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Old 3rd March 2003, 06:36 PM   #10
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Default W taper pot!

Hi dhaen!

Maybe the W is the abreviation of wrong

But the correct schematic was lost in the assembly chain...

Cheers

Jorge Santos
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