A new fashion tube design!

Tube_Dude · 3rd March 2003, 01:44 PM

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

fdegrove · 3rd March 2003, 02:04 PM

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,

Tube_Dude · 3rd March 2003, 02:14 PM

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

Joel · 3rd March 2003, 02:22 PM

Jorge,

It's just the volume pot. Am I missing something interesting?

Tube_Dude · 3rd March 2003, 02:27 PM

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

Joel · 3rd March 2003, 02:47 PM

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.

Tube_Dude · 3rd March 2003, 03:25 PM

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!

EC8010 · 3rd March 2003, 06:12 PM

Yup. Looks like a volume control inside a feedback loop to me too.

dhaen · 3rd March 2003, 06:23 PM

Hi,

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

Cheers,

Tube_Dude · 3rd March 2003, 06:36 PM

Hi dhaen!

Maybe the W is the abreviation of wrong

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

Cheers

Jorge Santos

3rd March 2003, 01:44 PM	#1
Tube_Dude diyAudio Member Join Date: Mar 2002 Location: Aveiro-Portugal	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

3rd March 2003, 02:04 PM	#2
fdegrove diyAudio Senior Member Join Date: Aug 2002 Location: Belgium	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, __________________ Frank

3rd March 2003, 02:14 PM	#3
Tube_Dude diyAudio Member Join Date: Mar 2002 Location: Aveiro-Portugal	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

3rd March 2003, 02:27 PM	#5
Tube_Dude diyAudio Member Join Date: Mar 2002 Location: Aveiro-Portugal	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

3rd March 2003, 03:25 PM	#7
Tube_Dude diyAudio Member Join Date: Mar 2002 Location: Aveiro-Portugal	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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3rd March 2003, 02:22 PM	#4
Joel diyAudio Member Join Date: Oct 2002 Location: Brooklyn, NY	Jorge, It's just the volume pot. Am I missing something interesting?

3rd March 2003, 06:12 PM	#8
EC8010 diyAudio Moderator Emeritus Join Date: Jan 2003 Location: Near London. UK	Bizarre Yup. Looks like a volume control inside a feedback loop to me too. __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

3rd March 2003, 06:23 PM	#9
dhaen diyAudio Moderator Emeritus Join Date: Jun 2002 Location: U.K.	Hi, Another odd thing is the volume control's "W" taper. Who knows, maybe with the feedback fighting back, it's necessary... Cheers,

3rd March 2003, 06:36 PM	#10
Tube_Dude diyAudio Member Join Date: Mar 2002 Location: Aveiro-Portugal	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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