Frank...the only interlocutor in town....
Moral must have a company that sell this piece of crap...as a High End amplifier...for all over the world...imagine the number of
people that spend their money in a thing like that...
To spend more time and money in a amp like that seems to me dobius...as if the output transformers are made by the same people....they don´t give me any trust....
And with the money of the sell he can chose another project ,even a kit and learn something in the processe...
The more you talk...the more i learn about your expertise in amplifier design....
But now talking to Foe...do what you think is best for you....
Arrivederci!!
Moral must have a company that sell this piece of crap...as a High End amplifier...for all over the world...imagine the number of
people that spend their money in a thing like that...
To spend more time and money in a amp like that seems to me dobius...as if the output transformers are made by the same people....they don´t give me any trust....
And with the money of the sell he can chose another project ,even a kit and learn something in the processe...
The more you talk...the more i learn about your expertise in amplifier design....
But now talking to Foe...do what you think is best for you....
Arrivederci!!
it would seem to me that the pot within the feedback loop would work (although I would not do that) as a gain control.
yes linearity would suffer at low levels as it does not have the feedback to clean it up
with the gain set high enough the maximum gain would be determined by the external loop
review the formula for gain of a feedback amplifier
Vo / Vi = a / ( 1 + a*b)
where Vo is output, Vi input, a is open loop gain and b is feedback (as a fraction)
as a becomes large (high open loop gain) the overall gain aproaches 1/b
as a is lowered the gain aproaches a/1 and the exernal feedback is not significant to aid in linearity and the linearity of the amp is dependant on each stage
yes linearity would suffer at low levels as it does not have the feedback to clean it up
with the gain set high enough the maximum gain would be determined by the external loop
review the formula for gain of a feedback amplifier
Vo / Vi = a / ( 1 + a*b)
where Vo is output, Vi input, a is open loop gain and b is feedback (as a fraction)
as a becomes large (high open loop gain) the overall gain aproaches 1/b
as a is lowered the gain aproaches a/1 and the exernal feedback is not significant to aid in linearity and the linearity of the amp is dependant on each stage
The lost post....
Sorry Foe i miss your post #35...only now i see it...
Yes...if not the amp can't work at all....
Because R9 is drived by a comum cathode stage and R8 by a ground grid stage...the diference in resistors values is for to compensate this diferences in gain...and reduce distortion.
If the R14 that i "think" is the feedback resistor is 1K the overal voltage gain will be 6...only....can't be...
Yes!
I have Jadis Orchestra heavily transformed even with remote control...and a Luxman SQ38 also heavily transformed...i´m a danger for the amps...heehehhehe...
For ending...are you sure that the pot at the input as been properly conected?'
Cheers
PS . if your final decision is to try to fix your amp...teel me...we will try!
Sorry Foe i miss your post #35...only now i see it...
Yes...if not the amp can't work at all....
Because R9 is drived by a comum cathode stage and R8 by a ground grid stage...the diference in resistors values is for to compensate this diferences in gain...and reduce distortion.
If the R14 that i "think" is the feedback resistor is 1K the overal voltage gain will be 6...only....can't be...
Yes!
I have Jadis Orchestra heavily transformed even with remote control...and a Luxman SQ38 also heavily transformed...i´m a danger for the amps...heehehhehe...
For ending...are you sure that the pot at the input as been properly conected?'
Cheers
PS . if your final decision is to try to fix your amp...teel me...we will try!
bournville said:
I haven't actively followed this thread, but pls note that in this amp the feedback is very weak, probably less than 10dB. So, the fb is not really "fighting back", and the volume control will have much more effect than you might think. I think it really is a volume control, but I agree it is quite inelegant. This is Not Done.
Jan Didden
I will survive !
Hi all,
Even if my amplifier is pure scrap, i have the secret hope to transform it info a true (not hi end but not so bad) amplifier.
Then, I will not sell it to my best frend.
I am now bak at the original shematics, and i can hear 50Hz when the volume is at the maximum.
OK, but how to solve it ? More feedback or less gain in SRPP ? I have no idea !
Anyway, does someone know ao "Tubes for Dumies" book other thas "Audio classroom". The question is how tocalculate the different usual kind of stage ?
Thanks to all and especialy to Jorge.
Gauthier
Hi all,
Even if my amplifier is pure scrap, i have the secret hope to transform it info a true (not hi end but not so bad) amplifier.
Then, I will not sell it to my best frend.
I am now bak at the original shematics, and i can hear 50Hz when the volume is at the maximum.
OK, but how to solve it ? More feedback or less gain in SRPP ? I have no idea !
Anyway, does someone know ao "Tubes for Dumies" book other thas "Audio classroom". The question is how tocalculate the different usual kind of stage ?
Thanks to all and especialy to Jorge.
Gauthier
The amp that becomes famous...
OK,let's work in it....
First of all....measure the values of the resistors R14 and R3 ...for that you need to take one end of the resistor out of the circuit...
After measure the voltage at the point where R4 conect to C2 and the pin 3 of the tube...
Check this two points ...and let me know!
Cheers!
OK,let's work in it....
First of all....measure the values of the resistors R14 and R3 ...for that you need to take one end of the resistor out of the circuit...
After measure the voltage at the point where R4 conect to C2 and the pin 3 of the tube...
Check this two points ...and let me know!
Cheers!
Foes,
No reason why your amp should not give good service - the circuitry from V2 onwards is fairly straightforward and non-controversial.
How loud is the 50hz hum? You say you can hear it at the full setting of the volume control - is it noticable at other levels?
(If you have no use for the EM80 magic eye in the amp, why not remove it and the associated circuitry? It will mean that your power supply will have less demand on it)
No reason why your amp should not give good service - the circuitry from V2 onwards is fairly straightforward and non-controversial.
How loud is the 50hz hum? You say you can hear it at the full setting of the volume control - is it noticable at other levels?
(If you have no use for the EM80 magic eye in the amp, why not remove it and the associated circuitry? It will mean that your power supply will have less demand on it)
Hi Jorge,
Why do you want to mesure the resistor, i know the values :
R14=1K 1W
R3=200Ohm 1/8W
I say that because it's difficult to desolder double side PCB's...
Anyway, i will mesure the voltage...
Hi Bournville,
The 50Hz is only noticable at high level, i mean from 3/4 of the max position of the pot @ the original position...
Indeed, i can remove EM80 but if the PS is so underdimentioned... no hope!
Why do you want to mesure the resistor, i know the values :
R14=1K 1W
R3=200Ohm 1/8W
I say that because it's difficult to desolder double side PCB's...
Anyway, i will mesure the voltage...
Hi Bournville,
The 50Hz is only noticable at high level, i mean from 3/4 of the max position of the pot @ the original position...
Indeed, i can remove EM80 but if the PS is so underdimentioned... no hope!
An unusal amp...
Well,
I understand that the volume pot is still in it's original position, as it is too difficult to remove from the PCB - therefore hum pickup must be around V1.
Have you tried leaving that pot at maximum, and connecting another pot for controlling volume at the input to V1 - that would mean that the feedback was always at maximum and help indentify if the hum pick-up was occuring in the input leads/connectors.
Well,
I understand that the volume pot is still in it's original position, as it is too difficult to remove from the PCB - therefore hum pickup must be around V1.
Have you tried leaving that pot at maximum, and connecting another pot for controlling volume at the input to V1 - that would mean that the feedback was always at maximum and help indentify if the hum pick-up was occuring in the input leads/connectors.
Dear Jorge,
I have mesured voltage on different point of the circuit :
R3.R2=0.2V
V1(2)=1.7V
V1(7)=86V
V1(8)=89V
V2(2,8)=9.7V
V3,4(1,6)=289V
V3,4(8)=14.1V
V3,4(2,9)=290V
Bad luck, when mesuring V2(4)and V2(6), it seems i have burned something. Hopefuly, The amp is under waranty. I will try to make warranty work...
Anyway,
R14=5.6K
R3=200Ohms
Dear Bournville,
In fact i have tryed to put at the input but it is now bak at the original position. Even with input short circuited, i ear 50Hz when pot is @ the max...
Regards,
Gauthier
I have mesured voltage on different point of the circuit :
R3.R2=0.2V
V1(2)=1.7V
V1(7)=86V
V1(8)=89V
V2(2,8)=9.7V
V3,4(1,6)=289V
V3,4(8)=14.1V
V3,4(2,9)=290V
Bad luck, when mesuring V2(4)and V2(6), it seems i have burned something. Hopefuly, The amp is under waranty. I will try to make warranty work...
Anyway,
R14=5.6K
R3=200Ohms
Dear Bournville,
In fact i have tryed to put at the input but it is now bak at the original position. Even with input short circuited, i ear 50Hz when pot is @ the max...
Regards,
Gauthier
Alive !
Hi, Jorge,
No i'am not joking,
Left channel is giving continuous 50Hz @ a quite high level in my speakers...
I have tryed to swap V1 and V2 between both chanel withour result.
Well, after reading your message, i have tried again. I think i have a bad contact on one soldering. ("Soudure sèche" in french).
I fix it soon. OK my amplifyer is still alive... Nice !
Hi, Jorge,
No i'am not joking,
Left channel is giving continuous 50Hz @ a quite high level in my speakers...
I have tryed to swap V1 and V2 between both chanel withour result.
Well, after reading your message, i have tried again. I think i have a bad contact on one soldering. ("Soudure sèche" in french).
I fix it soon. OK my amplifyer is still alive... Nice !
Doubts...
I don't understand...
You want to short V1(8) with V2(3) ??
Presentely V2(3)=0V and V1(8)=89V. V2(3) is a grid and i can probably force it to this level, but a dV of 89V between grid and cathode is quite high, isn't it ? (heuh, sorry, i'm maybe wrong, i am from the AOP generation...).
Anyway, what would be the improvement in yur proposition ? I don't realy understand, even if you are probabely right ...
Regards,
Gauthier
I don't understand...
You want to short V1(8) with V2(3) ??
Presentely V2(3)=0V and V1(8)=89V. V2(3) is a grid and i can probably force it to this level, but a dV of 89V between grid and cathode is quite high, isn't it ? (heuh, sorry, i'm maybe wrong, i am from the AOP generation...).
Anyway, what would be the improvement in yur proposition ? I don't realy understand, even if you are probabely right ...
Regards,
Gauthier
Only the one that think has doubts....
Yes they need to be conected directely with a wire...(conection directe)
If not the grid 3 of V2 will be at ground potencial and the current across R7 ...R8 ...R9 will be to low...
This is the problem with your amp...
When you conect directly V1(8) to V2(3) the cathode of V2 will folow the grid voltage ( 89 volts) and the resistor of the cathode becomes properly biased...and the current in each of the triodes of V2 will be aproxi. 3mA and at the anodes the voltage will became aprox.140 volts under the high tensionn voltage...
In this condition the phase spliter work fine...
Trust me...thats the problem!
Ps but to work propely you must:
Delect and put out of circuit R5-470k
Delect and put the the pot at the input(sorry...but it must be)
Delet C2
AND ONLY AFTER THAT....conect V1 (8) to V2 (3)...
Compris???
En avant vers la musique!!!
Yes they need to be conected directely with a wire...(conection directe)
If not the grid 3 of V2 will be at ground potencial and the current across R7 ...R8 ...R9 will be to low...
This is the problem with your amp...
When you conect directly V1(8) to V2(3) the cathode of V2 will folow the grid voltage ( 89 volts) and the resistor of the cathode becomes properly biased...and the current in each of the triodes of V2 will be aproxi. 3mA and at the anodes the voltage will became aprox.140 volts under the high tensionn voltage...
In this condition the phase spliter work fine...
The inprovement is that the cliping and the distortions will be gone...now the voltage across R8 R9 are to low...
Trust me...thats the problem!
Ps but to work propely you must:
Delect and put out of circuit R5-470k
Delect and put the the pot at the input(sorry...but it must be)
Delet C2
AND ONLY AFTER THAT....conect V1 (8) to V2 (3)...
Compris???
En avant vers la musique!!!
Afraid you'r right
Dear Jorge,
I 'm afraid you are right.
I still not have tested, after documenting myself, it's indeed to design this stuff like dat.
http://www.bonavolta.ch/hobby/fr/audio/split.htm#Long Tailed Pair
is interesting about this subject...
I will visit a frend to unsolder it cleanly and i say you the result...
Thanks,
G
Dear Jorge,
I 'm afraid you are right.
I still not have tested, after documenting myself, it's indeed to design this stuff like dat.
http://www.bonavolta.ch/hobby/fr/audio/split.htm#Long Tailed Pair
is interesting about this subject...
I will visit a frend to unsolder it cleanly and i say you the result...
Thanks,
G
Not so bad...
Hi Jorge,
I have tried the modifications you have proposed. I mean : Pot at the input C2 Shorted and R5 supressed.
The result is clearly better. No saturation due to high input level anymore. The sound is sharper also, i thing.
Well done, you where right.
I still have a quite high 50Hz noise in the speaker, but dificult to determine the reason why. Probably, this is generated (amplified) by the first stage, and now that i have no attenuation before the second one... I can hear it...
Another question also is the quite low curent in the first stage (89v-86v)/1.5k=2mA this is low for such a tube is'n it ?
Anyway, it's better, and thank you.
Regards,
Gauthier
Hi Jorge,
I have tried the modifications you have proposed. I mean : Pot at the input C2 Shorted and R5 supressed.
The result is clearly better. No saturation due to high input level anymore. The sound is sharper also, i thing.
Well done, you where right.
I still have a quite high 50Hz noise in the speaker, but dificult to determine the reason why. Probably, this is generated (amplified) by the first stage, and now that i have no attenuation before the second one... I can hear it...
Another question also is the quite low curent in the first stage (89v-86v)/1.5k=2mA this is low for such a tube is'n it ?
Anyway, it's better, and thank you.
Regards,
Gauthier
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