CES BELGES QUAND-MEME.
Hi,
I stand with EC8010 in that I doubt very much that this amp was intended for hi-fi use.
Foes,
You're only 15' away from where I live..Landen...if you want I can take a look at it.
BTW,decreasing the feedback will only make matters worse. As Jorge suggests, either put the volctrl at the front or junk it alltogether.
Cheers,
Hi,
I stand with EC8010 in that I doubt very much that this amp was intended for hi-fi use.
Foes,
You're only 15' away from where I live..Landen...if you want I can take a look at it.
BTW,decreasing the feedback will only make matters worse. As Jorge suggests, either put the volctrl at the front or junk it alltogether.
Cheers,
EC 8010, I hate you (i joke), you are not very sympathetic with my poor amplifier. Well, i will avoid to show you the internal design.
I Will first try to follow Jorges advices. Thanks Jorge.
I like this forum.
But... anyway exept this feedpot in the feedbak why does it seems so old fashioned ?
I Will first try to follow Jorges advices. Thanks Jorge.
I like this forum.
But... anyway exept this feedpot in the feedbak why does it seems so old fashioned ?
Is the amp old fashioned?
Well...
The valve choice for one thing. Even if you can use EL84s instead of EL41s why were these latter valves even considered in the first place? They were being replaced by EL84s in commercial equipment by the mid to late 1950s at best. This EM80 is also an old choice - the EM81 with the better display was being used in valve tape recorders in preference to EM80s by the 1960s. Incidentally, the option of using EL90s in the output is a bit strange - it is not a direct equivalent of the EL41/EL84 series (it has similar characteristics to the 6V6/6BW6 series) and to use it without alterations to the bias in the output stage is a bit naughty. Ideally, the whole circuit should be looked at if you use different output valves as the difference in HT consumption would alter the overall HT voltage and thus affect the working conditions of the other valves.
Other issues...probably a newer hifi amp would use ultra-linear or triode operation in the output stage for greater fidelity rather than normal loading. Some use of direct coupling to reduce phase shift and enable greater feedback maybe?
Well...
The valve choice for one thing. Even if you can use EL84s instead of EL41s why were these latter valves even considered in the first place? They were being replaced by EL84s in commercial equipment by the mid to late 1950s at best. This EM80 is also an old choice - the EM81 with the better display was being used in valve tape recorders in preference to EM80s by the 1960s. Incidentally, the option of using EL90s in the output is a bit strange - it is not a direct equivalent of the EL41/EL84 series (it has similar characteristics to the 6V6/6BW6 series) and to use it without alterations to the bias in the output stage is a bit naughty. Ideally, the whole circuit should be looked at if you use different output valves as the difference in HT consumption would alter the overall HT voltage and thus affect the working conditions of the other valves.
Other issues...probably a newer hifi amp would use ultra-linear or triode operation in the output stage for greater fidelity rather than normal loading. Some use of direct coupling to reduce phase shift and enable greater feedback maybe?
Hi Bournville!
In your first post in this tread you say that maybe the inclusion of the pot inside the feedback loop it is a designer option!
For me a design option is the type of tubes ,to use triode ,ultralinear or straight pentode loading...in this case everyone can have diferent choice no one is wrong.
In the case of the pot even if it was a choice...its tottaly wrong...a fatal mistake...sorry!
regards
Jorge Santos
PS: By the way my prefered output stage configuration is straigt pentod! i'm not a fashion folower!
In your first post in this tread you say that maybe the inclusion of the pot inside the feedback loop it is a designer option!
For me a design option is the type of tubes ,to use triode ,ultralinear or straight pentode loading...in this case everyone can have diferent choice no one is wrong.
In the case of the pot even if it was a choice...its tottaly wrong...a fatal mistake...sorry!
regards
Jorge Santos
PS: By the way my prefered output stage configuration is straigt pentod!
i'm not a fashion folower!
Jorge,
I agree with EC8010 and fdegrove that the amp was probably not designed for hifi audio work but perhaps for guitar, PA or some other purpose. If this is the case, the output transformer may not be of good enough quality for the reproduction of the frequency range normally associated with hifi jobs, but still improvements might be able to be made.
I agree with you about removing the pot, R5 (470k) will be providing the grid bias, and the pot could go at the input of the amp. However, I agree with fdegrove that Foes should not reduce the feedback, but instead perhaps increase it to help improve linearity and reduce distortion.
You may not be able to increase it much, as the amp was not designed to take large amounts of feedback, but likewise if you reduce it you might find hum and potential instability become problems.
I agree with EC8010 and fdegrove that the amp was probably not designed for hifi audio work but perhaps for guitar, PA or some other purpose. If this is the case, the output transformer may not be of good enough quality for the reproduction of the frequency range normally associated with hifi jobs, but still improvements might be able to be made.
I agree with you about removing the pot, R5 (470k) will be providing the grid bias, and the pot could go at the input of the amp. However, I agree with fdegrove that Foes should not reduce the feedback, but instead perhaps increase it to help improve linearity and reduce distortion.
You may not be able to increase it much, as the amp was not designed to take large amounts of feedback, but likewise if you reduce it you might find hum and potential instability become problems.
Link
Hi !
This is the link to te website of dared whitch develop all these new concepts in hifi...
http://www.daredtube.com/
Hi !
This is the link to te website of dared whitch develop all these new concepts in hifi...
http://www.daredtube.com/
Re: The Amp that come from Est!
Well Jorge,
In that case, what's the purpose of the EM80? What would be it's function in a hifi amp? At present it can indicate overloading in the first stage regardless of the setting of the (misplaced) pot, once you relocate this to the input of the amp (which is generally agreed is where it should be to avoid changes in the feedback) the EM80 has no purpose!
Tube_Dude said:
Well Jorge,
In that case, what's the purpose of the EM80? What would be it's function in a hifi amp? At present it can indicate overloading in the first stage regardless of the setting of the (misplaced) pot, once you relocate this to the input of the amp (which is generally agreed is where it should be to avoid changes in the feedback) the EM80 has no purpose!
Hi-Fi and marketing...a happy marriage!
Hi Burnville!
For me the (magic eye) EM 80 is doing the same function that the temperature gouge in same Marantz amps...and others.
Is a marketing decision because people like to have some gimmicks to play with and they do no harm.
There is a Portughese adage that say:
-We also eat with our eyes!...
this explain the sucess of the niciest girls!
Back to busines...if you go to the link that Foe gave you will see that the amps there are not only called Hi-Fi amps but....
... High End hi-fi amplifiers!
But i want to make clear that's only my opinion!...I don't want to be a guru here...there already many in that position.
Cheers
Jorge
PS: I remenber when i was a young the emotion of see (what i now call EM 80) moving with music in a Grundig reel to reel that belong to a girl friend of mine...
Hi Burnville!
For me the (magic eye) EM 80 is doing the same function that the temperature gouge in same Marantz amps...and others.
Is a marketing decision because people like to have some gimmicks to play with and they do no harm.
There is a Portughese adage that say:
-We also eat with our eyes!...
this explain the sucess of the niciest girls!
Back to busines...if you go to the link that Foe gave you will see that the amps there are not only called Hi-Fi amps but....
... High End hi-fi amplifiers!But i want to make clear that's only my opinion!...I don't want to be a guru here...there already many in that position.
Cheers
Jorge
PS: I remenber when i was a young the emotion of see (what i now call EM 80) moving with music in a Grundig reel to reel that belong to a girl friend of mine...
Green eyes but where is the rest ?
Hi Jorge and Bournville,
Sorry, i have not changed the pot position, i need a desoldering pump for that (it's PCB mounted), i will try to visit a frend soon.
I have checked how to do and I have noticed that they are not satisfied to use carbon resistors, they use capacitors they have in stock, despite of the shematics and seregraphy...
After the pot operation, i should try to replace carbon resistors by good Dale one and to // electrolitics with small mkp.
About the EM80, I agree with you, it's nice. But like girls which speak to much, it's boring after half an hour...
Bournville, you are right about the Magic eye, if i change the pot position, the cat eye will just indicate the input level after the pot...
Oh Sorry, i forget de most important R10,R11,R12 are connected to the ground...
The next question i ask me are :
1. Why R8 and R9 have different values.
2. Why R14 is just 1K in my amplifier, due to higher gain of the EL90 ./.EL41 ?
Doyou know Synthesis amplifier ??
What do you have @ home ?
Hi Jorge and Bournville,
Sorry, i have not changed the pot position, i need a desoldering pump for that (it's PCB mounted), i will try to visit a frend soon.
I have checked how to do and I have noticed that they are not satisfied to use carbon resistors, they use capacitors they have in stock, despite of the shematics and seregraphy...
After the pot operation, i should try to replace carbon resistors by good Dale one and to // electrolitics with small mkp.
About the EM80, I agree with you, it's nice. But like girls which speak to much, it's boring after half an hour...
Bournville, you are right about the Magic eye, if i change the pot position, the cat eye will just indicate the input level after the pot...
Oh Sorry, i forget de most important R10,R11,R12 are connected to the ground...
The next question i ask me are :
1. Why R8 and R9 have different values.
2. Why R14 is just 1K in my amplifier, due to higher gain of the EL90 ./.EL41 ?
Doyou know Synthesis amplifier ??
What do you have @ home ?
Jorge,
I agree - appreciation of audio fidelity is often a matter of opinion, and Foes certainly has an amp which with a few modifications could give hours of listening pleasure.
I remember those 'magic eyes' in tape recorders as well - I always ended up overloading the recorder when trying to use them to determine input levels!
I agree - appreciation of audio fidelity is often a matter of opinion, and Foes certainly has an amp which with a few modifications could give hours of listening pleasure.
I remember those 'magic eyes' in tape recorders as well - I always ended up overloading the recorder when trying to use them to determine input levels!
My Amplifier Strikes back !
Bad design... bad design...
I have tried to supress the potentiometer... The result is awfull.
I hear perfectly the 50Hz in the HP, I guess it's not the purpose of this stuff...
I suppose that the reason is a to high gain un the first stage (the SRPP).
At the same time the indications on the EM80 are smaler, probably because without the pot, output level is higher and then the feedback is also...
Pfff, such is life...
Bad design... bad design...
I have tried to supress the potentiometer... The result is awfull.
I hear perfectly the 50Hz in the HP, I guess it's not the purpose of this stuff...
I suppose that the reason is a to high gain un the first stage (the SRPP).
At the same time the indications on the EM80 are smaler, probably because without the pot, output level is higher and then the feedback is also...
Pfff, such is life...
Un conseil!!
There are onother great problem that i haven't remarked but a smart guy in sweden see it :
http://www.audioasylum.com/forums/tubediy/messages/26525.html
So if i was you...i rewired the pot in the inicial place...and try to sell this magnificent piece of High End engeering...
But please!!!...Not to a friend!!
Regards
There are onother great problem that i haven't remarked but a smart guy in sweden see it :
http://www.audioasylum.com/forums/tubediy/messages/26525.html
So if i was you...i rewired the pot in the inicial place...and try to sell this magnificent piece of High End engeering...
But please!!!...Not to a friend!!
Regards
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