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Old 15th November 2009, 05:12 PM   #121
Salas is offline Salas  Greece
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Even when compared to Evox Rifa's best?
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Old 15th November 2009, 07:03 PM   #122
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Only looked at the PEH 200 - and yes, by a small margin
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Old 15th November 2009, 07:14 PM   #123
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Cheers for investigating.
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Old 15th November 2009, 07:27 PM   #124
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YW - and I investigated for my own good as I am using them (got several types relatively cheap on Ebay). Having said that the difference is pretty small (35mm diameter 10 vs 12 nH, 50 mm 15 vs 16 nH) so I would use whatever I can get. Even small snap-in types are 20 to 25 nH, that is more of a difference though some will claim that it is completely exaggerated to look at such details.
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Old 15th November 2009, 08:00 PM   #125
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Quote:
Originally Posted by Joachim Gerhard View Post
The schematic in my last post contained an error.
T8 was upside down. Thank you AG for alerting me on this mistake.
today i post the corrected schematic with two additions :
one is the possibility to design the current mirrors in the input stage as Wilson types and second, one could shorten the bases of the input transistors ac wise to ground with big capacitors (say 2200 üF) reducing the noise by 3dB.
I did not try the Wilson current mirrors but i know from experience that the capacitors give an improvement in noise suppression.
Next time i will publish some measurements of this circuit compared to some others.
again the schematic does not show the actual values but shows the topology in principle.
On the positive rail by your schematic I read "V15" and on the negative rail "V25". Are there +15V/-25V supply voltage?
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Old 15th November 2009, 08:57 PM   #126
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Thank you martin for good advice. maybe then i take the stud mounted because thats a little easier to asemble. you can find the data i researched in the rs components catlog but i will lookup the data at epcos website too. they say that the 570 will last 10.000hr at 105° and the 550 5.000hr but i do not care any more, i trust you.
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Old 15th November 2009, 09:02 PM   #127
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what schematic do you refer too? i put quite a lot on this site. values you see on the schemetics are only default and do not represent the correct values. i am still optimising the MPP and when it`s ready and works for my satisfaction i will deliver the correct values.
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Old 16th November 2009, 03:02 AM   #128
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Quote:
Originally Posted by Joachim Gerhard View Post
I think it is a good thing when distortion is low and i think circuits with extremely high amounts of feedback can be made to sound good.

Hi Joachim,

thanks for noticing my question to you under syn08's HPS 4.0 phono stage thread and pointing me over to your thread here.

A bit off-topic question but I have to grab you here when I saw your reply under the following link:
HPS 4.0 phono stage
and in particular the part I'm quoting here above whereby a question raised in my head which I would like to forward over to you.
I am aware your reply was probably in the context of phono amplifier, but anyway here below goes my question.

As you have a profound knowledge of loudspeaker designing (Audiophysics) I would like to ask what is your view of amplifiers with high amount of feedback in conjunction with loudspeakers in terms of the overall system distortion?
The reason I ask is as we know, in general high feedback amounts into also very low output impedance of the amplifier and as such I am in particular keen on your view when such amplifier is connected with a loudspeaker.

btw, I remember very well your interview performed by Lars Mytting 1996 and I want to tell I appreciate a lot of your views concerning loudspeaker designing, thanks for your time.

Cheers Michael
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Last edited by Ultima Thule; 16th November 2009 at 03:10 AM.
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Old 16th November 2009, 08:44 AM   #129
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Quote:
Originally Posted by Joachim Gerhard View Post
from post #127: what schematic do you refer too? i put quite a lot on this site. values you see on the schemetics are only default and do not represent the correct values. i am still optimising the MPP and when it`s ready and works for my satisfaction i will deliver the correct values.
that one from post #28 #29 #40 #2 and #3
by the pos. supply voltage rail I read V15 and by neg. rail V25.
Therefore my question about the value of supply voltage
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Old 16th November 2009, 03:40 PM   #130
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hi michael !
my two reference amps are the MACE Amp and the Audionet Max 2, both with extremely high amounts of feedback. They work with nested feedback loops so unfortunately your question is hard to answer. Amps with high overal feedback can have trouble to damp the back EMF from the speaker in the first 10msec. See research done by Hannes Mayer and Peter Schüller of Stereoplay magazine. They are awaillable by e-mail or you can call them up. I have a third set of amps with tubes (LA Audio monoblocks). They sound very nice on my high sensitivity speaker. I build myself a pair of dipoles with SEAS Exotic driver just for fun. On speakers like that amps with low damping factor can be an advantage because bass and treble will be somewhat higher in level, partly compensating for the reduced bandwidth of those drivers. With speakers of such high sensitivity (96dB in that case plus 6dB difusefield from the dipol) the tubeamp can comfortably stay in class a for best performance. Amplifiers with high output impedance are interesting too because dynamic variation of the driver impedance dos not provoke distortion. I whould do that in an active sytem with equalisation. Nelson Pass can show you how it can be done. The Audio Physic Rhea and Terra subwoofers did something similiar. We used a compromise between constant current and constant voltage because we could not get the amp thermally stable with only constant current. Martin Colloms called the sound of that woofers "athmospheric". If i whould do a poweramp i whould eventually seperate the voltage amplifying stage and the current amplifying stage and add some sort of error feedback. I think Malkolm Hawsford called that kind od design "Pontoon" amps.
To tiefbassuebertr : i use +- 15V for the opamp section and +-12V for the input section
trickled down from the +-15V supply.
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