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Old 23rd November 2009, 04:42 AM   #201
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I do professional reviews from time to time in a music magazine called "ARS-Magazin".
you can find the website under ars-music » | Musik-Shop für CDs, LPs (Vinyl), DVDs und Hifi-Zubehör
Anyway, i think the next time i will build a fet version and keep the balanced version sleeping for a while. the noise is so low that i start to think myself that balanced will not be any better but i still give not up on that idea.
after having studied ScottWs differential VAS i got the following idea: see attachement
would it work ? maybe scott can tell me. anyway i have worked only a little on the values so that is not the finished design.
Attached Files
File Type: pdf MPP Fet Headamp Current Mirror.TSC - TINA.pdf (45.9 KB, 219 views)
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Old 23rd November 2009, 05:11 AM   #202
Salas is online now Salas  Greece
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Noise would matter on horn speakers mainly from this point on. Balanced should give a 3dB penalty, isn't that right?
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Old 23rd November 2009, 07:42 AM   #203
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yes, it has a 3dB noise (hiss, that is) disadvantage but external noise sources are better suppresed so it sounds different. i can bring the noise down to 0.5nVqHZ with current mirrors bypassed. that is stil 4.5dB worse then the best designs that Syn08 makes, but still 6 dB better then AD797, LT1115 for example. doubling the input devices whould give a 3dB improvement and than it gets wicked. see the latest Accuphase phonostage for a tour de force in "Faulknering".
why noise over horns should be more objectionable escaps me. yes, the noise from the power amp should be really low and they love class a and tubes but considering that the volume at the listening seat is the same the noise from the phonostage should subjectively be the same. one problem can happen: many horns that i have measured have a very ragged frequency response in the treble so some frequencies simply stand out more then others. such speakers can sound quite noisy i am shure.
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Old 23rd November 2009, 07:50 AM   #204
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you can download the chematics here :
http://www.accuphase.com/cat/c-27_e.pdf
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Old 23rd November 2009, 10:08 AM   #205
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Quote:
Originally Posted by Joachim Gerhard View Post
hi jan !
yes, the topology is quite similiar but with a transimpedance input (common base) and not a common emitter stage. that is simply not awaillable in IC opamps to my knowlage.
when you look at the MPP "Ultimate" you will see some similarity with the AD797.
Joachim,

You may want to check out the OPA860 if only for academic interests.

jd
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Old 23rd November 2009, 12:05 PM   #206
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Quote:
Originally Posted by Joachim Gerhard View Post
why noise over horns should be more objectionable escaps me.
Because horns have sensitivities of 96-102dB and hence the hiss is way more audible. HPS 3.1 and 4.0 are dead quiet in my Klipsch RF-83 horns (97dB), but everything over 0.4nV/rtHz is clearly audible, cartridge input shorted to ground, at maximum volume. I hate hiss.
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Old 23rd November 2009, 12:30 PM   #207
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Syn08, think again, it can not be true. soundpreasure is soundpreasure, no matter where it comes from. i only can asume that your speakers have a peaky treble or you listen very loud. anyway, i am not particular fond of hiss either and you are the low noise champion here, no question. give me some time. i am learning fast and this is not the end of the story. i have a different style of designing based on the asupmtion that good sound comes from relatively simple circuits but i start to think about more complex topologies too. at least in the way i will set the bias and offset. if then a desire comes up for ever so lower hiss i will invertigate that too. what do you think about a gallium arsenite design with peltier cooling? my friend in Trondheim makes WLAN positional sytems and they work with that kind of transistors.he is a great hifi designer too and may help with experience. anyway the noise in my setup is so low that my son was thinking the equipment was nor switched on but i agree. low noise IS important for dynamic range, you have me sold. by the way this ROHMS are exeptional. the noise sounds to my ear even "lighter" then Toshibas can.
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Old 23rd November 2009, 12:49 PM   #208
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Quote:
Originally Posted by Joachim Gerhard View Post
Syn08, think again, it can not be true.
Well, I do, and it's correct (both theoretical and practical). A 96dB speaker sounds twice as loud as a 90dB speaker, at the same power. And so is hiss. This is obvious even for those with tin ears like myself

You'd be very happy with BF861 cooled down via a Peltier device. My preliminary results are very good, I can tell that. Evacuating the condensation is not trivial, though.

Last edited by syn08; 23rd November 2009 at 12:52 PM.
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Old 23rd November 2009, 01:16 PM   #209
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Post High sensitivity speakers and noise

Logically I would have thought independently of the loudspeaker sensitivity we have to tune our little volume knob to get the same listening level, which would equalize out any difference in phono stage noise or anything else before the volume knob, right?

The only thing we can't equalize out is the noise produced after the volume knob, the noise in the power amplifier for instance.

btw the human ear perceives a sound pressure doubling closer to around 9 dB, don't remember right now the exact figures but I am sure Joachim knows that too.

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Last edited by Ultima Thule; 23rd November 2009 at 01:18 PM.
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Old 23rd November 2009, 02:08 PM   #210
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Ultima, good for you. The volume control makes all the difference.
Again, the difference between .3nV/rt Hz and .5nV/rt Hz is trivial, for MOST situations. This is because .3nV represents 5 ohms equivalent noise, .4nV 10 ohms, and .5 nV 15 ohms of equivalent noise. Please remember this is in SERIES with the MC cartridge, itself. So, if you have a phono cartridge with a 10 ohm source, then the ACTUAL noise is 15, 20, and 25 ohms in effective noise voltage the difference then between .3 and .5 in this case is effectively 2.2 dB. Not so very much.
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