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Old 29th August 2010, 11:32 AM   #1801
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Velvetsunrise, maybe you missed some parts of the thread but your circuit shows my Transconductance-Transimpedance (TC-TI) stage in simplified form that was discussed here before in detail. You can adjust the gain of that circuit over a very wide range by changing the the impedance of the RIAA network. I found circuits with gain from 56 - 66dB worked well. In this circuit everything is intermingled with everything. For example raising gain also raises distortion and lowers overload margin.
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Old 30th August 2010, 03:58 AM   #1802
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I have now the Olypos in my system with a TC-TI stage. I was curious how it compares to the Titan i so i did make some measurements. First i measured crosstalk with a 1kHz tone at 5cm-sec on my DIN testrecord. The Olypos with -40dB does a little bit better then the Titan i but the 3dB difference can be due to measurement tolerance.
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File Type: pdf Olympos Crosstalk @ 1kHz.pdf (7.5 KB, 43 views)
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Old 30th August 2010, 04:04 AM   #1803
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Then i measured frequency response with pink noise and anti pink filter. The Olympos does not suffer the slight 10kHz peak of the Titan i but has some more treble over 15kHz so this may acount to the notion that the Olympos sounds softer and more musical then the Titan i for some listeners that prefer clasical. I found the subjective difference rather small but i can understand why the Olympos is still considered the best Lyra cart of all time.
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File Type: pdf Olympos FRD with ULNSC.pdf (47.2 KB, 50 views)
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Old 30th August 2010, 04:11 AM   #1804
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Here is the noise of the TC-TI in its latest disguise. The right channel is somewhat better and when i crank the system i can here some more noise in the left channel that sounds impusive like crackers. At standart volume ( i listen loud ) this is a non issue still i think some noise screening could help and i am thinking about a reliable method for some time. Manuel Huber of FM Acoustic told me that they do it with electrostatic hedaphones by putting the transistors in a jig but when you see my maesurements the differeces show up. Especialy in the bass.
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File Type: pdf Olympos on ULNSC all curves.pdf (10.0 KB, 62 views)
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Old 30th August 2010, 04:27 AM   #1805
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Two things stand out. One is that the Olypos has around 3dB less distortion then the Titan i but again i do not trsust my measurements 100%. Maybe i have adjusted it better, maybe the needle was cleaner, maybe my room temperature was more comfortable, who knows. What you can really see is that making a phonostage with distortion less then
- 60dB may not help to make it sound any better. Distortion at that level ( 5cm-sec) is -46dB in the Olympos, all harmonics are present, exponentially falling. That distortion profile sounds jsut fine to my ears and the -90dB second of the TC-TI and the -110dB of nothing particular in the FPS are more then good enough. Again see the dynamic range of the vinyl record at around 72dB, just as burkhard Vogel sugested. Still you can hear a 1kHz sinewave at -30dB burried in the noise so subjective dynamic range of Vinyl can be very good. A friend of mine with superb listening found Harry Bellafonte at Carnegie Hall distorted in comparison to his lates Linn server with 24Bit-196K though. I am much more tolerant and find the Belafonte amasing in terms of involvement although i hear the technical problems too. It is like looking at an old black and white photograph so enjoying vinyl is also an eastetic experience that does not always tell the truth.
the other interesting thing is that i got rid of the 50Hz hum. I use the Hypnotise PSU and could not help to put at least one Elna Silmic2 330uF into the plus and minus feed but i think even that is not necesary with a Hypo board so me that has always decoupled generously have to rethink. all fine though. Saves me money and trouble.
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Old 30th August 2010, 04:30 AM   #1806
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Also visible ( blue trace from pink noise ) is that the heavy Olympos fits somewhat better into my arm in the lower reaches.
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Old 9th September 2010, 02:48 AM   #1807
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I have not being posting for a while because i was on a trip to Berlin and then to Hamburg. I had enough time in the train to think about what i should do next and one thing i really need is a passive Anti RIAA. I have build the Vogel active Anti RIAA but it is not always practical. For example i am planning to feed a high quality Digital Signal from my SACD player into some of my circuits to make a straight wire bypass test. Also i have to check RIAA accuracy of my latest TC-TI designs. Sofar they have been first simulated and then build but because i use current mirrors with finite output impedance a small mistake in the deeper regions under 100Hz can develop that comes out a bit different in reality although we simulate the impedance too. Current mirrors with very high, even infinite output impedance ( or negative ) can be build but a current mirror also has a transient response based on the topology. That all happens over 10MHz but still i found they all sound a bit different. Interestingly the simple Widlar mirror is the fastest without overshot. The Wilson is as fast but with a slight overshot.The Cascode mirror is only 1/3 of the speed of the Widlar but does not have an overshot and the 3 transistor mirror is even slower with the biggest overshot. So in praxis the mirror with the highest ouput impedance may not be the best choice for sound. If the mirror does not have an infinite output impedance the RIAA at lower frequencies will load the mirrror with say 100kOhm and when the mirror has 1Mohm at that frequency for example you have a loss of bass. That may not be much, say 1dB but it is not perfect so the RIAA has to be tweaked. A qiuck check with a passive RIAA can help and feeding for example a 100kHz squarewave shows how the RIAA hehaves concerning pahse and transient response. Even the clever Vogel circuit runs out of steam somewhere over 300kHz because gain in that circuit is not infinite at higher frequencies but the RIAA demands an even falling response to zero.
investigating the material i found on the net there is a good article on the Hagerman website. It starts with the legacy Lipshitz circuit and makes some additions and modifications. What still worries me is that the load impedance is not specified and with the exeptions that Hagerman specifies a 50 Ohm input impedance ( Lipshitz just labels "Low Z In") and remodels the Anti RIAA to give out signal at -40dB and -60dB ( the Lipshits specifies a somewhat curious -44.1dB ) i see no real innovation. The Neumann pole can be added to the Lipshits too so this is not exclusive for the Hagerman solution. It ocurred to me that a load impedance has to be specified and i decided on 300 Ohm. At least with my recent circuits that gave a very good subjective result with the cartridges my friends and i are using e.g. Low Output - Low Impedance types like the Lyras. Higher loading like 1kOhm and 47kOhm did not give any more information and the sound got sharp at times. Tubes or other circuits may behave different but at Maison Gerhard 300 Ohm is the norm. I decided to work on the Lipshitz, partly because i had the values at hand and partly because i never use the Neumann constant. I substituted the 604 Ohm resistor in the Lipschitz with 5x 113 Ohm Dale in series and 2 x 113 Ohm in parallel. With 300 Ohm loading this amounts to 612,61 Ohm.
1% off whould be 610.04 Ohm so i found that close enough. A load of 118 Ohm whould give 603,2 Ohm what is very close but also shows that loading down is posible without much change so the circuit is not particular sensitive which is a bonus.
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File Type: jpg Passive Anti RIAA.jpg (78.5 KB, 478 views)
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File Type: pdf Passive Anti RIAA.TSC - TINA.pdf (31.5 KB, 132 views)
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Old 9th September 2010, 03:16 AM   #1808
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Lipshitz makes a minor correction with the addition of 5pF//1n and 12Meg//75k in one of his articles.
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Old 9th September 2010, 03:20 AM   #1809
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5 pf is 5cm teflon solid core cable twisted but thanks anyway. With my Tube Voltmeter the RIAA stays pretty flat over 100 Hz and in the bass i see the small error. I will post measurements tomorrow.
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Old 9th September 2010, 04:12 AM   #1810
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He was compensating for generator's Z that drives the inverse. What is your generator's Zo?
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