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Joachim Gerhard 23rd December 2009 11:19 PM

Today i build the time domain subsonic filter or TDSF how i will call it. This time without fancy opamps because i had to use what i have at home. i took the workhorse OPA2134 for the input buffer and the old chestnut NE5534 as output buffer. I thought with the benefit of 100% feedback they whould do the job quite well. No dual mono power supply ether this time. Only two 9V alkaline blocks into 5600 uF Sprague elcaps, bypassed with 1uF Wima MKT and lokally bypassed with 100uF elcaps on each chip. I did not scimp on construction and did a 100% star earth grounding the way i learned from Dennis Morecroft. I used my favourte caps though: 0.1uF 630V Rifa PHE450 in parallel with 0.1uF 160V Röderstein/Vishey MKP. Resistors were standart 1% metalfilm.
I used the TDSF between the RIAA stage and the preamp and first checked for noise. Inserting the circuit i could hear no rise in hum or hiss, ear at speakers, high volume. I also installed a bypass switch.
Listening and using the circuit was quite fascinating. It did surprisingly little damage on the signal and it even improved certain aspects of the sound, the higher the playback volume was. What it lost was a certain siruppy and liquid, honey like tone in the bass and fundamental tone aerea and some feeling of depth (not in imaging but in size). It was replaced with a tighter, faster and more precise redition. Cone movement was not zerro, mind you, at high volume but the low frequency back and forth movement was gone. What i liked too was more precise focus and higher dynamic range. When the unfiltered signal could go on the nervs at extrem volume the filtered version could be played much louder without fatique. impact on imaging was little except the improved focus and slightly reduced size. Micro detail was intact so i can now safely recommend standart high feedback opamps at that voltage level. I am still not convinced if high NFB is a good choice for the first stage of a phonoamp or an I/U stage of a DA converter but here it did no harm even on tiny signals like acoustic information and micro noise. I wonder now how i could have lived without the benefit of a good subsonic filter for 35 years but the ones i tryed so far did not work. Most of the time they took away bass slam without the benefit of much reduced cone movement. I had to design one my selve to resolve the issue. This circuit may not work it“s magic i any system but i think a lot of people have a medium stiff cartridge in a medium to high mass arm. Highly recommended ! I will play that stage in Vegas after hours and i am eager to hear other opinions,

Holger Barske 23rd December 2009 11:30 PM

Let me see if I get this right: You are talking of a passive high pass filter seated between two OPs, inserted after the phono stage?
Amazing.

Joachim Gerhard 24th December 2009 12:40 AM

Yes, it“s after the phonostage and you can bypass it. The idea is also to compensate for the rising trend under 20Hz due to the resonance of cartridge and arm. In fact if you send me the response of your system for example measured with the Doc Feikert software i could calculate a matching filter. I will also design a kind of equaliser that will be able to follow other equalisations then RIIA AFTER the normal phonostage and also has the ability to compensate for room (notch filter) and programm deficiencies. Kind of modern version of the Cello Palette. Martina Schöner really bugged me for years on an universal equalizer ( she likes opera from the fist halve of the last century) but i never liked the concept of switching IN the phonostage, so that idea came up. My fortee is filters, i am a speaker guy from profession.

Joachim Gerhard 24th December 2009 10:29 PM

1 Attachment(s)
I do not use feedback in the TDSF so source buffers can be substituted for the opamps.
see the attached diagram for a symmetric B1 buffer.
Today i substituted the Hiraga Optime Transimpedance RIAA for a low Z Mpp with inductive RIAA. I had the TDSF in the circuit and the difference was easily audible. I am more and more convinced that the TDSF is virtually transparent, so instead of switching it in and out i left it in the system all the time. Today is holy night and we have a tradition to listen to my system with the whole family. My wife likes music from the 60th and 70th. She was a Hippy. So we listened to Jaques Brell, Melanie Safka, James Taylor, Bob Dylan etc. The sound was extremely enjoyable. I was specially surprised about the Melanie album. She was a minimal artist ! It“s so pure and clean with very little instrumentation. Later my son and i listened to Donald Fagen, Jenifer Warnes etc. He likes the same music then me and found out that the cones where not moving as much as they did before so we had an interesting discussion about the Doppler Effect.
The MPP Inductive RIAA did not disappoint. In terms of musicality it is better then the slightly cold Hiraga Optime Transimpedance. I still believe this is a great value and the MPP Inductive is much more expensive to make. Sound was again so good that we totally forgot about the HIfI and just listened to our favorite music. Frohe Weihnachten !

Onvinyl 25th December 2009 12:09 AM

Joachim, Frohe Weihnachten!

Is it that same Melanie that made the interpretation of 'these boots...' ?
It's extremly cool!

You are confusing me, however: which circuit is which? Did you post the TDSF? The inductive hiraga? (never heard of an inductive circuit from him)
Did you made the entire RIAA behind the hiraga transimpedance? I stood under the impression, you pulled down 75µS only here.

Have some nice days, all!
Rüdiger

Holger Barske 25th December 2009 12:17 AM

Quote:

Is it that same Melanie that made the interpretation of 'these boots...' ?
Me thinks this was Nancy.
Frohe Weihnachten, Jungs.

brianco 25th December 2009 12:29 AM

The "I've got a brand new pair of rollerskates' you've got a brand new key" Melanie.

Takes me back a loooong way!

Joachim Gerhard 25th December 2009 12:51 AM

2 Attachment(s)
Hi Holger, Rüdiger and Brian ! I hope you are well !
The name of the Artist is Melanie Safka. The track we heard was "Hey Mr. Tamborin Man ",
I am not shure but that may be a Bob Dillan composition.
Rüdiger, sorry if i have confused you. You will see the circuit i used tonight in the attachement. I think i have not published it in full here. see the 25mH coil. That makes the circuit inductive. Between this stage and the preamp i used my new subsonic filter called
TDSF and not TDFS as i wrongly stated. It“s an acronym for Time Domain Subsonic Filter. If you have any questions about the whys and whats of the circuit i can explain in more detail. How does the Instrumentation amp comes about ?
I show the TDSF here implemented with source followers. You can use any kind of buffers here. if you go back on this thread i have shown plenty.

Joachim Gerhard 25th December 2009 12:55 AM

Now i got confused but that is the result of too much CAVA.
The subsonic filter was always called TDSF when i go trough the files. Everything else in my last post is correct though.

Joachim Gerhard 25th December 2009 01:22 AM

1 Attachment(s)
In fact i am using a version with more sophisticated biasing to the parallel cascodes. it improved the sound a lot.


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