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Old 5th June 2015, 08:41 AM   #1
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Default 2 stage Passive LCR RIAA

Now that I have finished my SP10 turntable project, I want to build a high end phono stage to meet and exceed it. There is a well reviewed phono stage that has the following published details.

No caps or resistors in the signal path
Point to point
Pair C3g tubes in input stage, 2123 Hz, passive regulated DC heaters
Pair C3g tubes in the output stage, 50-500 Hz, AC heaters
LCR network transformer driven
39 db output level for MM
Step-up transformer for MC
Power supply 6CA4/EZ81 tube rectifier w/choke filter
Input impedance 47Kohm/200 pf
Output impedance 1200 Ohm
Gain 39 db

I found these transformers that have similar construction to the commercial unit. Noguchi Tranformers FMQL and FMQH RIAA equalizer coils.

Are there any known schematics that can be modified or anyone up to the task to sketch out? Or too difficult a task?
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Old 5th June 2015, 09:20 AM   #2
McLanz is offline McLanz  Germany
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Hello Coasttoast - very interesting - I'm also looking for a LCR based phone pre. I hook myself to this thread...
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Old 5th June 2015, 05:07 PM   #3
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I have spent quite a few hours searching for a schematic that is close to the outline in my first post, to no avail.

I did find this phono pre that has a very minimal part count, makes use of quality transformers, chokes and C3g tubes in two stages. My searching did not discover anyone that has built it.

I wrote the designer but he is not interested in implementing LCR.

ImageUploadedByTapatalk1433520266.913299.jpgImageUploadedByTapatalk1433520281.312419.jpgImageUploadedByTapatalk1433520297.351325.jpgImageUploadedByTapatalk1433520306.897983.jpg


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Old 8th June 2015, 12:06 PM   #4
McLanz is offline McLanz  Germany
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Hi Coasttoast, something I keep in mind is the "acoustic dimension" proposoal. They offer transformers for around 500USD a pair. But their schematic includes caps.
Acoustic-Dimension, high-end audio and components for tube audio (Look for transformers and LCR).

Question is if a LCR generally brings improvements even if the stage includes a cap. So a LCR could be purchased anyway for a project. Trying is everything. What kind of feedback have you received from other DIY'ers or friends owning one? How good is a LCR compared with ultra high end phono stages like Pass Xono or Audio Note? This question keeps spinning in my head.

CAPS: My feeling tells me that a stage without cap may not be the very last word just because all matters were going to avoid the cap - sometimes on costs of other points.

Of course if a phono stage works well in matters of design - a cap less design has to be superior I agree.

PS: Coasttoast, ever compared your SP10 to other high end drives? I'm really think how much money I should spend for a perfect bearing of my mass drive + a high end motor unit with intelligent motor controlling...Sometimes I think a SP10 is cheaper.

Sorry I cannot help much in your thread.

Regards
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Old 8th June 2015, 05:23 PM   #5
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Quote:
Originally Posted by McLanz View Post
Hi Coasttoast, something I keep in mind is the "acoustic dimension" proposoal. They offer transformers for around 500USD a pair. But their schematic includes caps.
Acoustic-Dimension, high-end audio and components for tube audio (Look for transformers and LCR).

Question is if a LCR generally brings improvements even if the stage includes a cap. So a LCR could be purchased anyway for a project. Trying is everything. What kind of feedback have you received from other DIY'ers or friends owning one? How good is a LCR compared with ultra high end phono stages like Pass Xono or Audio Note? This question keeps spinning in my head.

CAPS: My feeling tells me that a stage without cap may not be the very last word just because all matters were going to avoid the cap - sometimes on costs of other points.

Of course if a phono stage works well in matters of design - a cap less design has to be superior I agree.

PS: Coasttoast, ever compared your SP10 to other high end drives? I'm really think how much money I should spend for a perfect bearing of my mass drive + a high end motor unit with intelligent motor controlling...Sometimes I think a SP10 is cheaper.

Sorry I cannot help much in your thread.

Regards
McLanz, yes Acoustic Dimenson is where I found the Noguchi Transformers. They have 3 or 4 brands of LCR transfomers. But only the "Tango" and "Nasu" style schematic posted.

It seems there is a divide between the use transformers in place of capacitors. I guess each has its place (FYI, I have no hands on knowledge of electrical design, I picked up my first soldering iron less than 3 years ago!) but my practical side side tells me that the basic design of a cap is to store and release energy, then it's use at the very beginning of the electrical signal from the cartridge has to smear the sound some, and then get amplified several more times.

Also, this SP-10 is my first Turntable. I have not done any comparisons. I have not yet mounted my Koetsu yet, so still at the beginning of my vinyl journey.
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Old 9th June 2015, 06:46 AM   #6
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Searching again today I found a schematic in the right direction. Steve Bench. On Jacmusic.

Lundahl Moving Coil transformers.

Here is the schematic

image.jpg

Has anyone built this?
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Old 10th June 2015, 08:40 AM   #7
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Here is the power supply for the Steve Bench (now Stephie Bench) phono stage. The phono stage is actually an LR design.

image.jpg

After some more digging I have been told a couple of people have built this design and had "problems stabilizing it in the bass, presumably because of that positive feedback fix for the bass roll-off". I also understand that they were not able to overcome it.

I'm still researching to see if there is a solution or an update to the design.
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Old 10th June 2015, 09:59 AM   #8
DF96 is online now DF96  England
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I'm puzzled. If you arrange ordinary electronic components in order of nearness to ideal behaviour then resistors come first, then capacitors and finally inductors and transfomers come way behind. On what basis could someone then choose to avoid the most ideal components and deliberately use the least ideal components?

I'm not being funny; I am genuinely puzzled.

PS I know why early valve electronics (1920s) used transformers and chokes for coupling: they had very low mu valves so needed the extra voltage gain from a transformer, and resistor and cap technology was quite crude back then. Today things are different.
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Old 10th June 2015, 10:19 AM   #9
euro21 is online now euro21  Hungary
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Do you know Dave Slagle?

:: View Forum - Phono

Thomas Mayer (vinylsavor) use Dave's coils such topology.

VinylSavor: Making of a D3a LCR RIAA Phono Preamp - Part 1
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Old 10th June 2015, 05:08 PM   #10
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Quote:
Originally Posted by DF96 View Post
I'm puzzled. If you arrange ordinary electronic components in order of nearness to ideal behaviour then resistors come first, then capacitors and finally inductors and transfomers come way behind. On what basis could someone then choose to avoid the most ideal components and deliberately use the least ideal components?

I'm not being funny; I am genuinely puzzled.

PS I know why early valve electronics (1920s) used transformers and chokes for coupling: they had very low mu valves so needed the extra voltage gain from a transformer, and resistor and cap technology was quite crude back then. Today things are different.
Since I'm new to electronics and have no design experience, I have no preconceived thoughts on parts selection or preference to topology choice.

My choice in looking at building an LCR or LR phono stage is based on reviews of commercial equipment using this topology and from the recommendation by a personal friend who's ears I trust more.

One such commercially available product is the Yipislon.

As far as the "order of nearness to ideal behavior" goes, think about this. My Koetsu Urushi Black (yet to be mounted) is the basis of the beginning of the audio electronic trail. What is the actual stylus connected to? A resistor? A capacitor? A transformer! The next step in the electronic trail, since this is a MC cart is a step-up resistor? A step-up capacitor? A step-up transformer! (Well at least in what most consider high-end products)

At least this is some of the information I've read on my audio journey so far.
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