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Step up Transformers and phono pre-amps and when to use what? And how and when?


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When you get down to the LLOMC e.g. my Linn Asaka at 0.1mV it is my understanding that a SUT is really the best option.  As such I am in the throws of DIYing a SUT using CineMag 1254 to give 40 x step up to fed my VTA PH16 (also DIY).  This combination will give me a total of 77dB gain to my pre amp.

 

I just hope I have all my calcs right :unsure: but pretty confident as been using a 38 x SUT that has the volume level pretty similar to my CD player on the pre amp.

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There are some good semi-technical summaries of how to choose a SUT.  The link below is worth a read.

 

Unfortunately the best outcome does require 'tuning' of the SUT output, with a snubber network usually required to ensure  minimal ringing.  Similar to an oscilloscope probe needing its compensation adjusted to get a good square wave, or a power transformer secondary winding optimally snubbed using a quasimodo type tester.  That test situation is probably the nub of why so many observe such a wide difference in performance when they simply just connect a SUT and think it should perform perfectly 'out of the box'.

 

You may also be able to find a vintage microphone transformer for a couple of dollars that also suits an MC SUT.  That may appear a little aesthetically displeasing, but the performance of some would I suggest be very good indeed, and they were very well made.  For example a commonly found mic transformer is from Zephyr (who advertised in RTV&H) with 50 and 350 ohm inputs, and 42k output - the 350 ohm input provides an excellent 11:1 turns ratio.  The PA amp manufacturers also used stock mic transformers - STC had a CL5244-2 with the same spec as that Zephyr.  Some mic transformers used a higher turns ratio - AWA used octal valve holder mounted transformers such as 1TW14012 - although its 18:1 ratio would really only suit lower output carts.

 

 

http://www.rothwellaudioproducts.co.uk/html/mc_step-up_transformers_explai.html

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So if starting with a clean sheet, a MC phono stage with adjustable loadings is preferential to using a SUT and MM phono stage ?

 

Keep it simple for the best sound.

 

Chose a cartridge, chose a phono stage, get it hardwired with gain and loading etc to match your cartridge.

 

Adjustability is over-rated.

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Keep it simple for the best sound.

 

Chose a cartridge, chose a phono stage, get it hardwired with gain and loading etc to match your cartridge.

 

Adjustability is over-rated.

All the DIY MC stages I have built (currently I have four) all have 50/100ohm loading selection. My Ortofon is specified to sound best at 50ohms. Because most other MC carts prefer a 100ohm load and most of my gear gets sold in the end, I include the 100ohm selection. I had some golden ears around and changed, on the fly, the loading to my Ortofon. Mr. Golden Ears felt the 100ohm loading better, it appeared to allow a greater musical flow. But I went back to the specified 50ohms in the end. Really if there was a difference is was extremely suttle and if I only had 100ohm loading I could live with it.

The rule of thumb with MC cart loading is 10 X the carts resistance plus 10% or a bit more. So for a 4ohm cart -> 50ohms is the starting point but 100ohms may sound better as may 200ohms. One MC stage I have, my DIY Jean Hiraga with matched bipolar transistors, has 50/100/200ohm loading selection. My Ortofon sounded good on all of them!

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The majority of the vinylheads that have tried both have told me that they prefer the SUT to MM phono stage, especially when it comes to tubed phono.

 

Other than some wacko like @@andyr of course :P

 

Then again, I've recently changed to a dedicated MC phono with loading options because my main cartridge has such a low output that a tubed phono would produce a little too much hum on a loud volume.

 

That's not quite true....I prefer Headamps to transformers...... :)  ......and if you have the dosh....there are exotic valve headamps.... :)

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That's not quite true....I prefer Headamps to transformers...... :) ......and if you have the dosh....there are exotic valve headamps.... :)

Another wacko here :P

Sent from my iPhone using Tapatalk

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All the DIY MC stages I have built (currently I have four) all have 50/100ohm loading selection. My Ortofon is specified to sound best at 50ohms. Because most other MC carts prefer a 100ohm load and most of my gear gets sold in the end, I include the 100ohm selection. I had some golden ears around and changed, on the fly, the loading to my Ortofon. Mr. Golden Ears felt the 100ohm loading better, it appeared to allow a greater musical flow. But I went back to the specified 50ohms in the end. Really if there was a difference is was extremely suttle and if I only had 100ohm loading I could live with it.

The rule of thumb with MC cart loading is 10 X the carts resistance plus 10% or a bit more. So for a 4ohm cart -> 50ohms is the starting point but 100ohms may sound better as may 200ohms. One MC stage I have, my DIY Jean Hiraga with matched bipolar transistors, has 50/100/200ohm loading selection. My Ortofon sounded good on all of them!

 

Then you'd better make sure you don't sell any of your phono stages to people who own Benz wood bodies (as they - well Benz Ruby and LP, anway) are specced at min 470 ohms! :D 

 

Andy

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Then you'd better make sure you don't sell any of your phono stages to people who own Benz wood bodies (as they - well Benz Ruby and LP, anway) are specced at min 470 ohms! :D 

 

Andy

It's easy enough change, its only two resistors.

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  • 1 month later...

I have built and sold quite a number of MC pre-preamp and probably the only person to own a DIY Jean Hiraga bipolar\matched\single substrate all transistor MC stage. 

 

Of of all other MC stages I have use a Le Pacific based schematic - single FET one cap runs on batteries. But I wonder if an OPAMP based MC stage can't be better. All my three systems are 100% DIY apart from a media player or two and was just thinking that I have not seen an OPAMP based MC stage. There are lots of great OPAMP out there with ionic OPA2134 being the go to OPAMP of choice. I have also built a preamp with the very high performance OPA27. As some OPAMPS have FET front ends so do some have bipolar or transistor front end. There is a difference in Sound right there. 

 

Maybe be time to visit the OPAMP based MC stage.

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7 hours ago, mwhouston said:

As some OPAMPS have FET front ends so do some have bipolar or transistor front end. There is a difference in Sound right there. 

 

Maybe be time to visit the OPAMP based MC stage.

 

Yep,  tested many, for some strange reason I wanted FET input base opamps to be better to the ear, but somewhere ended with a bipolar input sage and it's staying.

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