Moving Coil Cartridge Step up Transformers.

the road not taken.
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ssegrub
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Moving Coil Cartridge Step up Transformers.

Post by ssegrub »

Hi folks' I am a newbie and have not been on a forum before so therefore I will need to learn the protocols...so please bear with me.
My interest and questions are about getting more gain from my Koetsu Rosewood Platinum Signature Moving coil cartridge (.2mV output)into the phono stage of my Convergent Audio Technology (CAT) SL-1 Tube preamp.I have been advised that I will only need a 10dB gain Step Up Transformer. As these are none standard,I have been enquiring about having a set custom made. Am I on the right track,or is 10dB to low?
dave slagle
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Post by dave slagle »

Welcome!

10dB seems very low to me. Are you using your koetsu directly into the mm inputs now? Can you turn it up to full volume?

dave
ssegrub
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Post by ssegrub »

Thanks Dave, I am running the preamp at 12oclock which is half volume.
on the CAT volume control.Any higher and tube noise can be heard along with the music.I have a set of NOS Telefunken 6dj8 and NOS Mullard 12ax7 in the Phono stage and these are very quiet and dynamic tubes.
The CAT has a combined mm and mc input into the phono stage and is ment for all cartridges to be used into the one set of inputs .
dave slagle
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Post by dave slagle »

I am beginning to understand things now. Your problem isn't gain, it is noise free gain. If you ignore the tube noise can you turn it up all the way or does it get too loud?

You are currently in a bit of a paradox since the more stepup you use, the less noise you get, but at the cost of excessive gain and attenuation. It seems that 12dB (1:4) would be the safest number to shoot for.

dave
ssegrub
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Post by ssegrub »

It gets louder but becomes blurry and lacks defenition as the volume increases beyond 12oclock . I would like to get more dynamic range and musical colours. I have had Koetsus in the past with higher output
and they can really sound warm and rich and involving.
The Koetsu Platinum has such a low output, but such a wonderful sound that I can hear how I am so close to achieving the sound I want.

My system is as follows
Turntable: New Well Tempered Amadeus
Cartridge: Koetsu RSP
Preamp : Cat Ultimate SL-1
Power Amps:Vacuum Tube Logic 150 Watt Mono Blocks
Cables : All Wire World Gold Eclipse Cable and Interconnects
Speakers:Magneplaner 1.6

I sold my Wadia 861 recently to go all analog and bought the Amadeus and Koetsu which I have no regrets about as now I listen for hours ,where before I would just nod off listening to CDs.
dave slagle
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Post by dave slagle »

Your best bet is to determine two things.

The loudest position on your volume control that still gives you good sound.

The position on your volume control that gives you the loudest desired output level.

Sped a fed days playing with these two levels (make marks on a piece of masking tape for reference.)

Then put on a test record with a 1K sine or pink noise and measure the two voltages at the final positions you come up with then we will know how much gain you need from your SUT... Then I'd add 3dB so you can turn it up to 11 :-)

Do you have any comprehensive details on the CAT? I googled a bit and didn't turn up a complete review.

dave
ssegrub
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Post by ssegrub »

Thanks Dave,unfortunatly I dont have a test record or the ability to measure voltage. I will dig around for CAT specs and post them here soon.
ssegrub
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Joined: Mon Dec 01, 2008 8:26 am

Post by ssegrub »

I hope this is not to much CAT Ultimate SL-I preamp info for the forum:
Design Concept
Power Supply
External power supply chassis lowers noise and allows for much larger transformers
Initial regulation and noise filtering are all performed in the outboard supply insuring ultra quiet DC power to the main chassis
Three independent fully regulated filament supplies eliminate the dynamic compression caused by filament to filament crosswalk. (These supplies are also noise filtered).
Slow filament power up extends tube life greatly.
Quadruple cascaded audio power supply combines twenty two zero feedback regulators with over thirty energy storage and bypass capacitors for unequalled dynamic life, soundstage precision and musicality.
Isolation transformers eliminates entry of radio frequency noise through the AC power line
Circuitry
Pure vacuum tube circuitry
Extraordinarily quiet, high gain phono amp (Optional) accommodates both high and low output cartridges.
Speed, openness and transparency without any of the high frequency circuit-induced edginess which slower pre-amps frequently substitute for real speed.
Very low output impedance reduces sensitivity to cables and load, even into long runs of cable.
Lowest open loop distortion of any pre-amp yields unforced detail and resolution that must be heard to be believed.
Low feedback ratios eliminate the aggressiveness of high feedback designs and yet still maintains correct focus.
Matched output impedance reduces reflections within interconnects, quickly, yielding exquisitely lucid midrange and treble.
Chassis
Very strong steel chassis with anti-RFI plating ensures hum & RF free operating environment for the circuits.
Damping material lines both chassis to stop mechanical resonance, which would otherwise modulate the electric fields in the pre amp.
Mechanical isolation from floor vibrations provided by high loss viscoelastic feet.
Quality
Exotic low loss circuit board material combines the transparency of hard wiring with low resonant signature and musicality of circuit board designs
Balance and volume controls are military grade rotary switches with solid silver contacts wired with precision resistors
CAT manufactured RIAA capacitors use a unique dielectric with several time lower loss than any other dielectric including TFE Teflon
The best sounding precision resistors are used everywhere for the best resolution and minimum unit to unit variability
CAT coupling capacitors are made to our specifications and are better than any other audiophile grade capacitor
CAT audio wire uses ultra pure, soft annealed copper and super low loss insulation
Rhodium/gold jacks for superior connection
Silver solder used for best electrical connection
Custom designed hermetically sealed switches
Convenience
Front panel-muting switch.
Automatic mute on turn on and off. Record/normal front panel switch eliminates the non-linear load of the turned off tape deck when in normal and provides uncompromising recording quality when in record.
Extra set of main output jacks for special audiophile set-ups.
LOAD jack allows changing MC cartridge loading while listening to music.
CD and A/V volume control tapers available.
Specifications:
Gain (@1khz):

Line 26dB, phono 47dB
IHF phono input sensitivity: 0.12mV.

Gain Tracking:

Line 0.05dB, phono 0.05dB.

Frequency response:

Line 0.1Hz to 600kHz +0, -3dB (rise time 0.6msec)
Phono RIAA 20Hz to 20kHz +/-0.1dB.

Harmonic distortion:

(@1 volt) Line<. 0005%, phono <. 001%

Slew rate:

Line 15volts/usec, phono 10 volts/msec.

Maximum output:

(@1kHz): Line 50 volts rms. Phono 50 volts rms.

Input overload:

Line 100 volts rms. Phono 250 mV rms. @1kHz.

Noise:

Line 112dBA below 2-volt output.
Phono 96dBA below 10mv input.
Separation:

Line greater than 90dB, Phono greater than 90dB.

Input Impedance:

Line 50kohms, 20pf
Phono 47.5k ohms, 180pf (user adjustable)

Output Impedance:

100ohms

Maximum load:

Line: Under 4000pf. over 5000 Ohms.
Phono: Under 4000pf. Over 10,000 Ohms.

Dimensions:

Main chassis 19.0" x 5.24" x 12.2"
Power supply 12.2" x 4" x 6"

Weight:

Net 64lbs, Shipping 70lbs

Price

$7995 Line stage, $9995 with phono

cheers
Paul.
dave slagle
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Post by dave slagle »

OK... when you are a 12:00 on your volume know, you have around 20dB of attenuation. Since the linestage has 26dB of gain it is a redundant part. (why attenuate 20dB so you can add 26dB of gain?)

I'd suggest 12-15dB of gain from the SUT. This will get your noise floor down considerably.

If you can just take the signal out after the phono stage it would be interesting to try a passive and a SUT with say 26dB of gain.

dave
ssegrub
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Post by ssegrub »

sounds interesting...how does one take the signal out after the phono stage?
dave slagle
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Post by dave slagle »

There may be a phono out that lets you gain access to the signal right after the phono gain. Otherwise you would have to pop the top and peek inside to see how to get the signal out.

dave
ssegrub
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Joined: Mon Dec 01, 2008 8:26 am

Post by ssegrub »

Thats a bit beyond me technicly sorry Dave... I do remember the "hotrod" concept that came up in the Absolute Sound magazine about 20 years ago which they used on an Audio Reseach SP 11 preamp. They recomended using the tape outs directly into your power amps. So I used the tape out outputs as the output into my then VTL 140 monoblock amps to by pass the volume and balance control control of my VTL Super Deluxe preamp. The cartridge ran flat out with full gain into the power amps. It sounded great for about an hour then one of my tubes blew!
so that was the end of that idea.

GOOD NEWS I have found a new audio buddy who is willing to bring his 20 dB Stevens and Billington step up transformer over for a listen/test early next week...so I will be able to let you know how my system sounds with 20 dB gain.He has a Koetsu Rosewood Signature ,which has .4dbB
out put.
Spock15
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Joined: Tue Dec 16, 2008 10:13 pm

Post by Spock15 »

Hi Dave,
I'm new here, but I use a (older) Koetsu cartridge too.

A Q about tube noise... am I correct in thinking here in ssergub's case that having a SUT in front of his preamp would allow him to operate at lower volume setting & therefore resultant lower noise level / lower S/N?

Secondly, if we were go for the 100 ohms commonly preferred loading for a Koetsu, then a 26dB gain SUT would get us pretty close with 117.5 ohms 'seen' by the cartr (with 47k preamp input), ie. 47,000/20 squared = 117.5.

Similarly, 20dB Gain SUT would present a 470 ohms cartr load.

Rgds, Owen
dave slagle wrote:I am beginning to understand things now. Your problem isn't gain, it is noise free gain. If you ignore the tube noise can you turn it up all the way or does it get too loud?

You are currently in a bit of a paradox since the more stepup you use, the less noise you get, but at the cost of excessive gain and attenuation. It seems that 12dB (1:4) would be the safest number to shoot for.

dave
dave slagle
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Post by dave slagle »

Spock15 wrote:Hi Dave,
I'm new here, but I use a (older) Koetsu cartridge too.
welcome.... the more the merrier :-)
A Q about tube noise... am I correct in thinking here in ssergub's case that having a SUT in front of his preamp would allow him to operate at lower volume setting & therefore resultant lower noise level / lower S/N?
absolutely. transformers give you noiseless gain at the cost of drive impedance, fortunately the grid of a tube doesn't provide too difficult of a load so SUT's work wonderfully.

Secondly, if we were go for the 100 ohms commonly preferred loading for a Koetsu, then a 26dB gain SUT would get us pretty close with 117.5 ohms 'seen' by the cartr (with 47k preamp input), ie. 47,000/20 squared = 117.5.

Similarly, 20dB Gain SUT would present a 470 ohms cartr load.
correct again. I am a fan of grabbing all the gain you can upfront and the 5 ohms of the koetsu really helps. I have done some 1:52's for a 3 ohm cartridge and it allowed the user to use a simple two stage LCR phono to drive a passive into his two stage amps. The gain structure was perfect and more importantly there was plenty of headroom.

dave
Last edited by dave slagle on Wed Dec 17, 2008 4:36 am, edited 1 time in total.
Spock15
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Post by Spock15 »

Thks, Dave.

Sorry, I meant of course... better S/N :oops:
Spock15
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Post by Spock15 »

Hi Dave,

I was trying to determine optimum load/gain choice for my own cartridge setup, by using an old Fidelity Research SUT with switchable impedances.

What would be simplest, safe way of measuring ratios of such SUTs? ie. Would a sig gen + scope run the risk of core magnetization?

Thks, Owen
dave slagle
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Post by dave slagle »

I'm not sure where the myth of permanent magnetization of a SUT came from but it makes me chuckle every time I see it.

the easiest thing to do is make a voltage divider using a pair of resistors with a 100X ratio. If your cartridge is 5 ohms place a 5 ohm in series with a 500 ohm resistor and place the 500 ohm end at + and the 5 ohm end at ground of your signal generator. Then apply the signal across the 5 ohms resistor to your primary of your SUT

set the voltage across the primary to about 5mv and measure the voltage across the secondary unloaded and loaded with a 47K resistor. The unloaded will tell you the actual turns ratio and the loaded will let you know what you are actually getting. Once you know the turns ratio, the desired terminating resistor (or primary load) can be put inot place to find out the actual in system gain.

dave
Spock15
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Post by Spock15 »

Thanks, Dave.

Ah yes :oops: ... no DC involved
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