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Don't know why. Maybe, I suspect I will have noise problems with an MC phono cartridge and a MM tube phono stage.
There are some simple designs out there, but where to get the transistors?? Do you guys ever just disassemble some common jettisoned gear for these parts??
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Hey Jedrider,
What Eli said...
http://www.kandkaudio.com/phonostage.html
just a thought:)
Stuben
I think that soldering a bunch of transformers myself makes a lot more sense. If I were ambitious, I would add additional RCAs and a switch, but I am not!
Anyway, looking at his preamps, $1K - $3K, depending upon options! I expect to spend a lot less, actually.
Nice site, thanks for the link.
Build the first stage of this Phono or if you want even simpler, just substitute the top tube with a 22K resistor or CCS (elsewhere on Dave's site).
A clean B+ pref regulated, and DC on the filaments is all that's required. 6C45P tubes ARE quiet enough for MC and many have built variations of this Phono now.
Alternatively a Fet / tube Cascode works well too but I prefer all tube.
Naz
Step up transformers (SUTs) are the simplest method. There's no fussing with NFB to linearize SS circuitry. Tubes simply aren't quiet enough for service at μV. signal levels. :> ( S/N ratio is EVERYTHING , at these tiny signal levels.
Sowter (www.sowter.co.uk) of England's model 9570 is quite compact and frequently can be tucked inside the phono preamp.
If you want to stay close to home, CineMag of Calif. offers their model CMQEE-3440APC.
Eli D.
Do I set the phono stage gain at the low or high setting if I am going to use the Cinnemags, let's say?
I presume the low gain, typical MM settings, are best. Low-gain is always best, I presume. (The settings means unsoldering a bunch of resistors and replacing them, unfortunately.)
It depends on the MM phono setup's spec's. Many a LOMC cart. needs a total of 65 to 70 dB. of voltage gain to reach line level. 20 dB. of voltage gain comes from a 1:10 SUT. So, you set the phono preamp to yield 45 to 50 dB. of voltage gain.
Eli D.
Thanks. That's perfect. I currently use an original Black Cube phono stage which has 40 dB and 60 dB settings. The 0.4 mV Ace I have works well with the 60dB setting and previously HO MC cartridges I had were happy with 40 dB. I always like all the source selections to be at roughly the same volume, which is nice.
The tube phono stage I am working with has 31/38 dB choice (actually variable as I must insert new resistors to get to 38 dB. I can always tune the load resistor by ear (I like 3K ohms with the Ace though, on purely subjective trial-n-error grounds.)
Many DIY "how to's" on the Vinyl Asylum. I love mine.
I wonder what they cost.
Lundahl I found out are $180.00, which while probably a bargain, I don't want to spend that much.
Cinnemags for $110.00 I guess are within range, considering the cartridge cost so much more anyway.
Yeah, if they work, a no-brainer compared to playing around with transistors ;-)
Thanks for the suggestion. (And, then, do I load them differently than the direct MC cartridge? I guess, I'll get to that part ;-)
e.g. if it has a 40 ohm coil impedance around 400 ohms up to say 600 ohms will be well damped electrically and will have little effect on the frequency response / tone.
The SUT transformer divides the 47kohm MM input impedance by the square of the step-up ratio.
In the case of a 10 times SUT the reflected load will be 47k / 10 x 10 = 470 ohms. pretty much perfect for an MC of 40-50 ohms OR LESS coil impedance. The voltage will be enough to drive the MM stage well and be quiet.
If say you had a classic low-z low-output MC it might need as much as 35 times as the step up ratio and this will give you a much lower reflected load of 100 ohms, or less. But because these cartridges will also have a very low coil impedance, of 10 ohms or less, they'll be quite happy.
I am against loading MCs heavily, IE at 1 to 3 times their coil impedance. You are also throwing away most of their power output / signal to noise advantage over MMs.
IME they will be under-damped and will almost always sound bright and light, almost zippy.
Yes MC's are only low-output in voltage terms, most are quite a bit more powerful than an MM.
It is now common for some MO MC's (> 0.5mv to 1.0mv) to have quite low coil Z's e.g. Dynavector, VdH, and Benz. Correctly loaded at about ten times the coil Z the step-up ratio MAY be enough to overload the MM stage. But valve based MM stages tend to have heaps of headroom, so this should NOT be an issue for you. Such a set up would have very good signal to noise and very low distortion.
JBTW it is NOT true, as stated in this thread, that an all-tube MC stage is impossible due to noise, I can think of several that work quite well, that in VTL's 5.5 series for one. They can usually only work well with an MC of about .3mv or better.
Thankfully most such still have an MM option, allowing a SUT & MC combo for the <.3mv MCs.
Note that a post in response is preferred.
Warmest
Timothy Bailey
The Skyptical Mensurer and Audio Scrounger
And gladly would he learn and gladly teach - Chaucer. ;-)!
'Still not saluting.'
> > I am against loading MCs heavily, IE at 1 to 3 times their coil impedance. You are also throwing away most of their power output / signal to noise advantage over MMs.
IME they will be under-damped and will almost always sound bright and light, almost zippy. < <
Actually, it's the opposite. Heavy loading = heavier damping = reduced out of band HF resonance peak. It also usually produces tighter but subjectively less extended bass. Having said that I agree that higher impedance load is usually better, it opens up sound.
Naz
close mono miked, pan-potted, phlanged, Aphex Aurally excited, reverbed, compressed, pitch corrected, posted in, and Eq'd mixdowns to 2-channels, sound 'different'???? !For me audio is primarily for listening to simply miked real stereo recordings of acoustic music in the same space and time. A system stands and falls on that criteria.
Next you'll be telling me that a short piece of black insulated silver cable can fix a poor circuit design.
If you look at Hageman's stuff on loading MC's here at FAQs you'll find that a higher ohms load is what suppresses out of band resonances AND gives the flattest FR, okay?
Note that a post in response is preferred.
Warmest
Timothy Bailey
The Skyptical Mensurer and Audio Scrounger
And gladly would he learn and gladly teach - Chaucer. ;-)!
'Still not saluting.'
Edits: 05/20/12
> > If you look at Hageman's stuff on loading MC's here at FAQs you'll find that a higher ohms load is what suppresses out of band resonances AND gives the flattest FR, okay? < <
Obviously, terminology regarding is the problem here.
From Jim Hagerman's site on MC loading "As mentioned earlier, the peaking is best damped by lowering the load resistance". This is EXACTLY what I am saying but lowering the load impedance that the cartridge sees (lower R) TOO MUCH can overdampen.
> > Next you'll be telling me that a short piece of black insulated silver cable can fix a poor circuit design. < <
This statement was uncalled for. Don't put me in that camp and don't be so defensive.
Naz
I'm prone to being cranky when I 'suspect' that someone's tail chasing after 'effects'.
I was wrong.
Note that a post in response is preferred.
Warmest
Timothy Bailey
The Skyptical Mensurer and Audio Scrounger
And gladly would he learn and gladly teach - Chaucer. ;-)!
'Still not saluting.'
in different ways.
BTW, I very much prefer that openness we discussed and find that while SUTs in general have nice mids they just can't quite compete with direct tube input in that respect. The trick is to find a tube with low enough noise for MC and a 6C45P does the job well, as does its predecessor the 6S15P.
Naz
My pre is a super 'blue-printed' example of an AWE/VSE FVP, with a HUGE regulated PSU etc, etc.
I may be able to find an Aussie winder of silver / silver-copper trannies and get a 30 times ratio for my 103D(VdH-coil/boron rod/type1) and raise the input R to 270 k. Giving precisely 300 ohms as the reflected load.
HiFiWorld once had a kit pre with a phono stage for MC which was okay for ordinary 0.3mv Denon 103s, but probably marginal for the D at 0.25mv.
A wood body is in the mix for mine.
Something from the 1.5 gm TF and 'MO and low-z' models now available is my other option.
Note that a post in response is preferred.
Warmest
Timothy Bailey
The Skyptical Mensurer and Audio Scrounger
And gladly would he learn and gladly teach - Chaucer. ;-)!
'Still not saluting.'
Continuing this discussion, the normal 47k input resistor on a MM RIAA stage is the recommended load for the MM cartridge. This resistor could be increased to 250 k or more to reflect a reasonable load on the MC with a higher turns ratio than in this example.
You're overlooking Dr. Miller. :> ( The grid to ground resistor at the preamp's I/P combines with the C Miller of the 1st tube to form a low pass filter. A few MM carts., along with a few SUTs, interact badly with a 47 KOhm resistor and a 12AX7 section. As the grid to ground resistance rises, the number of "indigestion cases" rises.
Eli D.
The resistor that participates in the Miller effect is not the grid-to-ground resistor, when the stage is driven from a lower impedance.
Instead, it is the source impedance, which in this example is scaled up by N^2 from the output impedance of the cartridge. If we are designing for > 10x coil impedance as a load, then the Miller resistance is <0.1x the physical load resistor (grid-to-ground).
For a MM cartridge, this source impedance can be inductive at high frequencies, which can make for interesting interactions with the grid-plate capacitance.
Edits: 05/20/12
> > The grid to ground resistor at the preamp's I/P combines with the CMiller of the 1st tube to form a low pass filter
Eli, I think I know what you are getting at but this statement could be taken the wrong way, please explain.
Naz
How about a Hashimoto MC transformer, and you neatly wire-up the RCA jacks in the enclosure?
Jeff Medwin
.
Have Fun and Enjoy the Music
"Still Working the Problem"
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