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Want to build a MC head amp -- simple design

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Posted on May 18, 2012 at 12:13:06
jedrider
Audiophile

Posts: 9937
Location: No. California
Joined: December 26, 2003
 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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Maybe something like this from Allen Wright, posted on May 18, 2012 at 12:45:44
Tre'
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Location: So. Cal.
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Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: Want to build a MC head amp -- simple design, posted on May 18, 2012 at 13:03:13
drlowmu
Manufacturer

Posts: 7365
Location: East of Kansas City
Joined: January 10, 2005
 How about a Hashimoto MC transformer, and you neatly wire-up the RCA jacks in the enclosure?

Jeff Medwin

 

RE: Want to build a MC head amp -- simple design, posted on May 18, 2012 at 17:35:46
Eli Duttman
Audiophile

Posts: 7596
Location: Plainsboro, NJ
Joined: March 31, 2000
 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.

 

I'll second the CineMag CMQEE-3440A , posted on May 18, 2012 at 19:41:18
1973shovel
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Contributor
  Since: June 17, 2009
 Many DIY "how to's" on the Vinyl Asylum. I love mine.

 

RE: I'll second the CineMag CMQEE-3440A , posted on May 18, 2012 at 20:24:18
jedrider
Audiophile

Posts: 9937
Location: No. California
Joined: December 26, 2003
 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 ;-)

 

Last question about using step-up transformers, posted on May 18, 2012 at 20:28:27
jedrider
Audiophile

Posts: 9937
Location: No. California
Joined: December 26, 2003
 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.)

 

RE: Last question about using step-up transformers, posted on May 18, 2012 at 20:41:37
Eli Duttman
Audiophile

Posts: 7596
Location: Plainsboro, NJ
Joined: March 31, 2000
 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.

 

The load teh MC should see should be at least 10 times it's own coil impedance., posted on May 18, 2012 at 23:32:06
Timbo in Oz
Audiophile

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Location: Canberra - in the ACT - SE Australia
Joined: January 30, 2002
 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.








Warmest

Timothy Bailey

The Skyptical Mensurer and Audio Scrounger

And gladly would he learn and gladly teach - Chaucer. ;-)!

'Still not saluting.'

 

It can be done with all tube and no SUT!, posted on May 19, 2012 at 05:02:42
Naz
Audiophile

Posts: 1868
Location: Sydney
Joined: September 2, 2005
 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

 

RE: The load teh MC should see should be at least 10 times it's own coil impedance., posted on May 19, 2012 at 06:57:06
TimFox
Audiophile

Posts: 589
Location: Chicago
Joined: January 14, 2006
 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.

 

RE: The load teh MC should see should be at least 10 times it's own coil impedance., posted on May 19, 2012 at 14:05:40
Eli Duttman
Audiophile

Posts: 7596
Location: Plainsboro, NJ
Joined: March 31, 2000
 You're overlooking Dr. Miller. :>( 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. 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.

 

RE: The load teh MC should see should be at least 10 times it's own coil impedance., posted on May 20, 2012 at 06:37:37
Naz
Audiophile

Posts: 1868
Location: Sydney
Joined: September 2, 2005
 >>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

 

RE: The load teh MC should see should be at least 10 times it's own coil impedance., posted on May 20, 2012 at 06:43:32
Naz
Audiophile

Posts: 1868
Location: Sydney
Joined: September 2, 2005
 >>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

 

RE: Last question about using step-up transformers, posted on May 20, 2012 at 07:37:56
jedrider
Audiophile

Posts: 9937
Location: No. California
Joined: December 26, 2003
 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.)

 

RE: Want to build a MC head amp -- simple design, posted on May 20, 2012 at 09:16:11
Stuben
Audiophile

Posts: 291
Location: Guber Ohio
Joined: December 30, 2005
 Hey Jedrider,

What Eli said...

http://www.kandkaudio.com/phonostage.html

just a thought:)

Stuben

 

Thanks, but no Thanks ;-), posted on May 20, 2012 at 11:39:03
jedrider
Audiophile

Posts: 9937
Location: No. California
Joined: December 26, 2003
 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.

 

RE: The load teh MC should see should be at least 10 times it's own coil impedance., posted on May 20, 2012 at 13:21:46
TimFox
Audiophile

Posts: 589
Location: Chicago
Joined: January 14, 2006
 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.

 

Openness is what MC's do, why throw it away?, posted on May 20, 2012 at 15:28:09
Timbo in Oz
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Location: Canberra - in the ACT - SE Australia
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 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?


Warmest

Timothy Bailey

The Skyptical Mensurer and Audio Scrounger

And gladly would he learn and gladly teach - Chaucer. ;-)!

'Still not saluting.'

 

Are we arguing the same thing?, posted on May 20, 2012 at 16:21:44
Naz
Audiophile

Posts: 1868
Location: Sydney
Joined: September 2, 2005
 >>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

 

Sorry, we had both ends of it!, posted on May 20, 2012 at 17:37:53
Timbo in Oz
Audiophile

Posts: 14978
Location: Canberra - in the ACT - SE Australia
Joined: January 30, 2002
 I'm prone to being cranky when I 'suspect' that someone's tail chasing after 'effects'.

I was wrong.





Warmest

Timothy Bailey

The Skyptical Mensurer and Audio Scrounger

And gladly would he learn and gladly teach - Chaucer. ;-)!

'Still not saluting.'

 

No probs, I thought we actually saying the same thing ..., posted on May 20, 2012 at 19:17:05
Naz
Audiophile

Posts: 1868
Location: Sydney
Joined: September 2, 2005
 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

 

I used to have a Verion better than the OTHER SUT I still use, an AT 650, posted on May 20, 2012 at 22:35:06
Timbo in Oz
Audiophile

Posts: 14978
Location: Canberra - in the ACT - SE Australia
Joined: January 30, 2002
 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.










Warmest

Timothy Bailey

The Skyptical Mensurer and Audio Scrounger

And gladly would he learn and gladly teach - Chaucer. ;-)!

'Still not saluting.'

 

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