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Old 24th December 2006, 12:00 AM   #1
rdr is offline rdr  United States
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Default MC head amp

I am a convert to vinyl, having long believed CD's were superior. I was wrong. So I am digging out all my old phono stuff and am about to buy a good MC cartridge.

I have an old Marcof PPA-1 grounded base MC pre-amp Anyone with experience with them? I think I am going to try it with a Denon 103 and see how it sounds. I used this many years ago and don't really recall what is sounded like. I no longer have transformers, except for some useless Danish JS ones with 244:1 gain/1.5 Ohm input impedance and I can't remember if I ever used them (It's been that long).

I know there is a difference of opinion regarding amps vs trans.

Here is an interesting exposition from the creator of the circuitry
http://users.ece.gatech.edu/mleach/headamp/
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Old 24th December 2006, 12:31 AM   #2
phn is offline phn  Sweden
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The JS trafos are not useless. You will not find a finer trafo at any price.

They are not 244:1 or 1:244. They are 1:20. There are a few step-up trafos with higher gain than that. Unless used for mic preamps, they should be avoided since frequency response decreases.

Having that said, there's no use for step-up devices for sold-state gear. Not to mention that the JS trafos might have too high gain for the DL-103. Denon's step-up trafos are 1:13, I believe.

I would look into the Phonoclone on this forum. It's simple and cheap to build and I don't think you can make a better ss phono stage.
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Old 24th December 2006, 12:40 AM   #3
rdr is offline rdr  United States
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My JS tannies are No. 75s, and have marked on them the impedance (1.5 Ohms) and the turns ratio (1:244). They are not the No. 251's that are used with MC cartdridges. Their gain and input impedance are not suitable for an MC cartridge.

The phonclone is a seems to be a low gain preamp using an op amp more suitable for an MM cartridges.
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Old 24th December 2006, 01:16 AM   #4
phn is offline phn  Sweden
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Quote:
Originally posted by rdr
My JS tannies are No. 75s, and have marked on them the impedance (1.5 Ohms) and the turns ratio (1:244). They are not the No. 251's that are used with MC cartdridges. Their gain and input impedance are not suitable for an MC cartridge.
OK. Then it is useless.

Quote:
Originally posted by rdr

The phonclone is a seems to be a low gain preamp using an op amp more suitable for an MM cartridges.
No, it's not for MM carts and it has two opamps.
http://www.geocities.com/rjm003.geo/.../diy_pho4.html
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Old 24th December 2006, 01:49 AM   #5
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rdr-

I think you have a better chance of someone being familiar with this circuit if you posted it in the solid state forum. It's not that it's in the wrong place here, it's just that this forum doesn't get near the traffic.

FWIW, Leach's stuff is generally good from what I know about it, however, you need to realize that there has been a quiet revolution of all things vinyl in that last couple of decades(and the technology that can be applied, the quality of the opamps in the phono clone for example). I have found that a great many of my perceived "truths" has had to be re-evaluated when I got back into it a couple of years ago...generally the quality of whats available has improved by an order or two( at least what's available to the DIY'er).

-Casey
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Old 24th December 2006, 11:11 AM   #6
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Hi,
finally, phn and me may share an opinion: I tried the phonoclone myself with the DL103, with slight modifications, and it sounds *very* good.
But, honstly, one (perhaps not me) can build much better solid state gear. But at the price of more complexity and, well, higher price.
Rüdiger
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Old 24th December 2006, 01:09 PM   #7
rdr is offline rdr  United States
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phn-

I was too quick. Yes the Phonoclone is suitable for MC cartridges. Thanks for the referral. I'm looking into it. I use Opamps in my crossover so I'm not adverse to this. The choice of op amp is going to be very important, and I think a TI/BB one could be found.
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Old 25th December 2006, 10:43 AM   #8
phn is offline phn  Sweden
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Just make sure to change R2 to 5k6 or so. 1k5 will only give the DL-103 60-65db gain.

As I understand it, the OP637 benefits from biasing, whereas the AD797 and many (most?) others don't. So adding a buffer should not necessarily make much of a difference, if any. If I understand it correct, that is. The only reason I can see to use anything other than the OPA37 is the slew rate. The AD815 will not work with this circuit, but would otherwise have been an interesting alternative.
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Old 25th December 2006, 01:23 PM   #9
rdr is offline rdr  United States
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phn-

Thanks for the info. The OPA637 looks very good. I went on the TI site. I am going to build this.
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Old 25th December 2006, 02:42 PM   #10
Calvin is offline Calvin  Germany
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Hi,

the OPA637 is definitively a fine OP, but itīs by far not the best choice for an MC-head amp! As a FET-type its noise is lowest with high impedance sources (>several kOhms), which an MC-Pickup isnīt. This excludes it as the prime input OP of the phonoclone. Since in the second stage the RIAA feedback places the OP into noisegains <5, the OPA637 canīt be used in this stage either without additional compensation.
The OPA37 on the other hand is as a low voltage-noise bipolar OP and the better choice for Mid- to High-Output MCs. The best noise performance is exhibited with source resistances ~400Ohms. Md- and Low-output MCs will be better run into a AD797 or LT1115 whichīs noise performance is best with source resistancec ~200Ohms. The AD797 can supply loads of current, so the minimum load resistance could be as low as 300Ohms (R3). Reducing the resistance values reduces noise contribution of the resistors (thermal noise) and therefore reduces the noise contribution of the whole second stage!
Since the first gain stage is the dominant one with regard to noise the OP27 is a good choice for the second stage.

jauu
Calvin
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