Audio Technica moving coil with CTP?

[Shaman]

Hi,

I'm thinking of getting an AT-OC9 MLII mc cartridge that has 0.4 mV output.

How is this going to work with the CTP 1000?

Soundcard is an Audiophile 2496.


http://www.lpgear.com/Merchant2/merc...gory_Code=XMAS

[DJBohn]

Shaman - I have the same Audio-Technica AT-OC9 MLII cartridge & I love it! Although the cartridge has a fairly high output for a moving coil design, I think the real problem would be matching the recomended load (impedance & capacitance) of the cartridge to the pre-amp. You would need an MC Matching Transformer or a pre-pre-amplifier. I don't have the CTP-1000, but I don't believe it is set up for Moving Coil Cartridges. Craig could tell you for sure on that.

I on the other hand, I am using a 15 year old PSAudio PhonoLink preamp that is set up to handle MC cartridges. The over all sound quality I am getting with the combination is nearly un-believable. Ruler flat response beyond 20kHz, & great punchy dynamics (with the right LP's - I could send you a sample MP3 of a restored audiophile LP if you would like). PSAudio was also well known over the years for having a very accurate Passive RIAA in their phono stages (you could maybe find a good one used on eBay...), while that AT cartridge has an extremely flat response across the entire range as well. Look at the small owner's page that came with the cartridge and it will show you what you need for an amp to match to the cartridge. The only other suggestion I could offer is for you to purchase a decent quality MM (Moving Magnet) cartridge to match your CTP 1000.

[Craig Maier]

I do not know what load resistance that the Audio-Technica AT-OC9 MLII cartridge requires, but the terminating input resistance on all of the CTP series preamplifiers is 47 KOhm. Detailed specs for the CTP-1000 can be found at this link:

http://www.diamondcut.com/vforum/sho...specifications

Note that its Voltage Gain is 28 dB which is a Voltage gain of roughly x 25. So, that would only take a 0.4 mV output level up to 10 mV. I do not know what the input sensitivity of the mentioned sound card is and whether or not it would be compatible. Probably not but you would have to look at the numbers.

[DJBohn]

Craig, I pulled out the literature on my cartridge. It states a step-up transformer or headamp is required for preamps without MC inputs. It also says if a transformer is used, input impedance should be 20 ohms or higher. If a headamp is used, ideal input impedance is 100 ohms. (The PSAudio PhonoLink has that setting) The cartridge has a MicroLine stylus which I liked. But it is a bit heavy being 8.0 grams in weight. I had to use an optional counter weight on my tonearm to even use it. It also requires a slightly heavier VTF than many cartridges - 1.25 to 1.75 grams. But I sure like the sound my cartridge/preamp combo puts out!

[Doug]

There was an article in electronics australia back in 1981 that showed how to make a solid-state (pre?) preamp for MC cartridges that went on the front end of a normal MM preamp stage. I can post it privately in pdf if interested. It used a LM394 chip (ultra well-matched NPN transistor pair) for the front end.

[DJBohn]

Hi Doug, long time no hear! You may wish to edit your post - you have the MC & MM transposed. My PSAudio can select 10, 100, or 100 ohms for use with MC cartridges. If the one you are talking about can be fitted with that ability plus maybe input & output level controls, it would be ideal with the CTP-1000 (and would be a great option for Tracer to sell as well)...

[Doug]

Doh!

Consider it done.

It was a DIY so all those little tid bits were user chosen when putting the circuit together.

[Craig Maier]

I have not tried this, but how about two CTP's wired in cascade with a shunting 100 Ohm resistor across the input(s) of the first one in the chain. That would yield 50 dB of gain which would take that 0.4 mVolts up to 250 mVolts. That sounds like it would be sufficient for most sound card inputs. And, looking at the specs, that combination would not overload or clip the second preamplifier in the chain.

Just a thought.

[Shaman]

Thanks for the input everyone..

I kind of thought that 0.4 mV was going to be a bit on the low side..

My other choice for a cartridge would probably be the AT440MLa with the same microline stylus as the MC AT cartridge.

The AT440MLa has an output of 4.0 mV and I foresee few problems with that.

Would the transformer below do the job for the MC cartridge?


NEW OLD STOCK ORTOFON T-5 MOVING COIL STEP UP TRANSFORMER

http://cgi.ebay.com/ws/eBayISAPI.dll...2543&rd=1&rd=1

[Craig Maier]

Shure A95 Impedance Matching Transformer

Another item to consider using to match an MC cartridge to a MM input on a Phono Preamplifier would be the use of a Shure A95 Impedance Matching transformer. While these are generally used to match low Z microphones to High Z mixer inputs, they seem to have the right characteristics. The one sitting in front of me is designed to accept either 50 or 250 Ohm input impedances which is selectable by moving a tap wire inside the unit. Its output impedance is 50 K with the specified input impedances, so it should work just fine.

Note: I have not tried this but the theory is sound. Also, please note that these transformers are XLR connector based so some adapters will be required to connect them up.

keywords: Matching MC Phono Cartridges to MM Preamps, MC Transformers, Moving Coil Transformers

[Shaman]

The mic transformer is a good idea, but the adapters are going to end up costing almost as much as the transformers, I'm afraid.

I found this NAD receiver with a dead FM section and MC phono inputs on ebay.

The only problem is that it has a built in RIAA eq, which kind of ruins the idea of using the flat amp for recording.

http://cgi.ebay.com/ws/eBayISAPI.dll...9180&rd=1&rd=1

[Craig Maier]

Shaman,

I am looking at this Shure A95 Z matching XFMR, and the XLR connector is removed by 1 screw located in the side of its barrel. It appears to me that you can simply remove the XLR and replace it with a female RCA which could be purchased from Radio Shack for about 25 cents or so. And, on the Hi-Z side, it looks like you could solder an old RCA patch cord to it and you would be in business.

[Shaman]

Thanks for the suggestion but I've spent a considerable amount of money by my standards on this project and I have no intention of kludgeing something together at this point.

Cheers,

Jon