2. amps-preamps
  3. 136389-114337

Looking for a better preamp match for AT OC-9/III

Hello! I'm looking for a new preamp to use with my AT OC-9/III cartridge.

Currently I use a Graham Slee Graham Amp 3 Fanfare and here are some of the specs:

* MC with 0.2 - 1.0mV output.

* The input impedance is fixed at 470 ohms


Here is some info about my AT OC-9/III cartridge:


Type: Moving coil (MC)
Freq response: 15 to 50,000 Hz
Output voltage: 0.4mV (1 kHz, 5 cm/sec.)
Channel separation: 30 dB (1 kHz)
Channel balance: 0.5 dB (1 kHz)
Tracking force: 1.8 to 2.2 g (standard: 2.0 g)
Coil impedance: 12 Ω (1 kHz)
DC resistance: 12 Ω Min.
Recommended load impedance: 100 Ω (when head amplifier is connected)

I'm running the turntable as a desktop system and going out of the preamp into the aux input of a set of powered KEF LS50.

My issue:

This Graham Slee appears on paper (from my limited knowledge) to be a good pairing, but I always have to turn the amp very high to the point that I hear "air" and also a tiny bit of hum in order to listen at a decent volume. This behavior is exactly what I'd expect running an instrument (like a keyboard) into a mixer and not having the volume set high enough on the instrument and having to use the gain stage on a mixer to pump it up until it is super hot and introducing unwanted hiss.

Is this something common to all MC cartridges? I have had this cartridge on two different tables, two different amps, 3 different pre-amps, in 4 different houses, with different speakers, and currently have all new high-grade cables. I even sent the cartridge to AT to make sure it was good. They tested it and sent it back, saying it was within their specifications and I had it professionally installed. Is this gap in gain that I seem to be perceiving typical behavior from an MC setup? Apologies for my ignorance. I am really stuck on this cartridge and have a huge knowledge gap when it comes to phono audio.
shanebarber
shanebarber OP
2 posts
 
Hello Matt and thanks for answering. I currently am not going into an active preamp. I am going into the LS-50's integrated amplifier directly (which does not have any type of gain stage). I suppose this could definitely solve the issue, or perhaps even a small line-level mixer? I just hate to introduce more items in the chain (unless my worries are unfounded).

I've read so much about trying to get "the best pairing" for the AT OC-9 and the only one I ever see mentioned along with Audio Technica is the Herron Audio VTPH-2 which seems like a tad bit of overkill for what I'm trying to accomplish. 

I also neglected to mention that the Graham Slee is currently making all sorts of odd noises like pulsing sounds so I'm still trying to troubleshoot if it is the preamp it self or some other element. If it is plugged in by itself, it sends pulsing sounds and introduces some crackles into my speakers.
johnss
582 posts
 
think you may be missing a few db of gain without the active preamp...the phono stage likely wont put out enough current to drive the amp quietly...

I have the OC-9III as well as the AT 1000, a benz LPS, and a few other LOMCs....I have tried several phono stages from the Musical fidelity XLPS
to the Manley Chinook, to the Pass Labs.... and have no issue with noise on any of them...but am running an active gain stage preamp too.

If you want to stay away from an active pre, then you'll probably need to look for a phono stage with 68-70db of gain instead of the more common 60db of gain....

The phono stage power supply design also makes a huge difference in noise or lack there of....need plenty of filter caps to remove the last traces of ripple on the rail voltages...

Have not heard the graham slee but have heard good things about it.
on any phono stage, you will also lower the noise floor considerably by using Vishay metal film resistors in the loading areas and on any signal shunt positions within the phono stage. 

good luck
 
jackd
1,074 posts
 
This will do what you need for not a lot of money.

http://www.vista-audio.com/products/phono-2/index.htm
shanebarber OP
2 posts
 
Cool, I will take a look at all of your options guys, thanks for the info. So if I bought one of those AT SUTs mentioned earlier, the point would be to bump it up before I go into a phono preamp, correct? And otherwise, I could either put a preamp after the phono preamp, or I could buy a phono preamp with more switchable loads as jackd mentioned. Thanks for the help.
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