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Old 2nd February 2013, 09:18 PM   #41
kevinkr is offline kevinkr  United States
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Excellent!
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Old 17th March 2016, 06:53 PM   #42
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Unhappy Ear piercing setup...

Three years...
and I'm wondering again.

Finally got a new cart wich was advised as a very good match for ma Thorens TD 318: an Ortofon OM 20 Super.
But it is way too bright, just enough not to play any record. Other sources sounds just fine on amp/speakers setup.
So I wonder on both ends of the Pacific: how and where to exaclty load it? Original post features a 100K, no cap, Scafas' circuit a no-value resistor, no cap.
It's there were I put what I want, say 47k/100pF as it is right now?
And finally, the other end, no driving difficulties for the Pacific with my passive 10k preamp?
My CD sounds "vinyl" beside it...

Thanks
Matthieu

edit: for TT gurus, in case I've done it wrong:

Cables capacitance: 98.8 and 95.7pF
VTF: 1.35g
VTA: 0

Load: 47k/100pf
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Old 17th March 2016, 07:32 PM   #43
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The technical data for the Ortofon indicate that it wants a higher capacitance on the input:
Type: MM
Fixing: Half-inch mount
Output voltage: 4,0mV bei 1kHz, 5cm/sec.
Amplifier-connection: Phono MM
Frequency range: 20-27.000Hz
Frequency range: 20-20.000Hz +2dB/-1dB
Compliance: 25m/mN (lateral)
Material: diamond, nude
Stylus type: elliptical r/R 8/18m
Tracking force range: 1,0-1,5g
Tracking force, recommended: 1,25g
Recommended load capacitance: 200-500pF
Weight: 2,5g (5g)

So double, triple or quadruple your current load capacitance. Also make sure that your tracking is correct.
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Old 18th March 2016, 04:26 AM   #44
Hikari1 is offline Hikari1  United States
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I've actually used that cartridge with that phono stage (actually the boozehound phono) and a passive preamp into a tripath amp (and later a pass F5).

Here's a few of my observations:

The Pacific topology has a lot of input capacitance into the first stage...I don't remember the specifics but I think it's around 200pf. Add your cables capacitance to this. Adding 100pf may be OK but I don't think input capacitance is your issue.

Also, the pacific lacks a buffer on output which is fine, but you are trying to drive a pot with it and then into an amp. In my case, it didn't work well. I added a buffer and it was way better. This may depend on what amp is after your passive and how long the interconnects are.

Also, I found the OM20 bright and airy. Images really well and a big soundstage but it is not rich or bassy. More VTF will help but will make it less airy. Also, you may want to lower the tonearm a mm or two.

Also, if you load it at 33K it might help. But I think in some ways, this is the character of the cartridge. I would say it's more flat than bright but you may be coming from a cartridge with more bass.

If you look at the Salas phono he has perfected this design. I am using one now and it is one of the best things I have ever built. Look at the output buffer...the cascoded input...all ways to remove the shortcomings of the le pacific. Maybe you can incorporate some of these things in yours?
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Old 18th March 2016, 09:33 AM   #45
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Hi guys,
thanks fortitudine for cart info, I'll play in that capacitance window.
Hikari I'll try that, and the 40k also recommended, at the end it is clear; not the right RIAA pre here.
I've had a look at Sala's one, great job as usual, but even with a buffer he stands great performance driving down to... 20k :'( no wonder my 10k is a burden to my Pacific!
And it's folowed by a pair of UCD400.

Maybe time for a new pre phono project...
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Old 18th March 2016, 06:51 PM   #46
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Fellows,
Loading at 33k and no extra cap (mind 100 from TT + 200pF from Pacific), has done no wonder but to make it listenable, at low levels, better than nothing.
Now looking around for a new -better suited- RIAA pre-phono. Advice on project or even commercial or used DIY units welcome.
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Old 18th March 2016, 07:03 PM   #47
Hikari1 is offline Hikari1  United States
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I think you should investigate buffered vol pots/passive preamps. The pass b1 would work well. In my experience, vinyl and passive preamps don't mix well though. Or build a jfet boz..run off batteries it's a really cheap experiment.

I gave up on passives even when using the pass f5 (100k input impedence). Iam not familiar with the hypex stuff but every amp I have used lacks dynamics and weight with a passive in front of it. Especially with a phono preamps lower current/ability to drive.

An alternative would be to add a buffer like salas did on the output. You will need another pair of 2sk170. An extreme alternative would be a mosfet buffer (lots of schematics out there for headphone amps) on the output.

Actually, the pacific I had was quite good run off batteries. Better than all the commercial stuff I tried. It worked best with a denon high mc cart which makes sense since it doesn't care about the input capacitance. I am not sure your issue is so much the phono stage.

One thing...a impedence mismatch or lack of ability to drive the amp would probably result in a lack of dynamics and a dull hi end. Which is not what you are describing. Also, I would say the pacific phono sounds warmer and duller than some other phono stages which is also not what you are describing. You sure your phono amp is working correctly?
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Old 18th March 2016, 10:13 PM   #48
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What are your speakers (for example)? I think - I know the pacific - your problems are the other stuff - if the pacific is build well. You have to tune a Thorens 318, the pickup is to decouple, change the origin wire, use very fine wire, no diameter - complete (pickup - amp)! No cinch (katastrophe in "high tones", exacter: in resolution!) ...
Do build a good little se-amp, no unnecessary amps, no complementer-pp! One or two stages (in my case the pacific drives a se-poweramp!), use good fullrange, do not use lace, do not use big diameters, do not use tweeters
...and so on.
Good luck and enjoy your hobby,-)
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Old 18th March 2016, 10:35 PM   #49
Salas is offline Salas  Greece
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Old 18th March 2016, 11:05 PM   #50
Hikari1 is offline Hikari1  United States
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Apparently UCD400 come with unbuffered and buffered inputs?

If you are using or only have the unbuffered input it appears to be 1.8K impedance...I don't know if putting a 10K pot is a good idea.

Would be easy enough to convert your phono to what Salas has given us. What a nice guy.
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