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PostPosted: 21 Jan 2011, 10:40 
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mwhouston wrote:
I must remark though I is quite bright. If your system is already bright this may not be the phono preamp for you.

HI.

Any phonostage can be trimmed to get the sound balanced.

My phonostage tuning experience shows that yr phono cartidge may not at its optimum load. 47KR is only a general guidelone for most MM cartridges. If you find it the sound not balanced, either too bright or too bassy, get a 50KR small trimming pot to replace the 47KR MM cartridge load resistor & trim it to get the most balanced sound.

You'll be surprise how this trimming pot can change the tonal balance of yr preamp.

c-J

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PostPosted: 21 Jan 2011, 18:04 
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Cheap-Jack: Does a heavier load e.g. 20K take some off the top-end or would you go for e.g. 100K to do that?

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PostPosted: 21 Jan 2011, 18:48 
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Hi.

Try a 100Kr trimmer pot & start at 50KR mid-point. You'll hear the different tonal balance.

c-J

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PostPosted: 21 Jan 2011, 20:35 
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I have an Opera day at my place today for some club members. All vinyl of course. The Pacific will be on show. Tomorrow I'll pick-up a few trimmers and try it. The other suggestion is a 100pf to 200pf cap across the load R to "smooth" the top end. I have the Grado wood body Reference Sonata. Any clues what may be expected as a load cap?

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PostPosted: 22 Jan 2011, 18:27 
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mwhouston wrote:
The other suggestion is a 100pf to 200pf cap across the load R to "smooth" the top end.

Hi.

Yes, with correct value of the bypass cap, the hi-end will be rolled off, for sure. But it is only a hi filter rather than an effective tonal balancing way by optimizing the cartridge load. A pretty passive way to me.

c-J

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PostPosted: 22 Jan 2011, 18:53 
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mwhouston wrote:
The other suggestion is a 100pf to 200pf cap across the load R to "smooth" the top end. I have the Grado wood body Reference Sonata. Any clues what may be expected as a load cap?

Hi Mark,
From the webpage: http://www.gradolabs.com/frameset_main.htm
Load R is 47k. 100 to 400 pF for the cap and I typically use about 200pF.

Let use know how the listening goes.
Cheers

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PostPosted: 22 Jan 2011, 20:54 
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200pf sounds high. Some phono preamps I have seen use only 100pf. I'll start with 100 and see hwo wir goes.

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PostPosted: 24 Jan 2011, 10:23 
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mwhouston wrote:
Some phono preamps I have seen use only 100pf

Hi.

A cartridges is an inductor which required an optimum AC load: resistive+inductive+capacitive.
Assuming the cable resistance is negligible vs the 457R of yr cartrige, the loading capacitance got to be right (=internal capacitance of the inductor coil, cartridge-amp I/P capacitance) to provide the optimum AC load for the cartridge to get its designed flat frequency response.

In case yr find yr phono preamp sound too bright, it means yr cartridge does not get the optimum AC load (R+C+L) from yr phono I/P stage. By adding a cap of right value or by adjusting the resistive load of yr phono I/P stage should fix it.

My experience tells me adjusting the resistive load give me very obvious sonic result.

c-J

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PostPosted: 26 Jan 2011, 07:24 
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I HAVE FOUND THE PROBLEM. YET TO BE PROVEN BUT LOOKS TO BE RIGHT.

After the sale of my BoZoaC (Bride of Zen on a Cap) the new owner e-mailed me and expressed his sheer delight with the preamp and how good it sounded. He couldn't believe it made such a big difference to his system. All this occured at a buy, swap and sell night at the Melbourne Audio Club. I'm currently Opera convenor (OK stop laughing. I like Opera).

Martin (the new owner) went on to say he was kicking himself for not pruchasing my phono preamp (OPAMP based) which was also for sale on the night. After some discussion he asked me to make him a Boozhoudlabs/Le Pacific phono pre (renamed Mongrel Dog Audio-Pacific phono preamp for my build) like my own (just completed but with some resonance issues).

See images below of the progress so far. While constructing his cct. brd. I realised in the original build I had put a 0.0034 cap where a 0.034 cap should be in the RIAA comp. section. So once I have finished Martin's and had a listen to prove this is the only problem with the preamp I will fix mine.

For Martin's I have used a Hammond Al case (yet to be lined with bitumen and Al foil) and some big heavy brass feet. I think it will look OK but if not the feet unscrew and thick silicon feet will be fitted. Hope to have it complete and running in the next few days.
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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
Website: retro-thermionic


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PostPosted: 26 Jan 2011, 12:59 
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mwhouston wrote:
some big heavy brass feet. I think it will look OK but if not the feet unscrew and thick silicon feet will be fitted.

Hi.

Leave the brass tip-tops there! Why? For better transparency, imaging & soundstaging :thumbsup:

FYI, ALL my equipment, from TT, CD, DVD-audio players, phonostages, passive linestages, even power amps, are 'floated' on steel spikes or brass tip-toes. My loudspeakers are mounted on steel tripods 'floated' on steel spikes !!! :smoking:

Why? To fight vibrations & resonances.

Don't miss those 'minor' details for better sound !!

PS: floating a TT is imperial to suppress the motor vibration/resonances.

c-J

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