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In the Forum: Analog Playback
In the Thread: The last phonocorrector: “End of Life" Phonostage

Post Subject: The horrors of calibrationPosted by N-set on: 7/14/2012

I'm pathetically slow with my 834 clone, but that's what I am....
Sorry for boring you but I treat this threat a bit like a blog on my "progress".
I've tried to fight more with PS induced ham and interference
by putting the PS transformers and HV rectifiers into steel tombs (pics below)
Did not help much, 5-7dB lowered the noisefloor, but did not remedy 100Hz and harmonics realted to HV operation.
Still, the ham free operation is when the PS is far away...I can't help the fact
that I'm floating in my apartment, all my efforts to find the earth failed...my HP400L
milivotmeter also did not want to operate below 3mV range in my flat (while runs perfectly
well in my friend's who has the earth).

I've also put better tubes: Telefunken(good used)-Sylvania(new)-Telefunken(good used) as a KGS (known good solution).
The noise floor did not drop compared to chinese 12ax7 I've been using so far. Sylvania is crazy...sort of....
at -1.05V bias it has 90-100V on the plate instead of 150V...to hell with that.

I've moved to calibration finally. I used Hagtech's iRIAA, I know it's a bit off at HF (and will try to remedy it
per Jim's instructions, need 6.2nF cap), but I wanted a
coarse calibration first. I managed to get a +/-0.3dB "flat" resp:

The HF roll-off is (mostly) due to my soundcard (Shit Blaster X-Fi or sth like that). Measured with a HP selective voltmeter
with 50R driving impedance, Tribute iron that I use showed -1dB at 50kHz. The LF roll-off is another problem...probbly Pieter wanted more HF,
assuming low imp. source. I have no idea what's Jim's iRIAA output imp. 50R?

The things went much more ugly when I used HFNR test LP and swept 20-20k. What was once "flat" had a huge bump at 10k.
So I have reaclibrated 834 to ameliorate it. Still, the effect is poor:

The spikes are dust/static artefacts, not important.
The LF rolloff is -3dB at 30Hz....bye bye lower bass...Pieter probably ignored my alerts that TSD15 is high impedance at 24R
and wound his standard. Then the HF horror...the cart is loaded as per EMT recommendations: 82k through 1:20 giving 200R at the cart.

I have too little experience to find a way out. Any ideas why the heck it's so ugly?
1) Shall I calibrate the 834 separately, without the cart, using e.g. iRIAA and make it as flat as possible
and then fight cart resonance with loading, or
2) Calibrate the phono-cart as a whole?

Here is some diy porn,mostly for my reference:

PS trannies in their tombs

HV rectifiers in their tomb...rest in hell with your RF garbage

DIY intershitconnect. Twisted cardas pair in teflon tubing, then heavy braid at each channel, heatshrink,
second braid on both channels, Vampire CU RCA plugs and amphenol 7pin to connect to EMT929 arm.
The master of stiffness, whoever worked with cardas knows what I'm talking about:

Connecting securely to the amr with that stiff kielbasa was a noghtmare, I fitted two adjustable bands, connected by 3 pieces of a steel wire. Works good:

Cheers, Nset.

PS I use iRIAA fed with pink noise to burn in the SUT's. The level at the SUT's secondaries is 10mVpp

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