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Old 1st May 2012, 09:23 PM   #1931
rjm is offline rjm  Japan
Richard Murdey
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The Phonoclone is sensitive to RFI. Mobile phones, light switches, radio transmittors.

Try 330 pF or similar value cap across IC1 inputs (pin 2,3).
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Old 1st May 2012, 09:29 PM   #1932
Toaster is offline Toaster  United Kingdom
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Thanks, that's saved me looking back over the rest of the thread. It wasn't a problem last night, but The Guitarist did mention picking up a Spanish radio station the day before!
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Old 1st May 2012, 09:50 PM   #1933
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Nearly every phonostage I've ever had will pick up the triad tone as a mobile phone checks in with its local mast. Often you can get continuous clicks too. Leaving the phone a short distance away solves it very effectively. Never picked up a radio station though...
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Old 1st May 2012, 10:17 PM   #1934
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The radio station is a sign of long and badly grounded/shielded/tagled cartridge or input cables. It s a sign that you need to better arrange the inner and outer wiring. Signal and power ones. Phono and turntable ones.
I never had a problem with the mobile, but I guess that all devices with amplification have some issues with them. Just keep it away from the phono

Last edited by dimkasta; 1st May 2012 at 10:25 PM.
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Old 1st May 2012, 10:40 PM   #1935
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Thank's Richard, that seems to have cured it.
Darrell.
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Old 2nd May 2012, 12:50 AM   #1936
rjm is offline rjm  Japan
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Quote:
Originally Posted by dimkasta View Post
The radio station is a sign of long and badly grounded/shielded/tagled cartridge or input cables.
Cables should be fully shielded and grounded at both ends. That's just good practice, but it is doubly important for high gain, low signal situations like MC phono stages.

The level of RFI pickup is a function of the signal strength, the receiving sensitivity (the efficiency of your audio system to act as an antenna), the circuit sensitivity (how well the circuit demodulates the RF signal into AF), and, finally, by the effectiveness of any countermeasures taken.

No strong RFI sources nearby, no problem, no matter how lazy your cable routing is.

However, the bipolar inputs of the OPA27 are pretty good at demodulating RF, and as stock there is no RFI protection built into the phonoclone circuit. If your cabling has any predisposition to act as an antenna, therefore, it will readily result in audible interference.

Fortunately, the cap-on-the-input trick seems to solve things 70-80% of the time.
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Old 2nd May 2012, 07:53 AM   #1937
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Quote:
Originally Posted by rjm View Post
Cables should be fully shielded and grounded at both ends. That's just good practice, but it is doubly important for high gain, low signal situations like MC phono stages.
Just a note, grounding the shielding on both ends can create ground loops.
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Old 4th May 2012, 11:25 PM   #1938
kor952 is offline kor952  Netherlands
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I would like to share some of my findings with two Phonoclones (PCBs 3.5c).
The first Phonoclone (a complete kit) I bought January this year, the second PC I bought a month or so later, this was not a complete PC kit, I did get the PCBs with most of the parts but not all.
The first one was kept original till lately. With the second one I experimented with a 78/79xx supply. With both I tried one and two PSUs with different Toroids
The only change on the first one was that I replaced the ouput cap of the kit by a Black Gate N series 4.7uF 50V, this because I found that the output cap in the kit sounded nice but thin (no bottom end). With the BG N series it sounds as there is no cap present.
I changed the second PC such a way that it does not need output caps (very low output offset of 1 - 5 mV).
The sound difference between PC one with X-reg and PC two with 78/7912 supply both with the same 50VA 12+12V Triad toroid was very small.

Following only tested on the second PC. Using 78/7915 regs on PC2 gave a duller and less dynamic sound. Using a single 225VA toroid 15+15V toroid did make it more dull. A 100VA 18+18V toroid sounded as good as the 50VA 12+12V toroid (78/7912 used). It seems as 225VA is overkill wich worsened the sound quality.

I tried BG STD 220uF 16V decoupling caps instead of the Nichicons 100uF16V the difference is just marginal with no winner. I did not have enough 100uF 16V BGs in stock.
I changed the dual Vishay bridges into a single bridge made of four MUR820. This change was a big jump forward. A faster and more open sound.
I also tried OPA627s instead of the OPA27s. Although it is said they sound better and have more detail I did not hear it, they sounded a bit softer as the OPA27s. The OPA27s gave better pace and rythm (more foot tapping sound). I stayed with the OPA27s.

Two toroids instead of one...I only could test with two 50VA 12+12V toroids.
The sound quality did marginal improve on the PC2 but there sure is more width, depth and space. On PC1 two toroids gave tripple more width, depth and space but also changed the sound quality it became harsh (a shouting kind of sound), the kind of sound that tells you to turn the volume control to the left.

I did learn a lot last months experimenting with the two PCs. Is there someone who can explain my findings with PC1 and the double toroid supply? Did try it twice with different connectors but with the same result.

Last edited by kor952; 4th May 2012 at 11:37 PM.
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Old 5th May 2012, 12:19 AM   #1939
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Your findings with PC1 agree with what I have experienced with x-reg. Dual transformer and bigger transformer gave a big improvement in clarity and stage width.
About the harshness, could it be that your VTA is on the high-side and the increased clarity brought it up? Do you use MURs on PC1?
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Old 5th May 2012, 12:36 AM   #1940
kor952 is offline kor952  Netherlands
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Quote:
Originally Posted by dimkasta View Post
Your findings with PC1 agree with what I have experienced with x-reg. Dual transformer and bigger transformer gave a big improvement in clarity and stage width.
About the harshness, could it be that your VTA is on the high-side and the increased clarity brought it up? Do you use MURs on PC1?
I use single bridges of four MUR820s on both toroids (MUR820 = MUR860 only difference they are 200V types and some datasheets say the 820 is faster as the 860). I recently checked my VTA, arm is level. Again listened to the PC1 with double PSU but after an hour I could not stand it and returned to PC2 (wich sounds very good with the same VTA). Maybe the BG N-series need more time to break in, they are in PC1 for a week now.

Ronald.

Last edited by kor952; 5th May 2012 at 12:49 AM.
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