Isotope MM phono preamp by doors666

The noise filter is not actually a tank ckt so to speak, but two 220 ohm resistors in series. The center point of this resistors is connected to a 470pf capacitor which is grounded. It works like this - the input signal + noise sees a resistance of 220 ohm and then another 220 ohm. The signal passes through the series resistance. But the noise being random and weak finds the second 220 ohm resistance too high and instead finds an easier path to ground through the 470pf capacitance. This is my own invention. The noise just vanished with this. I am thinking of increasing the second 220 ohm to 470 ohm.

That's an interesting arrangement.

Where is the output of this network tapped? Between the two Rs? Or at the ends of the two Rs?

If between, one could argue that first R and the shunt C form an LP, and the second R simply adds series resistance to the load. The later would be a voltage divider with the shunt C acting as a path for high frequency components of the signal. Of course I could be totally wrong. It would be nice if someone skilled could sim this.


The 2SK170BL has higher input capacitance which resonantes at around 18KHz and is not suitable for any phono preamp.

Actually there are phono preamps that use 2SK170.
 
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The noise filter is not actually a tank ckt so to speak, but two 220 ohm resistors in series. The center point of this resistors is connected to a 470pf capacitor which is grounded. It works like this - the input signal + noise sees a resistance of 220 ohm and then another 220 ohm. The signal passes through the series resistance. But the noise being random and weak finds the second 220 ohm resistance too high and instead finds an easier path to ground through the 470pf capacitance. This is my own invention. The noise just vanished with this. I am thinking of increasing the second 220 ohm to 470 ohm.

You have discovered 'T' filter. This is called 'T' filter. We just use is for high pass or low pass mode. What you described is low pass filter and attenuates high frequency and is low pass filter.
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Its cut-off frequency is fc=1/2(pi*RC) where R is addition of both resistances.
Just calculate cut-off here which comes to be fc = 769608.04203044[Hz].

Another point BF862 is SMD version and you need some adapter and matching before using it.
 
Yes, thats pretty much a standard RF filter. I use it in almost all my designs (amps or preamps), except for the phono preamp.

The capacitor is a load on the cartridge. e.g. Many of MM phono cartridges expect a load capacitance of around 250pf and load of 47k. This is comprised of the cartridge capacitance, connector capacitance, cable capacitance, any explicit load capacitance and miller capacitance.

An MM cart's acoustic response falls beyond 10khz, but mechanical response rises. When you have the recommended capacitance as the total load, cart's mechanical and acoustical response balance out to give you a flat frequency response. I use a 100pf load capacitance with my cart.

You have a 470pf of load on the cartridge + the rest of the other capacitances. Most probably it will cause problems with the high frequency response.
 
You have a 470pf of load on the cartridge + the rest of the other capacitances. Most probably it will cause problems with the high frequency response.

I failed to see that aspect, but it's true. The 470 pF is shunted to the cartridge so effectively the cartridge will be seeing the combined capacitances of {headshell wires + tonearm internal wire + tonearm cable + 470 pF + stray capacitances}. Considering that most MMs need to see circa 250 pF, the above figure is way too high.
 
Some further experiments:
Inspired by this audiogon thread which extols the virtues of long forgotten and long neglected MM cartridges, I decided to do some fine tuning and cartridge loading experiments.

But first, a paraphrase/gist of the thread:

a/ some MM cartridges costing as low as $50 are at least as good, if not better than, the best MC cartridges costing thousands of dollars.

b/ the best loading combination for most MM cartridges is 100 kilo Ohms (and not the conventionally accepted 47kOhms) with parallel capacitance of 100-150 pF (and not the usually ?recommended 250-300 pF or even higher). For those who own phono stages that allows changing of impedance and capacitance loading, this is a must try.

c/ the best vertical tracking (VTA) angle need not be parallel. Parallel means the tonearm tube and record surface are parallel. Many MM cartridges benefit from positive VTA (tonearm is slightly raised at the pivot so that the headshell droops down a bit). Some benefit from negative VTA. If the tonearm allows it, playing around with VTA is simple enough. Strictly speaking, one should check the stylus rake angle and not how parallel or not is the arm tube, but most of us are not equipped to measure the angle of the stylus rake. So the indirect indication from arm tube must be considered good enough.

d/ there is a "best" tracking force/weight for a cartridge. Example: if a cartridge has a recommended tracking range of 0.75 to 1.25 grams, experiment with different weights within this range, in steps of 0.1 grams. One could even go slightly beyond the recommended range. In general, if tracking force is too high the bass will be plodding and lazy. If too light, there will be nervous energy in the music, as if something is unresolved or is in suspense. In other words, it could sound edgy. At the right tracking force the music will snap into place/focus.

Additionally, some people swear by the correct antiskating force to balance the left and right channels (assuming azimuth is already correctly set).

Azimuth adjustment, if available in the tonearm, will set L/R balance as well as L/R channel separation correctly. For example, a cartridge may be rated for 25 dB of channel separation but we may not achieve that number unless the azimuth is correctly set.

So I started experimenting with vertical tracking angle. I normally set my arms to parallel. I noted the tonal balance with parallel VTA then tried both slightly positive and slightly negative. I noted my preferred sound and set it for that. I found slightly positive tracking angle sounding the best for my cartridge.

Next I weighed the actual tracking force and increased and decreased in steps of 0.1 grams. If using an unipivot arm with hanging counter weight like me, it is essential to cross check correctness of azimuth after changing tracking force. I went from the recommended 1.6g to 1.7, 1.8 and 1.9 and found 1.7g sounding the best. I had also gone as low as 1.3, 1.4, and 1.5g.

The last thing I changed was the resistive loading. I have found 1.8K Ohms the most balanced for my high output MC cartridge (approximately ten times the internal impedance of the cartridge). I had been using this value for a long time, except for brief spells trying out 1K and the usual MM loading of 47K. Based on the advise in the audiogon thread, I tried 100K.

Up to this point, there was definite improvement in the sound but a recent change in one interconnect cable had brought about substantial improvement to the sound (more resolving, better defined bass, better separation, etc) but had also brought with it an edginess to the sound. A sort of nervous energy that needed taming.

After changing to 100K loading the nervousness went away. The bass weight suddenly became more ominous. It gained substantial bass weight. But the greatest change was in the extension and smoothness of the treble. My cartridge, though decent, is a modest one, and I have accordingly limited my expectations of it, especially the quality of the treble. With the change in resistive loading, it sounds much sweeter, more like a much costlier MC.

So I would urge all you vinyl enthusiasts to try fine tuning your tracking angle, azimuth, tracking weight and if possible your resistive and capacitive loading. There is a lot hidden in the grooves, waiting to be uncovered without spending silly money on new analog gear!
 
if you have multiple TTs or carts requiring different loading, you can use a chassis mounted switch (dpdt) to toggle between them. Isotope supports two different loadings, it switches both the resistor and the capacitor. Currently if you are using jumpers to switch between the two, this can be replaced by the dpdt switch. Use short shielded wire for the switch. Or twist each triplet tightly and keep away from other wiring.
 
So I would urge all you vinyl enthusiasts to try fine tuning your tracking angle, azimuth, tracking weight and if possible your resistive and capacitive loading. There is a lot hidden in the grooves, waiting to be uncovered without spending silly money on new analog gear!

Add antiskate too to above list
 
Found a very good article on ground loops and noise reduction techniques. The article also debunks the notion that high-end cables are required for connecting phono inputs. Infact the article mentions that high-end cables would have high input capacitance which could work otherwise for phono inputs. Read the article fully before any commenting and not just scan through pages.

http://shure.custhelp.com/ci/fattach/get/97648/0/filename/Ground+Loop+_Bill+Whitlock.pdf
 
Some update: so I pulled out a Shure V15 type III from storage and swapped out the Denon DL 160 HOMC. Compared to the DL 160, the V15 cantilever has a low clearance so I had to take extra care in mounting so that the headshell screws don't hit the record when playing warped records.

I started off with a loading of 47K R in parallel with about 100 pF C, then did the usual tonearm adjustments. This combination doesn't sound any good, so I decided to follow the recommended loading in the cartridge data sheet. So I tried 47K R // about 400 pF, and it was much better. At this point I was paralleling three 100 pF ceramic caps as I didn't have anything better on hand. At least this loading combination had a much better tonal balance than the previous combo. Later I changed the ceramics to mylar film caps as that's the best I could buy from the local market, and it was a definite improvement over the ceramic. Later I changed the loading to 100K R // 400 pF and the highs snapped into place.

After getting the basic loading right, I proceeded to play around with VTA and find that a fairly positive VTA works best for this cartridge.

BTW, I also discovered yesterday while assisting a friend install a fancy new cartridge that some cartridges can be very sensitive to changes in VTA. After we had finished adjusting the arm with the fresh cartridge as per the rule book (namely proper alignment to the two nulls, setting the recommended tracking force, arm tube parallel to record surface, etc), we were greeted by a rather overhang bass that affected the rest of the spectrum. Gradually changing the VTA from slightly negative to flat to fairly positive produced a stunning change. It's seriously worth trying. We worry whether our tonearm cables are ideal, or sometimes think of upgrading our cartridges. I feel playing around with VTA and loading values can bring about substantial improvements.

I'm not done experimenting. Will try further fine tuning. The V15 is sounding its best ever in many years of ownership. There's probably more to extract.

PS: one more finding. I mentioned the new cartridge above. It's an MC with 0.5 mV output. The cartridge's literature recommended a resistive loading value of 2 to 3 times the internal impedance of the cartridge (12 Ohms in this case). The manual of the amplifier recommends ten times. The phono section of the amplifier has either 10, 30 or 100 Ohm loading options. We tried both 30 (~2.5x and 100 (8.3x) Ohms and both of us subjectively like the lower loading more. So don't be afraid to try various values for MC loading.
 
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@Jousha

How to reduce electrical noise pick-up.

I have fully resolved the RF & EMI noise, but a minor electrical noise could be heard in my Phono pre-amp especially when i turn on the Fans or tube lights which is distracting. Please advise.

I think its due to the placement of my volume control know which is very very close to the power transformer but am not able to confirm this. For other inputs (CD/Tape/TV) there is no electrical noise. So my suspect is the phono preamp picking the noise.
 
@Hari, do you mean something in your chain is picking up electrical impulse when light or fan switch is operated in the room?

Does it result in a loud, momentary crackling noise on the speakers?

If yes, then you're missing a small value capacitor somewhere.

I had this problem on two separate occasions. One was on one of my vintage TT. A 0.047 uF X2 rated cap shunted to the TT's on/off switch completely cured the problem. The cap is basically a spark suppressor and is used in most motor on/off mechanisms. Use X2 cap rated for 660V or 1100V as electrical impulses generated during switch on can be extremely high.

The second one was observed on Isotope phono when I was using it without any loading capacitor (since my high output MC cartridge doesn't care about capacitive loading). Basically I was giving it only resistive loading. The moment I added a 100 pF loading cap (100V rated, IIRC), and the impulse pick up was completely solved.

See if you've inadvertantly missed a cap somewhere.
 
@Hari, do you mean something in your chain is picking up electrical impulse when light or fan switch is operated in the room?

Does it result in a loud, momentary crackling noise on the speakers?

If yes, then you're missing a small value capacitor somewhere.

I had this problem on two separate occasions. One was on one of my vintage TT. A 0.047 uF X2 rated cap shunted to the TT's on/off switch completely cured the problem. The cap is basically a spark suppressor and is used in most motor on/off mechanisms. Use X2 cap rated for 660V or 1100V as electrical impulses generated during switch on can be extremely high.

The second one was observed on Isotope phono when I was using it without any loading capacitor (since my high output MC cartridge doesn't care about capacitive loading). Basically I was giving it only resistive loading. The moment I added a 100 pF loading cap (100V rated, IIRC), and the impulse pick up was completely solved.

See if you've inadvertantly missed a cap somewhere.

@Jousha - Thanks for suggestion. But i have added a capacitor 0.01 mfd across the switch and also across the AC terminals (1000v), but still the noise is not fully disappeared.

Also my input capacitance is around 180pf (Cartidge suggestion is between 200pf and 500pf by Ortofon) yet the switching of near by electrical devices like a cieling fan, Tubelight causes this momentary click/pop sound though very feeble to the ears.

I am doubting the position of volume control knob which is very close to the AC input / Transformer but am unable to confirm this. But again there is no noise in other inputs like CD player, DAC, Tape deck etc. hence the confusion.
 
@Hari, do you mean something in your chain is picking up electrical impulse when light or fan switch is operated in the room?

Does it result in a loud, momentary crackling noise on the speakers?

If yes, then you're missing a small value capacitor somewhere.

I had this problem on two separate occasions. One was on one of my vintage TT. A 0.047 uF X2 rated cap shunted to the TT's on/off switch completely cured the problem. The cap is basically a spark suppressor and is used in most motor on/off mechanisms. Use X2 cap rated for 660V or 1100V as electrical impulses generated during switch on can be extremely high.

The second one was observed on Isotope phono when I was using it without any loading capacitor (since my high output MC cartridge doesn't care about capacitive loading). Basically I was giving it only resistive loading. The moment I added a 100 pF loading cap (100V rated, IIRC), and the impulse pick up was completely solved.

See if you've inadvertantly missed a cap somewhere.

Hi Joshua, I have this problem in my living room fan when the music is playing I get a loud click kind of sound. Not sure which one gives this problem as I have the Soekris DAC, BA3 preamp, Aleph J power amp. I am guessing it could be with the BA3 preamp as I do not use any IEC filter like the Elcom ones but my DAC has a 3A Elcom filter and the Aleph uses a CL60 thermistor for the soft start. Any idea if its BA3 preamp where should I solder the cap and how much value on the power socket? Please PM me on how to go about it.

thanks
 
I am doubting the position of volume control knob which is very close to the AC input / Transformer but am unable to confirm this. But again there is no noise in other inputs like CD player, DAC, Tape deck etc. hence the confusion.

I feel the signal cable being near to power line should not be the cause, but it's a good engineering practice to keep small signal line and power line/transformer as far apart as practicable. If necessary, relocate one of them. I usually take great pains for maximum separation.
 
Is the transformer body and preamplifier chassis earth grounded? You need this if transformer is housed within same chassis.
Or TT is 3 pin mains power cord? See if earth ground is mixing in TT DC ground.
 
Is the transformer body and preamplifier chassis earth grounded? You need this if transformer is housed within same chassis.
Or TT is 3 pin mains power cord? See if earth ground is mixing in TT DC ground.

IIRC, Hari's chassis is wooden.
 
Hi Joshua, I have this problem in my living room fan when the music is playing I get a loud click kind of sound. Not sure which one gives this problem as I have the Soekris DAC, BA3 preamp, Aleph J power amp. I am guessing it could be with the BA3 preamp as I do not use any IEC filter like the Elcom ones but my DAC has a 3A Elcom filter and the Aleph uses a CL60 thermistor for the soft start. Any idea if its BA3 preamp where should I solder the cap and how much value on the power socket? Please PM me on how to go about it.

thanks

The problem I described is a loud pop audible on the speakers when any electrical switch is operated in the room (or even nearby room). It is momentary.

Are you facing same problem?
 
The problem I described is a loud pop audible on the speakers when any electrical switch is operated in the room (or even nearby room). It is momentary.

Are you facing same problem?

Yes whenever the fan which is close to the equipment is switched on/off this pop sound comes. But in my case its not so loud but it does comes whenever the regulator of the fan is operated as well.
 
Can you isolate if the pop is happening on analog chain, or on digital, or both?

If both, BA3 could be suspect because that's the first common point.

Also, please check if electrical ground is earthed to equipment chassis as mentioned by Om. For any non double insulated equipment operated with two wire AC supply, earthing ground is a safety requirement to prevent shock. Also please check how your signal ground is earthed.
 
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