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PostPosted: January 6th, 2023, 10:35 am 
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DaveR wrote:
TubeDriver wrote:
It is Class-A FET , DC coupled with no caps in signal path.


Doesn't the C in LCR stand for capacitor? Just because it's a cap to ground doesn't mean it's not in the signal path. When a signal goes through a node with a shunt component to ground, that component is one of the possible signal paths for the signal energy to follow. What doesn't go through the shunt component proceeds on its way down the "signal path". So how well a shunt component performs its intended duty absolutely affects the signal. Seems to me that shunt components are as important as components the signal goes through on its way to the output.


LCR is the network, it is hard to get away from using a capacitor in the RIAA network in the shunt position as you point out, even with chokes setting some of the time constants. There are very few examples of direct coupled LR phonostages (I have an op-amp based unit, Pete Millett’s LR phonostage, using AD797 opamps, which I need to dig out, unfortunately, I am presently using its power supply for my new linestage)


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PostPosted: January 6th, 2023, 10:37 am 
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Good point. I gather the output stage is DC coupled with no caps at output but you are right that the eq stage does use caps. I think there are some pure LR eq designs out there but these are rare beasts indeed.

DaveR wrote:
TubeDriver wrote:
It is Class-A FET , DC coupled with no caps in signal path.


Doesn't the C in LCR stand for capacitor? Just because it's a cap to ground doesn't mean it's not in the signal path. When a signal goes through a node with a shunt component to ground, that component is one of the possible signal paths for the signal energy to follow. What doesn't go through the shunt component proceeds on its way down the "signal path". So how well a shunt component performs its intended duty absolutely affects the signal. Seems to me that shunt components are as important as components the signal goes through on its way to the output.


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PostPosted: January 6th, 2023, 10:57 am 
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David, I have some work to complete this morning but should be finished up after lunch. Could swing by in the afternoon if that works for you? Text me times if this works for you. I mentioned "unusual" in the context of chokes being used, not so much the choke design. I gather a vast majority commercially available phonostages use RC eq? I don't love the Kitsune but I think it has a competent overall sound (and it stomps the crap out of another, older SS Roksan phono preamp that I have) and has a fair amount of input setting options (gain and impedance). One thing I have not tried is lower gain with an external SUT but I read somewhere that this was a good way to go.





David McGown wrote:
TubeDriver wrote:
David, I have been using a Kitsune LCR phono stage (designed by Kevin Valab) on one of my tables. It is more than your $1000 budget (current cost is $1500 or $2200 depending on the amount of magic dust added) but you are welcome to try it out for a couple weeks if you want? It uses EMI shielded 80% high nickel content Permalloy cores in the RIAA eq which I gather is somewhat unusual. It is Class-A FET , DC coupled with no caps in signal path. The only thing to really note is that the umbilical cord from the external power supply to the phono stage must be connected first, before you plug in the AC PS cord or it will become another doorstop to join your iFi. :D



Pete, I would love to try out the Kitsune phonostage. Are you at home today or over the weekend. It occurs to me it has been a while since you have heard my system…not sure if you have heard Charlie’s Nesterovic speakers, but your call, I appreciate the loan to get an idea of what is out there.

I am not wedded to $1K phonostages. At this point, I have to decide whether to go for something that will LAST in my system, or something again stop gap until I try to build someone better than I have done before. There is a lot of appeal (conceptually) to a FET phonostage over tubes, lower noise, consistent sound over time, not spending considerable time tube rolling to find just the right combination of NOS tubes to sound best. BTW, permalloy is pretty typically used for RIAA LCR cores. I actually have a pair of Silk 600ohm LCR networks (permalloy cores) that have a limited voltage capability (100VDC) that make them challenging to use in a tube phonostage direct coupled. A coupling cap for 600ohms input impedance is huge and undesireable, definitely would need a cathode or source follower driving it at a voltage within the limits which limits tube choices. Maybe a FET LCR project would be a good thing to attempt.


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PostPosted: January 6th, 2023, 11:05 am 
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TubeDriver wrote:
David, I have some work to complete this morning but should be finished up after lunch. Could swing by in the afternoon if that works for you? Text me times if this works for you. I mentioned "unusual" in the context of chokes being used, not so much the choke design. I gather a vast majority commercially available phonostages use RC eq? I don't love the Kitsune but I think it has a competent overall sound (and it stomps the crap out of another, older SS Roksan phono preamp that I have) and has a fair amount of input setting options (gain and impedance). One thing I have not tried is lower gain with an external SUT but I read somewhere that this was a good way to go.


Pete, I will be home all afternoon. Just leaving for a quick run to Rockville for a hand vacuum but should be back at Noon. So come over when you finish up.


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PostPosted: January 10th, 2023, 11:36 pm 
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Followup on the linestage project.

I "pre-modified" the linestage when I built it by setting the gain lower than specified since with my gain structure, I felt that the design gain of 3.7 (11dB) was high considering I can get by with a passive just fine from a gain perspective. I increased the feedback resistor from 10K to 22K which dropped the gain to around 2.2 (7dB). I felt that the sound was a little brighter than I like, particularly with the addition of the stepped attenuators. I decided to change the feedback resistor to the design value. I can say that the sound of the unit improved significantly, really not imposing much of any sonic signature, just super clean. It really helps to try something out as designed FIRST.

I also did a lot of phonostage listening over the past few days after zapping my iFi iPhono 3 BL in order to find something to use in its place for the short term. Pete (TubeDriver) let me borrow his Kitsune KTE LCR-1 MkV phonostage, which has been quite a treat, a very nice and musical sounding unit, even though it is Pete's second tier phonostage. But I also cycled through my various DIY phonostage projects from years past, sometimes doing a bit of an update to get them back in full working order with the gain I need (using MC cartridges). I found a particular synergy using the PassDIY Pearl 2 phonostage with the new linestage. Both were designed by Wayne Colburn, so no surprise there. The combination works so well together that I am thinking about a full function preamp combining both together. The bipolar supply for the phonostage (+/-24V regulated for each channel) also can work for the linestage. Currently, I am using a common +/-15V regulated supply for the linestage (borrowed from a Pete Millett LR phonostage, also auditioned, but not with the new linestage), so a dual mono setup would be an improvement.

The ham radio operator up the street may cause me to look for a well designed commercial phonostage rather than a DIY unit, I need really good RF rejection, so the double shielded construction and power line filtration of a unit like the Parasound JC3+ looks like it may help in my situation. I can get a pretty intense sidelobe from his antenna when he is pointing a particular direction.


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PostPosted: January 11th, 2023, 7:59 am 
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David:
I have designed my signal level power supplies for some time with the drop in power supply rejection ratio that happens with increasing noise frequency. Most differential circuits start to lose PSRR around 70 Hz and continue to the point that for some, the PSSR becomes negative, that is they amplify HF stuff coming over the PS lines. To solve that I use chokes at the output of of the regulators and a lot of capacitance after that so that you essentially have a 12 dB/octave low pass that matches the drop off in PSSR with increasing frequency. As a result, whatever PSRR in inherent to the active section remains the same as the frequency increases. You always want to use local bypassing right at the power input terminals of Op Amps. I use a 4.7uf tantalum paralleled with a 0.1 uf monolithic ceramic right at each power terminal. Here is a representative schematic.

Tom


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PostPosted: January 11th, 2023, 8:02 am 
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David,
Glad to hear you think the Kitsune is a decent unit, it is always informative to hear a reaction to a component when it is in a completely different system with different ears. It seems to have no big flaws overall, I like it but I can't say I love it.

Perhaps a project to consider is how to construct a Faraday cage around your entire listening room? Banish that pesky ham radio neighbor once and for all? :D


David McGown wrote:
Followup on the linestage project.

I "pre-modified" the linestage when I built it by setting the gain lower than specified since with my gain structure, I felt that the design gain of 3.7 (11dB) was high considering I can get by with a passive just fine from a gain perspective. I increased the feedback resistor from 10K to 22K which dropped the gain to around 2.2 (7dB). I felt that the sound was a little brighter than I like, particularly with the addition of the stepped attenuators. I decided to change the feedback resistor to the design value. I can say that the sound of the unit improved significantly, really not imposing much of any sonic signature, just super clean. It really helps to try something out as designed FIRST.

I also did a lot of phonostage listening over the past few days after zapping my iFi iPhono 3 BL in order to find something to use in its place for the short term. Pete (TubeDriver) let me borrow his Kitsune KTE LCR-1 MkV phonostage, which has been quite a treat, a very nice and musical sounding unit, even though it is Pete's second tier phonostage. But I also cycled through my various DIY phonostage projects from years past, sometimes doing a bit of an update to get them back in full working order with the gain I need (using MC cartridges). I found a particular synergy using the PassDIY Pearl 2 phonostage with the new linestage. Both were designed by Wayne Colburn, so no surprise there. The combination works so well together that I am thinking about a full function preamp combining both together. The bipolar supply for the phonostage (+/-24V regulated for each channel) also can work for the linestage. Currently, I am using a common +/-15V regulated supply for the linestage (borrowed from a Pete Millett LR phonostage, also auditioned, but not with the new linestage), so a dual mono setup would be an improvement.

The ham radio operator up the street may cause me to look for a well designed commercial phonostage rather than a DIY unit, I need really good RF rejection, so the double shielded construction and power line filtration of a unit like the Parasound JC3+ looks like it may help in my situation. I can get a pretty intense sidelobe from his antenna when he is pointing a particular direction.


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PostPosted: January 14th, 2023, 10:09 am 
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So I am listening to the radio this morning, courtesy of my backup Roksan phono stage. :D

Currently, a business discussion of security clearance for gov workers.

I will say the Kitsune LCR does not have the added feature of a tuner section so that is one downside for it.


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PostPosted: January 14th, 2023, 11:32 am 
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And unfortunately that is usually a single-station tuner section, no choices! ;)


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PostPosted: January 14th, 2023, 7:18 pm 
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Pete,

Funny about the radio on your phonostage. You might get a different station if you change the cartridge loading.

I read a suggestion about using clamp-on ferrite beads on the tonearm cable at the input to the preamp. I tried it, and it seems to reduce the volume of the rectified RF.

If you would like the Kitsune back, let me know. I am tied up tomorrow afternoon, but could drop it by tomorrow evening or Monday if you are home. Really appreciate the loan, but I have to admit I have been tweeking my PassDIY Pearl 2 to get the best sound out of it. Did an output cap change (Wayne Colburn used a 22uF/50V Silmic bypassed with a 0.1uF PP (Wima or similar). I swapped in a 10uF/50V Wima MKS (Mylar) bypassed with a 0.1uF Wima polycarbonate and a 0.01uF Vishay 1837 PP (too tight for a teflon). Nicer sounding than the eCap.

David


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