Saturday, November 19, 2011

My Great Little Phono
















This is the second and final instalment of my extensive refinement mods to Musical Fidelity V-LPS phono stage. It responded well to component changes that when it is done, every single capacitor on board has been replaced with something else. I like the final product a lot that I termed it my "Great Little Phono".

I kicked off the mods by having the JRC5534D op amps in RIAA equalization stage at IC201/301 replaced with OPA627BP which accorded the phono stage a tremendous jump in overall clarity and a velvety feel, followed by removal of caps no longer required at C207/207 and C209/309. Explanation as put forth by Thorsten L in a diyAudio forum thread: "NE5532/34 single op amp phono stages needs three coupling capacitors- one on the input to prevent input bias currents flowing in the cartridge, one in the NFB to ground leg to minimise offset and finally still one on the output. Using a precision FET op amp allows two of these three to be discarded." The sound, although clear and pleasant, lacks some ultimate bass weights and the recapping of Jamicon polarized electrolytics with higher ripples content and lower impedance Panasonic FM/FC restored balance and every spectrum of frequencies sound right thereafter (C1 was subsequently replaced with a Panasonic FM 2200uF/16V cap). Modders tend to stop here after adding an improved power supplies but I feel these mods merely lend a solid foundation for further mods. Or course, there is always risk of going overboard and the final product turns up way too clinical and unmusical.

4 pieces of Wima FKP2 polypropylene caps were fitted in at C206/306 and C222/322, replacing stock RFI filtering ceramics ones and not expecting much of sonic improvements but fact that Musical Fidelity is also replacing ceramic caps with polycarbonate/polyester ones in their factory upgrades is motivation enough for me to do likewise. End result is indeed positive - gone are the irritating edginess to sound and in place thereof a mildly warm and lush presentation with much nicer edges. Probable reason being, ceramic (especially C0G/NPO ones) has lower impedance than film cap and works better as a RF filter but film cap will sound better although, at best, it could filter out RFI just as good but not better. All caps impart their mojo onto sound and that of ceramic is far from pleasant.

Up next are the replacement of both 10uF polarized electrolytic input caps at C205/305 and 100uF non-polar electrolytic output caps at C216/316 with Vishay Roederstein MKT1813 4.7uF polyester type, its size and lead spacing fit the V-LPS board like a glove and with sonic that I enjoyed immensely with my T-amps. These caps lend a palpable, rich and liquid presentation to V-LPS. See http://www.ecp.cc/cap-notes.html for an interesting read on selection of coupling capacitors. As I am reverting to film caps, I opted for a value much lower than stock, reason being Musical Fidelity could have probably adopted a higher value since they are using electrolytics (with higher AC voltage across the cap by design) for coupling and the general consensus is to use a value 10 times greater than what is required, so I am basically undoing the compensation made by MF, see http://sound.westhost.com/articles/capacitors.htm and the comments made by Werner in a vinylengine forum thread: "For coupling using electrolytic caps, we actually need non-polar ones but could wire 2 polarized electrolytics in anti-series, i.e. their negative poles together and the dangling positive poles one each in the circuit holes. This halves the apparent capacity of the couple, so we need 2 of 10uF polarized electrolytics to replace one 4.7uF non-polar. An even better thing would be to add a bias voltage to the coupled-caps' centre points, as is done with the output coupling caps of the Analog Addicts Phono circuit."

His other comment (although meant for the 2 op amps per channel Cambridge Audio 640P) deterred me from entirely doing away with input caps: "Input caps keep the (very low, but still ...) bias currents of input stage transistors from flowing through the cartridge. They do not block any appreciable DC, and do not directly influence the op amp output DC offset. However, they do so indirectly as bridging the caps would create a new path for the bias current, so that the net voltage on top of R17 changes and thus the DC balance around the input stage changes too. The RIAA op amp has a lot of DC gain, so any natural offset of its op amp will be blown up. Hence, we can not do without an output cap. Likewise, even when the input stage op amp gives a low offset in that circuit (and why would it, with the transistor diff. pairs so unbalanced!), the tiniest amount of offset it creates must not reach the RIAA op amp, see reasons above. So that cap there is needed too."

I was initially a bit hesitant to replace the unbranded stock film caps which bore an uncanny resemblance to Taiwan made polycarbonate type seen in online pictures. I knew they are probably dirt cheap but was unable to ascertain whether they have been pair matched for both channels in RIAA section until I measured them. No, they are not. Their sonic signatures include a rather forward, flat and having a plasticky sheen to sound with a certain degree of mid bass hump. Perhaps V-LPS could have been voiced to sound exactly that. Tight-tolerance LCR Components FSC/FSCEX polystyrene caps are eventually fitted into RIAA equalization stage. These caps sound natural, wholesome and possess great treble extension that opened up the entire sound stage (height, width and depth) considerably. I am not into sound staging but could not help noticing the beautiful effect of layering after the caps change. They have a blue foil marking at one end, not polarity marking but "the outer foil to be connected to the lower impedance node. In the context of RIAA equalization stage of V-LPS, the output of the op amp and the inverted input are both low impedance, the node in the middle where all RIAA parts join by comparison is a high impedance node, so the marked ends are to be fitted towards the inverting input and/or the op amp output. C212 and C312 and C213 should point towards pin 6 of IC201. C210 and C211 should point towards pin 2 of IC201. Pin 6 is basically more or less 0 Ohm whereas Pin 2 is 82R to ground, so either node qualifies as low impedance." (Thorsten L)

The only pair of resistors I replaced in V-LPS are grounded output ones at R209/309 where I opted for 100K ohm over the stock 10K ohm so as to adopt a lower value output caps and with objective of matching output impedance of V-LPS to input impedance of my Simaudio i3 integrated amplifier closely to attain a more optimised interface between the 2 equipment. I heard a less noisy presentation with lower noise floor, better control and greater dynamic contrast thereafter.

The stock 12V DC 500mA wall wart measured to supply 20.5V DC without load is being replaced with another bigger 12V DC 1A unit that supplies 16V DC unloaded, an used unit with compliments from CM. The benefits of improved power supplies are known to all, ie. a cleaner sound, improved headroom, larger and better defined sound stage. A phono stage only draw the current it requires, hence having a more capable supply (usually triple the current available) is more than adequate. If it is way too high, some problems either in the form of component destruction or a change in the way how the circuit operates (possibly distortion) are to be expected.

I have recapped my V-LPS with caps from element14 and RS Components, nothing fancy or of boutique quality and price. Total costs of all new components including the 3 new op amps amounted to RM350 (US$110), pushing the full cost of my modded V-LPS to RM850 (US$270). The improvements in sound quality far exceeded the costs incurred and I have yet to come across a phono stage a few times its full cost sounding anything like it, at all. It has immense clarity, a huge soundstage, excellent treble extension that is beyond reproach by any standard, spot-on timbre and tone of instruments, liquid, organic and rich sounding, a dramatic presentation, palpable and solid imaging, expressive, agile, rhythmic and extremely dynamic. No, it does not transform all my LPs to sound better as only the better sounding ones actually sound better whereas mediocre ones worse. It does not smoothen out the presentation nor does it veil transients and inner details found in the grooves of LPs. On the contrary, I could now hear the individual violins within their section in a classical concerto/symphony performance when I only heard a mass of violins in that section previously. I could also hear lots of not-so-subtle details in the midrange now. It really is that transparent yet coherent sounding!

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7 comments:

voon8899 said...

Dear sir

The resistor R206 39k or 390k
. MY one is 390k.

tq

Y.C. said...

Hi Voon,

The RIAA equalization circuit diagram has been taken from http://www.vinylengine.com/turntable_forum/viewtopic.php?t=36631 whereby I only spotted an error: C211 (10nF 5%) in MC inputs diagram is actually C221. I only replaced the 10k resistor at R209/R309 with 100k and did not measure the rest of resistors, hence could not ascertain whether R206/R306 is 39k as stated in the circuit diagram or 390k in reality.

I am very keen to read about the mods you made to your V-LPS and how the mods changed the sound, mind to share them with me? You may drop me an e-mail if you do not wish to share them in the open.

Y.C.

voon8899 said...

HI y c,

Bro you can use battery power supply 12v 7ah .

Very good sound.

Voon.

Y.C. said...

Voon,

Thank you for the recommendation to use 12V 7AH battery on V-LPS. You are the third person to suggest so thus far and although I am fully aware that battery supply would be much cleaner than electricity, I may not take this route at all.

I am still hunting for a suitable PDIP dual op amp capable of lower input noise and higher output current than the stock JRC5532DD which limits V-LPS to operate at output current (typical) of only 38mA, definitely way too low even for a phono stage.

Cheers,
Y.C.

wushuliu said...

Curious since you have gone to such efforts to mod the V-LPS , why didn't you just buy a Hagerman Bugle (hagtech.com)? It can be bought fully assembled or in kit form for$140 and is extremely easy to work with. Just need an enclosure. I bring this up because the Bugle has been around for years and since you like to mod, it seems a perfect fit. In stock form it competes with $1000 - $5000 (US) phono amps. Lots of info across the web. External PS is also available on ebay or in kit form.

just my .02

w

Y.C. said...

wushuliu,

Hi, my reasons being :-

- I already owned V-LPS for a while before my mods and even enjoyed its sonic so I could easily revert to stock part(s) if sonic is worse than before ;

- Cost of V-LPS is already a sunk cost (used V-LPS not worth much), hence only the cost of new parts is applicable in my decision to mod or acquire another phono ; and

- There are several other phono available in kit forms out there, just do not have time to try out each. I am quite sure the Hagerman Bugle is a great sounding unit but from its specs, it caters only to MM carts whereas I am into MC after this.

Unknown said...

Y.C. I am just about to start your mod ...interesting it is 5 years ago you published it , my audio pal has proved to me how good the unit sounds after your re & re
can you tell me what you are up to now ? do you still use the VLPS ?
thanks ben