Hi All, I’ve responded to a few posts recently regarding the benefits of varying resistive loading in order to tune cartridge character. There’s been quite a few responses stating that this feature is not available on the respective phono-stages and there appears to be varied awareness regarding how to apply a parallel resistance in order to achieve this. Application of an incremental parallel resistance is a very simple and low cost method of delivering variable resistive loading. I did a quick trawl using the search facility to see if I could find a thread to direct any enquiries to, but struggled to find one. Apologies if this is old ground, but given the replies I’ve been getting, I thought it worth opening a thread just to run through the process. First up what’s the effect? Although most modern MM/MI/HOMC’s are supposedly designed around what’s become the standard 47k/50k ohm MM stage resistive load, this may not be the optimum setting for individuals personal taste or from a system matching perspective. The application of an incremental parallel resistance will reduce the overall MM stage resistive loading. This tends to dampen higher frequency response, but it’s not like a simple tone control that might affect a small range, it’s more of a total tonal change through lower mids all the way up. It can also tighten up a slightly woolly or loose lower end. Some carts are affected more than others and only need a subtle reduction to make a significant effect. HOMC’s tend to require bigger swings in resistance before the audible differences can be heard. Personally, I’ve found very few MM/MI/HOMC’s that deliver their optimum performance bang on 47k and tend to tweak most of them. For example here are a few preferred loadings (to my ears and on my system) of some popular cartridges; Audio Technica AT 440mla (MM) – 32k Denon DL 160 (HOMC) – 1k Dynavector 20XH (HOMC) – 1k Grado Reference Sonata (MI) – 38k Before we get into how, it needs to be stated that increasing the resistive load (to liven up the general character) requires phono stage surgery. The MM stage load resistor has to be replaced with a higher value item. I have done it, but IMHO it really is only for those who are totally comfortable with electronics and use of a soldering iron. I am not intending to go into that here. OK so how’s it done? Well as I say it’s very simple, you need to apply a parallel load to the MM input stage to reduce the overall resistance. Here’s the maths; 1/Rtotal=1/Rphono+1/Rplug Where; Rtotal is the modified delivered load Rphono is the quoted resistive load of the phono stage Rplug is the incremental plug resistance wired in parallel So if you had a 50k ohm phono stage and applied a 200k ohm plug you’d get a total load of 40k ohms. So how do we do it? First thing you need is a pair of good quality RCA Y splitters (1 male to 2 female) such as pictured here; The male plugs into one of the phonostage RCA connectors and the equivalent channel TT male connector goes into one of the females on the splitter. You then need to add your parallel resistance. The simple way is to buy some resistors and male RCA plugs and solder up like this; Ultimately you can make up a little kit that looks like this; Once the Y Splitters are in place it’s then a very simple process to replace the resistor plugs to vary the loading and understand it’s effect. Don’t forget – no plug at all means you’re right back where you started with the standard Phono Stage resistive load when doing comparisons. PLEASE ENUSRE THAT THE PHONO STAGE AND MAIN AMP ARE SWITCHED OFF WHEN SWAPPING THE RESISTORS You can get some pretty harsh spikes if you leave the amplification on, risking circuit and speaker damage. This is probably all you’ll need. All of these items are readily available through electrical retailers and on the bay. I personally have taken it one step further and built up this infinitely variable loading box; It uses a pair of calibrated potentiometers in two ranges. I use this to adjust resistance “on the fly” and it helps me home in on the optimal loading fairly quickly. But this has its dangers. I did induce quite a bit of hum with this unit and had to spend a fair amount of time getting the earthing sorted. There you go. I hope this is of some help. I certainly have not looked back since delving into this. Cheers Dave
Could you build another one of those loading boxes and sell it to me please? Or is it easy to build for a diy starter? A yery elegant solution.....
That is very similar to the system Keith Herron uses on his newest phono preamps: http://www.herronaudio.com/vtph2specs.html ...only he actually provides a socket on the back of the preamp where you just plug in the resistor mounted in an RCA jack. You will note that his preamp allows this for the MC input only.
That's a great idea. I run my Benz Micro Ace HOMC cart at 2k ohms and my Grado gold at 23.5k ohms. Both sound better than at the stock 47k ohms. I did mine internally. You can quickly work out what resistance you need here http://www.1728.com/resistrs.htm.
I have to chime in here to support Davey W's efforts He was kind enough to offer advice & the splitter to me when I was having problems with my SAS on a Shure 95ED. In my case my Yamaha CA600 offers 30 50 & 100 loading & I was disappointed in the tonality I was getting off the SAS. It was thinner & more clinical sounding & altogether less enjoyable than the original nude stylus I had. In fact I was of the opinion I'd been sent a dud stylus. The Y splitter with suitable plugs dropped the load to 45 & 41k Ohm & this has altered the SAS character & made it much more acceptable for my ears. I find that 45 load is generally the best but it does depend on the recording (& I suppose my mood) as I also like the 41 load on occasion. The Y splitter is well worth experimenting with & has given me my smile back. It did occur to me that variable load adjustment would also be useful but for the moment I'm happy listening to what I've got. Thanks Dave.
Ssshhhh! RED - Everyone will want some A friend in need 'n' all that..... Just glad I could help out. What you described to me re. your SAS reminded me of other carts I'd experienced with similar traits and corrected with loading adjustment. Thanks too, for the other responses. Cheers Dave
I put similar loading jacks on a tube pre I built in the early '80s. Still trying to decide whether to rebuild that thing again or just part it out, tube pre's tend to be a PITA due to the inconsistent and transitory nature of the active devices incorporated not to mention the cost.
I see that its also on the Blue Circle Fon Lo Thingee on another thread The Y splitters are inexpensive however & could even help avoid (or at least delay) the necessity to upgrade stylus, carts, or amps
That loading box really is neat to look at, Davey. Reminds me of my old 8 bit audio grabber for the Commodore Amiga, intergrated into a cigar box... Greetings from Munich! Manfred / lini P.S.: Btw, just as a short interims message, thanks for your nice email! Didn't really find the time to write a proper reply mail yet, though - as I had quite a busy week...
Last time I looked they only had capacitance loading kits. If you want the option of loading any value you want, directly into plugs or sockets, change the preamp load resistors to a very high value like 1Meg. Then you can load resistors of whatever value you want without having to calculate the parallel resistance. So if you want 62K for an M97 or 32K for a 440, just use that value resistor. I prefer solid body brass and teflon for Y adaptors, but I don't know if it really matters. The quality of the resistor does matter. The better your phono stage the more it matters. Resistors should be matched or get 1% or better to start out with. I like IRC RC55 series .1% metal film, 1/4 watt. You can get them at Mouser.com. They're around $1 ea. You don't have to match at that tolerance so you can get a bunch of different values to experiment. They seem clean and neutral without any sound of their own. Some resistors change value with temperature and some seem to sound fuzzy or woolly. I tried some carbon ones and they seemed sweet at first, but after awhile it sounded like my needle was dirty, but it wasn't. I didn't think it would make that much difference, but it seems to. neo
G'day all, yes I can certainly recommend good quality 'metal film' resistors for all audio circuit applications, especially in moderate to high 'impedance' applications. Carbon based resistors can exhibit very high levels of thermal noise. Some years ago I recall reading about noise in typical low noise audio preamplifier circuit applications and the potential high electrical noise produced by carbon based resistors was singled out for particular mention. Regards, Felix aka catman.
Hi Felix........I think carbon resitors can add thermal noise in series. But these are parrallel.....which reduces thermal(s). I have some of DavyW's splitters. They certainly don't add any noise to the system. to another who asked about the DB Systems splitters......yes they make them in both cap and resistance. Although I'm a big fan of David Hadaway and DB Systems products, my "DaveyW" plugs are prettier.
G'day mate, I wish that I still had that article, as it was really condemning of carbon resistors and thermal noise in the general sense. An example from personal experience. Many years ago I had a well regarded integrated stereo audio amplifier with an in built 'plug in' phono preamp module. One day I had a close look at the phono preamp module, and noted with a shock that there were only two metal film resistors on the whole circuit board, and they were the 47 k input loading resistors! It was obviously considered uneconomic to use metal film resistors throughout, and I often wonder how much quieter that phono stage might have been if they did. As I recall, it got a little 'hissy' as the volume was raised. :scratch2: Regards, Felix aka catman.
Hi Guys And thanks for the further responses. OK so if you do want to take this approach to the max then what Neo proposes is the way to go. Replace the MM stage loading resistor with something big and parallel load everything from there. I've done this on a spare MM stage - I actually went for a 100k ohm resistance. I've yet to find any cart (that's not a dud) that needs more than this. In my case I did'nt have the correct kit to de-solder and extract the required resistors. I resorted to snipping out the existing resistor bodies, leaving the wires proud and carefully soldered the 100k items directly onto these. Worked a treat and I use this MM stage for any carts that I believe require a higher load than 47k. I've not come across too many though. As Felix know's the M97x is one and I've preferred Empires tweaked up a little, but on the whole it's carts with a slightly bright and thin character I've persoanlly wanted to address, dictating a reduced loading. I possibly should have mentioned in my opening post that there are some example sound clips in my Cartridge Review Webpage of a couple of carts at various loadings. The best one is the Denon DL 160 where I've posted up a single track at a whole range of loadings. There's also a 1k/47k comparison with the DV 20XH. Here's the direct link to the Denon DL-160 Loading Clips Cheers Dave
I've been listening almost exclusively to a Denon DL-160 loaded at 4k for the past few weeks, using DaveyW's parallel resistive loading method. What sounded bright and thin at 47k is now lush and warm, with wonderfully bouncy musicality. It still retains all of the usual DL-160 strengths, especially the deep, wide soundstage. My DL-160, and my opinion of it, has been completely and substantially transformed!
For klutzes like me with no soldering skills, the DB Systems resistive loading kit is still available. I have one, and it works great. With a 47 KOhm phono stage, you can achieve loads of 9.9, 19.9, 49.9, 99.8 and 199.2 ohms (if my math is correct; the plugs themselves are rated at 10, 20, 50, 100 and 200 ohms). -Bob http://store.acousticsounds.com/d/6...no_Resistor_Loading_Kit-Turntable_Accessories
Actually the DB Systems kit referred to is w/o the "k" on the values. Geared more for low output mc loading. It does give you an empty set of plugs you could source your own resistors and use with.
