So, is it necessary to use the 630V Cast in electronics if the voltage will only be ~150V or so. I'm thinking that in a preamp one might be able to use the less expensive and more compact 200V CAST. Is that off base?
Capacitor log Mundorf Silver in Oil
I wished I could find a log with information on caps. I have found many saying tremendous improvement etc. but not a detailed account of what the changes have been. I have had the same speakers for many years so am very familiar with them. (25+ years) The speakers are a set of Klipsch Lascala's. They have Alnico magnets in the mids and ceramic woofers and tweeters. The front end is Linn LP12 and Linn pre amp and amp. The speaker wire is 12 gauge and new wire.
I LOVE these speakers around 1 year ago they started to sound like garbage. As many have said they are VERY sensitive to the components before them. They are also showing what I think is the effect of worn out caps.
There are many out here on these boards I know of that are using the Klipsch (heritage) with cheaper Japanese electronics because the speakers are cheap! (for what they can do) One thing I would recommend is give these speakers the best quality musical sources you can afford. There is a LOT to get out of these speakers. My other speakers are Linn speakers at around 4k new with Linn tri-wire (I think about 1k for that) and the Klipsch DESTROY them in my mind. If you like "live feel" there is nothing like them. In fact it shocks me how little speakers have improved in 30 years (or 60 years in the Khorns instance)
In fact I question Linn's theory (that they have proved many times) that the source is the most important in the Hi-Fi chain. Linn's theory is top notch source with lessor rest of gear including speakers trumps expensive speakers with lessor source. I think is right if all things are equal but Klipsch heritage are NOT equal! They make a sound and feel that most either LOVE or hate. (I am in the LOVE camp and other speakers are boring to me)
So here goes and I hope this helps guys looking at caps in the future. Keep in mind Klipsch (heritage Khorns Belle's and Lascala's especially) are likely to show the effects of crossover changes more then most.
1 The caps are 30 years old and
2 the speakers being horn driven make changes 10x times more apparent.
Someone once told me find speakers and components you like THEN start to tweak if needed. Don't tweak something you not in love with. Makes sense to me.
So sound
Record is Let it Be (Beatles)
The voices are hard almost sounds like a worn out stylus.
Treble is very hard. I Me Mine has hard sounding guitars. Symbals sound awful. Everything has a digital vs. analog comparison x50! Paul's voice not as bad as John's and George's. Voices will crack.
different lp
Trumpets sound awful. Tambourine terrible. Bass is not great seems shy (compared to normal) but the bad caps draw soooooo much attention to the broken up mid range and hard highs that are not bright if anything it seems the highs are not working up to snuff. I have went many times to speaker to make sure tweeters are even working.
All in all they sound like crap except these Klipsch have such fantastic dynamics that even when not right they are exciting!
Makes me wonder about the people who do not like them if they are hearing worn out caps and cheap electronics? Then I can see why they do not like them! If I did not know better from 25+ years of ownership that would make sense.
For the new crossover I have chosen Mundorf Silver in Oil from what I have read and can afford. I want a warm not overly detailed sound as Klipsch already has lots of detail and does not need to be "livened up" they need lush smooth sounding caps. Hope I have made the right choice?
When the crossover is in I will do a initial impression on same lp's. Right now it goes from really bad (on what may be worn vinyl) to not as bad but NOT great on great vinyl. (I know the quality of the vinyl because tested on other speakers Linn)
The new caps are Mundorf Silver in Oil and new copper foil inductors are coming. I will at the same time be rewiring the speakers to 12 guage from the lamp cord that PWK put in. PWK was a master at getting very good sound often with crap by today's standards components.
The choice of speakers would be a toss up now depending on what I am listening to. Klipsch vastly more dynamic but if the breaking up of the sound becomes to much to effect enjoyment the Linn would be a better choice on that Lp. If I could I would switch a button back and forth between speakers depending on song and how bad the break-up sound was bothering me.
I LOVE these speakers around 1 year ago they started to sound like garbage. As many have said they are VERY sensitive to the components before them. They are also showing what I think is the effect of worn out caps.
There are many out here on these boards I know of that are using the Klipsch (heritage) with cheaper Japanese electronics because the speakers are cheap! (for what they can do) One thing I would recommend is give these speakers the best quality musical sources you can afford. There is a LOT to get out of these speakers. My other speakers are Linn speakers at around 4k new with Linn tri-wire (I think about 1k for that) and the Klipsch DESTROY them in my mind. If you like "live feel" there is nothing like them. In fact it shocks me how little speakers have improved in 30 years (or 60 years in the Khorns instance)
In fact I question Linn's theory (that they have proved many times) that the source is the most important in the Hi-Fi chain. Linn's theory is top notch source with lessor rest of gear including speakers trumps expensive speakers with lessor source. I think is right if all things are equal but Klipsch heritage are NOT equal! They make a sound and feel that most either LOVE or hate. (I am in the LOVE camp and other speakers are boring to me)
So here goes and I hope this helps guys looking at caps in the future. Keep in mind Klipsch (heritage Khorns Belle's and Lascala's especially) are likely to show the effects of crossover changes more then most.
1 The caps are 30 years old and
2 the speakers being horn driven make changes 10x times more apparent.
Someone once told me find speakers and components you like THEN start to tweak if needed. Don't tweak something you not in love with. Makes sense to me.
So sound
Record is Let it Be (Beatles)
The voices are hard almost sounds like a worn out stylus.
Treble is very hard. I Me Mine has hard sounding guitars. Symbals sound awful. Everything has a digital vs. analog comparison x50! Paul's voice not as bad as John's and George's. Voices will crack.
different lp
Trumpets sound awful. Tambourine terrible. Bass is not great seems shy (compared to normal) but the bad caps draw soooooo much attention to the broken up mid range and hard highs that are not bright if anything it seems the highs are not working up to snuff. I have went many times to speaker to make sure tweeters are even working.
All in all they sound like crap except these Klipsch have such fantastic dynamics that even when not right they are exciting!
Makes me wonder about the people who do not like them if they are hearing worn out caps and cheap electronics? Then I can see why they do not like them! If I did not know better from 25+ years of ownership that would make sense.
For the new crossover I have chosen Mundorf Silver in Oil from what I have read and can afford. I want a warm not overly detailed sound as Klipsch already has lots of detail and does not need to be "livened up" they need lush smooth sounding caps. Hope I have made the right choice?
When the crossover is in I will do a initial impression on same lp's. Right now it goes from really bad (on what may be worn vinyl) to not as bad but NOT great on great vinyl. (I know the quality of the vinyl because tested on other speakers Linn)
The new caps are Mundorf Silver in Oil and new copper foil inductors are coming. I will at the same time be rewiring the speakers to 12 guage from the lamp cord that PWK put in. PWK was a master at getting very good sound often with crap by today's standards components.
The choice of speakers would be a toss up now depending on what I am listening to. Klipsch vastly more dynamic but if the breaking up of the sound becomes to much to effect enjoyment the Linn would be a better choice on that Lp. If I could I would switch a button back and forth between speakers depending on song and how bad the break-up sound was bothering me.
Showing 50 responses by ait
How about this: I have been reading this thread for weeks (or is it months)and have had the same thought the entire time - the BEST cap is no cap. Volleyguy, if you are this sensitive to caps, why not go to a single-driver system, or a multidriver, multiamp, electronic crossover system? I myself never heard real music in my home until I heard a high-end system with no passive crossover at all, with silver wire all the way to the voice coil. Even if you don't like the no-crossover sound, compared to the price of a system full of Duelunds, you could put together an impressive active x-over system. |
Volley, the idea of oil-soaked cotton resting on my hardwood floors or touching the exterior of my crossover/speaker cabinets just didn't sound too good to me, and I had visions of the oil getting on everything as I hooked the crossovers up to the speakers. Maybe that doesn't happen, but that's what bothered me. I'm sure the wire sounds great. |
I have not heard the CAST or VSF caps, but this whole "natural" vs plastic thing is a bit much for me. Are the Duelunds certified organic, too? It seems to me that synthetic materials can be engineered to provide better, more consistent electrical properties than "natural" materials, and will certainly be more consistent from batch to batch. Take "spider silk" for example, which I believe Duelund uses - how consistent can that be? Doesn't it depend on what type of spider it comes from, what they eat, whether they are healthy, the weather, the air they breathe, the stage of their lifecycle they are in, etc.? Does Duelund have a spider farm where they produce the silk under carefully controlled conditions (maybe they do - which could help explain the cost of these things!)? Mother nature is the consummate engineer, but she designs with an eye toward survival and reproduction, not optimum electrical and acoustical properties. Somehow I feel an anti-technology bias creeping in here; "natural" is a hot marketing category these days, and I wonder how much of the supposed superiority actually exists over synthetic materials, be they foods, medicines, clothes or capacitors? |
My parts (output transformer) will be here shortly to fix the one really quiet Fisher I have and then I am have the caps done and from what I have found out, plastic the coupling caps will not be. I am likely to order V Cap Teflon's. Ummmm....Volley? Teflon IS plastic. In fact, it's about the most plastic plastic that plastic can be. Or maybe Chris V has a new "natural" source of teflon - perhaps the noted teflon springs of the planet Cestus III? |
I'm rebuilding a set of Infinity RSIIb speakers with external crossovers and I'm using Cardas Copper Litz wire (Teflon insulation), 17.5 gauge on the tweeters, 15.5 gauge on the mids, and 11.5 gauge on the woofers. There are a total of 8 drivers, ten inductors, nine caps and four resistors per speaker. A little harder to work with but Litz wire is said to provide better transfer of high frequencies, and since every strand is individually coated with lacquer, it will never corrode. Will be a big step up over the original wire, which is actually Monster cable that had started to turn green from oxidation (it says "Wired with Monster Cable" right on the speaker). I thought about the Duelund wire but the oiled cotton insulation turned me off - it sounds a bit messy to me, especially since the wire will be outside the speakers due to my external crossover. There are some who feel that there are maximum gauges for each level of driver, i.e. don't use too big of a gauge on a tweeter or you will lose some of the detail. My speaker cables are Zu Ibis, pricey but very, very detailed. |
Be careful with the placement of huge gauge air core inductors - they throw off very large magnetic fields! I'm experimenting with some 12 gauge Northcreek inductors for my speakers, and they will actually cause music to play from a disconnected driver if it is passed with 2-3 inches of them, right through thin air! I can only imagine that the 8 and 10 gauge will produce even bigger fields than that. So be sure to orient the crossover components in ways that minimize these effects (axes at 90 deg angles, lots of space in between, etc.). There are placement diagrams on the internet to help with that. |
I am building outboard x-overs using the Northcreek inductors on the woofers and low mid, and Solen Heptalitz inductors on everything else (it is a 6-way design with 10 inductors, 9 capacitors, 5 resistors and three adjustment pots per speaker). Needless to say if I went Duelund for caps and inductors I'd be broke, so I'm using Mundorf Supreme caps and the above-mentioned inductors!! I might spring for some Duelund resistors, however. I did the driver induction experiment just to see how close I could get to the inductors before I heard interference - it was very surprising how much of a magnetic field they set up. If you put those inductors inside a speaker enclosure you'd better make sure they are far from the drivers. Also, inductors will interfere with each other (look up "inductor crosstalk"). The inductors need to be well separated in space if they are in the same plane (i.e. both lying flat), I found that the bigger inductors need ~8 inches between them in that sort of arrangement. If you place them with their axes at 90 degrees, you can get them closer - see the chart I linked below: http://techtalk.parts-express.com/showthread.php?p=1500176 Iron has a much higher magnetic permeability than air, and that causes the magnetic field of iron-core inductors to be contained in a much smaller space, so they can be placed closer together than air cores without interfering. Iron cores, however suffer from hysteresis distortion and can saturate at high power levels. I have not heard the Northcreeks in a finished speaker yet, only on the crossover prototype board with a driver wired into them - they sound good, but I won't know any more until I finish putting the speakers back together. |
I am not familiar with your crossover layout, but is it possible that the inductor is causing crosstalk with other components? Are there other inductors or coils near it? Is it directly next to the high-frequency section of the crossover? You may want to try moving the location and orientation of the inductor - if it is lying flat, try standing it on its side and turning it to point in different directions, and see if the noise decreases. |
One thing about shielding - although it decreases the radiated EMI, it also changes the inductance of the inductor being shielded, by as much as 20%. The magnetic field is where the energy storage occurs in an inductor, so messing with it will change the inductor's parameters. So either you adjust for the loss by buying a bigger inductor to start with, or you live with 20% lower inductance than spec. |
Tell him to use 4 separate new caps instead of the multi-section can if he can't find one. He can mount them under the chassis or in the old can if they fit (he'll need to clean out the old guts from the can for the latter). If they are mounted underneath, he can leave the old can in place for looks. Antique Electronics Supply has some new multi-section can caps; look there maybe you'll get lucky. If not, do the above. |
Low ESR = good High Ripple Current = good ASC caps are film caps; film caps are always preferable to electrolytics. And they are huge. I use Solens in the power supply of my Supratek preamp (replacing electrolytics) and they are definitely an improvement over the stock e-lytics. You need lots of room, however, to replace an electrolytic with a film, and I don't think your piece has that kind of room. |
By the way, the motor run caps (of which I believe your ASC is a variety) are not really oil caps. They are Polypropylene caps which are bathed in oil inside a metal can for heat dissipation purposes. If you shake the can you can hear the oil slosh around inside. The reason for that construction is that they are designed for applications on electric motors in industrial environments. |
I believe Ralph from Atmasphere was warning against using PIO caps in tube amps in another thread on Audiogon - his quote was: "Paper and Oil caps can develop electrical leakage over time that can damage other parts- this is something that most other dielectrics including Teflon don't tend to do!" I have heard various stories about the Mundorf SIO caps - some say they are metallized paper film in oil, other say they are polypropylene in oil. If they are truly paper, then I would hesitate to use them in that application. |
Well, I just took the plunge and ordered two Duelund 0.56uF 200V Cast Copper Foil caps for my Supratek Chenin tube preamp. I have extensively modded this preamp, moving from 6SN7 output tubes to 2C22, going from resistor/cap bias to diode bias with Cree SiC schottky diodes, and using a constant current source at 15mA on the plates of the 2C22. I've been running Mundorf Supreme caps on the output circuit and I think the sound is close to perfection as is, but I couldn't resist the urge to find out if there was more to be had. Let the waiting begin... |
From what I read, carbon composition resistors are the noisiest type - how does the Duelund resistor differ from an old carbon comp type, and why would this sound better than a bulk metal film? Is it because the graphite is not present as separate grains as in a carbon comp? I have used the Texas Components TX2575 metal Z-films in electronics and they are incredibly clear sounding, although only 0.6W in power handling; I'm thinking that paralleling a few of those into a higher wattage for use on tweeters should sound better than a carbon-based resistor, no? |
That's what I've heard about Duelunds, and I fully intend to try the Duelunds out. I was just asking a technical question of Duelund, I hope I didn't insult them. I'm just curious about how/why a carbon-based resistor can sound so good when carbon comps are known to be very noisy. Is it the monolithic nature of the carbon, i.e. no grain boundaries? |
I'm curious to hear your opinion of the Jensens, and I may want to move to them in the midrange of my Infinity speakers to build on the tonality of the CAST in the preamp. I am getting very addicted to the fuller midrange sound of the CAST as compared to the Mundorfs I had in there previously. I'm up to ~15 hours on the CAST, and they seem to be getting better bit by bit. CAST in the speaker midranges would be out of the question, as they are 23uF caps - I'd be looking for a new wife if I bought a pair of 23uF copper CAST caps! |
I received the CAST 0.56uF caps for my preamp and installed them last night, then spent about 4 hours listening. The main difference between the CAST and the Mundorf Supremes I was using is in tonal balance. The CAST has more rounded and fuller midrange, low midrange and bass than the Mundorf. The treble is about the same so far. I do feel that the Duelund sounds better due to the better tonal balance. Sax sounds more like sax, voices are especially nice. I'm using the 200VAC CAST, not the 630V "electronics version". They are smaller and just fit into the preamp - the larger 630V would not have fit without extensive modification. An added benefit is that they are also less expensive (but still close to $600 per pair). Both Duelund and PCX assure me that these can easily handle at least 200V DC, even though they are marked as 100VDC on the side of the caps; my preamp runs at 175V DC on the plates. |
I have just finished running the Supratek preamp for 4 straight days to get 100 hours break-in on the 200VAC Cu CAST caps. That was also a nice check on my other modifications: the constant current source on the output tubes, the new wiring and tube sockets, the Solen PP caps in the power supply, the bypassing of the mute switch, whether the 200VAC Duelunds can take 175VDC over long periods of time, etc. It passed the torture test with flying colors - no problems whatsoever. Now to the sound. I have to say I have never heard this preamp sound so balanced and natural, with excellent detail. The Mundorf Supremes I had been using previously sounded nice, but after hearing the Duelunds I realize that the Mundorfs over-emphasized the high frequencies at the expense of the lows and low mids. The CAST caps are wonderfully balanced, and I can hear all the music from low bass to high treble very clearly. I highly recommend the use of Duelund CAST caps in a preamp application. Since the preamp gets the full audio signal, it is critical that it amplifies and passes the signal on to the amp with as much neutrality and clarity as possible - the Duelunds do that superbly. The preamp may actually be the best budget application for Duelunds, as coupling caps are usually small values and preamp voltages are often in the range where the 200VAC "speaker" CAST caps can be safely used. |
Yes, those were the regular Supremes, which I considered a big improvement over the stock Auricaps. I didn't notice the high-frequency emphasis until after I heard the Duelunds in there; they had a much fuller sound, especially in the lower registers. Tonality is where the CAST caps excel most, in my opinion. Everything just sounds more real and more natural with them in the preamp. The Mundorfs gave a tiny bit more shimmer to a cymbal, but had a small amount of HF glare that the Duelunds don't have; the Duelunds are thus easier to listen to for extended periods - the Mundorfs sometimes gave me ear fatigue after extended listening; so far I have not experienced that with the Duelunds. |
Here's a little trick I found for improving the sound of the Mundorf Supremes in an equalizer I'm using. I love the tonal balance of the Duelunds in my preamp, and I wanted to see what would happen when I put the low-frequency equalizer that comes with my Infinity RSIIb speakers between the preamp and the amps. The equalizer came with the RSIIbs to boost the very low frequencies and help the transition from the two 10" woofers to the planar EMIM midranges. I had rebuilt the equalizer with premium parts including Mundorf Supreme coupling caps. When I put it back in line with the preamp (with Duelunds), I noticed that it added a little high-frequency glare and graininess to the sound that I hadn't noticed before, and removed some of the gorgeous tonality of the Duelunds. I have remedied harshness problems with tweeters in some other speakers by adding a .01uF Audiocap Theta tin foil and PP film bypass cap, so I tried it with the Supremes, and low and behold it really helped greatly! The tonality is not exactly equal to the preamp (with Duelunds) alone, but it is a lot closer, with a bit more treble extension than the Duelunds alone (I think I like it, actually). I later noticed that Tony Gee had done this to Mundorf Supremes using Vishay MKP caps as the bypass, with similar results, so I figure that it's not my imagination. The Thetas are only $3-4 each at Parts Express, so it's a cheap tweak you may want to try if you want to improve the sound of Mundorf Supremes. |
If you're interested in why small value bypass caps work, check out this link. Check out the scope traces that clearly show how bypassing (and/or DC biasing - but that's another story) reduces hysteresis (straight line = good, anything else = bad). Even nasty tantalum and aluminum electrolytic caps can be made to look presentable. Notice also how the paper-in-oil caps improve; might the already wonderful Duelunds get even better with a bypass? Hysteresis and Bypass Caps |
I just finished listening for 4 hours or so, a large part of it Tom Waits. I really think I like the CAST in the preamp and Supreme/Audiocap Theta in the equalizer better than the CAST in the preamp alone. Tom's unmistakeable voice just has a little more life to it, maybe it is from the Mundorf/Audiocap or maybe from the active components in the equalizer, but the equalizer was a negative influence until I added the bypass caps to the Supremes. Based on these results, I think I'll be adding Theta bypasses to the Supremes in my Infinity crossovers as well. |
Well, Duelund, I'd like to skip the equalizer, but the speakers were designed to use it, so I'm working to make the equalizer the best it can be. The output caps are 220uF aluminum electrolytic bypassed with 3.3uF metallized PP, bypassed with 0.01uF PP film and tin foil. They actually sound pretty good now that I put the .01uF bypass on there. |
Actually, I'm now running the CAST in my preamp and a combination of Mundorf Supreme and Supreme Silver/oil in the following low frequency equalizer/buffer. I find that when I connect the preamp directly I get more of the CAST sound (natural, quiet, tonally accurate) with bass that is slightly overstated. When I put the EQ/buffer in line between the preamp and amp, the Mundorfs give me more spaciality and 3D soundstage together with the Duelund tonality, and reduce the bass just enough that it is no longer overpowering. I experimented a bit and found that the use of ~10uF of Supreme together with .33uF of silver/oil gives me the best combination of detail and smoothness in the EQ application. So I'm finding that I like the Duelund/Mundorf combination best at this time. YMMV |
No way I can fit a VSF into the EQ/buffer amp. It is very small and the 10uF of Mundorfs only fit because I am using a cascade of 6.8uF, 3.3uF and 0.33uF (see picture in link). I need 10uF to reach a low frequency -3dB point of 2Hz with my amp. RSIIb LF Equalizer I have tried eliminating the EQ altogether, but it is needed for the RSIIb speakers for low bass extension and integration between the cone woofers and midrange panels. I have done extensive mods to the EQ, so it is now very transparent to all but the low frequencies it is meant to affect. To my taste, the CAST/Mundorf combo is very nice - the bit of added splash on top appeals to me. |
"Of course digital can not generate this "treble air"." Sure it can. Try upsampling. My Zero One Mercury CD/HD player has selectable oversampling and upsampling from 44kHz to 196KHz. I find that the oversampling modes (even multiples of 44KHz such as 176KHz) sound much cleaner and more natural then the upsampling modes (such as 196KHz), which tend to introduce the "treble air" you speak of. At first it sounds like an enhancement, but soon it starts grating on my nerves. I can also select the high-frequency filter to be the typical brickwall or several more gentle slopes; I find the HQ2 setting the best (between brickwall and very shallow slope) - too shallow a slope and you get unwanted high-frequency stuff introduced to the components that makes it sound markedly worse, too steep and you get noticable ringing on HF notes. Finally, I can also choose the dither setting used to reduce noise - in this case I prefer no dither at all. |
I have just completed re-wiring my Infinity RSIIb speakers with Cardas Copper Litz wire, 11.5 gauge on the woofers, 15.5 gauge on the mids, and 17.5 gauge on the tweeters. Litz is very interesting stuff as each strand of the dozens in the bundle is individually insulated. This structure results in a lower AC impedance as frequency rises (a higher Q value). The re-wiring was part of a larger project to build external crossovers for these speakers, using Mundorf caps and Northcreek and Solen heptalitz inductors. Litz wire can be difficult to work with, as the insulation must be removed from each strand before tinning/soldering, but I have found that a Dremel tool with a stainless steel brush makes the job very easy. The results of my project are stunning. Be advised that I also built complete external crossovers, so of course that will have had a very large effect on the sound, but the litz wire I used to wire up the crossovers to the speakers certainly also contributed. The sound is crystal clear and very detailed, and a big improvement over stock. So there is another wiring option for you. |
I believe it is the commingled strands you object to, not the copper wire itself. Try copper litz wire from Cardas, with each strand individually insulated - much better than stranded standard copper, and much cheaper than silver. I use silver wire inside my electronics but I use copper litz in my speakers - 11.5 ga for woofers, 15.5 ga for mids, and 17.5 ga for tweeters. |
The Cardas Copper Litz with teflon insulation is between $1-3 per foot at Handmade Electronics, depending on the gauge. It is a bit harder to work with as the insulation must be stripped from the ends on all strands - I have found that a stainless steel wire brush on a Dremel works very well. For silver wire I've been using DH Labs Revelation teflon coated wire, which is more expensve at ~$9 per foot at PCX. |
Tweak, I would think that a magnetic material such as steel would not be ideal for placing around crossover components, especially air-core inductors. That would definitely interact with the magnetic fields produced by the inductors, in unpredictable and probably deleterious ways. Non-magnetics would be preferable IMO. |
Undertow, Texas Components is a manufacturer in Texas which makes their own resistors using the Vishay Z-foil (part # TX2575). I just ordered 4 of them yesterday. Just call them and order whatever you want (1 part minimum!), and they will make any custom value you need for no extra charge. http://www.texascomponents.com/ . |
Of course you can always convert the amp to a parafeed-type configuation with a CCS or choke on the plate instead of a resistor and eliminate the PS caps from the signal path completely. That's what I did with my preamp and the results were astonishing. Horizontal load lines are a wonderful thing. Might be more mods than you are willing to do, however. |
Yes, in most designs the last PS cap is in the signal path, because the signal path is not isolated from the PS current path. The PS caps are still there in a parafeed type design, but they are isolated from the signal path by the circuit design. For example, a constant current source (CCS) supplying the plate voltage will have an almost infinite AC impedance, meaning that the signal can't get through it (high power supply isolation in other words) - a resistor does not even come close to that, and so a good portion of the signal will pass back through it. What you end up with in the parafeed design is two current loops, one for the signal and another for the power supply, instead of having them commingled. This is a bit of a complex subject, and in order to understand it you will need to read up on CCS theory, plate chokes, parafeed topology, and general amplifier circuit design (as I did). The DIYAudio tube forum is a good place to start. |
A cheap experiment might be to just pot the stock inductors in some type of ABS container using epoxy potting compound. That will eliminate the noise from vibrating loosely-wound coils and give some of the effect of a CAST-type inductor while keeping the same inductance and DCR value. If you're just going to toss them then it might be an interesting experiment anyway. |
Check out Solen Heptalitz inductors. I use them on the parts of my RSIIb crossovers that handle above 1000Hz, where their higher Q versus solid wire inductors comes into play. They sound spectacular for high mids and treble. They also have somewhat higher resistance for the same overall gauge versus solid wires, which helps to match the stock inductors better in some cases. I use Northcreek 12 gauge below 1000Hz in my speakers. |
There are a lot of manufacturers, I've used MG Chemicals and GC Electronics epoxies in the past. I'd go with a clear epoxy to avoid any possible ill effects from the filling pigments. I don't see an issue with putting a tube in the center to reduce the volume. Yes, ABS plastic. Do a search on the net, there are many suppliers of ABS containers, in an almost infinite array of shapes and sizes, with and without lids. You need to figure out the size you need based on the components you want to pot. If you have a source of vacuum like a vacuum pump and a vacuum container or oven you could pot the item and then draw down a vacuum to assist with the penetration and air bubble removal. Gentle heating can also help with air bubble removal, although it shortens the available working time (pot life). There are even automated industrial vacuum potting systems that maintain the resins and target objects under vacuum during the entire process, but that's only useful if you have access to something like that. You may want to practice on one of your smaller reject coils first - you wouldn't want to mess up a nice Northcreek. |