Hi guys ,
I want to upgrade the coupling caps in a ST35 amp I built a few years back.
I got these NOS Vitamin Q on ebay and ordered some Auricaps as well. Before I start messing with my amp I would like to listen to your opinions about if the Vitamin Q's are even worth trying or should I just wait for the Auricaps to arrive.
These are the Vitamin Q
They measure fine (.1uF), I just wonder if these NOS usually go bad or I can trust them... I just want to mess with the amp as little as posible...
Thanks in advance for your help.
Cheers
vitamin Q ( PIO caps) are for guitar
Another nice Polypropylene! but its in oil so probably too posh for me.
Not posh for old people who have it in drawers and boxes.
From working days, of course
Polypropylene is the way to go. That said, there are some decent polyester caps to be had too. There is zero point in going for anything expensive for coupling purposes.
If you are unhappy with the sound from your amp then it won't get better by using boutique $$$$ exotic "ear wax" or "snake oil" coupling caps.
I use ero MKT1813 and MKP1839 and MKP1845 - these are all very nice and do the job. Also wima's can be good. I know MKT1813's are polyester, but they perform very well.
If I'm feeling really flush with cash then I might spend as much as $1 on a coupling cap. The MKP1845's are a nice shade of blue, in case I think someone might look in there.
If I'm feeling like nobody will ever look in there, then I might stick in a cheap polyester cap. Good luck hearing any difference!
btw - here are some numbers for dissipation factor (DF) I recently found online, smaller is better:
Polyester (PETP) .5%
Polycarbonate .05%
Polyphenylene sulfide (PPS) .05%
Polystyrene .05-.02%
Polypropylene .025-.01%
Teflon (PTFE) .025-.01%
What speakers are you using that mask the music so all caps sound the same?
There might be a logical answer to that question. I *think*...
In an amp that makes use of negative feedback, I don't think you'll hear the differences between coupling capacitors unless there are really gross differences, such as using paper in oil capacitors instead of modern MKP types.
If an amp does not use negative feedback, you'll probably hear the differences between parts types more easily. Or at least that's what I've found. Of course, if using a (so called) zero-NFB amp, you'll also be hearing more harmonics generated in the amp, so you'll get more intermodulation products during playback. Picking a capacitor that mates well with the harmonic signature of the zero-NFB amp you're using may take some 'taste testing.'
All opinion there, from my own experiences. No facts to back that up. Take it for what it's worth.
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In an amp that makes use of negative feedback, I don't think you'll hear the differences between coupling capacitors unless there are really gross differences, such as using paper in oil capacitors instead of modern MKP types.
If an amp does not use negative feedback, you'll probably hear the differences between parts types more easily. Or at least that's what I've found. Of course, if using a (so called) zero-NFB amp, you'll also be hearing more harmonics generated in the amp, so you'll get more intermodulation products during playback. Picking a capacitor that mates well with the harmonic signature of the zero-NFB amp you're using may take some 'taste testing.'
All opinion there, from my own experiences. No facts to back that up. Take it for what it's worth.
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Problem from EE101:
Calculate the difference in ESR between 0.1uF of both types, and then the effect of embedding them between a 10k ohm source and 100k ohm load. Is there a difference in the way they sound? Justify your answer.
The answer may be different between say, 6.8uF caps working against a 0.3 ohm source and a load consisting of an 8 ohm tweeter in parallel with 800uH of inductance.
Problem Solving EE101.1:
Simplifying the complex problem into a simple solutions.
1. Remove the Crossover components
2. Look for Full Range Driver that is relative flat from 20Hz-20KHz that sounds neutral with sensitivity of 90dB or above
3. Build Multi-driver OB Line Array to obtain 100dB or above overall sensitivity
4. Enjoy!
Yes. And even a 5% difference is not likely to be audible in a coupling cap (e.g., 0.22uF vs. 0.23uF with a 470k resistor load).
I also meant to say that the differences are extremely subtle, and are only really noticeable if you go for truly gross differences, such as replacing a perfectly good MKP with a Vitamin Q (paper in oil), which has very different performance. If I switched a WIMA MKP-10 for an 'audiophile grade' MKP and then went to take a bathroom break, and while I was away my buddy swapped the WIMA MKP-10 back in, I'm certain he could fool me into thinking the 'audiophile grade' caps were in there and how wonderful everything sounds because of them. But I think anyone can hear the difference when a paper/oil cap is in an important spot in the circuit.
Morgan Jones posited an idea of why film-and-foil caps *might* sound a little different than metalized film of the same dielectric material. That is, there may be a type of partition noise caused by the microscopically rough texture of the sputtered electrode on a metalized film compared to the smooth texture of the foil electrode material in film-and-foil constuction. He compared it to the etching of metal film resistors to fine tune the resistance value. It sounds plausible to me, but I'm not trained in these things.
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That's an excellent cap if you want to experiment for yourself with the effect of parts on sound. It's long been highly rated, well made and the leads are stranded, making them less prone to mechanical issues as long as the iron doesn't hit the body. Old PIO caps require special care.
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Film and foil have lower ESR than metalized film due to both the film being really thin and the surface roughness of the metalized caps. Which cause the ESR to increase with frequency due to the skin effect. But film and foil have more inductance, which can be more important (less negligible) in a low impedance circuit. It's thicker, it takes more winding, period. In a speaker crossover, pick your poison. Whichever results in the proper loaded filter Q and corner frequency is the right one. You could design around most anything (even electrolytic), but swap it with something else at your own risk. In a high impedance circuit a 5000% increase in ESR or ESL might not even be measurable.
PIO caps have their place too - in circuits where even a low DF cap could overheat. The oil and metal can act as a heat sink. I can't think of any place in audio where that is a requirement. Even in an output filter in a mulit-kilowatt class D amp, MKPs don't overheat or blow up. Tubes run hot, but not THAT hot, so a regular cap works just fine.
WIMA MKPs are likely to be better than boutique caps, because they make them to be capacitors, used in many applications where they need to work as capacitors, not just to separate audiophiles from piles of money.
PIO caps have their place too - in circuits where even a low DF cap could overheat. The oil and metal can act as a heat sink. I can't think of any place in audio where that is a requirement. Even in an output filter in a mulit-kilowatt class D amp, MKPs don't overheat or blow up. Tubes run hot, but not THAT hot, so a regular cap works just fine.
WIMA MKPs are likely to be better than boutique caps, because they make them to be capacitors, used in many applications where they need to work as capacitors, not just to separate audiophiles from piles of money.
Thanks for your answer. That's exactly what I want to do, experiment. Like I said I don't have any problem with the amp as it is right now, it sounds great. I just want to know if these caps will improve the sound in some way... It's going to require some "surgery" to remove the old ones and put these in, but it can be done...
What kind of special care do PIO caps require?... just curious
DF96 hits the main one, old caps should be carefully full voltage and leak tested to confirm they still operate properly. In the case of metal bodies PIOs, my sample have easily measured capacitance between their leads and the body. Fixing the cap body to a ground plane or chassis makes that leakage capacitance part of the circuit, potentially causing unexpected behaviour. Your Qs are a special case since the body is a lead. Opinions on this differ (vehemently) but personally I try to avoid passing audio through hunks of steel.
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You are wrong about the construction of the vitaminQ. The body is made of brass! Yes, brass. I have converted many of the grounded body type of caps to leaded just by soldering a high quality solid 20 awg wire. You just need to wire brush the end, clean with acetone. Put the cap in a vise and put a spiral in the lead wire so that it will nicely sit on the cap and use some solder rosin and a hot iron to solder. It is best to insulate with some heat shrink. I am not sure about orientation as I did not try both ways to find out if the B+ on the metal body sounds better than the signal on the brass body.
I have found after testing 100s of PIO caps with ceramic end seals, most of them ex-military, that if they are NOS they all test perfectly and have all pass the high voltage test on my Heathkit capacitor checker. I always use them except when I go for an "all out" build where I will use a Teflon cap.
Sound wise they always sound "good" but whether you prefer that sound to another type of sound is a personal preference. To me if one likes the "Hifi" type of sound you will like the plastic insulated capacitor. If one likes a softer more natural sound the PIO cap fits the bill.
So, whoever, the OP is, don't put away those pio caps, you should really give them a try! regards, 808
I've tried out a bunch of different cap types, and I personally don't get what all this talk about roundness and such is with these PIOs.
Granted, I've only used unused PIOs. Still, I think it mostly depends on the circuit used. PIOs were most used in circuits that sound slow and round, so people associate that sound with the caps.
My current work horse amp has very good transient response, and uses PIO caps for coupling. Nothing slow or round about them at all, in my opinion.
Granted, I've only used unused PIOs. Still, I think it mostly depends on the circuit used. PIOs were most used in circuits that sound slow and round, so people associate that sound with the caps.
My current work horse amp has very good transient response, and uses PIO caps for coupling. Nothing slow or round about them at all, in my opinion.
That's interesting. I did my cap swap test on a simple 5687 line preamp with gain. I tried a couple of 1uF Vitamin Q's, some vintage Gudeman 0.47uF PIO paralleled up to make 0.94uF, Axon 1.5uF polypropylene film/foil, WIMA MKP-10 1uF, and generic yellow 1uF 400V MKT film caps. I think I even tried a pair of WIMA MKC 1uF caps.
The plastic film caps all sounded very similar. The exception was the Axon film/foil, which I liked the best out of the bunch.
The Vitamin Q's sounded very good. I thought I heard a smoothness, sort of 'round' compared to the metalized poly film caps, but not 'dull.' But the effect was subtle, and to me they're not that different from the film caps, overall. The Gudeman PIO caps were a completely different story. They gave a real parody of a 'PIO sound.' They sounded kind of 'dead' or 'blunt.' Difficult to describe, but it was almost like everything was overly damped, like a dull sounding tweeter. Strange. They'd be good in a guitar amp, I think.
In another build where I needed 2.2uF, I put in ERO MKP caps. At first I thought they might sound a bit 'harsh' but after a few days I thought they sounded just fine. Really good. Later, I needed to reduce the value to 0.22uF. I had some ERO metalized polyester caps handy, so I put them in. Again I thought I heard a slightly rougher 'edge' to the sound, but you know how it goes -- I left them in for a few days and either I or the caps got 'broken in.'
In the end, I think all this cap swapping is a quick road to insanity. In simple triode circuits, getting the operating points just where you like them makes a bigger difference than which cap you use -- as long as you're using good quality parts (WIMA MKP being one example).
I'd like to try WIMA FKP sometime...
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