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In Reply to: Re: Fisher SA-16 posted by el_37 on February 27, 2007 at 16:03:47:
The disc caps in the SA-16, Eico HF-14 and Fisher 30a are considered by some to be the reason why they sound so good.Power supply caps and cathode resistors are another story- they need to be replaced for safe long term operation.
Great sounding amp BTW !
Best,
Ross
Follow Ups:
CERAMIC DISC CAPS BEING THE "SECRET"!!! What next- bias ply tires being the secret to better handling on race tracks???Also for the record- the Fisher 30-A (and the 20-A) did not come from the factory with ceramic coupling caps.
Just take a look at the scope traces on the following link...and it will give you a visual at how terrible ceramic caps are.
“Just take a look at the scope traces on the following link...and it will give you a visual at how terrible ceramic caps are.”I think you dismiss the ceramic cap too readily. There are many types of ceramic caps with widely differing characteristics. One typical requirement is for high capacitance in a small pkg. This is achieved with high “K” insulator material which produces a cap with less than ideal characteristics. While fine for the intended apps such as RF bypass and so on it’s probably not so good for audio. However, there is one form of ceramic cap that really isn’t all that bad from an ideal vs reality perspective. These caps use a lower K insulator and carry a COG or NPO designation. In a lot of cases they perform about as good as polyester caps. I find these in the audio sections of much vintage equipment. Steve Bench tested Z5U types which are probably not the first choice for audio use.
My experience with quality vintage equipment is that swapping out ceramic caps with film types in the audio sections doesn’t always improve things. Sometimes the sound is actually degraded in minor ways. It’s as if the original designers had accounted for the characteristics of the ceramic caps when they “voiced” their designs. (Actually, I doubt that golden age designers consciously “voiced” equipment but that’s a different issue) As a result, I no longer routinely replace ceramic caps in the audio section when repairing older equipment. If a ceramic cap is bad (rare) I try to replace with a similar part if at all possible.
A lot of people point to Steve Bench’s cap test page as proof of the nastiness of ceramic and electrolytic caps …and to the overall goodness of their beloved type of month, esp paper/oil. No one ever seems to question the test methods, results or potential biases. So I will.
My observations from Mr. Bench’s posted info:
1. All test results are presented as objective in that the subjective “sound” of the caps was not considered directly; only “objective” measurements.
2. The use of scope traces to quantify the cap characteristics is inherently low resolution for all but the worst cases. To my eye, the film caps all look pretty much identical considering the limitations of photographing a scope trace. IOW interpreting scope traces tends towards subjective.
3. The test set-up itself makes use of caps of unstated “quality”. How are the “defects’ of the “reference” caps accounted for in the test results? Mr. Bench doesn’t discuss this aspect of the test set-up from what I was able to find.
4. The paper/oil cap comes up best when this dielectric is generally acknowledged to be inferior to most all film type materials. This is not an expected result. This is an objective measurement of a cap/dielctric characteristic in conflict with other objective measurenements of the same set of characteristics.
5. The polystyrene cap seems to come up second best when the general consensus is that PS is probably the best commercially avail material for cap dielectric if temp limits and size are factored out. This is not an expected result. See #4 above.
6. The investigation comes about because Mr. Bench was asked to evaluate a new paper/oil cap, presumably for a client although he’s not clear about this relationship. IMO this is a potential bias.Bottom line for me is that the Bench cap test is interesting but not the last word in cap quality. If I’m out of line here, please point it out.
One last observation is the apparent or convenient inconsistency of audiophile dogma these days. On one hand, true believers can totally discount an objective test of audio such as DBT when it doesn’t reinforce their beliefs. On the other, they will embrace an objective test (as here) if it does reinforce their beliefs.
Good job Steve.Out of all the brands I'd be the least inclined to do wholesale replacment of parts in fisher gear. They used good stuff and were well voiced. They balanced the sound and performance of one cap against another. And they did a darn good job.
Russ
Steve, you make some very good points...but my arguement is made via my own experiences with gear and some very specific experiences with the SA-16.I pointed out the "Sound of Capacitors" website because it was easier than typing out an arguement...but I seem to be typing now so I guess it was a moot point.
I have rebuilt several SA-16 and 30-A's. The two are extremely similar (one just has to glance at a schematic to see this) and even share the same output transformer (except the SA-16 has two since it is a stereo amplifier). I carried out tests using my own ears and others on a stock SA-16, and found in every case (that is every persons ears) that the ceramic caps were what was holding the amp back. The only thing changed at this point was the bypass electrolytic in the bias circuit.
Now the stock SA-16 did not sound like total sonic dreck, but there was a layer of grit to the sound and some people made comments about the sound being "off". Since everyone seems to agree that ceramic caps (like mica caps) "last forever" I do not think it had much to do with the ageing of the components.
I then changed the coupling caps to polyprops, and we listened again. The amplifier did not "completely" change as some people like to say, but it did wake up and become much more "involving" (as hi-fi reviewers like to say) and the previous layer of grit was completely absent.
Now to be fair, on the next SA-16 I get in the shop I will change the original ceramic caps to new production ceramic caps and perform some more listening tests...but I still feel that they are a big no-no.
My comments aren't directed so much at your equipment specific observations but more towards the broad-brush dismisal of ceramic caps in general and then pointing to Steve Bench's tests as back-up. I believe the results he presents regarding ceramic caps are a bit misleading because he uses Z5Us which are really pretty bad WRT characteristics relevant to audio. Specifically, Z5U capacitance vs voltage is pretty wild (see that site you linked way below in another thread). Cap vs voltage is what Bench's test looks to measuring for the most part.I know I don't have Bench's creds but I think someone needs to point out the potential weaknesses in what he presents.
If you do end up running your ceramic cap listenening test on your next SA-16 (why not any amp?) the caps should be NPO/COG type. The problem I'm finding nowadays is that these caps don't seem to be available in much above 100VDC in new production/leaded construction.
No real testing experience, but I have seen all kinds of caps in gear, and it is difficult to make generalized statements. For example: the Suzuki oil caps used in Sansui gear suck, but the silver mica coupling caps used in Western Electric gear are very nice. As for voicing, well, I suspect the electrolytic coupling caps used in some Fisher preamps were justified by space and price issues, not sound.Rodney
I'm with you on the Ceramic caps! I've nerver heard of anywone recommending them for coupling caps. I have used them to good effect for powerline noise, bypassuing the power cord with one in a Conrad Johnson PV-3 preamp.Dave
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