Mylar Film Caps From Input to Output

If you dig deep enough into the subject of audio, and especially vintage audio, sooner or later you will read all about the ins and outs of various kinds of capacitors and the effects they have on audio quality. It is a huge concern of audiophile techies and I think it is often overblown, but there really is something to it.

Preamps, amps, tuners, and all other audio gear have various stages of amplification and processing inside. These stages are practically always connected to one another through a capacitor. As such they are called coupling capacitors. In the simplest of integrated amplifiers, there are usually 8-10 coupling caps per channel for a solid state amp, and 4-5 in a tube amp. In the large quad units like a 9001 there can be as many as 50-80.

By the nature of their design, tube amps use small caps, usually 0.01-0.1uf for coupling. Solid state amps use caps almost 100 times larger, usually 1-10uf. Solid state gear is constructed on printed circuit boards and so the physical size of the coupling cap is a major concern. In the past, with older design film caps, there just was not enough room to replace them all with films.

Here is a loose ranking of what most audiophiles consider the best cap types, best to worst.

Hand wrapped foil/paper/oil caps, can be very expensive.

Esoteric paper in oil caps made in Russia 25 years ago (I’m not kidding)

Film caps like polypropylene and mylar.

Various audio grade electrolytics

Standard electrolytics

Bi-polar electrolytics

Ceramics like Z5U and others

Tantalum electrolytics

The top 3 on this list are very close in their sound quality. I think most people would be very hard pressed to reliably tell the difference between paper in oil and film type caps. There are very hearable differences as you proceed on down the list, though.

Now, Sansui was aware of this way back in the 60’s. Their first top of the line integrated amp was the AU999 and it fairly bristles with Mylar film caps from input to output. They are the shiny green blob looking things on all of the PC boards.

So why not use the film types everywhere? Three reasons. Cost, size, and availability. Typically they have cost 100X what a comparable electrolytic costs. Size wise, film types were huge when compared to 1-10uf electrolytics. I’m not sure what the availability of film types from 1-10uf back in the 70’s but I think, they were just plain unavailable over about 2uf.

By the time Sansui got to the mid 70’s, Sansui was using very few mylar caps, and instead were using standard electrolytics for coupling. At that time there were no “audio grade” electrolytics available. However Sansui had identified what they considered to be the best electrolytics available at the time, and those are the orange ones you see all over the mid 70’s pc boards.

On the AU999 they still had to use electrolytics, especially on the tone control boards, simply because the circuitry called for larger capacitors, 3-10uf. Sometimes they put a small mylar film cap in parallel with an electrolytic, which works pretty good and mostly sounds like a big mylar.

So, what’s the point? Why am I writing a page about this? Because… electronic components keep getting smaller and cheaper. In the last year or so a new line of miniature mylar caps have come out from Wima and Kemet that are small enough to replace all the signal path electrolytics in a solid state amp from input to output. And since… when we do a recap/restore we are changing all the caps anyway… why not change all the signal path caps to mylars, like Sansui started out doing in the beginning?

We’ve done this to several amps now. A 5000X, a 5000A, an 890db (same as 8080db), and a 9090. When paired with our Differential Current Balance mod the result is the best sound we have ever gotten from any of these Sansuis. The early amps with cap coupled outputs like the 5000 are remarkably improved also.

Curiously, there is a very noticeable improvement in low end quality, which is something I was not expecting so much. I’m convinced this comes from the tone control section which typically uses several 3.3uf – 10uf electrolytic caps in complicated circuitry. Boost and cut tone controls achieve their action with complicated signal feedback circuit that depends as much on phase as it does amplitude, in order to function. Cap quality really affects that. More on this in a minute.

I don’t like to add more options for our customers that can be added to the cost of restoring an old Sansui. I fully believe this is very worthwhile and if it turns out that every customer is getting this upgrade, we just might incorporate it into the standard price… or perhaps just one upgrade that is either just the mylar caps alone, or the “Diff mod” + mylars depending on the type of amp.

Film caps from input to output

Here’s how this came about.

I don’t know how long they have been available, but I recently noticed a series of Mylar film caps available from Wima, while looking on Mouser. They looked to be a lot smaller than usual, so I ordered some.

They are a lot smaller than film caps available in the past. My hope was that perhaps all signal path electrolytic coupling caps, from input to output could be replaced with films, in the Sansuis we work on. Here’s a picture of the new caps (red ones). They are left to right 1, 2.2, 4.7, and 10uf at 50v. Included is a 0.47uf polypropylene film  cap, and a 1uf @ 50v. electrolytic.


They looked small enough that they might be able to drop right on to printed circuit boards. Next up on my bench was a 5000X that had been “traded in” on some other work we did. Great. There are not that many signal path caps in the 5000X, and it would be a quick and easy trial.

You can see that the older 0.47uf film cap was just too large to use most anywhere, especially where a little electrolytic was already existing on the board with other components crowded around it.

Here’s the input board of the 5000X. All inputs go through this board and it serves as the phono preamp to boot. Each channel has a 1.5uf and two 10uf in the signal path. The 10’s are a little tight, and I replaced the 1.5uf with a 4.7, which dropped right in.


And here’s the tone board. Everything fit.




And here’s the output driver boards. 2 signal path caps on each. The input cap to this board, stock, is a 0.22uf mylar, replaced with a 1.0uf mylar. The other one is a high quality 2.2uf electrolytic, replaced by a 4.7uf mylar. The one soldered on the bottom of the board replaces the stock .22uf input mylar, which had leads a little too far apart to comfortably fit on the top. In other words the existing Mylar was too big for the 5X replacement to reach the through holes!


We have now done this on 4 different Sansuis, two early cap coupled amps, and two later complementary output amps.

On the two cap coupled amps, the result was stunning. We already do an upgrade to the big power supply cap and the two output caps in our normal restoration. Typically, we will upgrade the power supply cap to 4700uf at whichever voltage the amp uses, and we will upgrade the output cap, which is either a 1500uf or 2200uf to at least 10,000uf. We have gone as high as 15,000uf for the output cap.

When all the signal path caps were converted to mylar film caps on the 5000X, there was a general improvement in audio musicality and what I would call transparency. But… the most noticeable improvement was in the low end. I think this was due to the replacement of electrolytics in the tone control section.

Because of how tone controls are designed, caps of up to 10uf are required to make the bass control work. The film caps allow a high definition low end, using the bass control, something I have only heard with DC amps before.

The complementary style amps, (9090, 9001, most others after 1972) had the same sort of improvement, the improvements about equal in the tone controls and overall transparency. Justin commented when he did the first one, an 890db, that the film caps didn’t seem to make a lot of difference until he also added in the Differential Current Balance mod, which is the last thing we do with a restoration. Then he felt the difference was quite noticeable. I agreed with him. It’s kind of like the “Diff” mod brings the complementary style amps up to the level of quality that can be achieved with the upgraded early cap coupled amps, and then the film caps were a worthwhile addition.

At this point I am convinced that this is a true quality upgrade, and something we should offer, like we do the Differential Current Balance mod. I have struggled a bit with figuring out what to charge for this addition.

The new miniature mylar caps are quite expensive, costing us about $1-3 each. When we can buy in quantity, that price will come down some. The audio grade electrolytics (Nichicon UKW) we normally use in the signal path typically cost 8-10 cents each in 1000 qty lots. That’s a big increase in cost to add the mylars. We can eventually get the price down appreciably by buying in 1000 qty lots, but that will be a $8-10,000 investment in parts for us.

But fortunately, the number of signal path coupling caps is small. In the 5000X I did, there are 18 of them. However, in the 9001 there are 40 in the 4 amplifier channels, 18 on the quad processing boards, and 22 on the CD4 board, for a total of 80. The only way we can price this addition is to do it for each model. What we will do is just figure the cost for the caps, as there is very little increase in the labor required, since we are already changing out the caps anyway.

Our “Diff” mod is mainly a labor charge, as it takes a few hours to install and calibrate the parts. Most of the time is spent waiting for circuits to stabilize and then making adjustments. The parts are very inexpensive, you are paying for our expertise and time with that upgrade.

So for now, we will just quote a price for the mylars to go with each model. When we have done this for a while, we will get more structured about it.

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