Film Caps & ESR compensation

slow_polk7

Film caps have significantly lower ESR than their electrolytic equivalents.

In an upgraded crossover, it seems obvious that this would have an effect on the speaker's sound signature - perhaps, most notably, in driver output volume.

Anyone have any experience in compensating for this via inline resistor, L-pads or other techniques?

DeRod

I am not 100% sure about the lower ESR in film caps that you're referring to but when I replaced the electrolytic caps with higher quality film caps my speakers sounded louder. With the old electrolytic caps they sounded dull and not as loud.

What crossover are you planning to re-cap?

pitdogg2

Worrying about the ESR difference between electrolytic and film is way over thinking it. The only reason speaker manufacturers use large value electrolytic caps is cost.
L-pads and inline resistors, forgetaboutit.
If you're that worried replace the lytic with another of the same value, just remember that lytics have a huge +/- value as high as 20% compared to the 1-3% in film caps.

Gardenstater

I know just enough to be dangerous about this stuff but from what I have learned online:

I think Polk specified Dissipation Factor in the Series II schematics to be less than 5% so that would be a good guideline. DF and ESR are proportional to each other. DF and ESR rise, especially in electrolytics, as the capacitors age and reach end of life at some point when it rises above an acceptable level. DF and ESR are much higher in electrolytics to start with vs polyester and polypropylene film caps. If I can find a chart I screenshotted some time I'll post it here.

Someone tested their caps for DF and ESR....maybe MrGeology

Here's all I have. Doesn't include electrolytics but you might assume around DF = 5% for them to get an idea how much greater it is.

slow_polk7

Just to be clear -- this isn't a purely mental thought experiment. I love the sound of both my early 5s and 7s, though in both cases the peerless tweeters border on slightly bright for my taste.

Capacitors are relatively simple components with complex impedance and reactance characteristics. It's not as simple as swapping one cap for another so long as the farad ratings match.

The last thing I want to do is rework my crossovers, bolt everything up and then find that the magic sound is gone.

DeRod

Your magic has probably been gone for a while now. Recap those speakers and bring the magic back.

I just recapped my 7s with Jantzen cap. The Jantzen caps are inexpensive and sound really nice. Do it, you’ll be glad you did.

Gardenstater

If you change out the electrolytic shunt cap in the M5 or M7 to a film type, if anything the voicing should de-emphasize the tweeter ever so slightly and lower the impedance of the speaker ever so slightly.

It was not noticeable in my 7Bs.

slow_polk7

Gardenstater wrote: »

If you change out the electrolytic shunt cap in the M5 or M7 to a film type, if anything the voicing should de-emphasize the tweeter ever so slightly and lower the impedance of the speaker ever so slightly.

It was not noticeable in my 7Bs.

That would be great if that's the case.
And maybe we're talking about two distinct effects: (1) change in character of tweeter sound, and (2) change in tweeter overall volume.

DeRod

Your monitors need maintenance for old age. 1st on the list should be glueing those magnets if you haven’t done so.

Gardenstater

ESR is higher than I thought. About 2.9 Ohms in a 250V 33uF polarized electrolytic hifi cap here:

https://partsconnexion.com/product_images/downloads/FTCAPSeriesASpecSheet.pdf

So far I'm not finding any specs for ESR for 33uF film caps we typically use, to compare to this. They seem to only talk about "low ESR" and DF but don't give the ESR.

slow_polk7

Gardenstater wrote: »

ESR is higher than I thought. About 2.9 Ohms in a 250V 33uF polarized electrolytic hifi cap here:

https://partsconnexion.com/product_images/downloads/FTCAPSeriesASpecSheet.pdf

Exactly -- meanwhile a typical film cap of the same uF rating has ESR of about 10 milliohms.

Gardenstater

@MrGeology to the rescue......hasn't been around much lately sadly.

Anyways, he measured ESR of .36 and .51 Ohms on his original 34uF electrolytics.

On his 34uF Sonicaps he got ESR of 0.28 Ohms.

Not much difference. Why I do not know.

https://forum.polkaudio.com/discussion/198508/mw6500-dats-t-s-parameters-revised-pics#latest

Edit- in reading this thread I see that Polk specified < 3% DF in Series II. My memory apparently sucks.

slow_polk7

Thanks George
I'll do the same test once I get these apart.

F1nut

slow_polk7 wrote: »

Just to be clear -- this isn't a purely mental thought experiment. I love the sound of both my early 5s and 7s, though in both cases the peerless tweeters border on slightly bright for my taste.

Capacitors are relatively simple components with complex impedance and reactance characteristics. It's not as simple as swapping one cap for another so long as the farad ratings match.

The last thing I want to do is rework my crossovers, bolt everything up and then find that the magic sound is gone.

Those Peerless tweeters are pretty darn smooth even with old out of spec caps. I suspect the issue is upstream.

Perhaps you could share with us what is upstream.

Edit: Ah, I found the source of your issue.

In '88 I replaced that with a Sony ES receiver (80 wpc), which I use to this day.

Sony has an inherently bright sound signature.

slow_polk7

F1nut wrote: »

Edit: Ah, I found the source of your issue.

show previous quotes

In '88 I replaced that with a Sony ES receiver (80 wpc), which I use to this day.

Sony has an inherently bright sound signature.

I think you're onto something!

I don't want to split hairs, but I'd call the late '80s ES Sonys "revealing" rather than "bright"
I often swap in a slightly newer STR-GX90ES (120W/ch) and both have impressively accurate frequency response curves.

Nonetheless - In my experience, amplifiers do indeed have sound signatures and this may well just be a less-than-optimum pairing.

My question to you: what do you recommend in a currently mfd. integrated amp of 100 watts or so, with a "warmer" sound?

F1nut

Not sure what price range you are looking at, but I'll recommend the Marantz Model 30 for starters.

slow_polk7

OK - that's a little bit out of my range - but what a beauty - and fully discrete components.

Gardenstater

Cripessakes looks like I posted the wrong MrGeology thread above.

I can't help but marvel at how good the old electrolytics measured in ESR. Not much worse than new Sonicaps or Jantzen Crosscaps. Maybe Polk selected very high quality ones.

https://forum.polkaudio.com/discussion/197124/monitor-7b-crossover-upgrade-questions#latest

Here's some info about ESR from a manual of an ESR meter:

Gardenstater

The old 34uF electrolytics had about 0.8 ohms greater ESR at 120 Hz though, compared to new Sonicaps. Probably lowers impedance a bit at lower frequencies. Since it is the shunt capacitor would it decrease output a little and would it be noticeable?

VR3

To date I have never experienced nothing but positive results shedding crossovers of ceramic inductive resistors, electrolytic caps, iron core inductors, and cheap thin trace circuit boards...

Gardenstater

To be clear, my comment wasn't directed towards the other components or overall sound but that I was wondering if that ESR difference (0.8 ohms) at low frequencies only could actually reduce noticeably the very low frequency output.

Of course the ESR was probably lower when they left the factory. How much we don't know.

heiney9

slow_polk7 wrote: »

Just to be clear -- this isn't a purely mental thought experiment. I love the sound of both my early 5s and 7s, though in both cases the peerless tweeters border on slightly bright for my taste.

Capacitors are relatively simple components with complex impedance and reactance characteristics. It's not as simple as swapping one cap for another so long as the farad ratings match.

The last thing I want to do is rework my crossovers, bolt everything up and then find that the magic sound is gone.

A lot of people here have upgraded/updated crossovers and I don't recall a single time where anyone "lost the magic". In many instances the improvements were not subtle.

By now the Monitor series x-over components are at the end of life or have been for awhile.

I guess my best advice is, if you like the magical sound you have now, why would you change it? Leave them alone if you're stoked with the way they currently sound. Most people have gone the refresh route because 35 year old caps don't sound good any longer. Also technology in non-electrolytic caps is miles better than 35 years ago. Non-inductive resistors are better than sandcast resistors, etc, etc.

I can tell you from much experience though, they can sound a lot better if you do a cap refresh and get rid of the old tweeters (sl2000, etc.).

Just my .02c