EQP-1a : Still mystified about how to select capacitors
« on: June 11, 2020, 12:41:10 AM »
I've read so many posts on the GroupDIY forum about capacitor selection, and I know that it mostly boils down to personal preference and simply listening to determine what you like, however, as a relative electronics neophyte, I find myself in a gray zone where I don't have enough experiental data to make informed decisions and I don't have the financial freedom to buy numerous capacitor types and experiment with them in circuit.

Therefore, I am wondering how more experienced builders determine right off the bat, roughly, what capacitors they will use for various blocks in a project's circuit board...especially when cloning vintage units where original components may not be readily available for purchase.

For example, when building a Pultec EQP-1A.  The perceived sonic consequences of capacitor choice will vary based on the choices made for transformers/inductor and tubes, however I really could use some help in establishing a basic jumping off point for what capacitors would best service various sections of a circuit.

With the Pultec I've seen so many recommendations,  for the audio sections polystyrene for lower capacitance values and polystyrene for higher values.  I've seen recommendations for certain capacitors in the high frequency filter vs the low frequency filter.  And then there are untold options for brands....Sprague Orange Drop, Mundorf, Wima, russian paper-in-oil.

I'm confused about where in any particular circuit it is worth it to "upgrade" your capacitor choices.  In the EQP-1A, would it make sense to upgrade the capacitors in the audio filter only or are there places in the amplification or power section that upgrades would make sense?  For instance, in the power section does it makes sense to upgrade from Rubycon 47UF  450V to Sprague Atom's?

How can I bridge this gap of uncertainty when looking at a schematic filled with a clear blueprint of capacitor values but having no idea how to select from the numerous brands and types of capacitors?

With the Pultec there are several distinct sections of the circuitry....the passive filter, the input and interstage transformers, the push/pull amplifier, the high-voltage power supply and the heater supply.

I truly appreciate any clarity or wisdom that more experienced builders can offer.  I really want to learn.

« Last Edit: June 11, 2020, 03:37:26 PM by earth tones »


Re: EQP-1a : Still mystified about how to select capacitors
« Reply #1 on: June 11, 2020, 04:24:19 AM »
Most talk about upgrading capacitors is audio phoolery. Where you need electrolytics e.g. the power supply, modern types from reputable manufacturers perform better than the ones available to the original designers of vintage equipment. There is zero benefit in choosing expensive exotic types (other than to the guy who sells them to you).

Similarly for non polarised capacitors, most current film capacitors from reputable manufacturers perform better than the ones available to the original designers. Again there is no benefit in choosing expensive exotic types.

Only if you believe an important element of the sound of vintage equipment is created by the limitations of the components they had available at the time do you need to seek out those vintage components but I bet if you asked the designers what they would have done if better components were available they would have used them.



'The only people not making mistakes are the people doing nothing'


Re: EQP-1a : Still mystified about how to select capacitors
« Reply #2 on: June 11, 2020, 04:36:18 AM »
..and just try it for yourself; build e.g. the pultec filter, fill in with all sorts of capacitors you have at hand, and see for yourself if you can detect a significant difference between types. This can be an eye opener if you tend to believe that strict component typing is most important :-)

/Jakob E.
..note to self: don't let Harman run your company..

Re: EQP-1a : Still mystified about how to select capacitors
« Reply #3 on: June 11, 2020, 10:31:28 PM »
Bear in mind original Pultecs used mica and mylar caps. Mylar are considered the worst by capacitor listeners. Oh and The Mastering Lab custom built mastering EQ’s used CDE mylar caps.

Regarding choices for your build, I used polystyrene and polypropylene caps for the filter section. I am partial to Sprague caps for power supply and coupling.

tony hunt

Re: EQP-1a : Still mystified about how to select capacitors
« Reply #4 on: June 12, 2020, 12:42:01 AM »
For a neophyte the polystyrene caps can be a challenge if still learning how to solder. They can be more sensitive to heat damage.

I see no reason to "upgrade" a Rubycon 47uF to a Sprague Atom. The latter are a niche product for guitar amps to imitate the physical size of the old cardboard tube electrolytics. If you want to be picky about electrolytics, look for 105˚C rated ones or 3000-5000 hour ratings.

Try the suggestion from Jakob to inform yourself on one or two signal cap locations at a time.  I did this when I was a lost but curious neophyte. It made me a DIY-existentialist. It gave me freedom and my own sonic opinion on this subject. 


Re: EQP-1a : Still mystified about how to select capacitors
« Reply #5 on: June 12, 2020, 01:55:33 AM »
I like to use film-foil (not metallised paper) polyester (mylar) caps for blocking and filter applications. Usually CDE WMF caps if the right values and voltages are available.  If you want to build the EQ a bit old school with the power supply caps hanging out the back then any of F+T, Sprague or ARS have worked well for me. Otherwise, and as mentioned, higher temperature and rating and longer hours for electrolytics.


Re: EQP-1a : Still mystified about how to select capacitors
« Reply #6 on: June 12, 2020, 02:49:42 PM »
Everyone who starts DIY wants to know the exotic details. It's the fun stuff to talk about when the basics are covered. Like in audio engineering you might think above 15K and below 40Hz is the most important thing to get right because it often comes up as a topic of conversation. It's exactly the opposite.

It's way more important to get the boring stuff right. Like quality soldering technique and test and measurement. Like playing an instrument, only after you have the fundamentals down can you start worry about the little details. Worrying about the exact tone means nothing if you can't play in tempo or in tune.


Re: EQP-1a : Still mystified about how to select capacitors
« Reply #7 on: June 16, 2020, 09:14:39 PM »
I second what everyone wrote here.

Check this video also on the subject:


Personally I never buy unbranded or unknown brand or cheap chinese caps just for assurance and confidence.
I also never buy extremely expensive, audiophile or "Audio caps".

For Electrolytics I always use Panasonic rated at 105 (any series)
For Film caps, I use Wima, Panasonic, Phillips, Mallory or Vishay
For Ceramics I don't check brands I use C0G/NP0
For Polystyrene, I use whatever the supplier sells

I'm not doing this because I think the caps sound better, but to be on the safe size by using a good standard brand and paying an exaggerated price.
Specially electrolytics, Panasonic lytics from Farnell are not expensive and the quality is really good


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