Improving the Coupling Capacitors for Better Tone Sounding

[ricardo]

Although there have been a lot of advances in capacitors, some of the silver mica caps are definitely worth looking into.

Guru Scott Wurcer investigated caps for LN stuff. I had some correspondence with him on the subject and I think he put some of this in his Linear Audio articles on condensor microphone amps.

He found Polystyrenes microphonic and Silver Micas introduced a strange noise. The best small caps were NPO/CGO ceramics. If the voltage / values / size fit, use them.

Tantalums and some of the uber Electrolytics also introduce noise at a very low level. If LN is your thing, use cheapo Aluminium Electrolytics and bias them properly.

 

[Matador]

The best small caps were NPO/CGO ceramics.

I recently swapped some NP0/C0G ceramic MLCC's into a Fender tremolo circuit, and along with LED biasing, it gives for rock stable tremolo frequency, from the start of the gig when the bar is cold, to 2am after 12 beers.

 

[soapfoot]

…but where’s the fun in that?

 

[opacheco]

Guru Scott Wurcer investigated caps for LN stuff. I had some correspondence with him on the subject and I think he put some of this in his Linear Audio articles on condensor microphone amps.

He found Polystyrenes microphonic and Silver Micas introduced a strange noise. The best small caps were NPO/CGO ceramics. If the voltage / values / size fit, use them.

Tantalums and some of the uber Electrolytics also introduce noise at a very low level. If LN is your thing, use cheapo Aluminium Electrolytics and bias them properly.

I never heard about the NPO/CGO ceramics capacitors at least with those names!; do you have more info about the Scott Gurcer study or investigation? Where I can find this investigation paper or notes?

Thanks a lot,
opacheco

 

[opacheco]

Use only capacitors hand carved from Unobtainium and solid BS by virgins !
If you send me US$100 in used bank notes, I'll send you a sample. You can just stick it to the chassis with BluTak to enjoy improved clarity and definition. No need to even solder it in.
No Confederate money please

Sorry what you talking about? I don’t understand nothing you say!

opacheco

 

[opacheco]

……most friends who used tube amps with those old mustard yellow colour Mullard capacitors stated that the amp sounded best after twenty minutes warm up. Technically those caps were not so temperature stable as modern MK types, so perhaps there was some kind of drift. But I think we all probably got used to the sound after 20 minutes...
most friends who used tube amps with those old mustard yellow colour Mullard capacitors stated that the amp sounded best after twenty minutes warm up. Technically those caps were not so temperature stable as modern MK types, so perhaps there was some kind of drift. But I think we all probably got used to the sound after 20 minutes...

ok, I will considering that too!
Thanks
opacheco

 

[JohnRoberts]

Sorry what you talking about? I don’t understand nothing you say!

opacheco

He's joking

JR

 

[opacheco]

He's joking

JR

 

[Newmarket]

He's joking

JR

"Joking without the G" ?
In memory of the late great BBC Radio DJ Steve Wright

 

[Cqwet Dbdfte]

Hi to everyone!

I am trying to improve the tone quality of this tube amplifier at maximum! and I would like to know what kind of coupling and dis-coupling capacitors can I use in order to achieve this superior sound quality, instance to the actuals Mica cheap capacitors used actually?

I have attached the schematic for your considerations and advices.

Thanks in advance!
opacheco

Lots of mythology runs thru capacitors.
"Tone" is very subjective, and good coupling caps should pass the lowest desired frequency and not leak any DC as to destroy the bias of the next tube.
You can EASILY measure leakage with a DVM: remove connection on low voltage side of cap, measure voltage with the DVM, take the number of volts and divide by 10,000,000.
The number should be very small.
Old caps can be leaky, giving unwanted surprises.
Replace as suggested with PP caps.
Paper in Oil, PIO, may have some dielectric absorption effect, maybe audible. Maybe OK?
As "tone" is not measurable hard to say.
Some PIO are shipped with metal shorting clamps to keep surprises to a minimum.
10kV 4uF is no joke.

 

[RCAguy]

Coupling capacitor distortion is relatively easy to reduce. Now with reduced-size audio-grade ‘lytics (even tantalums), just oversize so they have barely any voltage drop at the lowest frequency of interest, say 16Hz, then calculate for f3 of 1.6Hz.

The reason: Oversizing means no voltage drop at the lowest frequency of interest, so there can’t be any distortion imposed. - Douglas Self

 

[JohnRoberts]

The reason: Oversizing means no voltage drop at the lowest frequency of interest, so there can’t be any distortion imposed. - Douglas Self

Yes, and.

When designing an audio path with multiple DC blocking capacitors, the HP poles in series accumulate, so it is just good practice to tune the poles well below the audio bandpass. Ideally in premium designs we try to use a single film or other very linear capacitor filter stage to define the dominant LF cut off.

The typical aging mechanism for electrolytic capacitors is loss of electrolyte, and therefore loss of capacitance. Tuning these DC blocking poles very low insures many years of useful product life with minimal audible frequency response changes due to aging.

JR

 

[CalavoBob]

Here's the straight science for your high-pass coupling cap break frequency. At fc you'll get +45 degrees of phase shift and an amplitude drop of 3 dB. If you move that break frequency down to 1/10th of your desired lowest useable frequency, the phase shift drops to +5.7 degrees. This means you use a capacitance that is 10 times the cap that would have made fc at your design's lowest desired usable frequency. Remember that cap causing the break frequency is the old C= 1 / (2 PI fc R). Another reason for pushing that break frequency down is that your amplitude response is going to be -3dB down at the original break frequency, but if you use a capacitance that's 10x what that equation says, your voltage amplitude drop is only 0.0995 of the original signal at your lowest useable frequency. If you use an even larger capacitance, the phase shift and amplitude response effects are even smaller. The cap value you choose is is limited by size, cost and availability.

 

[ruffrecords]

I think at Neve back in the 70s we had a set of simplified equations for calculating coupling capacitors for 1dB, 0.5dB and 0.1dB loss at 20Hz for any given impedance. I will see if I can dig it out.

Cheers

Ian

 

[kidb]

Depending on what capacitors are in there right now, quality caps might help a small amount, but imo tube swapping will do more for the color than cap swapping. try some NOS RCA 7199s would be my suggestion, "but thats just, like, my opinion man" - Lebowski-ish

 

[kidb]

Depending on what capacitors are in there right now, quality caps might help a small amount, but imo tube swapping will do more for the color than cap swapping. try some NOS RCA 7199s would be my suggestion, "but thats just, like, my opinion man" - Lebowski-ish

Oh but for "tone" maybe try one high quality ceramic disk somewhere, or mkt1813 polyesters. mylar, polyester, pio, seem to have some flavor.

 

[GrannyGremlin]

People say PIO caps are prone to fail over the years.
Don't really know if there's any sonic benefit,
but here is an interesting video:

Yes - PiO will all eventually leak and be a right bloody mess inside your chassis (never buy NOS). They leak slowly and still work (everything just gets a bit greasy). I'd rather use an electrolytic in the signal path than a PiO. Pure snake oil.

There have been other vids showing that there is no tonal difference between cap types in a guitar tone control. All tonal variance could be explained by capacitance value (within tolerance - very few .047 caps are actually exactly .047, so comparing 2 different caps could be meaningless if one is .051 and the other is .043).

As folks have mentioned up above, there is a known psychological effect where a tester, knowing what they are testing, will expect something to be different or better and perceive it that way. Marketing/hype - it's a hellova drug. Listening tests are meaningless unless they are at least double blind, even better if you can back up the listening test with some sort of measured difference.

 

[Whoops]

Yes - PiO will all eventually leak and be a right bloody mess inside your chassis (never buy NOS). They leak slowly and still work (everything just gets a bit greasy). I'd rather use an electrolytic in the signal path than a PiO. Pure snake oil.

I remember some years ago (15 years) when I started to work/service/restore Tube amps, Tube gear and vintage microphones, that many people advised to replace all old PIO caps for new film capacitors, in case there was any PIO in that specific old gear. The reasons were that:
- they didn't age well and are known to deteriorate over time, making them unreliable
- you couldn't depend on then and they can fail in a few different ways
- the dielectric can break down over time
- they can also leak, and once the oil leaks out of them they're useless
- could have corrosion around the edges and pins
- the paper can absorve humidity leading to breakdown

Probably some other reasons, I don't remember all.
But I did as the more experienced people advised, so I always replaced them in old equipment.

It was a surprise to me that in the last years a PIO Hype grew and people started to buy NOS PIO (NOS = OLD) caps to use them in their equipment. It seems they are now popular again for guitars, microphones and other gear.

I don't know if it's just hype and Snake oil or if they really sound better/different,
but I find it really funny that old caps once considered unreliable are now considered the holy grail for some duties.

 

[Matt Syson]

Well it seems that almost all the digital recording systems are so good that musicians now have to learn to play/perform properly.
Even the early 16 bit convertors were too 'sterile' compared to multitrack tape that may or may not have been correctly aligned.
EVERY live performance is unique in at least some details and there is more variation of 'tone' by mic placement than any change of capacitor.

 

[rh001]

Hi to everyone!

I am trying to improve the tone quality of this tube amplifier at maximum! and I would like to know what kind of coupling and dis-coupling capacitors can I use in order to achieve this superior sound quality, instance to the actuals Mica cheap capacitors used actually?

I have attached the schematic for your considerations and advices.

Thanks in advance!
opacheco

Hi!

If the caps you want to replace are old and if they are without pedigree then an improvement will be had with either Sprague "Orange Drop" capacitors or WMF (I think they are CDE brand, aka Cornell Dublier). You will find these on ebay. I think both can be found new. WMF are expensive. Orange Drop can be polyprolpylene or polyester...I have used both....don't hear much difference. Guitar players like them. WMF has a great tone overall, big and warm...probably the best sounding cap ever. They tend to be expensive. Just say no to paper in oil (or anything from former USSR) or any paper , that's old tech that is often decaying like salmon that has spawned.