Improving the Coupling Capacitors for Better Tone Sounding

[opacheco]

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

 

[ruffrecords]

Use good quality film caps (e.g.MK) everywhere except the electrolytics (for you should use low ESR types wherever available.

However,

I would not expect these changes to make a significant difference to the the "tone quality at maximum". That depends mostly on the output transformer and the power supply.

Cheers

Ian

 

[opacheco]

Use good quality film caps (e.g.MK) everywhere except the electrolytics (for you should use low ESR types wherever available.

However,

I would not expect these changes to make a significant difference to the the "tone quality at maximum". That depends mostly on the output transformer and the power supply.

Cheers

Ian

Ian
Thanks for your fast response!. Ok I will more infor about the “MK” capacitors; o never hear of them.
Btw: this amp have very good output transformer and in this sense I won’t have trouble I think. The actuals capacitor look like very cheap and I thought in polystyrene capacitor, what do you think about?

Thanks again
opacheco

 

[opacheco]

How about the “Paper in Oil Audio”? I found some K40P-2 Russians NOS units.

opacheco

 

[Newmarket]

How about the “Paper in Oil Audio”? I found some K40P-2 Russians NOS units.

opacheco

No need for that. Audio myth stuff.

 

[k brown]

The most that signal path cap 'upgrades' can do is a very slight smoothing/sweetening of the top octave; will not change the overall 'tone' of the circuit.

 

[Newmarket]

"Better" caps in this context have lower / negligible voltage coefficient. Also tempco but that won't show over the short term. Lower HD. If wanting colour/distortion then go with the cheap caps.
Apart from that consider whether you want a specific cap to define a high pass filter frequency. If not then go for the largest value practicable.

 

[ruffrecords]

Ian
Thanks for your fast response!. Ok I will more infor about the “MK” capacitors; o never hear of them.
Btw: this amp have very good output transformer and in this sense I won’t have trouble I think. The actuals capacitor look like very cheap and I thought in polystyrene capacitor, what do you think about?

Thanks again
opacheco

I should have mentioned they are made by a company called WIMA. Much respected in pro audio circles.

https://cpc.farnell.com/w/c/electro...apacitors/prl/results?brand=wima&st=capacitor

Cheers

Ian

 

[soapfoot]

It depends to a degree on what your goals are for "improvement."

Let's start by setting expectations: most claims of capacitor "sound" are at least moderately-overstated. Typically, in most applications, capacitor technology is at most tinkering at the margins. Don't expect a transformation (however, if you do expect a big change, it's likely that your mind will convince you to hear one!)

If you want "straight wire with gain," this is fairly easy to accomplish without the use of anything exotic. Any nice polypropylene film-and-foil capacitor should do the job for medium-sized values, C0G/NP0 ceramic for very small values, and a nice-quality aluminum electrolytic for large power supply capacitors. In that last application, you could also try (very-physically-large) metallized polypropylene film (e.g. Solen "Fast") if you want to truly go overboard.

If you want "vibe" or "character," you can experiment with less-optimal technologies. Many older devices are loaded with tantalum capacitors (even in signal-coupling applications!)--The classic Neve 10xx modules everyone loves used a ton of them, as did the most sought-after Ampex tape machines--and these do have "a sound." Technically, it's distortion, but it's distortion some people subjectively like. Likewise for Class 2 ceramics.

Polyester (PET or "mylar") film will for all practical purposes perform much like polypropylene film, but are slightly less-optimal and some will claim to hear a difference.

 

[Matt Syson]

Doug Self wrote about some capacitor distortions and probides useful comments. Mylar and other constructions CAN have a mid freauency range 'distortion' that is strongly signal LEVEL (across the caps) dependent so as usual 'It all depends' where they are used and what they NEED to do. Just been looking at a 'Disco mixer' that is almost completely DC coupled and reportedly 'sounds great' BUT all the pots 'scratch and fortunately there are no signal cutting switches except the PFL switch otherwise all the DC offsets will make their presence HEARD. The High pass filter (to protect mega bass speakers) conveniently covers up the various random offsets (sneaky).

 

[CJ]

Plug and play, its nice to have a big box of stuff to try.

What sounds good in a mic preamp might not sound good in a guitar amp.

I hear that Fender is having the original blue coupling caps made again. I like the brown ones too , the ones with the box like shape.

Russian oil caps are popular with amp builders but you have to be careful with the metal case.

I replaced all the coupling caps in that Kay amp downstream, did not sound as good. Turns out they were leaky and were driving all the grids positive, nice saturated sound, had the blusey funk, i thought about adding high resistance resistors across the coupling caps to simulate a leaky cap, maybe 10 meg or something, you could even use a 10 meg pot as a variable saturation control, I don't believe I have ever seen those that done, maybe for good reason.

So if you take a handful of vintage amps of the same model, they will all sound different depending on which caps are leaking and how bad.

 

[tony hunt]

If I could advise two small tips from an old codger with solder induced memory loss:

1. use the same build type and physical size of capacitor as in the original amp. (MK are designed for modern pcb boards. That schematic suggests to me that the coupling caps are axial type.)

2. make sure the voltage rating is correct for the application.

The tone quality is subjective and I have no comment,
except that 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...

Bye for now, have fun, I will be at the bar.

 

[Whoops]

How about the “Paper in Oil Audio”? I found some K40P-2 Russians NOS units.

opacheco

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:

 

[opacheco]

It depends to a degree on what your goals are for "improvement."

Let's start by setting expectations: most claims of capacitor "sound" are at least moderately-overstated. Typically, in most applications, capacitor technology is at most tinkering at the margins. Don't expect a transformation (however, if you do expect a big change, it's likely that your mind will convince you to hear one!)

If you want "straight wire with gain," this is fairly easy to accomplish without the use of anything exotic. Any nice polypropylene film-and-foil capacitor should do the job for medium-sized values, C0G/NP0 ceramic for very small values, and a nice-quality aluminum electrolytic for large power supply capacitors. In that last application, you could also try (very-physically-large) metallized polypropylene film (e.g. Solen "Fast") if you want to truly go overboard.

If you want "vibe" or "character," you can experiment with less-optimal technologies. Many older devices are loaded with tantalum capacitors (even in signal-coupling applications!)--The classic Neve 10xx modules everyone loves used a ton of them, as did the most sought-after Ampex tape machines--and these do have "a sound." Technically, it's distortion, but it's distortion some people subjectively like. Likewise for Class 2 ceramics.

Polyester (PET or "mylar") film will for all practical purposes perform much like polypropylene film, but are slightly less-optimal and some will claim to hear a difference.

Excelent experience notes!
Thanks
opacheco

 

[opacheco]

Interesting analysis and experienced test!….I will need to test your recommendations!

Thanks
opacheco

 

[Matador]

If anything, I would focus more on the size of the capacitor rather than the type/brand. For example, the 0.02uF coupling capacitors are sized to pass down to around 10Hz, so decreasing them will change the bass response of the amp. Whether or not it's "good" is up to you. In a guitar amp it's common to filter everything down below 60Hz because it too much bass can make the guitar sound "flabby".

 

[k brown]

If anything, I would focus more on the size of the capacitor rather than the type/brand. For example, the 0.02uF coupling capacitors are sized to pass down to around 10Hz, so decreasing them will change the bass response of the amp. Whether or not it's "good" is up to you. In a guitar amp it's common to filter everything down below 60Hz because it too much bass can make the guitar sound "flabby".

'Value' a better term than 'size', which suggests physical dimension.

 

[ricardo]

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

 

[Mihobro]

Love that you are looking into this. Although there have been a lot of advances in capacitors, some of the silver mica caps are definitely worth looking into. One of the oldest type of capacitor, some of these caps are 60+ years old and still have no problems. While old electrolytics will be all over the place. Back in the day most musicians used the same axe for a lifetime and durability and consistency were considered cool.

 

[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.