Ceramic Cap Discussion from Jazz Mode Video Demo With Stratocaster and 102

[10thTx]

Interesting article on X7R, X5R & COG caps.

https://www.allaboutcircuits.com/techni ... tor-types/

[martin manning]

So for those interested here are some of the different type ceramics Dumble used...

Several of the caps pictured have only value, tolerance (J=5%, K=10%), and voltage rating in the markings, so the dielectric is unknown. Looking at data sheets, X7R is still quite good for temperature stability, and Z5U is among the worst. The change is still on the order of normal tolerance at 50C, though. In all types, the value will drift up after soldering, and then recover after some time (weeks), and it continues to drift downward logarithmically (Vishay, General Information on Ceramic Capacitors). The capacitance change is real and measurable, and will shift frequency response- 12% is a whole step, musically speaking. The difference in timbre for the various dielectrics is a matter of opinion ;^)

[erwin_ve]

So for those interested here are some of the different type ceramics Dumble used...

Several of the caps pictured have only value, tolerance (J=5%, K=10%), and voltage rating in the markings, so the dielectric is unknown. Looking at data sheets, X7R is still quite good for temperature stability, and Z5U is among the worst. The change is still on the order of normal tolerance at 50C, though. In all types, the value will drift up after soldering, and then recover after some time (weeks), and it continues to drift downward logarithmically (Vishay, General Information on Ceramic Capacitors). The capacitance change is real and measurable, and will shift frequency response- 12% is a whole step, musically speaking. The difference in timbre for the various dielectrics is a matter of opinion ;^)

Indeed it is a matter of taste, do you know why Aiken advise to stay away from X7R types? It's on his Q&A page.
Edit: not being retorical, Just found some interesting paper: http://www.johnhardyco.com/pdf/990.pdf last page.
And other source claim the x7r dielectric has piezo qualities which make them microphonic.

[talbany]

Yes god forbid we put anything in a guitar amp that generates harmonics/Distortion and or is slightly microphonic. While we are at it let's go ahead and get rid of those pesky noisy preamp tubes that have the same anomalies!..This is what happens when engineers get involved with building guitar amps.
NOT signaling anyone out Just sayin!

Class 2 are the ones generally used in guitar amps.

BTW. If you have a bunch you want to try just pick up a row of SIP sockets and roll through a few until you find one that rings. Also this way you won't alter the contact resistance between terminals and electrodes by applying the hot solder


https://www.peconnectors.com/sockets-si ... oCF0zw_wcB

Tony

[martin manning]

Erwin, there is a lot of good information in there; measured data and references. Great stuff! I think temperature stability is a good thing, and harmonic distortion may be a good thing (but note that the THD levels shown for X7R are quite low by guitar amp standards). The capacitance change with voltage is interesting, in that frequency response will shift in opposite directions with increasing DC voltage and signal voltage. The DC shift could be compensated for by selecting the appropriate capacitance value, so the capacitance shift with signal level remains, and will tend to shift frequency response up at high volume. That might be undesirable.

Aiken's comments from his Technical Q&A:
Ceramic capacitors should be avoided, as they are usually horribly microphonic, have very high odd-order harmonic distortion (the "bad, or harsh-sounding" kind), typically mostly 3rd and 5th and 7th harmonics, and have poor temperature stability. If ceramics must be used, the COG/NPO type has the best temperature stability and much, much lower harmonic distortion - stay away from X7R and Z5U types, and ceramic disk capacitors, in particular. Silver mica capacitors aren't without their problems, however, as they seem to have a high failure rate in the field, generally in the form of leaking DC. If used in a tone stack, for instance, they can make all the pots sound "scratchy" due to the presence of a DC voltage across them from a leaky silver mica treble capacitor.

Presumably, it's the microphony, poorer temp stability, and higher distortion he doesn't like.

[norburybrook]

microphony and distortion are maybe contributing to the 'hair' on the OD that Tony and others have mentioned. I am about to swap my SM for ceramics in my BM this coming week. as always I shall report back.



M

[Colossal]

Erwin,

a 47 and 68 pf for a choice on the master
M

Hi Marcus,

Any commentary on that? Different caps for different guitars?

Best,
Dave

Dave,

No I'll try and see which one sounds best. The Ceriatone uses 68pf on the Master volume and also has a 33pf on the OD master. The layout tony did just has the 47 pf on the master.

I'll see which I like, I doubt I'll put on on the OD master.


M

Thank you, Marcus. That is helpful. I am pretty sure I used 68pF for a D-Lite build I did for a fellow, many years ago.

[norburybrook]

Dave,

i've just stuck a 68pf ceramic on the clean MAster and swapped the 470pf on the V1b for a ceramic. I can't hear any difference YMMV



M

[martin manning]

I recall Gary (Glasswerks) tried some NP0/C0G and found that they sounded good, but not different from other types he had been using. The post is here somewhere, but I can’t find it.

[10thTx]

Some of my amps are Dumblish inspired but not Dumble clones. My experience is that in some positions, I found ceramic caps (either the cheapo disc or COG/NPO) to sound better and in other positions found Silver Mica to sound better. I did not find one type to be universally and consistently "better" for my amps. However, since my amps aren't clones this may not be relevant to Dumble clones? I will say that I've had several problems with Silver Mica caps going bad & adding noise.

With respect, 10thtx

[Colossal]

Dave,

i've just stuck a 68pf ceramic on the clean Master and swapped the 470pf on the V1b for a ceramic. I can't hear any difference YMMV

M

Thanks Marcus, that is good to know. I am building a #102 right now, so this discussion is interesting and relevant.

[norburybrook]

I think this goes to show there's still no 'one size fits all' with these amps some amps suit different players, different guitars, you just don't know until someone plugs in and plays. I'v e heard people say listen to this great tone and when I've listened thought it was dreadful or not my cup of tea so it is indeed a very personal thing.





MC

[talbany]

I recall Gary (Glasswerks) tried some NP0/C0G and found that they sounded good, but not different from other types he had been using. The post is here somewhere, but I can’t find it.

https://ampgarage.com/forum/viewtopic.p ... aps#p99700

[talbany]

Dave,

i've just stuck a 68pf ceramic on the clean MAster and swapped the 470pf on the V1b for a ceramic. I can't hear any difference YMMV



M

Marcus
Your not going to hear much of a difference on V1B grid like I said in my last post. Bypass around the pot is dependant on where you have the pot set the difference is subtle but is there with the pot set low. Also when you do your testing make sure you don't have any crap (pedals,loop/w outboard gear) hooked up to the amp as this can color the sound. Strat and a cable straight in. BTW Stll waiting on the results of your Plate resistors you got from Charlie.You were going to try on your 2nd gen or did I miss that post?
Tony

[martin manning]

Your not going to hear much of a difference on V1B grid like I said in my last post.

Tony, which post are you referring to? I'm trying to understand why the type of cap used in this location would not matter...