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Condensator for modding a peavey classic 30

Started by medium85, April 29, 2015, 06:53:24 AM

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medium85

Hello everyone.
I will start to apologize for my english, i'm a Swede so bare with me.

Im sitting here researching how to modify my peavey classic 30 combo amp, and i found a good guide called the blue mod.
The guide links to several webpages that carries all the electrical components to make this modification.
The problem im having is that these websites are all located in the states, and i live in Sweden.
I've made an order from a big firm that carries lots of different condenser/capacitators/resistors, but some of the components needed are not available.

The salesman at the company suggested that i could buy a different kind of capacitator, the question i have is, will work if i switch to the ones they had available?
The capacitators i need are called mica capacitator, and they are ranging from 270pf to about 1000pf, the answer i got to my request from the salesman is:

The capacitators you needed are of the mica-type, they are called glimmercapacitators. The closest thing to these capacitators that we have in stock are polypropylen. Do you want this type or axial (round with pins from both sides)?

I hope i'm making myself understood, there are some words in english that i dont know if i've translated correctly.

Thankful for help.

Regards

Roly

Hi medium85, welcome.


1. please post a link to the mod page so we can see what you are talking about and get a better idea of what you are trying to do.

2. silvered-mica capacitors are generally high quality and used in radio frequency circuits because of their stability.  Generally this level of stability is not required in audio circuits and polyprop or in fact just about any other dielectric, with the exception of ceramic, should do just fine.  Ceramic can be used and often are as a cheap substitute but they can also be microphonic.


A lot of what is written with great authority about capacitors and the effects that their dielectrics have on "tone" is imaginary rubbish intended to sell cheap components expensively.  We call these people cork-sniffers.




If you say theory and practice don't agree you haven't applied enough theory.

medium85

#2
Thanks for the response.

http://blueguitar.org/new/articles/blue_gtr/amps/peavey/c30_origmod.pdf

So in your opinion this mod is a waste of time and money, or is it just the quality of the component that doesnt matter?

I have never listned to a modded amp, i have only heard youtube clips, and the sound is different than what my amp is putting out.
Could that be because they changed the speaker (and tubes) and that it is recorded through a mic?

Roly

Quote from: medium85So in your opinion this mod is a waste of time and money, or is it just the quality of the component that doesnt matter?

By far the most important thing is the value of the cap.  If you change a cap value, particularly in the tonestack, then the response is going to change in some way in proportion and you are likely to hear it.  But if you simply change all the caps for different dielectrics and the same values you are not going to hear it (whatever they claim - dielectric effects are real but truly microscopic in the context of a guitar amp).

{a great little free fun tool for playing with tonestacks is Duncan's Tone Stack Calculator.}

I am both a tech and a musician and I use both test instruments and my ears.  I can see distortion on my oscilloscope and I can measure it with my distortion meter, but I need my ears to tell me if it's nice or nasty sounding.

I know that my trained ear can just detect about 1% Total Harmonic Distortion (and about half that of crossover distortion), but my meter can measure down to at least 1/100th of that, way below what I can hear.

"Audiophiles" worry about distortion caused by capacitor dielectrics and try to eliminate them entirely, and claim they can clearly hear these effects.  The problem is that tests on various modern capacitor dielectrics with top end equipment cannot find any signs of distortion products down to 0.001%, so "hearing" something smaller than this has to be an illusion, a self-deception.

{in a dead silent environment the lower limit of hearing is due to the noise of blood pulsing near your ears, your heartbeat, and breathing.  And that's only if you have never played loud and got some Tinnitus, then that becomes your noise floor.  :(


}


The quality of components carried by reputable companies is more than good enough for any use in a guitar amp (or any amp for that matter).  The suggestion that there is something "wrong" with inexpensive over the counter parts, and that you need to spend a lot of money on special "mojo" capacitors with fancy names, is simply bunkum.  There is nothing wrong with Orange Drop caps and the like, it's just that they are normally vastly over priced for what they are.  {an exception are paper-in-oil which I wouldn't fit to anything.}


Quote from: medium85I have never listned to a modded amp, i have only heard youtube clips, and the sound is different than what my amp is putting out.
Could that be because they changed the speaker (and tubes) and that it is recorded through a mic?

Changing the cap values will have the biggest effect, changing the speaker may have some effect, changing the valves/tubes will have little or no effect.

Then it is where the clip was recorded and with what microphone/recorder.


If you want to experiment with changing some cap values, then just buy the values you need that your local electronics store stocks, change them, and use you own ears in your own space to evaluate the changes.  Don't like it?  Then just put back the components you changed.
If you say theory and practice don't agree you haven't applied enough theory.

medium85

Ok, i've never modded anything and have no clue about electronics so im thankful for your help.

That was my plan to begin with, have some components with different values to switch between to find the sound i like, was just concerned that it would matter if i couldent get a hold of those silver mica caps.

Just orderd the components, so will start this mod next week.
Thanks for everything


J M Fahey

In a nutshell: silver mica capacitors *are*  good, nobody denies that, and they *probably* let more highs through than other common ones (think the dreaded PIO or paper-in-oil ones) ... in 1930 and 1940  :o

After WW2 (which ended in 1945) hundreds of tons of high quality Military surplus Electronic parts were available for peanuts, literally, often sold by the pound , go figure, so everybody used them.

Leo Fender started making commercial amps in 1948, market was flooded by cheap high quality parts, so it's no surprising that Leo often used *radio frequency*  rated parts (hint: silver mica capacitors) all over the place, even if unneeded for *audio frequency*  duty.

But he used them because of the (capacitance) *value*  , not because of the dielectric (mica).

In fact, in the 80's his amps were chock full of cheap ceramics, go figure  ::)

Enter the superstitious old amp worshippers and they want to do everything like in "the old days" , including other nonsense such as getting angry when a Tech replaces old unsafe (in fact: *forbidden*) 2 wire power cable by a properly grounded 3 wire one.

There was a LONG thread at TGP  ::) by a guy who was very angry at his Tech because he had enlarged a little the power cable chassis hole to fit a slightly thicker (duh!!!)  3-wire and so had *destroyed*  the amp Mojo ... or so he claimed.

What's crazy is that about 50% of the answers told him "no big deal" or straight "don't be stupid".... but the other half agreed with him and told him to sue the Tech or punch his nose  :duh :loco