NOS Mallory capacitors for Rhodes Piano

[Skiroy]

I want to thank You Fahey for being patient with me. And I dont want to be stubborn here but my multimeter has 4 digits so it should be able to read up to 9999 MFD theoretically right? Sorry if Im not getting something but I am new.

And as far as my 5 MFD caps reading 6-7 MFD I get that they are in specs and functional but would you here a difference between these caps from 4.7 to 6.6 MFD? For example there is alot of stuff on the web as far as .022 MFD vs .047 MFD caps in guitar tone pots for tone differences and this is a very minimal difference compare to 5-7 MFD.

There was alot of emphasis on me reading the capacitance of the original caps but I assume the point wasnt to just see if they work so Im waiting for those who suggested this to chime in on what the tone difference would be with these capacitance values. I ESR is a factor but I just want to focus for now on the effect of capacitance on the frequency filtering and what values I looking at for it to make any audible difference.

I mean the capacitance vales for caps in a guitar cicuit seem to vary alot less than this and there is tons of stuff online about how this effects te tone of the guitar and a Rhodes is based on a Pickup design like a guitar so it ant be to far off. Granted a guitar doesnt have a active preamp like a Rhodes.

[Chuck H]

And I dont want to be stubborn here but my multimeter has 4 digits so it should be able to read up to 9999 MFD theoretically right?

Well my cars speedometer goes up to 150MPH. But my car won't go that fast. A dinner plate can easily hold five pounds of hamburger. But that doesn't make it a proper meal.

Your meter almost certainly has a capacitance limitation well below 9999mfd.

For example there is alot of stuff on the web as far as .022 MFD vs .047 MFD caps in guitar tone pots for tone differences and this is a very minimal difference compare to 5-7 MFD.

Nope. .022uf to .047uf is a 115% increase in capacitance. 5uf to 7uf is a 40% increase. The difference between .022uf and .047uf is more significant.

I just want to focus for now on the effect of capacitance on the frequency filtering and what values I looking at for it to make any audible difference.

The audible difference between a .022uf rated cap value (for example) where one measures .020uf and another measures .026uf is pretty much mice nuts. The profound difference you describe isn't a capacitor value difference. The exception being if the old caps are grossley out of spec. The real difference is more likely in the the peripheral parameters of the old caps. As semiconductors there is leakage and esr to consider. Since these parameters can change dramatically with age so the old caps could be affecting the operation of the amplifiers in a way that you find more agreeable than absolutely proper function. To ignore this is to miss the point entirely and you are lost in a place where no one can help you.

[Skiroy]

Well my cars speedometer goes up to 150MPH. But my car won't go that fast. A dinner plate can easily hold five pounds of hamburger. But that doesn't make it a proper meal.

Your meter almost certainly has a capacitance limitation well below 9999mfd.



Nope. .022uf to .047uf is a 115% increase in capacitance. 5uf to 7uf is a 40% increase. The difference between .022uf and .047uf is more significant.



The audible difference between a .022uf rated cap value (for example) where one measures .020uf and another measures .026uf is pretty much mice nuts. The profound difference you describe isn't a capacitor value difference. The exception being if the old caps are grossley out of spec. The real difference is more likely in the the peripheral parameters of the old caps. As semiconductors there is leakage and esr to consider. Since these parameters can change dramatically with age so the old caps could be affecting the operation of the amplifiers in a way that you find more agreeable than absolutely proper function. To ignore this is to miss the point entirely and you are lost in a place where no one can help you.

So in my case ESR is the whole difference here,which is cannot be duplicated so its either put the old ones back in or leave the new ones,

I know this is very off topic but when it comes to using guitar pedals with keyboards,synths ect., is there anything to consider as far as impedance or do you just treat a Motiff keyboard or Moog like a guitar and you can plug them straight into the pedal or guitar amp?

[Chuck H]

So in my case ESR is the whole difference here,which is cannot be duplicated so its either put the old ones back in or leave the new ones,

Sure you can duplicate esr. Or close enough. If you've been reading the posts you'll have seen where I said your old caps are like a capacitor in parallel with a resistor and in series with another resistor. Adding small value resistors in series with the caps will simulate esr. Though esr also changes with frequency. So to get really accurate you would need to build a circuit of other R/C filters as well. It just gets too complicated.

I know this is very off topic but when it comes to using guitar pedals with keyboards,synths ect., is there anything to consider as far as impedance or do you just treat a Motiff keyboard or Moog like a guitar and you can plug them straight into the pedal or guitar amp?

Older keyboard are capable of much higher output than guitars. 100mVAC to 500mVAC for a guitar and up to line level (just under 1VAC) for a keyboard. WRT guitar amps best results come from using the "low" input for keyboards.

Most pedals will take a line level signal just fine. Results may vary with multi effect signal processors. Some preamp based pedals, like distortion pedals, vary greatly in how well they handle higher input signals. Experimentation is the best way I know of to find what sounds good and works well. "Experimentation" includes researching your process and materials. For example. It's generally bad to run distortion pedals in an effects loop. But there is a reason why. Learning that reason is knowledge that can help you in other areas as well. Read owners manuals and operating intructions. Research terms and phrases you don't understand. Learn about the equipement.

[Skiroy]

Does ESR on the the decoupling Caps any effect on the tone?

[J M Fahey]

Dear Skiroy, you are barking at the wrong tree.
Your preamp schematic (to which, by the way, you never referred) , shows 103 parts (I might have missed 1 or 2) which *can* and *will* affect tone.
Why are you focusing on the least likely to do so?
Out of them there's a grand total of four 5uF NP electrolytics.
Let's review them one by one:

1) the one which feeds the tone controls.
Its value variation can explain nothing within the audio band. It´s feeding 2 x 6K8 resistors, one in the treble net, one in the bass net.
Being coupling capacitors, they have a "cutoff frequency" below which they cut audio at 6dB/octave ; above it they do nothing.
They are "flat", pass audio unimpeded. Do nothing.
The cutoff frequency of 5uF and 6K8 is around 5 Hz, WELL below audio frequencies, and from 5Hz up, they do nothing.
*If* they are, say, close to 7 uF , cutoff frequency lowers to around 3.5 Hz.
NO EFFECT ON THE RHODES AUDIO BAND.

Now on ESR:
Suppose they have 100 ohm ESR.
Those 100 ohms will be in series with those 6K8 resistors. Nil (as in inaudible) effect.
Now suppose they have an impossibly high 1K ESR (as in microwaving them or equivalent abuse)
In series with 6K8= 15% difference.
Will this affect VOLUME? Maybe, to the tune of less than 1 dB loss.
Will this affect TONE? No, because you will lose 1 dB on the treble leg, 1 dB in the bass leg, tone remains balanced.

2) the one which feeds the tremolo LDR network,
Same considerations as before, with the difference that it feeds a 3K3 resistor to ground, which rises cutoff to around 10 Hz, still well below the audio band. Above 10 Hz, nil effect.
Possible ESR effect: unmeasurable since it feeds a 10K resistor and 2 LDR in series with 47K each.
Same as before, *if* you had an impossibly high ESR, frequencies would be evenly attenuated in a flat, non tone affecting fashion.

3) the ones which leave the board towards the power amps.
Didn't check them, but I'm sure the designer specified them for a cutoff frequency around 10 Hz, precisely to remove them from the tone equation.
At least that's what he did at the all important preamp input, why change design style now?

4) the power supply decoupling capacitors have an even smaller effect (as in zero) than the ones which are really in your audio path.

5) anyway, to satisfy your doubts, get somebody who can trace your preamp with the warm fuzzy smooth original capacitors and again with the cold sterile new ones.
Then superimpose both sheets of paper and look through them .
There´s your answer.
Good luck.

6) do not cheat.
FIX those pots in a certain position and do not touch them again.
Slightly moving a treble, bass or volume pot 1 mm each side, will change your sound 1000 times more than any coupling or decoupling cap.

Good luck.

[Steve Conner]

Oh come on, this has gone on long enough! Fix the preamp and then run the thing through a tube amp of some sort, that will warm and fuzz it up as much as you like. It's also an excuse to get into tube gear if you don't have any already.

[Chuck H]

The only thing I would add is that leaking capacitors can affect proper amplifier bias. And therefor amplifier function and "tone". This would be the "resistor parallel to the capacitor" effect I spoke of as part of a circuit to emulate the failing function of old capacitors. And FWIW NO ONE DOES THIS. It would be an exhaustive exercise to achieve improper amplifier function.

Old electrolytic capacitors are prime suspects for leakage. Obviously this is most important in circuits that block DC. Not nearly as important in tone shaping circuits UNLESS those circuits also need to block DC. For all the concearn about the old cap tone vs the new caps, it may only be ONE leaky cap in a specific DC blocking circuit making the difference. Almost certainly not all of them. The actual tonal difference between same type capacitors that are functioning correctly is so small that you will never hear it. THE ONLY WAY TO KNOW if a cap is leaking is to TEST FOR IT (he said, ad nausium).

[keys26]

I replaced my pianet preamp caps with modern electrolytics and it sounded terrible so i located some vintage valvo caps like the original ones and all is well. New caps sound terrible sterile in most vintage keyboards .I am trying to get rid of ticking in my peterson preamp and replaced the white caps with some valvo and sounds great. got them on ebay. Good luck and dont let anybody tell you that new caps sound the same.

[J M Fahey]

Nobody says so.
Modern new caps sound "sterile" which means "without distortion" , "low ESR", "accurate value", "transparent", etc.
Old caps did about the same, as well as they could , when they were NEW.

Old caps *today* are 30/40/50 years old, are worn, dried out, drifted all over the place, add distortion, series resistance, lose highs, **are lossy**, you name it, sound becomes wonky fuzzy dirty dull .
Yes, I agree this sounds different than that of properly functioning parts.

Do YOU prefer that?
Please be my guest

[Mick Bailey]

The same with modern radial tyres on my car. The handling is terrible - it brakes, stops and steers perfectly and is so sterile.

Now, those old crossplys from the 60s with their hardened sidewalls and goofy tread pattern are just what I'm looking for. They have character and mojo, and bring back the excitement to motoring. In fact, they bring the excrement back as well.

[Enzo]

Welcome to the place keys.

No one claims new caps and old caps sound the same. Problem is we can't listen to what the old caps sounded like when they were new. You can find NOS caps, but they are still 40 year old caps, with all the age implies. We grow into an amp, it sounds good to us, we like it. Like an old worn but comfortable shoe. The leather has softened, it no longer holds its shape as well, the finish has worn off in places, the sole has worn thinner in spots. One day the amp needs to have the caps replaced, so instead of the nice comfortable old shoe cap sound, we have the sound of fresh new caps. They are not as worn and fuzzy as the old ones. They filter the power better, they hold voltage better. They don't sound the same. it isn't the cap that is different, it is the age. Ther just isn't any way to compare a new 1964 Mallory cap with a new 2017 Mallory cap.

[gbono]

How do you do ABx listening when comparing a change in components? Of course you start by testing whatever it is you are playing through - amplifier, preamp, etc. and making sure it meets it's original design specs/features. You make changes and restest the system yes? Then you retire to your 30 meter anechoic room where you do your listening tests. You play the exact same program you used before with the system in the exact same position - on axis off axis and you record the results of MLS test signals in both cases with your $1500 B&K microphone. BTW you have your hearing tested regularly to make sure you aren't hearing artifacts that aren't there or really are there......I won't go into the issues with old capacitors and their associated reliability concerns which vary depending on the various capacitor dielectrics - aluminum oxide, polymer film, tantalum pentaoxide, ceramic, mica, etc.

[Leo_Gnardo]

Who knows maybe there's something to it? Until today I'd only seen Valvo vacuum tubes, a little poking around on the interwebs turns up some old film caps, electrolytics, other odds n ends. OTOH I'm sure as hell not going to spend time and $$$$ digging up & shipping old capacitors to use in repairing customers' gear.

Also be aware our friends in China are capable of recycling ANY old brand name, sticking it on substandard parts, and flogging that crap on ebay.

Valvo films from Holland on ebay, probably the real thing:

2 PCS. Valvo Mustard Capacitor 1.5nF / 0.0015uF / 400VDC | eBay

Electrolytics:



And, the unexpected:



In green no less, just in time for St. Patrick's day. Wow, that's some chapeau! You STYLIN' dude! Could set a whole new trend in stage wear for rock bands, who knew?

[g1]

Did you check the value of the 'new' old caps? If they are a different value than the original spec, maybe brand new caps of the wrong value would also give the same preferred sound.