Capacitor replacement

[Moosehead]

This is probably a dumb question, but here it goes....

Can I replace film capacitors with electrolytic ones of the same value? Specifically, I'm referring to the 1uf caps at the input/output buffers in my Tubescreamer clone (a la this schematic: http://tonepad.com/getFile.asp?id=81).

The reason I ask is because the only film caps I could find are so huge that I've bent them overtop the circuit board...not unlike giant umbrellas. I just drilled up a new Hammond box for this circuit, and I'd really like for this thing to fit properly!

Thanks in advance guys.

[jlullo]

yes, just make sure that they are non polar... i remember reading somewhere on here that you can use polarized caps if you orient them a certain way, but just to be sure i'd stick to NP

those film ones are monsters sometimes

[Processaurus]

Ah, the big cap blues.  With electrolytics the plus side needs to go toward the higher voltage, but since it looks like the voltage will be the same (Vb, 4.5v)on either side of those caps, my hunch is that it won't matter.  You should double check with your multimeter if one side is higher than the other, I don't have a TS in my life to check for you.

You can make a real non polar 1 uF out of two 2.2uFs in series, with the negative ends tied together, and the plus ends connecting to the circuit.

Also you can parallel two .47uF film caps to get a ~1uF non polar film cap.

[oldrocker]

You can make a real non polar 1 uF out of two 2.2uFs in series, with the negative ends tied together, and the plus ends connecting to the circuit.

Actually if two regular electro 2.2uFs are in series with negatives tied together,  with electos one cap cancels out the other so you end up with a non polar 2.2uF.  If they were film or ceramic types then the value would be 1uF.
To make non polar 1uF out of an electro you would need two 1.0uF electros with the negative leads tied together.

[sfr]

If you used the tonepad layout, the "box style" 1uF NP caps that smallbear sells (I don't remember the manufacturer off the top of my head) fit perfectly.  FWIW.

[mac]

Film capacitors sound a lot better than electros. I replaced the std 2.2uf and 22uf in a fuzz face and the differences are really big... as big as the film cap 
When I need to buy film >1uf, I always found ones with a max voltage of 100V and above. A 2.2uf 25V film size should not be so big.
Even ceramic and tantalums sound a lot better and do not suffer from aging. Electros die on high freq. Another possibility is to mix caps, a big uf electro with a film of about 0.47 to 1uf to help the freq response.

There is a recent post with a link to a company that makes small size film caps. Use the "search" button.

mac

[Mark Hammer]

A big part of how the TS-9 "works" has to do with complementary filtering of the low and high end.  Now, it is extremely common that DC-blocking caps in pedals produce rolloffs that are wayyyyyyyyy below what another component elsewhere might produce.  It's not uncommon to find that a DC-blocking cap at point X results in a rolloff around 3hz.  In effect, that particular cap could be chopped in value considerably without detracting from bass response.

This is the long way of asking whether a 1uf value is absolutely necessary or whether the design could easily accommodate a value of, say, .22uf without any audible change in bandwidth at the low end.  If 1uf was only critical for cosmetic duplication, but not for auditory duplication, then that could make life a helluva lot easier for a lot of folks.

So, do we need it (1uf NP) or are we just blindly copying something that was overdesigned?

[R.G.]

We're blindly copying.

In particular, the first 1uF produces a rolloff of 15.9Hz, so the cap could easily be changed to .22uF to get a rolloff below guitar's 82Hz and much below the limitations already applied by the first input cap.

The second 1uF sees about 33K load, so it could be as little as 1/3 of the 0.22 - say 0.086uF. Use a 0.1u.

I doubt if one could hear much difference. Maybe some golden ears could, and it may not be all that good for bass as is, but then the TS isn't all that good for bass anyway.

[Mark Hammer]

Thank you, sir.  I think that may have eased the strain on a great many people, given how easy and cheap higher quality caps of those values are to obtain.   Some of those board layouts also run a little tight and assume that one has purchased NP caps of a given convenient size.  being able to safely stick in a smaller value without having to contort the leads will be nice.

I wonder how often we make this same sort of blind assumption with other "classic" pedals?

[Gus]

 There are small films that fit no problem.  Google or search mouser or digikey or....

F= 1/2 pi R C is your friend

Ohms law
DC power

[Moosehead]

If I was smart, I would have known to series two caps to equal 1uf. But, as seems to be the case, I need to be told what I should already know. My apologies.

So, according to what Mark and RG were saying, I can substitute a much lower value for these mammoth 1uf caps without much audible difference? If so, should I use the values suggested (.22uf input, .1uf output), or could I use a value as close to the original 1uf as possible...provided they fit inside the enclosure?

Or will it make any lick of difference whatsoever?

[Mark Hammer]

So, according to what Mark and RG were saying, I can substitute a much lower value for these mammoth 1uf caps without much audible difference? If so, should I use the values suggested (.22uf input, .1uf output), or could I use a value as close to the original 1uf as possible...provided they fit inside the enclosure?

Or will it make any lick of difference whatsoever?

When it comes to caps in the signal path, the rule is that rolloff goes up an octave every time you halve the cap value.  RG notes the bass rolloff  as starting just below 16hz when using 1uf caps are used in the circuit.  The "rolloff" point is defined by the frequency where amplitude is 3db down from an otherwise flat frequency response.  So, at 16hz or so, bass is down a couple of db from 32hz, but 32hz is not down from 64hz.  Cut the cap value to .22uf and the rolloff is now (theoretically, because of the assorted tolerances of the components involved) around 73hz.  That's not ruler flat down to 73hz.  Rather, 73hz is down a couple of db, which defines it as the corner frequency (point where the rolloff begins).  Make that substitution once at one point, and you probably won't notice any impact.  Make that substitution in several places, and the effect is cumulative.

So, the question to ask yourself is "What will the cumulative impact of the cap value substitutions be?" and make your component selection based on that.  That will lead you to favour larger "smaller" values (i.e., .33uf instead of .27uf).

But superimposed over absolutely all of this, however, is the reality of that .047uf cap in the gain stage.  That cap, in tandem with the 4k7 resistor creates a bass rolloff starting around 720hz.  At 6db/oct attenuation, that provides around 24db of cut by the time you get down to 45hz.  In the face of that rather substantial bass cut, and in the grand scheme of things, a couple of db loss around 60hz is not really going to be all that noticeable.  IF the design of the pedal did not depend on that tone shaping (and in this case it does very much), then you'd probably want to adhere more closely to the original cap values, but since the bass loss imposed in one part of the circuit is so much more robust and extensive than the rather feeble attempts to preserve bass in other parts of the same circuit, that buys you the latitude to take a bit of a "bass hit" if the only caps you have handy that will fit are a smaller value than 1uf.  So the sonic penalty for using a value as low as .22 should not be terribly big, given what else is going on in the circuit.  If you have a .39 and a .22, stick the bigger value in earlier in the signal path.

The underlying lesson here is to think in terms of the broader picture and ask yourself a couple of pertinent questions:

• Is there any point in the circuit that radically reshapes or limits the bandwidth of my signal, and how (and how much) does it do so?
• Is there any impact of my attempts to preserve bandwidth either upstream or downstream from that point?
• What will the potential cumulative impact of all those limits imposed on my bandwidth be? (this includes not just within the individual pedal/effect, but across any combination pf pedals you might consider using, such as TS + Phaser + Chorus)

Keep those basic principles in mind, and you'll more frequently end up with "comfortable" choices in components, and a tone that meets your needs and satisfaction.

[R.G.]

I wonder how often we make this same sort of blind assumption with other "classic" pedals?

All the time. Especially with the Originality Police running rampant.

There are several pitfalls in inter-stage rolloffs to be avoided. One is that if you put the same rolloff at each one, the -6db at the half power point cascades. You get -6db at the first rolloff point; not too bad. But you also get -12db at the second, -18db at the third and so on. The more stages you have, the more losses get cascaded.

In general, if bass rolloff or treble rolloff is important to get right, you need to do it all at one place, and make the other places not matter by being far outside the desired rolloff. Otherwise, the tolerances of every stage get into the act. Not to mention that there's a heavy computational load on the designer to get all of those things tinkered to be just right.

It's like the principal of eggs in a basket. Either don't put all of your eggs in one basket, or do put them all in one basket and watch the basket carefully. Both work for different situations.

In the case of the tube screamer, they did this by putting that 720Hz rolloff in a single place, and flipping in relatively huge values for other interstage bass rolloffs.  Less huge doesn't matter for the huge ones.

[Mark Hammer]

In 1998, I had the pleasure of being part of a team assessing applicants to a management training program. These were all bright-eyed and bushy-tailed recent graduates who were looking to move up the ladder.  We ran them through a variety of exercises over the course of an 8hr day, intended to provide fodder for a fairly comprehensive assessment.  One of the activities involved a role-playing exercise in which I was an irritated contractor who had tendered a bid that really ought to have won, but due to an administrative screwup I was shut out.  The applicant had to play the role of the manager.

All the folks playing manager were to acquaint themselves with some organizational policy documents before I walked into the room (and I'm pleased to say some thought I was a professional actor hired for the role-playing job; maybe HBO has a place for me yet  ).  Interestingly, they tended to sort rather easily into "little Nazis" and flexible administrators.  The flexible administrators tended to be folks who, when we had a friendly chat afterwards at the end of the day, had a long affiliation with organizational policies in one form or another, whether it was organizing the high school yearbook, overseeing fundraising activities at university, or supervising Brownies or Boy Scouts.  The little Nazis were people who, although quite bright, simply did not have enough fundamental understanding of the way that policies are forged and work, and how organizations work, to render a decision that was anything other than "These are the rules!" and blindly adhere to them because they believed it was how to show their integrity.

I mention this because understanding how things actually work, and especially how everything fits together, buys you SOOOO much flexibility.  Some of the "Originality Police" you mention are no doubt rigidly adhering to specs because of financial considerations (i.e., responding to potential clients whose own lack of understanding makes them clutch their wallets more tightly because they can't adequately judge when something is only negligibly different versus very different).  But many are people whose naive belief in original specs becomes more fervent the less they understand about those specs and about how the object in question works in the real world.  You will note that many of the questions about the acceptability of certain parts substitutions often come from those who often know the least...by their own admission.

I don't mention all of this to make fun of anyone or denigrate them.  Rather, it is encouragement to understand a little more about both the theory behind things, their "mechanics" or inner workings, and at the other end, the "big picture" of how they operate in the broader context.  It is tremendously liberating and buys you much more flexibility.  Most of the things we make here are exceptionally tolerant of changes in component values or types, but one needs to think about where those parts fit into the big picture to realize that.  On the flipside, many of the things that we can often engage in ridiculously nitpicky debates about simply stop mattering the moment the volume knob goes past 4 or the loudness goes above conversation level, or the moment some other pedal is plugged in ahead or after the circuit in question.  Knowing more about theory, and thinking more about context, will always help you to be able to identify when some things matter, and when they don't.

And Brother Keen, nice post.

[Moosehead]

Curse those "little Nazi's" and their willful ignorance. I have zero patience for such people, in any area of life.

But back to the point...the reason why I seem to be harping on the whole 1uf thing is that I was quite fond of my TS9 the way it was.

I run my guitar's pickups through an internal buffer (the Tillman buffer, to be exact), through the naturally un-bassy TS9, and through the rest of my true-bypass pedals. Thus, I end up going at the front of my amp with a lot of high-end, which I tend to prefer.

I was just a little worried that dropping the values of the input/output caps too much on the TS9 would brighten the overall sound excessively. I suppose it doesn't really matter in the grand scheme of things...I can always compensate later on in the signal chain, or in the amp's tonestack.

Thanks for the help guys. I really appreciate it!