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[Tom Young]

I have usually noticed blocking caps to be rated above 200 MFD rather than 30, which I pictured above.

DC blocking capacitors were used in an actively crossed over system, in series between the power amp and the HF driver. They represent a 6dB-per-octave high-pass filter and are centered well below the crossover point so they do not effect the sound. If I recall correctly, 1/2 the crossover frequency was the rule-of-thumb. They block DC (in the old days we often used consumer amps and there were also "pro" amps, both of which would frequently fail and output DC) as well as the high-level LF energy emitted when the system is turned on or off (thump).

Note that such capacitors cannot be used in passively crossed over systems without adversely effecting the crossover's performance.

Here's a handy looking calculator:

http://www.fuzion.co.uk/Support/Calcs/HFprotect_form.aspx?Title=HF%20Driver%20Protection%20Capacitor%20Calculator

Motor starting capacitors are used primarily for their higher voltage (power) handling. They typically have not been used in crossovers because they are large and expensive. Plus they may not be readily available in the lower capacitances required for most crossover filters.

Blocking capacitors are hardly used these days as power amplifiers are far more reliable and are designed to not output DC when they do fail. The higher order crossovers used these days usually protect HF drivers from system on/off thump (and DC) plus many amps have delayed turn-on and turn-off. 

[John Halliburton]

I've been rebuilding a section of crossover in a pair of SM200 wedges, where the 30uf/100v electrolytics completely blew apart, some resistors got really hot-enough to melt the plastic bobbin on a nearby coil, and make the hot melt adhesive run.

I opted to go with 30uf poly caps with a 400 volt rating as replacements.  Much larger, but hopefully a bit more robust.

Admittedly, the wedges were used for a DJ's monitoring pleasure...one woofer was blown along with the handful of crossover parts.

Parts Express is another source-I've been a longtime customer of them and Madisound(since 1982!).

Best regards,

John

An update on the SM200 wedges-got everything stuffed into place and rewired(two 30uf caps, three coils, four resistors replaced in each wedge-identical work in each), reassembled them, with the one reconed woofer.

Off to QA and have a listen.  My workmate calls me over, and he points out that they both sound the same, except for the reconed wedge has a tighter low end response.  The other woofer we conclude, is "tired"(to quote Tom D.), and moves more under use(more "woofy" in the true sense of the word);>)

Customer passes on the second recone due to budget requests/allocations/paperwork/end of year situations.

Best regards,

John

[Bob Leonard]

I have always been cautious when selecting capacitors for use within the tone section of any device, active or passive. Capacitors types do effect tone, and it's an effect that can be heard. Some of you may know that I rebuild fender amplifiers, and that the amplifiers I rebuild are often singled out for their great tone. This is not an accident, but more a practice of having found and then using a specific manufacturers cap and manufacturers specific type of cap within the critical sections of the amplifiers, or crossover, that I repair. And, each type will have it's own tonal qualities.

I highly suggest that people rebuilding or repairing quality hardware refrain from using almost all Chinese manufacturers capacitors. There are many reasons for my recommendation, just be aware that most chinese caps are not reliable and seldom meet specs.

I have listed a number of links to supply houses that I use for NOS or quality capacitors, resistors and parts.

http://www.hoffmanamps.com

http://store.marshamps.com/product_info.php?cPath=25&products_id=44&osCsid=l246odgr884hgsphuq8i2b1ri3

http://www.mojotone.com/amp-parts

http://www.kendrick-amplifiers.com/mm5/merchant.mvc?Screen=CTGY&Store_Code=KOS&Category_Code=060401A

[John Roberts {JR}]

I have always been cautious when selecting capacitors for use within the tone section of any device, active or passive. Capacitors types do effect tone, and it's an effect that can be heard. Some of you may know that I rebuild fender amplifiers, and that the amplifiers I rebuild are often singled out for their great tone. This is not an accident, but more a practice of having found and then using a specific manufacturers cap and manufacturers specific type of cap within the critical sections of the amplifiers, or crossover, that I repair. And, each type will have it's own tonal qualities.

So if i understand what you are saying, not only the type of cap (dielectric) but different manufacturer's caps will have different "tonal" qualities. I ASSume you mean these differences exist even with all else equal. So same value, same tolerance, same breakdown voltage, same construction (radial/axial/etc), same dielectric, but from a different manufacturer, will sound different??

Have you dug any deeper into the capacitor spec sheets to find stated performance differences or do you consider them unreliable too?

I highly suggest that people rebuilding or repairing quality hardware refrain from using almost all Chinese manufacturers capacitors. There are many reasons for my recommendation, just be aware that most chinese caps are not reliable and seldom meet specs.

"Most are not reliable and seldom meet specs". That seems a bold statement.

I have listed a number of links to supply houses that I use for NOS or quality capacitors, resistors and parts.

http://www.hoffmanamps.com

http://store.marshamps.com/product_info.php?cPath=25&products_id=44&osCsid=l246odgr884hgsphuq8i2b1ri3

http://www.mojotone.com/amp-parts

http://www.kendrick-amplifiers.com/mm5/merchant.mvc?Screen=CTGY&Store_Code=KOS&Category_Code=060401A

I do not dispute your personal experience, and agree that using the correct parts for the task matters. Capacitors used in audio frequency tone shaping circuits will have changing terminal voltage across them at audible frequencies, so terminal voltage related nonlinearities (like voltage coefficient) certainly matters. To answer my own question "WTF does this have to do with loudspeaker crossovers"? they too have changing terminal voltage at audible frequencies, so also need good voltage coefficient performance.

I find your claims more than a little hyperbolic, but agree with the general thesis that the performance of components used will matter, more so in some applications than others.

JR

PS: I have used quite a few capacitors over the years (too many to count), and I have experienced US made caps that didn't meet their own specs too, but in my experience the vast majority of components do what their makers claim they do on their spec sheets, or they get to buy them back. Been there, done that too.... but i didn't buy parts onesy twosey from ebay.

[Bob Leonard]

So if i understand what you are saying, not only the type of cap (dielectric) but different manufacturer's caps will have different "tonal" qualities. I ASSume you mean these differences exist even with all else equal. So same value, same tolerance, same breakdown voltage, same construction (radial/axial/etc), same dielectric, but from a different manufacturer, will sound different? ?


Have you dug any deeper into the capacitor spec sheets to find stated performance differences or do you consider them unreliable too? "Most are not reliable and seldom meet specs". That seems a bold statement.
I do not dispute your personal experience, and agree that using the correct parts for the task matters. Capacitors used in audio frequency tone shaping circuits will have changing terminal voltage across them at audible frequencies, so terminal voltage related nonlinearities (like voltage coefficient) certainly matters. To answer my own question "WTF does this have to do with loudspeaker crossovers"? they too have changing terminal voltage at audible frequencies, so also need good voltage coefficient performance.

I find your claims more than a little hyperbolic, but agree with the general thesis that the performance of components used will matter, more so in some applications than others.

JR

PS: I have used quite a few capacitors over the years (too many to count), and I have experienced US made caps that didn't meet their own specs too, but in my experience the vast majority of components do what their makers claim they do on their spec sheets, or they get to buy them back. Been there, done that too.... but i didn't buy parts onesy twosey from ebay.

John,
Never ASSume. To your first point you are correct. The manufacturers assembly methods and capacitor type (dielectric) will make a difference in tone. Certain older capacitors are well known for their smooth tone qualities while some very popular newer style capacitors tend to accentuate high frequencies. Sprague "black beauty" caps are an example of old school build technique that will result in a wonderful smooth tone across the entire frequency spectrum. Yet, Sprague "Orange drops", a good high quality cap, are often over used and will more often than not result in an amplifier that sounds brittle and with an eccess of high end. And please note that where the cap is located in the circuit will determine the type which should be used.

Open any classic amplifier and you'll find very few ceramic disk type caps, which are fine for use in tremelo control sections and power and first stage input sections, or in tone stages where you might want a slightly dirty tone. Leo had his shit together here. He found a combination based on available parts and held on to that combination of components through every one of his amplifiers. A combination so well thought out that James Marshall copied it.
 
For my own use when blueprinting or rebuilding an amplifier I use purpose built caps that are manufactured using the same materials and methods as used by Sprague 60 years ago. The biggest difference in the manufacturing process is the foil thickness and foil type.
 
A quick look at spec sheets seems to indicate all things equal. What I, and many others have found is that most, but not all, Korean and Chinese manufacturers electrolytic caps used for the express purpose of power supply filtering or used in crossovers (Sprague Atom, axial lead, 450v replacement cap) tend to have over rated voltage ratings. Simply put, a 450v Korean or Chinese cap will usually fail at or around the rated working voltage, where most US made caps will not, and can often be pushed harder at higher voltages, even as much as 100v higher than the caps specified rating without failure. These caps seldom effect tone other than to say poor power supply filter caps can result in too much B+ sag which will equal low headroom, low output, and increased distortion. Yes it was a bold statement, but experience has proven that chinese caps will usually fail when least expected, especially when higher voltages or current is a part of the equation.
 
Also note that nothing is what it seems to be. Sprague builds their caps to electrical and physical specs, i,e, exact replacement type. Open a Sprague Atom cap and you'll find a smaller cap inside a larger housing, built using newer materials and techniques, but electrically equal to anything built before now.
 
"To answer my own question "WTF does this have to do with loudspeaker crossovers"? they too have changing terminal voltage at audible frequencies, so also need good voltage coefficient performance."
 
You are correct and that is my view as well. How well does a specific manufacturers cap sound in the circuit. As with any sound producing device the circuit type, quality and type of components used will make an audible difference. If that were not the case there would be no reason for me to have chosen an APB board over a Behringer board, or an Avid board over an LS9. Some companies get it, some people get it, others don't. Leo F. and Chuck A. certainly "get it", but it wasn't by chance. What it took was a critical ear and a good amount of experimentation topped with lot's of knowledge, experience and a desire to give people what they wanted.
 
I like you have seen more than enough caps in my lifetime, but not one from an Ebay purchase. I buy in small bulk, usually 100-200 at a time, enough to find some bad caps in an order from time to time. Hell, nothings perfect (especially me).

 
What type caps do I use in the amplifiers I rebuild?? You'll have to look at the pictures. One tip for the masses. All caps regardless of type have a ground side. In an electrolytic this is the negative side of the cap. In other types that have no polarity this is the terminal or lead where the foil is attached.
 
Best practice is to run all of the caps in the same direction making sure that the ground end of the cap runs to the chassis ground side of the circuit even though, excepting electrolytics, electrically it won't make a difference. This will result in the lowest noise floor. How do I know if a non polarized cap needs replacement? Lift the ground side, apply voltage to the circuit and measure for voltage coming back through the cap. Some times being old can be usefull.    I guess what I'm saying is that I don't feel you can be too careful when selecting caps used in tone circuits. To me every type has a purpose and not all are created equal regardless of specs.

[John Roberts {JR}]

John,
Never ASSume. To your first point you are correct. The manufacturers assembly methods and capacitor type (dielectric) will make a difference in tone. Certain older capacitors are well known for their smooth tone qualities while some very popular newer style capacitors tend to accentuate high frequencies.

I don't expect much mystery there. Modern caps are most likely improved in their HF characteristic, while better on the bench measurement, may not sound better where HF roll off is euphonic.

These are not unknown or hidden from spec sheets.

Sprague "black beauty" caps are an example of old school build technique that will result in a wonderful smooth tone across the entire frequency spectrum. Yet, Sprague "Orange drops", a good high quality cap, are often over used and will more often than not result in an amplifier that sounds brittle and with an eccess of high end. And please note that where the cap is located in the circuit will determine the type which should be used.

no doubt...

Open any classic amplifier and you'll find very few ceramic disk type caps, which are fine for use in tremelo control sections and power and first stage input sections, or in tone stages where you might want a slightly dirty tone. Leo had his shit together here. He found a combination based on available parts and held on to that combination of components through every one of his amplifiers. A combination so well thought out that James Marshall copied it.
 

A great deal of guitar amp design was trial and error, lets see what happens if we do this? Parts selection is part of that grand experiment. While the amp designers I know and worked in the same office with are not of the same notoriety as a Leo Fender, they did good work, while I don't expect Peavey to get much respect due to brand image and positioning. 

Before we make more sweeping generalizations about ceramic dielectric, modern NPO/COG dielectric can be as linear as the best films.  Of course many cheaper ceramic dielectric intended for constant voltage PS decoupling, are not very concerned about voltage coefficient so use cheaper approaches.

For my own use when blueprinting or rebuilding an amplifier I use purpose built caps that are manufactured using the same materials and methods as used by Sprague 60 years ago. The biggest difference in the manufacturing process is the foil thickness and foil type.
 

For the record this thread is about repairing a crossover, which is not generally reliant upon non-linear capacitor behavior for voicing. While the parts should equal or exceed the original equipment parts.

A quick look at spec sheets seems to indicate all things equal. What I, and many others have found is that most, but not all, Korean and Chinese manufacturers electrolytic caps used for the express purpose of power supply filtering or used in crossovers (Sprague Atom, axial lead, 450v replacement cap) tend to have over rated voltage ratings. Simply put, a 450v Korean or Chinese cap will usually fail at or around the rated working voltage, where most US made caps will not, and can often be pushed harder at higher voltages, even as much as 100v higher than the caps specified rating without failure.

Not so funny story... I know an amplifier designer who used to depend upon conservative capacitor specs in his design work to save a few dollars by using under rated parts. Until it bit him very hard in the ass... with entire production runs of amps that would hand grenade in the field from even moderate over voltage. 

Prudent designers do not ignore spec sheets. it is the written contract the vendor must meet.

These caps seldom effect tone other than to say poor power supply filter caps can result in too much B+ sag which will equal low headroom, low output, and increased distortion. Yes it was a bold statement, but experience has proven that chinese caps will usually fail when least expected, especially when higher voltages or current is a part of the equation.
 

I doubt we could completely avoid Chinese components if we wanted to. While I have visited inside Mexican capacitor factories back in the good old days. 

Also note that nothing is what it seems to be. Sprague builds their caps to electrical and physical specs, i,e, exact replacement type. Open a Sprague Atom cap and you'll find a smaller cap inside a larger housing, built using newer materials and techniques, but electrically equal to anything built before now.
 
"To answer my own question "WTF does this have to do with loudspeaker crossovers"? they too have changing terminal voltage at audible frequencies, so also need good voltage coefficient performance."
 
You are correct and that is my view as well. How well does a specific manufacturers cap sound in the circuit. As with any sound producing device the circuit type, quality and type of components used will make an audible difference. If that were not the case there would be no reason for me to have chosen an APB board over a Behringer board, or an Avid board over an LS9. Some companies get it, some people get it, others don't. Leo F. and Chuck A. certainly "get it", but it wasn't by chance. What it took was a critical ear and a good amount of experimentation topped with lot's of knowledge, experience and a desire to give people what they wanted.
 

I actually know Chuck and the other APB lads pretty well. I coded the software in the ProDesk series meter, but know them from earlier Crest days, and JP from even before that. I won't attempt to characterize their design philosophy while I am tempted to from my years of knowing and working with them. The results of their effort speak to the sound quality their customers appreciate, and I routinely discuss actual data sheet specs with JP (even about passive components on rare occasion).

I like you have seen more than enough caps in my lifetime, but not one from an Ebay purchase. I buy in small bulk, usually 100-200 at a time, enough to find some bad caps in an order from time to time. Hell, nothings perfect (especially me).

 
What type caps do I use in the amplifiers I rebuild?? You'll have to look at the pictures. One tip for the masses. All caps regardless of type have a ground side. In an electrolytic this is the negative side of the cap. In other types that have no polarity this is the terminal or lead where the foil is attached.
 
Best practice is to run all of the caps in the same direction making sure that the ground end of the cap runs to the chassis ground side of the circuit even though, excepting electrolytics, electrically it won't make a difference. This will result in the lowest noise floor. How do I know if a non polarized cap needs replacement? Lift the ground side, apply voltage to the circuit and measure for valtage coming back through the cap. Some times being old can be usefull.    I guess what I'm saying is that I don't feel you can be too careful when selecting caps used in tone circuits. To me every type has a purpose and not all are created equal regardless of specs.

I don't think we are in disagreement about the actual science. As i said before tone circuits, have terminal voltage across the capacitors in use, so will express voltage coefficient errors. All stuff found on the data sheets and used by design engineers.

JR

[Bob Leonard]

The grand experiment. To me that's what it's always been and shall remain. for the record, Peavey made and still makes some pretty high quality guitar amps with tone as good as, if not better than most. Highly under rated, built with good attention to detail, and better quality parts all around. To me Peavey has always been given a bad rap. Just like any other mfg. there were and are some clunkers, but Peavey isn't a name I would be ashamed to have attached to my guitar or in my rack. My hat's off to you Mississippi boys. (Did I spell that right?)

[John Roberts {JR}]

You spelt it rite but I'm not really a Mississippi boy...  Born in NJ and citizen of several states since then (including a few years in Boston, MA back in the late '60s).. But I have to admit MS is pretty easy living these days. Not big easy, but easy. :-)

I went to MS to help peavey kick Japanese butt and well...they are no longer taking over the audio world. While It's a little harder these days to keep score by country. China kind of leap frogged south America, and Korea, and a list of others "cheap" countries for where to actually build it.
===
I really miss my house band from back when I worked at Peavey and had beer parties at my house every few months... The lead bass amp designer, and lead guitar amp designer, not to mention the industrial designer who won "best guitar player in MS" two years in a row... would come out with prototype experimental guitar amps and rock the house...   Yes there was "tone" present.    Usually two or three local working bands would take turns jamming. While they would usually show up real early and/or real late.  They would start hitting the chili (and beer) around noon... sometimes it (the chili) was gone before the civilians showed up. I never ran out of Johnny beer.

I still have the home brew beer going on... just no mo hard partying at the house.     My house band is now spread across the country... I think. Lost track of a few.

JR

[Curtis H List (Too Tall)]

Hi,
I have been building crossovers for Pro speakers since 1998.
Everything should be designed to handle the power of the most highly rated drivers, in most cases a 500watt to 1kwatt woofer.

Even with this information how much the power that capacitors, inductors and resistors will see is complicated.
Either you need modeling software that lets you know or you have to use high power parts everywhere. Also the kind of filters you build with them and where they are in the xover makes a huge difference.

First to look at is the resistors. You said a resistor showing heat stress was next to a capacitor that swelled and blew up.
Odds are the cap did not die from over voltage, but was cooked to failure by the resistor that was too close and too hot.
To stop this use high power resistors such as the 25watt sand cast wire wound resistors that Madisound sells.

Looking at what my modeling tells me if I put 64 volts in the xover the xover overall will see over 500watts.

When you build the L-pad for turning down the horn you may find the series resistor will see 80watts.  The resistor is a 12 ohm.
To handle the power you need four 25watt 12 ohm resistors built in series and parallel to make a 100watt  resistors at 12 ohm.

For capacitor it is less complicated.
The electrolytic caps have a limited shelf life and low voltage handling. For modern pro drivers they are a bad idea.

I use SOLEN poly 400volt both at MADISOUND and PARTS EXPRESS.
The Solen brand is not expensive, it just that the BENNIC and other electrolytic are cheap as dirt.
Note that there are a many “Audiophile” Brands caps that cost a fortune. The Solen brands is not one of them. It is a great product at a very fair price. Again, just because there is something very cheap, does not mean it is a good idea in a Pro speaker.
The main use for electrolytics is use where there is limited space such as a camcorder. Very expensive camcorders use dozens of electrolytic caps because if they used Solen poly the camcorder would be the size of a microwave oven.

Also speaker companies have used cheap parts and often fewer parts because the customer does not see they are being screwed.
OUT OF SIGHT OUT OF MIND!

This can also happen because they use a filter circuit that gets pounded.
To take care of BAFFLE STEP you use an inductor and resistor in parallel with each other and more importantly they are in series with the woofer. It is often the first circuit after the power amp.
So this resistors gets pounded with a full bandwidth signal and burns up when you clip the power amp (or sooner).

Understand that this works fine in most home audio speakers with 30watt woofers, but goes up in smoke when you try to run a PRO speaker rated at 500watts.

So use the Solen caps.

Use the 25watt sand cast wire wound resistors.
 Use more than one where needed. They only have so many values they make so you often have to use a 12 ohm and a 15 ohm in parallel to make a 6.7 ohm 50watt resistor.

Lastly look at the inductors. For highs use 18 gauge wire and air core.
For the low pass for the woofer use as large a gauge wire as you can.
16 Gauge at a minimum.
I use iron core inductors for High power woofers to keep the resistance (DCR) down. If the xover point is higher than 2kHz I bite the bullet and use air core.

[Charlie Hughes]

I really miss my house band from back when I worked at Peavey and had beer parties at my house every few months... The lead bass amp designer, and lead guitar amp designer, not to mention the industrial designer who won "best guitar player in MS" two years in a row... would come out with prototype experimental guitar amps and rock the house...   Yes there was "tone" present.

That, my friend, is a serious understatement if ever I've heard one.

I miss Johnny beer, too!

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