Using Higher Voltage Rated Film Caps in ALTEC Crossovers

[LowOhms]

This is not written for the vast majority of this Forum users, but I want to make public some very recent initial findings for current and future ALTEC users. A little-discussed possibility, for folks to consider.

It is in regard to multiple film cap bypassing of crossover caps, and using higher-voltage rated caps.

I am finding that the voltage-rating of a crossover cap can play a very audible difference through VOTT A7-800s, driven with my Type 45 SET amplifier.

Except for my Dad’s 604Bs as an 8 year old, I have only been in the ALTEC “camp” for about two years. Have had A7-800s going, for only seven months. I tend NOT to follow conventional approaches discussed up here, for ALTEC speaker and amp set-up. I tend to rely heavily on just a few people I respect and mostly - what I hear.

I find from what I’ve heard, that no ONE cap will “have it all” as far as possessing audio goodness “in all ways and in all frequency ranges”, no matter how expensive it may be.

This leads me in 2016 to employ multiple film cap bypassing to my 2-way ALTEC DIY crossover, in an attempt to get the most enjoyment from my audio system.

Done wrong, multiple bypassing can easily degrade a system in one’s room. It will spectrally “overlap”, smear, and can cause a fuzziness to the presentation that is disconcerting.

Done ideally, it will bring out many good things, such as more life-like instrumental timbres, with higher dynamic range, wider perceived bandwidth, and a generally greater believability of the sonic presentation in one’s listening room.

There are NO instructions, on how to achieve “ideal ” film cap bypassing, and in the end, the EAR seems to be THE determining factor - as to what to use.

A classically-trained E.E. may narrowly see that the voltage signal handled by the crossover will not exceed “ X” VAC, and so, they will specify a cap rated in a voltage slightly ABOVE this “X” voltage, as “seen” in the crossover.

When one uses grossly-higher voltage-rated caps, I am lately finding the dielectric and construction may give it an AUDIBLE advantage, over the same Manufacturer’s cap, at the same uF ( capacitance ) value, except having a lower-voltage rating.

ALTEC drivers, when well set up, have tremendously good transfer function capabilities, and so, small changes anywhere and everywhere in the audio system are PERCEIVED through ALTECS, easily to a careful listener.

So far, over the last couple of weeks, when I go to a higher voltage rated crossover bypass cap, ( same type, same manufacturer, and same uF value ) the system to my ear easily (a) almost always plays louder (b) with greater dynamics, and (c) increased transparency.

When multiple film cap bypassing, audio people up-till-now, might consider all the following things:

a) The uF value(s) of the bypass cap(s) one will employ,
b) The type of film cap, its basic construction,
c) The use of “mixing” types of constructions, to see if one can gain each type’s benefits, and NOT lose coherency
d) The Manufacturer of said cap, and there are many to choose from
e) The cost of said cap, versus one’s budget, they can easily go over a kilo-buck !!
f ) Uniform orientation of the film cap’s outer winding

g) To (a) through (f) above, I suggest we need to ALSO consider (g) : the voltage rating of the multiple bypass cap, because, so far, in “ general ” to me - higher voltage rated film bypass caps usually sound better, ( on a somewhat optimized ALTEC A7 VOTT system, driven with good source material, and better electronics. )

How many ALTEC users have taken all of the above, (a) through (g), into account ????

For the record, my present DIY A7 crossovers are textbook at 800 HZ, 16 ohms, 12 dB , Butterworth, with a pad-down resistive network to GPA re-magged 802Ds, on Emilar EH-500 Horn clones. The woofers are 515B The VOTT enclosures are stock, with about 300 pounds of added mass-loading on each 825 enclosure, concrete blocks from the garden supply section of “Lowes”.

This recent higher-voltage-rating experimenting was done last two weeks - as so :

(a) Russian K72P-6 teflons, 0.033 uF value, in 500, and 1,600 VDC values. Also,

(b) Russian K-75-10 “ high-energy-discharge” Lavsin / Oil caps, 0.68 uF value, 250, 500 and soon, next, 1,600 VDC ratings.

(c) With 12 dB networks, ANY multiple cap bypassing done to the tweeter section, must ALSO be done totally equally to the woofer section’s film caps, to get optimized listening results. I found there is no free lunch.

I am NOT YET finished with this A7-800 implementation, its NOT acceptable sounding to me quite yet, but I hope it eventually gets to where I want it to go. These ALTEC drivers are superbly sensitive, do many things well. How we implement them - is usually the “rub”, to my ears.


If anyone else is on a similar path, or cares to helpfully contribute, we all would be pleased to see their comments, or learn from their direct experiences. Thanks everyone.

Jeff Medwin

[Nickd]

Thanks for the post Jeff,

Looks like you are not afraid to dabble into capacitor listening tests (and brave enough to post about it). I have listened to many caps over the years and found the more I learn the less I know. Capacitor's are a bit of "black magic" to most of us it seems.

Some believe there can not possibly be a difference if It can't be measured. I believe I can gear the differences in most higher-end caps but am not sure the manufacturers even know how or why different materials and windings interact and affect the sound.

If you want to hear something fun, try some of the Jupiter flat stacked copper and wax caps. Bit of "magic" in those indeed.

Best regards & please let us know anytime you find caps that blend well with the Altec drivers.
Nick

[gdmoore28]

I'm not an electrician, and have no training, so everything you guys talk about is a good education for me as I strive to understand crossover design.

I followed you on everything that you posted (thank you) except for the following point:

(c) With 12 dB networks, ANY multiple cap bypassing done to the tweeter section, must ALSO be done totally equally to the woofer section?s film caps, to get optimized listening results. I found there is no free lunch.

Could you explain in a little more detail?

GeeDeeEmm

[LowOhms]

I'm not an electrician, and have no training, so everything you guys talk about is a good education for me as I strive to understand crossover design.

I followed you on everything that you posted (thank you) except for the following point:

(c) With 12 dB networks, ANY multiple cap bypassing done to the tweeter section, must ALSO be done totally equally to the woofer section?s film caps, to get optimized listening results. I found there is no free lunch.

Could you explain in a little more detail?

GeeDeeEmm

When you go above first-order crossovers ( higher than 6 dB ) you use at least one cap AND a inductor on each each driver. However, with 6 dB, you only use a single cap for the tweeter and a single inductor for the woofer, as elements of your speaker's crossover.

I find, whatever combinations of multiple film caps I use to roll off the tweeter ( in my 12 dB networks ), I NEED to use the same exact combination of bypassing caps on the woofer section of the crossover.

Maybe it has to do with phase coherency, or some EE parameter, I don't know. I DO find, on ALTECS in MY system, its totally audible, and always best to have the exact / matching multiple bypassing caps, for the woofer and tweeter.

So my friend, imagine this, lets say I use FIVE ( under 1 uF ) multiple film caps for the tweeter cap's bypassing, and the smallest film cap value, which will respond to the upper-most frequencies, is 0.0022 uF or 2,200 pF . ( That is heard as uppermost " air " to the music. The speakers play ambience and " reach to the ceiling of my listening room ". with 2,200 pF. ) :

OK, so my point is, the system as a whole sounds BEST to my ear, with the same exact type and value bypass caps ALSO applied on the woofer's crossover cap !!!!!!!!!!!!!!!!!!

I am not sure WHY this is, but what is most important to me is, " I hear it as such ", and thus, will DIY build accordingly. The reality of what I hear, the end result, is what interests "me" the most. As for the "reasons" it is so, I usually happily leave that for others, so inclined, to debate.

" Don't tell me about the Pregnancy, just SHOW ME the Baby !!! "

Hope that I was clear for you !! Have fun.

Jeff

[Elitopus1]

Please forgive my ignorance about this guys, but what is the purpose of using bypass caps instead of just using a good quality, regular value crossover caps. I have always heard of people using bypass caps to bypass crappy caps in the crossover or to make it more affordable to buy better quality caps (with the thought that the smaller value caps are cheaper to buy).

Are you using a good quality crossover cap and then bypassing it with something else? Is this similar to a crossover EQ circuit? Like it boosts the HF and VHF?

I am running a very similar speaker setup to you Jeff and am interested in improving it.

Thanks

[LowOhms]

Please forgive me ignorance about this guys, but what is the purpose of using bypass caps instead of just using a good quality, regular value crossover caps. I have always heard of people using bypass caps to bypass crappy caps in the crossover or to make it more affordable to buy better quality caps (with the thought that the smaller value caps are cheaper to buy).

Are you using a good quality crossover cap and then bypassing it with something else? Is this similar to a crossover EQ circuit? Like it boosts the HF and VHF?

I am running a very similar speaker setup to you Jeff and am interested in improving it.

Thanks

Reasonable question. As I stated in my first post :

I find from what I’ve heard, that no ONE cap will “have it all” as far as possessing audio goodness “in all ways and in all frequency ranges”, no matter how expensive it may be.



I think it would take a single film cap costing several hundreds of dollars, if not over a thousand dollars each, to approach ideal.

What YOU need to do is hear such things for yourself on YOUR well-set-up ALTECS.

I suggest you try a 0.68 uF at 500 VDC rated K75-10 Russian military cap, across your existing crossover cap, and tell me if it doesn't improve DYNAMICS in the midrange of your system ??

After you hear that for yourself, experience it directly, tell me WHERE you can find a single full-range cap with as dynamic a presentation as THAT??? Will you be happy with less? I am not !!

On my VOTTs, I found the 500 VDC ( higher ) rated K75-10 0.68 to be NICER sounding, simply more FUN to hear, than the 250 VDC rated ones, so... "IN" went 500 VDC rated parts on my A7-800 crossover.

Today, in the mail, I received K75s that are 1,600 VDC rated, 0.68 uF, and so, in the coming week, I will get a chance to A-B that part, versus 500 VDC rated K75-10s. The 1,600 VDC rated new cap may, or may NOT, be better.

BTW, if you web search carefully, one ex-USSR audiophile , living in the LA area, says the K-75 was designed for maximum PEAK energy discharge. He says it was rumored to be used to set off Hydrogen B--bs.

I sure do like what it does DYNAMICALLY, on the ALTEC drivers' middle mid range!!!! Its a little dark sounding, as are most oils, so I will only use one in a crossover, and just at the value I stated, in conjunction with other types - typically smaller uF values.

As the question of " will multiple bypassing improve a system " that remains an OPEN question IMHO.

I contend VERY LITTLE has been done on ALTEC ( highly sensitive, great transfer function !! ) speakers, to seriously try to optimize multiple film bypassing. In my first post, I described the pros and cons of single versus multiple film caps.

I tend to THINK, with idealized bypassing, I can get the timbres and dynamics of the individual instruments to be portrayed by the drivers , IN MY ROOM, to a MUCH more realistic degree. But one must be careful with a loss of coherency, due to overlap. It NEEDS to be worked out I say !!! Don't give up !!

Just you experiment with a 500 VDC K75-10, 0.68uF on your own, and give that a listen for yourself.

Oh, to answer your one question, my " basic " crossover cap is typically a WIMA DC LINK cap, which is a modern cap, technology-wise, very low in ESR, not a bad industrial cap at all, not " boutique ". The bypass caps are all reasonably good, often Russian military, Teflon K72P-6s, Oil K75-10s, etc etc.

Other considerations :

My crossover's wiring is above average, ( I used typically 14 AWG, Military spec, teflon jacketed, copper stranded, silver plated ) with only Wonder SOLDERED connections ( into the crossover, inside the crossover, leading out of the crossover, and the lead-outs are DIRECTLY soldered to the 515B and 802D driver's voice coil wires. )

I use Bob Fulton wire lengths, which is 57 1/8th inches, multiples and divisors of same. My ONLY physical connectors are the NLA XLOs ( best dynamics from a spade lug I have yet to hear ) coming off Cardas high-end speaker posts. Oh, and I tried the speaker wiring in both directions, and got that idealized . So easy on ALTECs !!! My output trannie is a Magnequest DS-025 and by Finals tube is a single device, in class A1, globe Type 45 ( or a 245 ).

Hope this helped you. Is there anyone out there who had done extensive film cap bypassing crossover tests on an optimized ALTEC system ??

Jeff Medwin

[Elitopus1]

Jeff,
Good info. I had been biamping my A7's with an active crossover but lately I have been using Altec N809-8a crossovers (with binding posts installed in place of the 1/4" jacks).

So if I understand what you are saying, I can run a bypass cap on both of the 18uf caps on the xover. That sounds easy enough. I have Jantzen caps in there now

I am going to try some of the caps you mentioned. Thanks for posting

Btw-Where have you found the best prices on the K75-10 caps?

[LowOhms]

- - - Updated - - -

Jeff,
Good info. I had been biamping my A7's with an active crossover but lately I have been using Altec N809-8a crossovers (with binding posts installed in place of the 1/4" jacks).

So if I understand what you are saying, I can run a bypass cap on both of the 18uf caps on the xover. That sounds easy enough.

I am going to try some of the caps you mentioned. Thanks for posting

Btw-Where have you found the best prices on the K75-10 caps?

----------------------------------------


My favorite eBay supplier :

4X 0 68 uf 500V Russian Hybrid PIO Capcitors K75 10 New | eBay

You will need four caps. With 500 volt rated caps, they are reusable in DIY tube amps, I have them where I can fit them in my SET 45 amps, as a bypass. :-)

If your stock ALTEC crossovers have the original stock caps in them, ( Pyramid ?? as I recall ) the stock ALTEC film caps of that era are a very weak link and should be replaced. Before doing so, just parallel across each stock 18uF cap, a 0.68 uF K75-10 0.68 / 500V., and LISTEN to what that does. Gain direct listening experience for yourself.

Its NOT $800 for four caps either !! Under 25 dollars shipped !!

re: Biamping : IMHO, IF ( a big word, my Daddy told me ) you have really good amps, you are best-off using a good passive speaker-level crossover, and having ONE amp's time constant and signature on the A7. Especially if you know how to build a good SET with zero negative feedback, and a great power supply. KISS rules, in highest-end audio. The best amps I have heard on ALTECS will all be under five watts, under $20K, two stage, always direct coupled, with LOTSA performance capability in the milliwatt range.

Have fun.

Jeff

[604man]

I think GM posted a link to bench's page on caps
here it is again .


The "Sound" of Capacitors

from what I understand, it is critical how the wires are connected to
the foil in the capacitor for low inductance .
this would effect the self resonant frequency of the cap.

.........GC

[LowOhms]

I think GM posted a link to bench's page on caps
here it is again .


The "Sound" of Capacitors

from what I understand, it is critical how the wires are connected to
the foil in the capacitor for low inductance .
this would effect the self resonant frequency of the cap.

.........GC

Thanks very much for contributing GC,

But your post does not address HOW to best bypass film caps in an ALTEC speaker-level passive crossover, IF they should be bypassed at all. It is strictly theoretical in nature, what you refer us to.

Whats the BEST WAY to use caps in a DIY ALTEC crossover ????? Actual practice ??

Recall from my earlier post sir :

The reality of what I hear, the end result, is what interests "me" the most. As for the "reasons" it is so, I usually happily leave that for others, so inclined, to debate.

" Don't tell me about the Pregnancy, just SHOW ME the Baby !!! "

Hope that I was clear for you !! Have fun.

Jeff