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Replacing Dahlquist DQ-10's 80uf electrolytic cap

kirk57 said:
Whether the cap is plus or minus 10 percent is easily measured with a capacitance meter. The same holds true for a single caps or 8 caps in parallel. What will be changed, and is probably of little consequence, is the ESR (being very very low with all those pseudo resistors in parallel) and power handling, which is ridiculously high.

My own feeling is that very large caps like this can be NP electrolytics, if that was speced originally, since I'm sure Jon Dahlquist accounted for the ESR of each cap. Having spent some time rebuilding this crossover, it's clear to me he was EXTREMELY detail oriented about his crossovers...

Also, I think the benefits of film caps (which manifest themselves in the higher frequencies) don't really come into play when used to block the lower end for the midrange, as used here, I think at 500 Hz or so.
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Every rebuild I've done I've used poly caps with the exception of my KEF 105.1s they absolutely accounted for the ESR in the electrolytics so that's what I used. I know people have switched to poly caps in that crossover and then added series resistors to adjust, but I don't know, mine sound great. I also believe that there isn't much benefit to using poly caps where lower frequencies are in play. This is why I'll only use poly caps up to 60uf. Unless somehow there is a higher valued one in a mid circuit and is said there is great benefit to using poly.

I just rebuilt some Polk Monitor 10s and in the "woofer" or "mid-woofer" circuit it uses a 34uf cap. The other two were 12uf. So I replaced all caps with poly, that is an example of when I'd use poly in the woofer circuit. Not sure what frequency that 34uf cap comes in to play, but I did it anyway.
Dan
 
When I change C1 to poly, there was a definite increase in the little bass that the DQ's put out, and it seemed to have better attack, but they were original old caps I replaced. I work very hard at not letting my imagination into my evaluations. I did not put the old ones back in to confirm it though.
 
I gotta finish-up this project. Bought one of those spiffy Econo record cleaning wands and I have been obsessed washing all my vinyl. I'm down to the last little pile so maybe the DQ's will get some love soon~!
 
Finally back to finish up this little project. As suspected, there is ample room to mount the cap stack beside the crossover. Looks like it's tight but there is actually plenty of room between the screen, leg and the cap stack. The "wet" looking spot is where I cleaned the dust off the base. :eek:

Haven't had a chance to listed with any volume yet - the Wifey is in bed.

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-reverb- said:
I was a little bored yesterday; it was raining so I couldn't do anything outside. I mentally went through my audio projects in search of something small.

My Dahlquist DQ-10's has all poly caps expect for the 1 80uf electrolytic. That's a pretty small project!

I shuffle through my box of caps trying to find a couple of 80's or something that can be ganged together to total 80. Nothing. Nada.

I then remember a huge box of 10uf polys I bought from Madisound for like 40 cents each. I could gang 8 of those together to get the 80uf I need. It may be overkill - not sure if it's even in the signal path, but they are just sitting in a drawer and 80uf is 80uf regardless if it's poly or lytic, right?

I cobbled together an off-board sub-crossover with flying leads to replace the 80uf on the Dahlquist crossover. No way 80uf's worth of poly will fit in the original location. All the caps are soldered and hot-glued together to form a nice, solid block. Measuring with my meter I get 78.9uf for each one. Not too shabby.

I plan to either mount it to the Dahlquist cabinet with 4 small screws, or more likely use an industrial strength hook & loop fastener (Velcro). Here's a peek - shown beside a standard-size BIC lighter for scale.I mounted my dayton poly 75uF to the upper array leg because it is big. and brought the speaker back to life.

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Thoughts and/or suggestions?
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I disagree with thopse who say a film is not important for the c1. this mid bass also covers higher frequencies in the mid bass driver and if you don't have either a poly film or high quality lytic your midbass diver will suffer in the upper frequencies. I thought mid bass was going bad until I removed the cheap lytic that I had in c1 and installed a 75uF dayton poly film. The mid bass sounds fine now.I'm sure Dahlquist put a good quality lytic in the c1.At lest do a good quality lytic if you don't do a film you will hear the difference. Remeber this is a 1st order crooss over and the bands are wide.
 
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