My Monitor 7s Back in Action ... wow!

lawdogg

Picked up these M7 series 2's in sad condition. Re-capped with Dayton caps, added a .01uF bypass cap, grabbed RD0198s, glued the MW6502s' magnets and put a new dust cap on one, re-assembled with hurricane nuts and hex bolts ... amazing. I listened before the re-cap a bit, and found the bass to be pretty muddy for Jazz. Put on Dave Brubeck first thing, and that bass muddiness is GONE!

All that's left to do is real veneer, maybe someday ... First listen, next to my JBL L26s (horrible cell phone pic):





Maybe I'll re-cap my 3.1TLs and M10a's someday too ...

Nightfall

N64 and SNES, nice!

Nightfall

It's hard to tell being a cell phone pic but I do believe that is Goldeneye 007 in the N64.

lawdogg

Good eye ... loves me some Goldeneye!

Yes I replaced the screws with 8-32 hex bolts to go with the hurricane nuts and I also really like the looks of the SS bolt heads against the black drivers.

Here's what I used:

http://www.amazon.com/gp/product/B0002ZPETA

http://www.amazon.com/gp/product/B005DS9LGS

http://www.amazon.com/gp/product/B000FN82SE

Braddles63

Nice work

deucekazoo

Nice, I do like the contrast between the black and the SS screws.

lawdogg

Thought I would post the pics of the Dayton caps in place. For those wondering if Daytons are a bad idea, I'll vote in favor of their cost effectiveness. Can't get any better for the money. I've run Dayton and Jansen in all my re-cap jobs and am a happy customer ... I've never heard those fancy caps though, maybe if I did it'd change my mind. I'm not confident it would though.

westmassguy

You will hear a difference with better caps. The Electrolytic in the Hi-Pass is also a no-no. Looks like you bypassed the other 12uf. That's not needed. Mills Resistors would also be a better choice than the Sandcast.

lawdogg

Hey, thanks! They are actually poly.

Re: bypass and resistor - why?

westmassguy

lawdogg wrote: »

Hey, thanks! They are actually poly.

Re: bypass and resistor - why?

You have an 8uf NP Electrolytic shunting the resistor, which is in the Hi-Pass circuit.
You also have a small bypass cap across the Dayton Cap, that's what I was referring to.

lawdogg

Thanks again! Re: electrolytic, ah yes forgot about that one - yes, I decided to keep it electrolytic like the original. Why is that a no-no?

Re: the bypass cap over the Dayton, curious as to why not?

And just a note on the design theory - intentionally kept everything cost-efficient to prove you don't need to spend a ton of money on fancy caps. The bill from Parts Express was just $45 shipped for all the caps & resistors! And like I mentioned, the sound has cleaned up considerably over OEM. Would dropping $100 more on caps and such make the sound even better? I can't say but I sure hope so! If there are better caps to use at the ~$50 total price point, that would be great info - I have a pair of M10a's next in line for caps, so it would be a fun A/B to use something different ...

westmassguy

Electrolytics SUCK, especially when used in series with the tweeter. Their Equivalent Series Resistance (ESR) is much greater than a Quality MP Cap. They can be used as shunt caps for the lo-pass, but they are strictly budget.
Metalized Polypropylene Caps should not need small bypass caps. Silver Mica bypass caps were used years ago on Mylars, to improve their sound.
Smaller Bypass Caps also react faster than the large Cap they're shunting. This can result in phase anomalies, and some, with excellent hearing, can detect this.

tonyb

In any event, glad to see the old girls up and running. My favorite of the Monitor series for sure.

RandyCroissant

I noticed a significant improvement with my Sonicap/Mills upgrade on my CS-350-LS center. Crisp, detailed sound.Excellent upgrade, thanks WMG Dave for the suggestion.

motorhead43026

I used Sonicap/Mills in both my M10's and SDA 2B's. Sound superb, and I am sure better than new.

lawdogg

It's fun to get involved in the audiophile debates! So here we go.

The small bypass caps over polys do result in a discernible sonic improvement to me - they have impressed me so much that I've used them on every speaker I've recapped since the first JBL L26s. For the sake of argument, I'll remove them and re-listen, and if I'm wrong I'll admit it, I promise!

The electrolytic - if Polk designed the crossover with the ESR of an electrolytic, wouldn't switching it out for something with lower ESR affect the crossover point?

Sonicap / Mills have great results in the Polk camp - like I said, I would hope so at their price point! (Seems like roughly $100 for this combo assuming the Mills is used for the shunt?) On the other hand, Daytons are simply not unworthy, are not unworkable, and are a good upgrade capacitor for those on a budget who don't want to drop around $100 worth of capacitors into their speakers.

westmassguy

What type of bypass cap did you use? Looks like a small value Dayton 5%.
Polk, like many other mass production speaker companies, use Electrolytics because they are cheap and do the job well enough. Price points had to be made. That doesn't mean improvements can be made. Most of the upgrades we do on Polk Crossovers were approved and recommended by MP and his engineers.

lawdogg

Thanks again for looking at this - Yes it's a Dayton .01uF. I've read references that bypass caps are snake oil, as well as references that they are not. For the L26 recap, the prodigious "Zilch" in the JBL camp recommended .01uF's used over Dayton caps but not Solens. So I'm looking forward to directly A/B'ing them with one removed.

On the electrolytic shunt cap, I think then that replacing it with a new electrolytic like I did is the budget option - to bring the spec back to factory, but without going another step and improving it over factory. An MP cap in its place might be the first step over the budget re-cap.

westmassguy

Bypassing a 1% Dayton MP with a 5% Dayton MP does absolutely nothing.

lawdogg

Why don't you think it does?

westmassguy

It serves no purpose. They're both Dayton MP Caps correct? What purpose does bypassing a 1% Tolerance 12uf Cap with a 5% Tolerance .01uf Cap from the same company, made from the same exact materials?

mhardy6647

I thought that the idea of bypassing a large capacitor with a small one was to provide low(er) impedance across a broad(er) range of frequencies than would a single, relatively high capacitance value capacitor.

westmassguy

mhardy6647 wrote: »

I thought that the idea of bypassing a large capacitor with a small one was to provide low(er) impedance across a broad(er) range of frequencies than would a single, relatively high capacitance value capacitor.

If you were using a poor quality large cap, and the bypass cap was much better quality, I could see the possibility of improving the lesser cap. In this case both caps are essentially the same. Smaller caps react faster, and can cause phase issues when the two caps are passing the same frequency.
That's why when you add caps in parallel to make a custom larger value, it's always best practice to use caps of equal value or as close as possible.
I would also add, a .01uf cap is passing frequencies beyond the range of human hearing.

[Deleted User]

Actually there are electronics designers who are advocates of bypassing capacitors and even triple-bypassing them. For example Richard Marsh who designed the Reliable Capacitor Company's Multicap has found a way to parallel up to 10 capacitor values around a single axis. Many feel that bypassing a 1.0uF capacitor with a 0.1uF and a 0.01uF capacitor produces a lower impedance across a wider bandwidth, especially in circuits with fairly low negative feedback. Granted it does increase the series inductance (this is why Mr. Marsh invented a machine that winds all the caps at the same time) and series resistance, but this is outweighed by the possible benefits.
I'm not sure how this would function in a speaker crossover, but the added inductance of parallel capacitors would be small compared to the hundreds of feet of wire used in the speaker's voice coil.
Try it and see.

mhardy6647

KennethSwauger wrote: »

.... Many feel that bypassing a 1.0uF capacitor with a 0.1uF and a 0.01uF capacitor produces a lower impedance across a wider bandwidth, especially in circuits with fairly low negative feedback. Granted it does increase the series inductance (this is why Mr. Marsh invented a machine that winds all the caps at the same time) and series resistance, but this is outweighed by the possible benefits...

This was my belief/understanding.

westmassguy

I've read quite a bit from both sides with regards to crossovers. Some swear by them, others feel they're snake oil. I've tried them on several different crossovers. They made no sonic difference to my ears, except one case, a pair of Monitor 5s, they sounded very odd in the treble region. Their use in other electronic circuits, I can't speak to.

lawdogg

Well I've intended to tear these apart and remove the bypass caps but I just can't bring myself to stop listening to them. They sound too good!

michaeljhsda2

Is the 0.25uF cap in the 1.2TL crossover considered a bypass cap? If so, should it be removed if all the caps in the crossover have been upgraded to Sonicaps? I seem to recall Ben (Ben62670) did not replace the 0.25uF caps in the 1.2 TL crossover, he just eliminated them altogether.

westmassguy

Eliminate them

lawdogg

Ok finally did this - somewhat scientifically - satisfied by the results. Conclusions are, from strongest conviction to weakest:

(1) a poly cap in the tweeter circuit behaves much better than an electrolytic, and I would add a poly cap as a part of the reference budget re-cap;

(2) sound deadening behind the woofer may clean up the mid to upper mid range, I would agree with this step as one beyond the purely budget re-cap;

(3) a bypass cap may bring out subtle tweeter detail and may slightly brighten the tweeter, I would retain this cap in the reference budget re-cap.

I took back to back videos with the same song (Sara K. with Chris Jones), I may upload to youtube. I am not sure how conclusive it is, since I recorded it with my mobile phone, and the quality may be too low to evidence anything significant.

Step 1 was a baseline with the bypass caps in place and the electrolytic in the tweeter circuit.

Step 2 was the same but with the bypass cap removed.

Step 3 re-connected the bypass cap and replaced the 8uF electrolytic cap with an 8.2uF Dayton.

Step 4 added a 5.5" tall strip of sound deadening behind the woofer, extending laterally from wall to wall, and vertically no lower than the bottom of the woofer hole. (I used PE's Sonic Barrier and followed Westmassguy's advice re: width and placement of strip.)

Scientific method aside, WOW!!! They sounded great before, and they sound great now -- but even better! Thank you Westmassguy et al for your great advice.

And finally ... Step 5 was to hook up my Monitor 10a's which are completely stock, to use as a yardstick. They do sound amazing, I love the Peerless tweeter. Hard to say conclusively, but they have a little "thinner" of a sound to them. They also may be a little more forward than the M7's. They also may have more dirty resonance in the mid-lows. Can't conclusively put my finger on it ... but that's the fun of all this!

fredb44118

I also have some Monitor 7s that I think need to be re-capped, but have some questions. I'm new to repairing speakers, so please bear with me.

I'm hearing a little static from the tweeters when there is a high frequency sound. It is not a constant static - it only happens when an instrument hits a high frequency. Also, volume level doesn't matter as I can hear it on high and very low volumes.

I've changed speakers wires, checked all connections, and tried 3 different receivers and can replicate the issue every time. It is definitely a problem with the speakers.

Would re-capping the crossovers resolve my issue? Or do I have a bad tweeter?

If re-capping is necessary, I would prefer to only replace the "bad" capacitor, as the speakers sound great otherwise - no issues with bass or mid.

Thanks in advance for any help!