Did I create the correct electrical schematic of my existing crossover?

[motleypixel]

Hi gang,

*Please skip first paragraph if you just want the meat of my ask thank you.

So I want to take baby steps here. First, I picked up a pair of Phase Technology PC-60 bookshelf speakers. The variant of gen I that I have is the oldest (confirmed by an audio engineer at Soundtube that is owned by MSE which also owns Phase Tech now). This audio engineer also reports to vice president Ken Hecht, son of Bill Hecht that founded Phase Tech and was the inventor of the soft dome tweeter. Anyway, I did hook these speakers up as-is and they sounded fine but one was cutting in/out which I suspect was from poor speaker spring connections. The speaker drivers are in fair shape with the woofer surrounds in great shape (thankfully). So now I'm in the process of restoring them because the cabinents were a bit rough but they look pristine now. I noticed the crossover board that is screwed into the back inside was clearly removed at least once because there are two sets of self wood screw tapped holes. The number of components on this darn thing is mind boggling, so I decided that I need to break it down, document it (block/logical) and test each component. I plan to re-use the inductors, I just need to re-orient them, but a number of caps have pretty high ESR. 2 of the 7 caps in total are electrolytic (75uF and 15uF) so depending on size/cost I may just go with quality audio electrolytics again.

*I mapped out logically in a block diagram exactly how I found these crossovers. With Spkr Term signal input being the binding posts and points A/B +/- woofer connection and points C/D -/+ tweeter. I'd like to start with asking if I drew a correct representation of the woofer ckt based on the exact block diagram I drew. The goal here is to create both a formal and readable electrical schematic of the woofer and tweeter ckt so I can ask questions if needed and get suggestions, esp. because I think I have a previously modified crossover.

Thank you.

 

[motleypixel]

This is what I came up with. Look correct?

 

[AnalogSteph]

For starters, the 1.8 ohm in series with the woofer looked sus to me, and sure enough, that should actually go between the 3 capacitors and ground.

Inductor C' is at the wrong spot, it (along with its series resistance) should go the the left of the 5µ||0.05µ.
The 10µ||0.05µ also are connected in series, not in parallel. (Imagine what that would do to speaker impedance - not something that many amps would fancy driving.)
So effectively the tweeter gets a near 4th-order highpass.

 

[bmc0]

Look correct?

No. Here's a direct schematic representation of your layout drawing:

 

[MAB]

Did you confirm that the drivers are working? Is the cutting-out behavior due to the connections?

 

[motleypixel]

Did you confirm that the drivers are working? Is the cutting-out behavior due to the connections?

Yes, just dirty spring speaker terminals.

 

[motleypixel]

For starters, the 1.8 ohm in series with the woofer looked sus to me, and sure enough, that should actually go between the 3 capacitors and ground.

Inductor C' is at the wrong spot, it (along with its series resistance) should go the the left of the 5µ||0.05µ.
The 10µ||0.05µ also are connected in series, not in parallel. (Imagine what that would do to speaker impedance - not something that many amps would fancy driving.)
So effectively the tweeter gets a near 4th-order highpass.

LOL, yeah, I knew more than my head would hurt if I wired it up like I did the wiring diagram (amp and/or speakers). I have all new components to install now and I know I can just twist, solder, and put it all back together as I found it, but something tells me I need to dig more.

So my thinking here is to first get a good normal, readable diagram, like @bmc0 provided, because with that, coupled with speaker info and box type/dimensions, others can comment more effectively.

So for now, I'm going to eat the cost of these components from Parts Express, I feel like I will get into this hobby more so having those spare film caps and resistors on-hand will be good. I have purchased a Dayton Audio DATS V3 to run some sweep and impedance curves on the tweeter and woofer (Phase Tech doesn't publish this data on their drivers). From there, knowing the box volume/dimensions and that is is not ported I can maybe just build a new crossover from the ground up?

I'd prefer not to have the push/reset bkr and rather a good ole fuse holder/fuse and I'd also prefer to omit the POT if that seems like a good idea?

Thank you very much

 

[motleypixel]

No. Here's a direct schematic representation of your layout drawing:
View attachment 485068

First, Thanks a million and then some!

Second, do you feel this ckt is okay for a 2-way bookshelf by Phase Technology back in the mid 80's? It's certainly possible the crossover was modified, but I'm only about 10% sure it was modified. I have yet to find in the wild web archives any crossover from PC-60s that look like this. Here's a thread on AK that has them but the back plate is completely different only has a fuse, no pot and the crossovers shown in the thread are far less components than mine. https://audiokarma.org/forums/index.php?threads/phase-technology-pc-60-crossover-recap.854799/

I re-attached your drawing, would the speaker terminals labeled as ABCD in my logical drawing correspond correctly?

Attached is what I came up with at work today on break. I think my attempt is close, that 1.8ohm resistor I put in series to the positive on the woofer. I'm seeing how you translated it and it makes sense. I'm still tracing and following, this is fun!

I don't think I'm putting this crossover back as-is with my new components just yet. I want to explore more. These are Phase Tech 6.5 direct piston 4ohm 88db sensitivity woofers and 1" silk dome PT tweeters in a non-ported box that is 8932 cubic cm. I ordered a Dayton Audio DATS V3 to begin the journey of possibly building a new crossover from the ground up?

I would like to omit the BKR and instead just use a fuse. What's typical for this type of ckt as far as fuse amp rating and blow type?

I would also like to ditch the POT if that seems like a good idea. and if so I guess I would need to increase that 3.9ohm resistor?

I want to KISS as much as possible.

Thank you.

 

[bmc0]

do you feel this ckt is okay for a 2-way bookshelf by Phase Technology back in the mid 80's?

The circuit looks fine to me based on the provided information, but I can't say much else without more data (inductor values & ESR, electrical impedance of the drivers, and acoustic measurements of the drivers mounted in the cabinet). The small 0.1µ and 0.05µ bypass capacitors serve little purpose and can be omitted.

would the speaker terminals labeled as ABCD in my logical drawing correspond correctly?

Looks to be correct.

What's typical for this type of ckt as far as fuse amp rating and blow type?

I've never looked into it, but perhaps someone else here has a suggestion. Personally, I'd just omit it and try not to be too cavalier with the volume knob.

I would also like to ditch the POT if that seems like a good idea. and if so I guess I would need to increase that 3.9ohm resistor?

Yes (unless it sounds best with the tweeter level at maximum).

 

[MAB]

The crossover looks fairly standard. The woofer crossover is ~2nd order (12dB/oct).

For example, let's make a few rough assumptions (I don't know the value of the inductor or the impedance of the driver). If I assume 8 Ohm woofer, and use the impedance and frequency response from some old Vifa measurement I have, and trget a 2 kHz crossover point, you get this:

This crossover using a 0.15mH inductor (red) with the rolloff of this old Vifa woofer (green) produces a near 24dB/oct rolloff.

This is just an example. You would need to find the actual inductor value, and measure the frequency response and impedance of the woofer. But the above could be integrated with a tweeter using 24dB/oct acoustic and have a chance at good sound.

 

[MAB]

I also should point out, none of the components in the woofer crossover likely need changing or improving. The 75, 15, and 0.1 uF capacitors are just a 90.1 uF cap. These are likely fine, not able to be improved. Same for the resistor and the inductor.

The tweeter pot may need attention. But maybe not. People will probably say you need to replace the electrolytic capacitors since they don't always age well. If you do and change them to a film capacitor, you will likely change the equivalent resistance of the tweeter circuit. This may change the response of the tweeter audibly. May be negligible. If you replace with capacitors with similar ESR, you will retain the original response characteristics of the crossover. I can't tell you what will be better, a low ESR film cap or new electrolytic of similar characteristics of the original parts.

While I mostly try to keep things original, I might consider changing to a pair of binding posts. Parts Express and others have some that may fit well.

It all looks like fun. Do you have pictures of the whole speaker?

 

[voodooless]

I see one possibility audible improvement:

These inductors should not be placed like that!

 

[motleypixel]

I see one possibility audible improvement:
View attachment 485107

These inductors should not be placed like that!
View attachment 485108

Fantastic, yes I have been informed in several of my other posts on AK and facebook groups. You are the first to provide a nice diagram. What does the 0" 4" and 8" distances mean? I only assume that it's best to separate as far as possible and orient as denoted in the diagrams? Another thought there is the inside of the speaker cabinent, those inductors are VERY close to the large magnet of the woofer. These woofers have larger than normal magnets due to being a piston style. I'm almost wondering if attaching the crossover on the back outside would result in better performance at a major cost of functionality/looks?

Thank you!

 

[voodooless]

What does the 0" 4" and 8" distances mean?

" is inch

 

[motleypixel]

I also should point out, none of the components in the woofer crossover likely need changing or improving. The 75, 15, and 0.1 uF capacitors are just a 90.1 uF cap. These are likely fine, not able to be improved. Same for the resistor and the inductor.

The tweeter pot may need attention. But maybe not. People will probably say you need to replace the electrolytic capacitors since they don't always age well. If you do and change them to a film capacitor, you will likely change the equivalent resistance of the tweeter circuit. This may change the response of the tweeter audibly. May be negligible. If you replace with capacitors with similar ESR, you will retain the original response characteristics of the crossover. I can't tell you what will be better, a low ESR film cap or new electrolytic of similar characteristics of the original parts.

While I mostly try to keep things original, I might consider changing to a pair of binding posts. Parts Express and others have some that may fit well.

It all looks like fun. Do you have pictures of the whole speaker?

Thanks @MAB I went with Parts Express' brand audio electrolytic in a 68uF and 22uF and then a new .1 MPT film cap. Going all film I would probably struggle fitting the crossover board through the front woofer hole. As it is the crossover board just fits and it's square which means I can't have any component over-hanging any of the sides.

All the film caps that are yellow in my OP measured fine but I still plan to replace with Dayton Poly film caps. The two purple electrolytic caps 75/15 measured 84/20 and had at the top end of the charts, high ESR. The two resistors 1.5ohm each in II measured twice what they should be as-is in II which should be per calculations .75ohm. Upon close inspection they both each had one that had what looks like a small fisher/crack and bulging. I'm replacing that with a .8ohm green 2% 10W quality audio resistor.

I am on the fence with upgrading to binding posts, while I would prefer them, I would alter the nice OEM anodized AL back plate quite a bit when removing the spring mount module. I will look into that option more.

These were the original PC-60's and honestly there are not many to be found documented on the web. Most of the original have a different backside with binding posts and a fuse holder. I even reached out to Soundtube, owned by MSE parent that also bought PhaseTech and a sound engineer there reports to Ken Hecht son of Bill Hecht that founded PhaseTech and was the inventor of the soft dome tweeter. At first he thought I had a Frankenstien pair and instead referenced and said the OG's looked like the binding post variant. Stating we never had a POT etc. Then after a few days I did receive a reply with a correction that they did make it but was a short run on production moving to the more simplified version. And I mean simplified, this AK thread shows the crossover of the second build, much more simple: https://audiokarma.org/forums/index.php?threads/phase-technology-pc-60-crossover-recap.854799/

Makes me wonder if I should simplify mine?

The cabinets needed complete refinishing. Some deep cleaning, light sanding and 5 wipe on coats of General Finishes Arm-R-Seal Satin. Drivers are in good working order, surrounds on woofer are in great shape. Grills are in great shape too. *note the POT knob was not re-installed for these pics.

 

[motleypixel]

" is inch

Yes which is why I mentioned "distances" denoting I knew it was a measurement, just like ' = foot But what does it mean in context of the chart. Looks like to simply keep 4" distance between N+ inductors?

 

[motleypixel]

The circuit looks fine to me based on the provided information, but I can't say much else without more data (inductor values & ESR, electrical impedance of the drivers, and acoustic measurements of the drivers mounted in the cabinet). The small 0.1µ and 0.05µ bypass capacitors serve little purpose and can be omitted.


Looks to be correct.


I've never looked into it, but perhaps someone else here has a suggestion. Personally, I'd just omit it and try not to be too cavalier with the volume knob.


Yes (unless it sounds best with the tweeter level at maximum).

Thank you @bmc0 I will lift leads and measure the inductors with my fluke multimeter. For ESR this is only on the capacitors? These are all bi-polar, can I still use my ESR on them? I have new components that just arrived as well.

Next Monday I will have a Dayton Audio DATS V3 to measure my existing drivers, should I measure them out of the speaker box, in the speaker box with the acostastuff and back sealed or both?

When you mean "omit it and not to be too cavalier with the volume knob" you mean take out the POT and not drive the speakers too loud with my pre-amp volume control/knob right? I never crank up anymore like I did in my teens/early 20's so that shouldn't be a problem.

Speaking of cranking up, one area that concerns me at times is when I do use REW to do a 2.1 sweep to help me with sub and mains positioning, that 75db target volume so that the REW program is happy and can take the measurement scares me sometimes when it sweeps. I wonder if folks have killed drivers using REW before?

Thank you.

 

[voodooless]

Looks like to simply keep 4" distance between N+ inductors?

Yup, that is basically it. But at 4 inches, the orientation matters a lot.

 

[MAB]

Thank you @bmc0 I will lift leads and measure the inductors with my fluke multimeter. For ESR this is only on the capacitors? These are all bi-polar, can I still use my ESR on them? I have new components that just arrived as well.

Next Monday I will have a Dayton Audio DATS V3 to measure my existing drivers, should I measure them out of the speaker box, in the speaker box with the acostastuff and back sealed or both?

When you mean "omit it and not to be too cavalier with the volume knob" you mean take out the POT and not drive the speakers too loud with my pre-amp volume control/knob right? I never crank up anymore like I did in my teens/early 20's so that shouldn't be a problem.

Speaking of cranking up, one area that concerns me at times is when I do use REW to do a 2.1 sweep to help me with sub and mains positioning, that 75db target volume so that the REW program is happy and can take the measurement scares me sometimes when it sweeps. I wonder if folks have killed drivers using REW before?

Thank you.

You can also use the DATS to measure the passives too, it has a decent LCR meter function built in.

Yes, REW can be used to blow drivers if not careful. All of these electronic test procedures need to be done carefully, testing only after you have established proper levels. If in doubt, test a cheap driver before you test your vintage speaker.

 

[MAB]

Thanks @MAB I went with Parts Express' brand audio electrolytic in a 68uF and 22uF and then a new .1 MPT film cap. Going all film I would probably struggle fitting the crossover board through the front woofer hole. As it is the crossover board just fits and it's square which means I can't have any component over-hanging any of the sides.

All the film caps that are yellow in my OP measured fine but I still plan to replace with Dayton Poly film caps. The two purple electrolytic caps 75/15 measured 84/20 and had at the top end of the charts, high ESR. The two resistors 1.5ohm each in II measured twice what they should be as-is in II which should be per calculations .75ohm. Upon close inspection they both each had one that had what looks like a small fisher/crack and bulging. I'm replacing that with a .8ohm green 2% 10W quality audio resistor.

I am on the fence with upgrading to binding posts, while I would prefer them, I would alter the nice OEM anodized AL back plate quite a bit when removing the spring mount module. I will look into that option more.

These were the original PC-60's and honestly there are not many to be found documented on the web. Most of the original have a different backside with binding posts and a fuse holder. I even reached out to Soundtube, owned by MSE parent that also bought PhaseTech and a sound engineer there reports to Ken Hecht son of Bill Hecht that founded PhaseTech and was the inventor of the soft dome tweeter. At first he thought I had a Frankenstien pair and instead referenced and said the OG's looked like the binding post variant. Stating we never had a POT etc. Then after a few days I did receive a reply with a correction that they did make it but was a short run on production moving to the more simplified version. And I mean simplified, this AK thread shows the crossover of the second build, much more simple: https://audiokarma.org/forums/index.php?threads/phase-technology-pc-60-crossover-recap.854799/

Makes me wonder if I should simplify mine?

The cabinets needed complete refinishing. Some deep cleaning, light sanding and 5 wipe on coats of General Finishes Arm-R-Seal Satin. Drivers are in good working order, surrounds on woofer are in great shape. Grills are in great shape too. *note the POT knob was not re-installed for these pics.

I can't see the AK images, I'm not a member over there. Not sure if they are the same circuit with fewer parallel components, or if it is new. This 90 uF capacitor could replace the three film capacitors in your woofer crossover (75, 15, and 0.1 uF) for example. 90 uF and 90.1 uF are sonically equivalent to much better than 0.1dB. It was (and still is) popular to add a small-value capacitor in parallel with larger caps, allegedly improves transients (it does not), it all could be replaced with one big 90 uF capacitor.