Biamping Hartley Concert Master VI - Xover Mod Opinions Please

[toxcrusadr]

I’m looking at the crossovers from litefootdan’s pair of Hartley Concertmaster VI speakers. These are massive speakers with a special 24” woofer. Hopefully Dan will post some pics and info here or in another thread, but in the meantime, I need to pick your brains about the crossovers. Dan wants to biamp these and I volunteered (in a beer and BBQ induced haze at the KC Twangfest gathering at Jaymanaa’s last spring ) to look at rebuilding the crossovers. I would like to tap the collective brain on the proposed plan.

Here’s the stock crossover schematic drawn from the crossover itself (I didn’t find one online). Pretty standard 3-way except for one item.

Notice how the woofer input doesn’t come off the +input but is tapped after the 0.28mH midrange inductor, L2. It then goes through the 3.75 mH L4 into the woofer.

Dan wants to biamp these so as to maintain the crossover circuitry for all the drivers and create two inputs, one for the woofer and one for the mid/tweeter. They could still be strapped together to run with 1 amp.

Here’s what I figured. The woofer has a total of 4.03 mH in series with it. In order to maintain that inductance for the woofer circuit, since inductance is additive, we could disconnect L4 from L2 and either add in another 0.28 mH in series with it, or get a 4 mH inductor to replace L4 (now called L4A, which looks like L44 in my chicken scratch). The mid circuit still sees the original 0.28 mH on its input, and the woofer has the same 4 mH in series with it.

Dan says that Hartley said they didn’t want to do this mod because of something about overlapping. I am not sure how this crossover behaves in the mid/woofer crossover region - does the design do something with the slopes that would be lost here? I considered that maybe they did it to save money on inductors, but with a high end speaker like this, the difference between a 3.75 vs. a 4 mH inductor is peanuts.

How would this change affect the performance? Is the solution really as simple as I've drawn it or is there more to it?

 

[WmartinB]

I don't know the answer to your question - But I'd kill for a pair of Concertmasters

Interested in impressions if you do attempt the mod

-Will

 

[Retrovert]

Dan says that Hartley said they didn’t want to do this mod because of something about overlapping. I am not sure how this crossover behaves in the mid/woofer crossover region - does the design do something with the slopes that would be lost here? I considered that maybe they did it to save money on inductors, but with a high end speaker like this, the difference between a 3.75 vs. a 4 mH inductor is peanuts.

I've seen that very same doubled inductor weirdness on the Stromberg-Carlson RS series, along with a shared contour filter that made no sense at first. Here's what I remember about that. I make no claim for the accuracy for this, because it's based on what I read on the InterWebs, not direct knowledge, and it was a while ago.

Series inductors are normally used to save money and parts, by piggybacking on an earlier filter, but this technique can (as I recall) be used for greater voltage drop to do driver balancing. Voltage drop is additive with inductors and current increases. The series inductors also affects damping factor but I don't remember how, or if this is good or bad.

Do the inductors share a common core? I read somewhere this can sometimes make a weird, but inexpensive, autoformer/autotransformer. Someone with better knowledge of inductors and coils can likely clarify.

Looks like 2nd order filter phase differences on the midrange should require polarity to be reversed, but it isn't? The phase difference will make the midrange appear louder, which is why Bozak did it and why Tobin undid it.

 

[toxcrusadr]

I don't know the answer to your question - But I'd kill for a pair of Concertmasters

Interested in impressions if you do attempt the mod

-Will

Looking forward to it myself. :thmbsp:

The inductors do not have a common core on this particular speaker, they're all separate air core inductors. However, I've seen pics on the web of (as I recall) of a different production of this same speaker with inductors wound on a common ferrite rod. This one is not built that way.

As for driver polarity, I only have the crossover but it's got clearly labeled terminal strips and we went off that to draw the schematic. If the midrange ends up being too forward, it would be a simple matter to reverse the leads to one set of inputs when hooking up the amps and see if that helps.

 

[toxcrusadr]

Here's a thread over on the Asylum about some VI's.

http://www.audioasylum.com/cgi/vt.mpl?f=speakers&m=340902

The crossover is the same topology but with different cap values. The tweeter cap on Dan's is 6.2, the midrange 50, and the woofer bypass caps 300. The Asylum set has 3, 150 and 150 respectively. Unfortunately the OP's link to photos is no longer working even though the thread is from March 2015.

Interestingly they also mentioned normal polarity on the mid instead of reverse, further evidence that that's the way Hartley intended it.

 

[Fitero]

I am the culprit of the dead link over at AA.
I saw the word Concertmaster and automatically clicked on this link, and was surprised to see that the crossover varied so much from my own.

I wonder what that is about?

Here is a new link to the photos I made;

https://picasaweb.google.com/fitero...&authkey=Gv1sRgCPyM7ai0id7HBw&feat=directlink

 

[toxcrusadr]

[EDIT: Hi Fitero! I didn't think to look for you on AK yet. Thanks for the link!]

The same owner posted over on DIYAudio though, and this thread has pics!

http://www.diyaudio.com/forums/multi-way/270992-hartley-concertmaster-crossover.html

The crossover has all the inductors lined up, but they look like air cores on plastic spindles that are just stacked together. I swear I saw a pic of multiple windings wound directly on a ferrite bar. I'll keep looking for it.

That's all kind of academic since we're trying to keep this pair as original as possible. I just wanted to find out whether splitting up the two series inductors would be a non-starter. So far it seems like the answer is that it won't violate any major principles but may have some subtle effects and we'd just have to try it out.

150 lb speakers with 24" woofers sporting 14 lb magnets, response down to 16 Hz. Almost in a class by itself.

 

[toxcrusadr]

I am the culprit of the dead link over at AA.
I saw the word Concertmaster and automatically clicked on this link, and was surprised to see that the crossover varied so much from my own.

I wonder what that is about?

Here is a new link to the photos I made;

https://picasaweb.google.com/fitero...&authkey=Gv1sRgCPyM7ai0id7HBw&feat=directlink

I suspect this crossover has just gone through some redesign over the years. I'm not totally up on the company history or how long they've been making this model, but the company has changed hands over the years. Evolution is not that uncommon and doesn't always result in a new model number. I sure would like to see some response graphs of these two designs modeled with the driver parameters. Hartley probably has them but they're not on the web as far as I know.

 

[Fitero]

Hi Toxcrusadr,

Yep, I posted on 3 sites when I began mucking around with the Concertmasters.

I hope litefootdan posts some pics of his crossovers. The only ones that I have seen on the web are like mine; e.g. the inductors have a common axis.

My hope is for one of the obsessive compulsive CM owners to do an all out assault to perfect the crossover and share the results.
Something akin to Nelson Pass's L300 crossover.

I know next to nothing myself, and would only be able to copy what someone else designs.

 

[Fitero]

So, if logic serves.... the crossovers with the separate inductors would most likely be a later version than my own, given that a row of inductors all in one line is considered a no no correct?

The serial numbers on mine are 172197-DT and 172198-DT.

Will litefootdan post his serial numbers to compare?

 

[toxcrusadr]

I'm sure he will. I have pics of the crossover as I received it which I'll post later. It's contained in a small black plastic project box with a flat aluminum lid with terminal strips on it for the hookups. Dan recapped it with film caps (some of which are rather huge) so it didn't really fit in the box anymore. I'm going to remount everything on a square of pegboard. I understand there's so much real estate inside the speaker than it doesn't really matter how big the crossover board is.

Inductors would definitely interact if lined up like that but whether that's a bad thing may depend upon the specific circuit. The general rule of thumb is to avoid it though.

 

[toxcrusadr]

If AK has no objections I'm going to order some 0.28 mH (or as close as I can get) inductors to add in and proceed with reconstructing the first crossover.

 

[litefootdan]

litefootdan is latefootdan

I know, I know. Pictures will be coming. I cannot get out of a heavy work deadline right now. Then I'm out of town for the weekend. But when I get back I'll find the files of the crossover "deconstruction" and recap. Tox is right, the plastic box was tinsy tiny- with all the stuff jammed in. So tightly that the manufacturers trimmed the plastic spools of the coils in order to get it all to fit. It was a unsettling. I really don't know anything of crossover theory. I'd recapped AR 2ax's, 5's and 3a's, so I figured I'd do the same with these. They had those black and red caps that KLH used in them and nondescript electrolytics too. The dayton replacements improved the sound. But my Torii doesn't have enough gusto for those woofers. That is why I asked someone to have a look at the crossover for possible bi-amping. Tox stepped up for the job. What a gentleman. In the end I do not want to change the speaker, I am just curious if its possible to allow me to bi-amp them.

What turned me on to Hartley speakers was a chance happening. I was in an antique shop while my better half was off teaching software. After some looking around I turned to the store owner and said "have a nice day" as I was waking toward the door. She asked if I was looking for anything particular and said well I guess speakers. She said a man was coming to her shop later with a pair of "big old wooden speakers". Needless to say my mind went into fantasy mode.... ALtec, JBL, Electrovoice, Jensen, and so on. She said if I could wait a couple hours I could speak with him here. Unfortunately, I didn't have the time and she was nice enough to give me his number. We agreed to meet at his house so I could see them. They were the Hartley Holton A's. He had no amp, no source, no meter, no anything so I stopped by Radio Shack and picked up some leads and some douple A's. I did get continuity with the "test" so I asked him if he'd sell them to me. He said that the sale had to go through the woman at the antique store. So back I went. And we fought for an hour or so about what she thought was an appropriate price. She was a mean fight, but we ended on an agreement and I brought the Holton A's home. Each cabinet houses a fullrange driver called the Hartley 220MSG and a Mylar dome tweeter in parallel with a 3uf cap. I was so taken with them that when a pair of Concertmasters were available I bought them immediately. I've since used the Holton A's as my only listening speakers. Well that isn't completely true, if I feel like reminding myself how much I like them, I listen to something else. Then I am reassured. Now I am quite interested in having the Concertmasters back in the mix. With any luck I will be able to drive them how they need to be driven. I think I've read that the woofer comes in around 200hrz on the Concertmasters. So it might be like adding a sub to the Holton A's.

Wow, I took a break from this post and have realized that I've done quite a bit of rambling..... When I come back I'll have pictures for you fine people.

Thanks everyone who has chimed, and especially to Tox.

Oh yeah, here is a good read on some Hartley information

http://www.lencoheaven.net/forum/index.php?topic=7029.0

 

[damacman]

Those are some very uniquely equipped speakers. Tuned in.

 

[toxcrusadr]

Thanks Dan, and no rush on posting pics. AK will be down for the weekend anyhow, and this project is moving at a glacial pace on my end too.

Here's a teaser pic of the crossover components laid out on a new board. Missing the additional 0.28 mH inductor and the input/output terminal strips. I have to dig around for the 'before' pic. This gives you an idea of how big the parts are.

 

[litefootdan]

Mmmmm! Purdy!!!

 

[Retrovert]

This gives you an idea of how big the parts are.

Dude, what's the scale! I'd guess about 4.5 inches if the holes are on 0.5 inch centers. Or if they are on 0.75 centers it would be about 7 inches. No way to tell!

I had a colleague who always asked about scale when units were omitted from a (in those days Polaroid) photo of a scope trace or samples. He had a good point, though, which is honored more in the breach.

 

[toxcrusadr]

Sorry, that's about an 8x8 or 9x9 inch square.

EDIT: BTW, there is a standard 1" hole spacing for Perforated Hardboard products.
https://en.wikipedia.org/wiki/Perforated_hardboard
My error, of course, was A$$uming that everyone knows that.
Bottom line: Huge speakers with huge crossovers. :thmbsp:

 

[Retrovert]

Sorry, that's about an 8x8 or 9x9 inch square.

Wow. Those are monstrous inductors!

BTW, there is a standard 1" hole spacing for Perforated Hardboard products. My error, of course, was A$$uming that everyone knows that.

Ahhh, but I thought it was built on phenolic perfboard so I was primed to think about small spacing! Didn't realize it was perforated hardboard. It wasn't brown!

 

[toxcrusadr]

Yes the inductors are huge. 3.75 and 4 mH with fairly thick gauge wire.

The pegboard is some commercial 1/4" thick heavy duty stuff I salvaged a bunch of, it's prepainted that pale yellow color. Nice stuff for the shop, I have sheets and sheets of it. Amazing what people throw away.