AR-3a Limited crossover in AR-3a Improved cabinets

[jam1n]

Hi all

I'm considering replacing the crossover in my AR-3a Improved speakers with the AR-3a Limited version, as recommended by JKent here. I'm trying to understand exactly what would be involved and I have a few questions.

1. I'm planning to replace the tweeters with the Midwest ones. RoyC said here that no changes are required to the 3a Improved crossover with these tweeters. Does this also apply to the 3a Limited crossover (pic below)?
2. If I build the Limited style crossover and place it in the Improved cabinet, as RoyC said he'd done here, would the L-Pads and the extra pair of binding posts fit in the circular space where the existing binding posts and switch are, or would I need to adapt the cabinets somehow to make room for the extra hardware?
3. If I just use one pair of binding posts, can I just attach the woofer circuit to them directly?
4. Would it be better to leave the old crossover in place or should I try to remove it?
5. Is there anything else I should be aware of?

 

 

Thanks

Ben

[RoyC]

4 hours ago, jam1n said:

Hi all

I'm considering replacing the crossover in my AR-3a Improved speakers with the AR-3a Limited version, as recommended by JKent here. I'm trying to understand exactly what would be involved and I have a few questions.

1. I'm planning to replace the tweeters with the Midwest ones. RoyC said here that no changes are required to the 3a Improved crossover with these tweeters. Does this also apply to the 3a Limited crossover (pic below)?
2. If I build the Limited style crossover and place it in the Improved cabinet, as RoyC said he'd done here, would the L-Pads and the extra pair of binding posts fit in the circular space where the existing binding posts and switch are, or would I need to adapt the cabinets somehow to make room for the extra hardware?
3. If I just use one pair of binding posts, can I just attach the woofer circuit to them directly?
4. Would it be better to leave the old crossover in place or should I try to remove it?
5. Is there anything else I should be aware of?

Thanks

Ben

Ben,

1- The Midwest tweeter is more like the original 3a Limited tweeter, so it will be a better match for this version of the 3a than for the 3a Improved (which was equipped with the original 3a tweeter).

2- I don't recall...Send a photo of the rear terminals of your speakers. I replaced the entire board.

3- Yes, just connect the circuits internally.

4- I can't think of a reason to leave the old crossover in place unless it is just easier to do so. There is no "vintage" value to the old crossover. You will obviously have more room if you remove it.

5- Just take your time and ask questions if something comes up. Feel free to contact me directly if you have any questions or issues along the way.

Roy

 

 

[jam1n]

On 6/26/2020 at 2:05 AM, RoyC said:

On 6/26/2020 at 2:05 AM, RoyC said:

2- I don't recall...Send a photo of the rear terminals of your speakers. I replaced the entire board.

 

Thanks Roy!

Here's a picture of the back of the speakers. I think the aperture for the terminals/switch is the same size as on the AR-3a. In fact, I think you implied in another thread that the 'Improved' may actually have been a marketing ploy to get rid of the remaining stock of European style cabinets.

I'm in no rush with this. Electronics is completely new to me and I've still got some work to do on the cabinets before I'll be ready to get stuck into the crossovers. 

I do have a few more questions:

1. Replacing the whole board where the binding posts are sounds sensible. How would I go about getting the old board out and what material should I use for the replacement? 

2. Is it worth reusing any of the components from the old crossover or would it be better to scrap them and use new components? Some of the coils/capacitors have the same values and the 150uf caps I've found so far seem quite expensive. I'm not averse to spending the money if its going to make a difference to longevity or sound but I don't want to replace them if there's no good reason.

3. I think I read in another thread that the L-pads should be 15W. Is that right?

4. The capacitors in the schematic are all labelled as 100V but the ones I've found online so far are all rated higher. Do they have to be 100V exactly or is this a minimum?

5. There are no Ohm ratings or wire guage listed for the inductors on the diagram but these are seem to be specified on all the coils I've looked at online. Which ones should I be looking for, or doesn't it matter?

Sorry for the long list of newbie questions. 

Thanks again! 

Ben 

[JKent]

1. Use a block of wood and a hammer. Make new out of Masonite if necessary but I'd re-use the old. You can plug the switch hole and drill new holes for the L-pads.
2. Re-use coils. Replace caps. For 150uF use NPE, they're cheap.
3. 15w
4. 100v minimum but anything over that is fine
5. If you need new coils use 18ga. I believe the originals are 17ga. Re-use any originals you can.

No offense intended but this is an ambitious project and you are a novice. You sure you want to do this?

Kent

[jam1n]

33 minutes ago, JKent said:

No offense intended but this is an ambitious project and you are a novice. You sure you want to do this?

Thanks Kent!

No offence taken. I'm not sure yet, which is why I want to understand as much as possible about what's involved. But I do enjoy a challenge and I like learning new skills. I've spent a lot of time reading on the forum and I get the impression this would be the best way to give these speakers a new lease of life. Also, I'd like to replace the binding posts and the capacitors at some point and, please correct me if I'm wrong, but I got the impression it might actually be easier to build a new crossover than doing that with the existing one in place.

BTW, thanks for all your advice on the forum about cabinet repair (and Glen's), which has given me the confidence to tackle some nasty water damage where a few of the panels have separated at the joints. I've restored a few pieces of furniture before but this was by far the most ambitious repair I've taken on. I finished the first cabinet this afternoon and it has come out very nicely!

One more question. There is a 0.51 Ohm/22W resistor in the limited crossover. So far, I've only found a 10W one. Would that be an acceptable substitute or do I need to find another option with a higher power rating? 

Ben

[JKent]

Well, we're here to help and encourage.

Since you are rebuilding the entire xo yes, it may be easier to work outside the cabinet.

I can't find an AR-3a Improved crossover schematic but your speakers "may" have the needed resistors. In the AR-3a that resistor was a piece of nichrome wire. When I built an AR-3a crossover from scratch I used two 1-ohm 10w resistors in parallel. This yields a 0.5 Ohm 20w resistor, which should be fine.

The 1st pic below shows an exceedingly neatly laid out crossover by CSP member xmas111. Notice the silver wire between the 2 coils on the bottom left part of the board. That's nichrome.

The second, considerably less neat xo is mine. You can see the two 1 Ohm resistors in the middle of the board.

Kent

 

[jam1n]

Thanks for the pictures, Kent. That really helps to visualise what's involved. 😃

I'm putting together a parts list and I have a couple of questions about how accurately I need to match the coils/caps in the limited crossover.

Jantzen seem well regarded and do custom value inductors. There's a longer lead time but I'm in no rush. They have 17AWG/1.2mm & 18AWG/1mm coils. I'm assuming that 17 would be better than 18 if that what was used in the originals but, in some of the coil values, they have two 17AWG options with different stated DCR. After reading RoyC talking on another thread about how important it is to match the DCR of the originals as closely as possible, I'm wondering if anyone knows the values for the coils in the limited crossover? Or am I over complicating this? Obsession with detail can be a blessing and a curse - sometimes it's hard to tell which! 😜

In a similar vein, the closest values I can find to 4uf/40uf in most ranges of capacitors are 3.9 & 39. That's off by 2.5%, which is within the tolerance range of most of the capacitors I'm looking at. Is this close enough, or is it worth spending the extra to make up the exact values by combining caps?

Thanks again

Ben

[RoyC]

7 hours ago, jam1n said:

Thanks for the pictures, Kent. That really helps to visualise what's involved. 😃

I'm putting together a parts list and I have a couple of questions about how accurately I need to match the coils/caps in the limited crossover.

Jantzen seem well regarded and do custom value inductors. There's a longer lead time but I'm in no rush. They have 17AWG/1.2mm & 18AWG/1mm coils. I'm assuming that 17 would be better than 18 if that what was used in the originals but, in some of the coil values, they have two 17AWG options with different stated DCR. After reading RoyC talking on another thread about how important it is to match the DCR of the originals as closely as possible, I'm wondering if anyone knows the values for the coils in the limited crossover? Or am I over complicating this? Obsession with detail can be a blessing and a curse - sometimes it's hard to tell which! 😜

In a similar vein, the closest values I can find to 4uf/40uf in most ranges of capacitors are 3.9 & 39. That's off by 2.5%, which is within the tolerance range of most of the capacitors I'm looking at. Is this close enough, or is it worth spending the extra to make up the exact values by combining caps?

Thanks again

Ben

Hey Ben,

The  AR-3a Limited had 18 ga coils. By the time the Limited showed up the 17ga AR coils were long gone. So 18 ga air core coils are what to shop for, and dcr will be what it should be.

Where are you located? Parts Express has the capacitors you need in exact values. You can also build capacitors. For example, two 20uf caps wired in parallel make one 40uf cap.

Roy

[jam1n]

1 hour ago, RoyC said:

Hey Ben,

The  AR-3a Limited had 18 ga coils. By the time the Limited showed up the 17ga AR coils were long gone. So 18 ga air core coils are what to shop for, and dcr will be what it should be.

Where are you located? Parts Express has the capacitors you need in exact values. You can also build capacitors. For example, two 20uf caps wired in parallel makes one 40uf cap.

Roy

Thanks Roy

18 it is. I'm glad I asked! Just to double check the inductor values before I order:

L1 - 2.60 mH

L2 - 0.7 mH

L3 - 44 uH = 0.044 mH

L4 - 160 uH = 0.16 mH

Also, what width of gasket tape do I need for the drivers? The woofer foam needs replacing and one of the tweeters didn't have any at all!

I'm in the UK. I've never been a particularly patriotic person but, in these bizarre times we live in, I'd like to support the HiFi industry here if possible and I've heard good things about ClarityCap from people whose judgement I trust.

I realise that 'high end' capacitors are a divisive issue and I'm not looking to dive too far down that rabbit hole, but I was tempted to go slightly higher up their range. Doubling up to make exact values gets expensive pretty quickly though, so I think I'd better rein myself in!

Ben

[RoyC]

6 minutes ago, jam1n said:

Thanks Roy

18 it is. I'm glad I asked! Just to double check the inductor values before I order:

L1 - 2.60 mH

L2 - 0.7 mH

L3 - 44 uH = 0.044 mH

L4 - 160 uH = 0.16 mH

Also, what width of gasket tape do I need for the drivers? The woofer foam needs replacing and one of the tweeters didn't have any at all!

I'm in the UK. I've never been a particularly patriotic person but, in these bizarre times we live in, I'd like to support the HiFi industry here if possible and I've heard good things about ClarityCap from people whose judgement I trust.

I realise that 'high end' capacitors are a divisive issue and I'm not looking to dive too far down that rabbit hole, but I was tempted to go slightly higher up their range. Doubling up to make exact values gets expensive pretty quickly though, so I think I'd better rein myself in!

Ben

-Your inductor values are correct, Ben.

-3/8" gasket tape works well for the woofer and mid. I prefer to cut my own tweeter gaskets from foam sheets found in craft stores.

-The 3a Limited had a film cap for the 4uf tweeter capacitor and modern electroytic capacitors for the large values. The largest value, 150uf, consisted of (3) 50uf caps wired in parallel. Frankly that is the way I would go. There is no reason to purchase costly large value film caps for these speakers. If all goes as planned, they will sound as AR intended, and you will love them.

Roy

[jam1n]

13 minutes ago, RoyC said:

The 3a Limited had a film cap for the 4uf tweeter capacitor and modern electroytic capacitors for the large values. The largest value, 150uf, consisted of (3) 50uf caps wired in parallel. Frankly that is the way I would go. There is no reason to purchase costly large value film caps for these speakers. If all goes as planned, they will sound as AR intended, and you will love them.

Thanks Roy

My priority is to get the speakers sounding the best they can. I've been enjoying them a great deal already, but I sense they're capable of more. I had the impression the consensus was that film caps sound better than electrolytics when used in the signal path?

I'd planned to use NPEs for the 150uf and film caps for the rest, as per Kent's advice above. I was looking at the Mundford ECap for the woofer circuit. The 150uf is only 63V and they don't have a 50uf but I can combine 68uf + 82uf to get to 150 and the 100V version is very reasonably priced. Would that do? 

The 40uf film cap I'm looking at for the mid is not too expensive either. The speakers were given to my father by an old neighbour whose wife considered them an eyesore, so I don't mind spending a bit to breathe some new life into them! Unless you think they'd sound better with an electrolytic capacitor in there as well?

Ben

[JKent]

6 hours ago, jam1n said:

My priority is to get the speakers sounding the best they can. I've been enjoying them a great deal already, but I sense they're capable of more. I had the impression the consensus was that film caps sound better than electrolytics when used in the signal path?

Hi Ben

Best advice on these speakers will be from Roy. You may have noticed he knew the coils were 18ga and not (as I had written) 17.  Nevertheless, I'm going to throw in my 2 cents (2 pence?) again.

Film caps may sound different. That may be due at least in part to having a different ESR than electrolytics. Is different necessarily better? One reason for using film is that they don't degrade, so if you plan to hand these down to your grandchildren film may be the way to go.

Electrolytics will go out of spec eventually. How long? I dunno. I've seen 20 year old 'lytics that were off and 50 year old 'lytics that were spot on. btw, the spec on capacitors used to be -25%/+75% so the actual values could vary considerably.

Ken Kantor (developer of the AR-303, co-author of "Restoring the AR-3a", founder of NHT, bon vivant) advocates replacing electrolytics with electrolytics. The speakers were designed with electrolytics.

Although I have no experience with them, several members here speak highly of the Mundorf E-Caps you mentioned. I'm sure they would be a fine choice.

The prevailing wisdom seems to be, as Roy suggested, to use film for small values and electrolytic for large values.

Disclaimer: I have only used film caps in my 12" ARs (AR-3a, AR-91) and in other speakers. I have used electrolytics in some 12" KLH speakers (Five, Twelve) and they sounded very good but my septuagenarian ears are far from "golden".

Hope these ramblings are helpful.

Kent

PS: I think 63v is fine for speaker caps.

[jam1n]

9 hours ago, JKent said:

Hope these ramblings are helpful.

Thanks Kent. Very helpful indeed. Your comment about ESR sent me down another very interesting rabbit hole.

I think I understand better where Roy is coming from now. Keeping to the spec they were designed to makes a lot of sense. It's probably the sensible place to start.

From what I read about ESR, it seems that using three 50uf caps in parallel would significantly reduce the ESR. I can get 50uf/100V ALCAPs selected with a 2% tolerance from Falcon Acoustics here in the UK, so I'll probably do that for the woofer circuit to match the original. 

I'm still on the fence about the mid. It seems there are some advantages to film caps but also some potential drawbacks in deviating from the original crossover design. I'm going to have to give this one a bit more thought.

Ben

[lARrybody]

I have used the Jantzen Audio Premium Elko Electrolytic 33uf and 6.8 uf caps wired in parallel for the 40uf cap. You can also use the Mundorf Ecap MLytic 70 in the same sizes. In fact they are the same caps manufactured in the same place.  I also include a .01uf  film and foil by-pas cap, but that is up to the individual user.

[jam1n]

3 hours ago, lARrybody said:

I have used the Jantzen Audio Premium Elko Electrolytic 33uf and 6.8 uf caps wired in parallel for the 40uf cap. You can also use the Mundorf Ecap MLytic 70 in the same sizes. In fact they are the same caps manufactured in the same place.  I also include a .01uf  film and foil by-pas cap, but that is up to the individual user.

Hi IARybody. Thanks for the recommendation. Is there any benefit to using the ‘plain’ ECaps in the woofer bypass as well or would the ‘raw’ etched version suffice here since it’s not in the signal path?

Also, what are your thoughts on the 4uf (with the Midwest AR-11 type tweeter)? I noted on this thread that you’ve used the Jantzen Superior/ClarityCap CSA/Mundorf Supreme. I’d love to know how you’ve found these compared to the Daytons, whose virtues I saw you extolling on AK in an older thread. Which do you think would play best with the ECaps?

I’m leaning towards the CSA, on the basis that they might help to tame the slightly forward character of my amp in the top end. But I’m also very curious about the Jantzens. Any thoughts?

Ben

[lARrybody]

As far as the plain E caps verses the raw etched version I don't know the answer. The raw caps are physically smaller, cost less and have a higher voltage rating.  I just go by the assumption that if it cost more it probably is better. A Lexus is going to drive better than a Hyundai. Maybe? Maybe not. Anything you use is probably going to be better than original caps. And as Kent has said earlier the lower voltage of the  plain caps is probably sufficient.

I have used all kinds of caps. I really like the Daytons (5% and 1%), Erse PluseX and other affordable caps. For some reason I am not a big fan of the Solen PB caps. I used Jantzen Superior 2.7uf and 3.3uf paralleled on the tweeter circuit of some 1969 AR3a's.  Some Mundorf Supreme caps in AR2ax crossovers. That combination is probably crazy. Maybe I should of saved my money and went with Daytons, but I plan on keeping those speakers. You wont get your money back if planning on selling them. Currently I am on the Clarity CSA bandwagon. I have read that the CSA have a ESR that is closer to the original electrolytes. Also the mylar caps like the Carli are closer, but they are getting hard to find. Unless there is a big problem such as sibilance most caps will work fine. 

I have these CSA caps waiting to go into a set of AR3's as soon as I figure out what to do about the midranges. They have been matched by Parts Connexion. Someone suggested to me that they may be more relaxed than other caps. That is what I would want for some AR3's. Also I read that Clarity is one of the few manufactures that make their own capacitors.   

If you plan on going the CSA route I would either parallel two 2uf caps or a single 3.9uf with a 0.1 bypass cap.  I personally would use a film cap on a tweeter circuit over a electrolytic.  Hope this answers your questions. You really can't go wrong as long as the new caps are close to each other. In my opinion the condition of the drivers are going to make a bigger difference than any cap.

[jam1n]

Thanks for your help everyone! My crossover upgrade project has been on the back burner for the last few weeks while I finished up restoring the cabinets and gave my wife a well-earned rest from discussions (i.e. monologues) about capacitors. I had some trouble with one of the joints where the water damage was quite bad but I got there in the end. I still have to finish the grills but the speakers are looking much more presentable and I'm confident they are now structurally sound.

I received the new Midwest tweeters a few weeks ago. It took a bit of getting used to the change as the original tweeters' output was very low and I'd been quite enjoying that rolled off sound. I thought there was a problem with them at first as I got hung up on the sibilance in Diana Krall's 'Stop this world'  – until I listened to it on my headphones and realised it was on the recording. I also thought I was losing my hearing in one ear for a while until I realised that a bad contact meant there was no output from one of the new tweeters after I installed its foam gasket. I thought I was going mad for a while but, now everything's working properly, the speakers are sounding amazing and I'm falling in love with my music collection all over again.

I'd still like to rebuild the crossovers, but I'll probably wait until September, when the kids are (hopefully) back at school and I should have a bit more time. I might order a basic capacitance meter in the meantime, so I can see how close to spec the capacitors are actually performing. For now, I'm just enjoying the music!

[JKent]

3 hours ago, jam1n said:

For now, I'm just enjoying the music!

Good. As our late friend Carl said, "It's all about the music."

If you do rebuild the crossovers to 3a Limited you'll have L-pads to tame those tweeters.

An LCR meter is useful. LCR will test Inductance (L) and Resistance as well as capacitance. There are dirt cheap but surprisingly good basic meters from China on ebay for less than 10 bucks! Even less without the case. And they also measure ESR and a bunch of other stuff. This is from an ad:

Quote

1. Add boot voltage detection function
2. Automatic detection of NPN and PNP transistors, N -channel and P-channel MOSFET, diodes (including dual diode), thyristors, transistors, resistors and capacitors and other components
3. Automatic test out the pin element and displayed on the LCD
4. Can be detected to determine the transistor emitter forward bias voltage of the transistor, MOSFET protection diode and the amplification factor of the base
5. Measure the gate threshold voltage and gate capacitance of the MOSFET
6. 1602 lcd display uses LCD (12864 LCD with backlight)
7. High test speed, valid component test: 2 seconds (except in the larger capacitor of large capacitance measurement also takes a long time, the measured time of one minute is normal)

Sometimes an old capacitor will measure within spec for capacitance but the ESR is off. It's also useful to test brand new capacitors before installing. Personally for TOTL speakers like the 3a I'd go with new caps.

[jam1n]

On 8/10/2020 at 1:50 AM, JKent said:

There are dirt cheap but surprisingly good basic meters from China on ebay for less than 10 bucks! Even less without the case. And they also measure ESR and a bunch of other stuff.

Thanks Kent

Does this look like the kind of thing you had in mind? 

https://www.ebay.co.uk/itm/154026431801

Ben

[JKent]

The one I have is like this

https://www.ebay.co.uk/itm/1PCS-LCR-T4-ESR-Meter-LCR-led-Transistor-Tester-Diode-Triode-Capacitance-PNP-MOS/401233943772?hash=item5d6b681cdc:g:fBsAAOSwiONYO~-w

but I think the one you linked is similar, just in a fancy case 😉

[jam1n]

I’m nearly ready to build the crossovers. I took Roy’s advice and matched the original spec as closely as possible. I have all the capacitors/inductors and some18ga tinned copper wire. I‘m just waiting for the L-Pads and a decent soldering iron.

Does anyone have any recommendations on what to use for the crossover board? I have various bits of scrap wood lying around, including wood fibre board, chipboard, ply and MDF. Both the pictures Kent posted look like pine boards. Is solid wood better?

[jam1n]

Thanks for all the help everyone - especially RoyC and JKent!

I managed to finish the crossovers, with a bit more help along the way from Roy. The speakers are now fully re-built and sounding fantastic. I'll post some pics of the crossovers below. 

I have one more question. What position should the l-pad knobs be in for a flat response?

Thanks again! 

Ben 

[jam1n]

Here are a few pictures of the original AR-3a Improved crossover I removed from the cabinets and the AR-3a Limited crossover I built. Not bad for a complete novice. I couldn't have done it without all your kind help! 😃

 

[JKent]

Looks good!