Wharfedale W90s - How I Replaced My L-Pads

[bce22]

Good Day AKers,

I have a very early pair of Wharfedale W90s from 1962. These have all AlNiCo drivers and dual ports. They also have 53 year old electronics! The W90s (and other "W" series Wharfedales) have attenuation dials on the rear of the speakers. In most cases (but I don't believe in all "W" variants) these dials are L-Pads and there are two of them. One controls the output of the midrange drivers and one controls the tweeters. L-Pads are passive devices that allow you to adjust the output level of the speaker without changing the impedance seen by the amp.

Picture of W90s placed in my small (12 X 12) listening room


On my set of W90s there were two issues with the original L-Pads. A couple of the pads were pretty "scratchy" even after attempting to clean them with Deoxit. The L-Pads are sealed and it is really difficult to get Deoxit into them for cleaning. I have read that it is possible to open them up, however I couldn't find a good way to do this without probable destruction. Needless to say, using DeOxit on the L-Pads without opening them up didn't work out that great for me. The other issue was a slight distortion in one midrange driver. I hoped that the combination of a recap (still waiting for caps to arrive from Estonia and the Ukraine) and a change of the L-Pads would fix this problem.

Original L-Pads



____________________________________________________________________________
PUBLIC SERVICE ANNOUNCEMENT

The original L-Pads (and possibly other parts) are covered in white dust. This white dust is Cadmium. It's toxic so wear a mask and gloves! Breathing cadmium is worse than getting it on your skin.

More info about Cadmium poisoning: https://en.wikipedia.org/wiki/Cadmium_poisoning

Cadmium (audio): http://www.audiokarma.org/forums/in...-inside-some-vintage-speakers-cadmium.520981/
____________________________________________________________________________

Before deciding to replace the L-Pads, I read as much as I could on AK and other forums. There isn't much regarding Wharfedale "W" variant L-Pad replacement. I'm fortunate that at least some threads exist. Below are a few I came across:

http://www.audiokarma.org/forums/index.php?threads/wharfedale-w90-l-pad-replacement.568429/

http://www.audiokarma.org/forums/in...needs-what-resistor-to-bring-to-specs.620906/

http://www.audiokarma.org/forums/index.php?threads/replacing-tweeter-l-pads.169785/

I purchased L-Pads from Parts Express. They are 50 watt stereo L-Pads with a 1" shaft made by Dayton. Here is the link: http://www.parts-express.com/speaker-l-pad-attenuator-50w-stereo-1-shaft-8-ohm--260-260

EDIT: UPON FURTHER REVIEW THE L-PADS PURCHASED SHOULD BE MONO RATHER THAN STEREO. MORE INFO IN SUBSEQUENT POSTS.

There are definitely outstanding questions about replacing the original 50 ohm pad with an 8 ohm pad. After reading up on it, I am comfortable with the 8 ohm pad replacement. You'll ultimately need to make your own decision about whether or not you agree. It's worth mentioning that contemporary replacement 50 ohm L-Pads don't appear to exist. Therefore your choices are restricted when looking for replacements. If you are truly concerned you can add resistors to bring the pad up to 50 ohms.

Without question the replacement L-Pads are HUGE compared to the originals. They are at least THREE TIMES THE SIZE!

New L-Pad vs Original


Wiring the L-Pads was about as straight forward as it gets. The stereo L-Pads have 3 tabs for each channel labeled 1, 2 and 3.

The #2 tabs are bridged together and the wire from the speaker (blue wire for tweeters and a black wire for midrange in my speakers) is soldered to one of the #2 bridged tabs (the top one in my speakers). The Ground wire is soldered to one of the number #1 tabs (the top one in my speakers) and the lead from the capacitor is soldered to one of the #3 tabs (the bottom one in my speakers). This matches exactly the original L-Pad wiring.

Midrange L-Pad wiring with Tweeter L-Pad in the background


Since these L-Pads are much larger than the original, it's a pretty tight squeeze to fit them in while re-attaching the panel to the cabinet. When I first attempted to place the completed panel into position, I had a moment of fear that the top L-Pad was too big. It hit the stop that the panel screws into (where the top center screw goes). Once I "smartened up" by angling it slightly it slipped into place without a problem.

Also, I had to turn the midrange L-Pad slightly to get the 24uF cap lead to fit without creating an extension.

In my opionion these are the largest L-Pads that will fit in this application. I can't imagine that the 100 Watt L-Pads would fit without major modifications!

New L-Pads placement orientation


After wiring them in, I glued the midrange and tweeter Min - Max dial plates to the rear of the speakers and press-fit the new dials onto the shafts. The plates fit with a gap of about 3/8 of an inch between them. The original dials are slightly wider and can't be press-fit onto the new L-Pad shafts. The original dials can absolutely be glued, which is my plan. I will probably use silicone so they can be removed if necessary.

Min-Max plates and dials


I find the new L-Pads provide a large sound improvement. Distortion in the midrange driver disappeared as well. I am glad that I made the change!!!

More pics below for your viewing pleasure.

New L-Pad vs original with boxes


Wired up!






Plates installed


Dials too








Regards,

Brad

 

[PastTechFan]

Wow!! That's very nice work! Thank you for the thorough photo documentation (and adding to the W90 lore)!

The (mid) pad in one of my W90s is getting scratchy. I've been avoiding doing anything about it. I thought I could get away with new "mono" L-pads, assuming that's what was there originally.

I understood that each of the two L-pads (in each cabinet) were composed of two stacked (mono) pots bridged together (to prevent impedance change), and that each (mono) L-pad then served a pair of mids or tweets. I'm still very much learning this.

Your way looks very professional. Just wondering if the stacked (stereo) L-pads is completely necessary, or if (smaller) monos might suffice.

Maybe I need to look at some crossover diagrams again.

 

[bce22]

Wow!! That's very nice work! Thank you for the thorough photo documentation (and adding to the W90 lore)!

The (mid) pad in one of my W90s is getting scratchy. I've been avoiding doing anything about it. I thought I could get away with new "mono" L-pads, assuming that's what was there originally.

I understood that each of the two L-pads (in each cabinet) were composed of two stacked (mono) pots bridged together (to prevent impedance change), and that each (mono) L-pad then served a pair of mids or tweets. I'm still very much learning this.

Your way looks very professional. Just wondering if the stacked (stereo) L-pads is completely necessary, or if (smaller) monos might suffice.

Maybe I need to look at some crossover diagrams again.

Thanks PTF for the wonderful compliments!

I want to give back as much as I can to this amazing community that helps so many folks!!! By the way, I also am "still very much learning this".

I originally wrote up a response, posted it and ended up deleting it after your comments finally sank in to my thick skull

Since the only wire that touches both "levels" of the L-Pad stack happens to be the bridged speaker wire attached to the #2 location, I do not know the reasons that a double-stacked L-Pad was used in the original application. It would seem that you could connect the Ground to #1, Speaker to #2 and Capacitor to #3 on the same level to achieve the same result. Since I am not an expert in these matters I cannot comment. Hopefully one of our resident AK experts can shed a little more light on the subject. In my case I simply replaced the original L-Pad with as similar a device as I could find.

In regards to your comment on the original being a "two stacked Mono Pot" I have some questions. What is the difference between a two stacked mono pot and a stereo pot? I always thought that 2 mono channels = stereo. Isn't this similar to the way that many audiophiles use 2 x monoblocks to play stereo source material?

Just for completeness I have attached pics of both the mono L-Pad and stereo L-Pad available at Parts Express. Of course the text and arrows I added myself.

MONO


STEREO


ADDENDUM: If you absolutely want smaller L-Pads, Parts Express does sell 15 watt versions. These are most certainly smaller. Personally, I wouldn't use the 15 watters since the 50 watt versions definitely fit in the W90s, unless you are 150% certain that you will ALWAYS stay below 15 watts using a relatively low wattage amp (most likely only tube amps). I decided that the higher wattage L-Pads provide a safety net. Currently I am powering the W90s with an H/K 730 receiver (rated 40 watts per channel) but will end up using a restored H.H. Scott 299B integrated tube amp when I get it back from my tech. The 299B is rated at 21 watts per channel. I feel more comfortable with the 50 watt version L-Pads even though I am 100% certain that my watts output is much, much, much lower.

 

[bce22]

ORIGINAL L-PAD SETTINGS VS NEW L-PAD SETTINGS

Using a clock face as a template, The new L-Pads can be adjusted from approximately 7 o'clock through 5 o'clock. I believe the originals have a slightly smaller range, which is closer to 8 o'clock through 4 o'clock. With the original L-Pads, I would set them to about 3 o'clock on both the tweeters and midranges. Sometimes, I would set the tweeter L-Pads a smidgen higher than the midrange pads.

On the new L-Pads, I keep them both around 12 o'clock or less. It goes without saying that I need to spend MUCH more time with the new L-Pads to dial them in perfectly with the music, and sources, I listen too. Of course, Your Mileage May Vary!!!!!!

Also, when I wire in the 3 X 8uF NOS KBG 400V 5% PIOs into the mids and the 8.2uF Rike Audio S cap PIOs into the highs, my L-Pad settings may change significantly. I promise to share not only my recap in great detail (with pictures) but also all that I learn about setting the L-Pads with the new caps installed.

 

[PastTechFan]

Thanks PTF for the wonderful compliments!

I want to give back as much as I can to this amazing community that helps so many folks!!! By the way, I also am "still very much learning this".

I originally wrote up a response, posted it and ended up deleting it after your comments finally sank in to my thick skull

Since the only wire that touches both "levels" of the L-Pad stack happens to be the bridged speaker wire attached to the #2 location, I do not know the reasons that a double-stacked L-Pad was used in the original application. It would seem that you could connect the Ground to #1, Speaker to #2 and Capacitor to #3 on the same level to achieve the same result. Since I am not an expert in these matters I cannot comment. Hopefully one of our resident AK experts can shed a little more light on the subject. In my case I simply replaced the original L-Pad with as similar a device as I could find.

In regards to your comment on the original being a "two stacked Mono Pot" I have some questions. What is the difference between a two stacked mono pot and a stereo pot? I always thought that 2 mono channels = stereo. Isn't this similar to the way that many audiophiles use 2 x monoblocks to play stereo source material?

Just for completeness I have attached pics of both the mono L-Pad and stereo L-Pad available at Parts Express. Of course the text and arrows I added myself.

MONO


STEREO


ADDENDUM: If you absolutely want smaller L-Pads, Parts Express does sell 15 watt versions. These are most certainly smaller. Personally, I wouldn't use the 15 watters since the 50 watt versions definitely fit in the W90s, unless you are 150% certain that you will ALWAYS stay below 15 watts using a relatively low wattage amp (most likely only tube amps). I decided that the higher wattage L-Pads provide a safety net. Currently I am powering the W90s with an H/K 730 receiver (rated 40 watts per channel) but will end up using a restored H.H. Scott 299B integrated tube amp when I get it back from my tech. The 299B is rated at 21 watts per channel. I feel more comfortable with the 50 watt version L-Pads even though I am 100% certain that my watts output is much, much, much lower.

Hi bce,

Thanks for your thoughtful response. I really do appreciate what you're doing here.

I'm a big fan of the HK730 (and would be running my 90s with them myself, except the amp end needs some service, so it's doing pre-amp service in the basement, feeding my open baffles). I bet it sounds really good. For now, I'm using my little HK330B. I'm very much looking forward to hearing about your 299B on the 90s when it gets back. I have a Scott 399 receiver (with the 299 amp circuit) that I want to get up to snuff. Haven't nerved myself up to tackle a recap yet. I've never done one, and I'm not sure if this is the one I should learn on.

Back to the L-pads.......I've got some old Radio Shack mono units to the tweeters in my open baffles. They look very like the mono ones you've posted. When I was looking for some, I did some googling. As I understand it, there are some L-pads that are self contained (2 wipers bridged internally?), but I saw some (earlier?) ones made up by 2 potentiometers stacked together on the same shaft (with an external bridge wire connecting the 2 wipers). As the impedance rises in one pot, it's offset by a drop in the other. Thus, two pots can equal one L-pad. I suppose you could even make an L-pad out of 2 separate (bridged) pots, but you would have to constantly be adjusting the second for every change in the first.

I'm going to get late for work if I keep this up much longer, so I'll reply further later. What I'm trying to get at is, it seems to me that the Lpads in the 90s are (each) composed of two (concentric?) mono pots, bridged together, comprising a single (mono) L-pad. But for the bridging, they could function as a single stereo pot (but not a stereo Lpad). I think.....

 

[bce22]

Hi bce,

Thanks for your thoughtful response. I really do appreciate what you're doing here.

I'm a big fan of the HK730 (and would be running my 90s with them myself, except the amp end needs some service, so it's doing pre-amp service in the basement, feeding my open baffles). I bet it sounds really good. For now, I'm using my little HK330B. I'm very much looking forward to hearing about your 299B on the 90s when it gets back. I have a Scott 399 receiver (with the 299 amp circuit) that I want to get up to snuff. Haven't nerved myself up to tackle a recap yet. I've never done one, and I'm not sure if this is the one I should learn on.

Back to the L-pads.......I've got some old Radio Shack mono units to the tweeters in my open baffles. They look very like the mono ones you've posted. When I was looking for some, I did some googling. As I understand it, there are some L-pads that are self contained (2 wipers bridged internally?), but I saw some (earlier?) ones made up by 2 potentiometers stacked together on the same shaft (with an external bridge wire connecting the 2 wipers). As the impedance rises in one pot, it's offset by a drop in the other. Thus, two pots can equal one L-pad. I suppose you could even make an L-pad out of 2 separate (bridged) pots, but you would have to constantly be adjusting the second for every change in the first.

I'm going to get late for work if I keep this up much longer, so I'll reply further later. What I'm trying to get at is, it seems to me that the Lpads in the 90s are (each) composed of two (concentric?) mono pots, bridged together, comprising a single (mono) L-pad. But for the bridging, they could function as a single stereo pot (but not a stereo Lpad). I think.....

Very interesting info about L-Pads and specifically the L-Pads in the 90s. I also would like to learn more about them. Hopefully we'll get some additional folks to chime in.

The H/K 730 is a pretty awesome little receiver. They have a sweet sound and work real well with efficient speakers. I absolutely can't wait to get the Scott 299b back. Should be this week.

 

[Bucky Badger]

 

[PastTechFan]

So I did a little more googling about the L-pads. It looks to me like a lot of earlier (mono) ones were two stacked pots, with the center lug bridged, and one of the other lugs on each pot deleted. See:


Also, if you google Mallory (stereo) L-pads, you’ll see some old ones are a stack of four pots, two bridged pairs.

The newer (mono) L-pads seem to use a single wiper on two concentric tracks in the same housing (so no need for an external bridge).


Some interesting info here: http://www.bcae1.com/lpad.htm

As an aside, while it might be possible to hook up a stereo volume pot as an L-pad, it might be of limited use, since it seems the ohm rating of the "parallel" attenuator is often different from that of the one in series.

I brought up all of this, not to criticize your excellent work, but because the bridged link between your two mono L-pads has me wondering whether you've got more attenuation (resistance?) than you wanted (need?). I'll have to try and draw out your circuit for my own comprehension. Obviously you've got signal passing, I'm just wondering what all it's passing through.

By the way, I think your post hasn't gotten more interest (from some of the real cross-over experts) ibecause "British Audio" is a bit of a limited interested "niche" forum. You might want to ask one of the moderators to move this thread to "Speakers". At that point I would expect you'd get the benefit of those more knowledgeable than I.

 

[bce22]

So I did a little more googling about the L-pads. It looks to me like a lot of earlier (mono) ones were two stacked pots, with the center lug bridged, and one of the other lugs on each pot deleted. See:
View attachment 644523

Also, if you google Mallory (stereo) L-pads, you’ll see some old ones are a stack of four pots, two bridged pairs.

The newer (mono) L-pads seem to use a single wiper on two concentric tracks in the same housing (so no need for an external bridge).
View attachment 644524

Some interesting info here: http://www.bcae1.com/lpad.htm

As an aside, while it might be possible to hook up a stereo volume pot as an L-pad, it might be of limited use, since it seems the ohm rating of the "parallel" attenuator is often different from that of the one in series.

I brought up all of this, not to criticize your excellent work, but because the bridged link between your two mono L-pads has me wondering whether you've got more attenuation than you wanted (need?). I'll have to try and draw out your circuit for my own comprehension. Obviously you've got signal passing, I'm just wondering what all it's passing through.

By the way, I think your post hasn't gotten more interest (from some of the real cross-over experts) ibecause "British Audio" is a bit of a limited interested "niche" forum. You might want to ask one of the moderators to move this thread to "Speakers". At that point I would expect you'd get the benefit of those more knowledgeable than I.

Hi PastTechFan,

Wow, that is alot of great information. I'm glad you are questioning what the ideal replacement for our applications should be. I'll read the information you linked later tonight. I did post a quick thread in the speaker section right before I saw your recommendation to have the thread moved. I've asked for additional expertise to help get to the bottom of this. If that doesn't help us get more interest, I will ask a moderator to move the whole thread.

Thanks again,

Brad

 

[bce22]

If you hook up to one set of terminals then that is all you need! Dual mono design.
DC

Based on DC's response in the other thread it looks like I purchased the wrong pads and the mono pads are a better fit. Should I rewire the L-Pads to use only one set of terminals rather than use it the way it is? What is the difference in regards to the actual signal between the way i wired it and rewiring to the bottom terminals only and removing the bridge? Is there something I should test?

 

[Bucky Badger]

All good questions. I will be watching this thread with great interest as I will be doing the lpad/recap thing to my 90's as well and if I can learn what works best then that's a good thing.
Thanks for all the good info guys and please, keep it coming.

Good info in that link PTF. Thanks.

 

[spkrdtr]

OP, you replaced the L-pads (nice job!) but not the caps??????

 

[bce22]

OP, you replaced the L-pads (nice job!) but not the caps??????

Thanks spkrdtr for the kind words. The caps are next. I am waiting for them to come in the mail. I ordered 3 x 8uF (for 24uF) Kbg 5% 400V PIOs for the midst and an 8.2 Rike Audio S Cap PIOs for the tweeters.

The KBGs are arriving today. The Rikes are MIA {not showing any tracking info since 10/23 from Estonia)

 

[spkrdtr]

Thanks spkrdtr for the kind words. The caps are next. I am waiting for them to come in the mail. I ordered 3 x 8uF (for 24uF) Kbg 5% 400V PIOs for the midst and an 8.2 Rike Audio S Cap PIOs for the tweeters.

The KBGs are arriving today. The Rikes are MIA {not showing any tracking info since 10/23 from Estonia)

 

[PastTechFan]

.......Should I rewire the L-Pads to use only one set of terminals rather than use it the way it is? What is the difference in regards to the actual signal between the way i wired it and rewiring to the bottom terminals only and removing the bridge? Is there something I should test?

Well, I've attempted to figure out how your (bridged) stereo pots are working (at all) the way they're hooked up, but it looks to me like they're just fine. Here's my crude drawing:

As I see it, you're using a resistance track from one L-pad, (inner or outer, I'm not sure which), and the opposite track from the other L-pad. Given they're the same, it looks "all good". It might be tidier to do all the hook ups to one L-pad or the other, but no harm done.

 

[bce22]

Well, I've attempted to figure out how your (bridged) stereo pots are working (at all) the way they're hooked up, but it looks to me like they're just fine. Here's my crude drawing:

As I see it, you're using a resistance track from one L-pad, (inner or outer, I'm not sure which), and the opposite track from the other L-pad. Given they're the same, it looks "all good". It might be tidier to do all the hook ups to one L-pad or the other, but no harm done.

Crude??? No way! That's awesome. Thanks so much for doing that.

My KBG PIOs arrived from the Ukraine yesterday though I'm still waiting on my tweeter PIOs that I ordered from Estonia. They are MIA. When I get in there to recap I will wire all connections on the Lpad to the lower set of terminals. I am interested to see if it makes any difference.

 

[Progducer]

What kind of speaker wire would guys recommend to rewire the speakers to the Xover? The plastic/sheathing has dissolved on mine. The wire itself isnt copper, not sure what it is. Any recommendations? Also, OP can you post a parts express link for the correct Lpad or is it literally the mono version of the link you posted earlier. I'm very interested in the results after your change your wiring since you noted a significant improvement with the new stereo lpads. Of course now your opinions will change by putting in new caps at the same time. I used Sonicap Gen1s in my W90s and the sound improved, but now im wondering how much i am missing out by not choosing PIO type, or NOS.

 

[bce22]

What kind of speaker wire would guys recommend to rewire the speakers to the Xover? The plastic/sheathing has dissolved on difference. wire itself isnt copper, not sure what it is. Any recommendations? Also, OP can you post a parts express link for the correct Lpad or is it literally the mono version of the link you posted earlier. I'm very interested in the results after your change your wiring since you noted a significant improvement with the new stereo lpads. Of course now your opinions will change by putting in new caps at the same time. I used Sonicap Gen1s in my W90s and the sound improved, but now im wondering how much i am missing out by not choosing PIO type, or NOS.

Hi Prog! Thanks for your interest in this thread.

If I was to do it again I would purchase these from parts express. It's the 50 watt 1" shaft mono versions almost half the price of the stereo ones.

http://www.parts-express.com/parts-express-speaker-l-pad-attenuator-50w-mono-1-shaft-8-ohm--260-255

I still plan on wiring mine all to one set of terminals soon to see the difference.

When I get home from work I'll respond to your other questions. In the meantime hopefully others will.

Regards,

Brad

 

[Bucky Badger]

Thanks for that link Brad. Looks like those mono Lpads will be the ones I get. Unless I hear differently.
Anxious to hear what happens when you re wire yours.

 

[bce22]

What kind of speaker wire would guys recommend to rewire the speakers to the Xover? The plastic/sheathing has dissolved on mine. The wire itself isnt copper, not sure what it is. Any recommendations? Also, OP can you post a parts express link for the correct Lpad or is it literally the mono version of the link you posted earlier. I'm very interested in the results after your change your wiring since you noted a significant improvement with the new stereo lpads. Of course now your opinions will change by putting in new caps at the same time. I used Sonicap Gen1s in my W90s and the sound improved, but now im wondering how much i am missing out by not choosing PIO type, or NOS.

Hi Prog.

I used 18gauge hookup wire to install my KBG PIOs for the mids. I took a bunche of pictures and will post the recap of my mids in the Wharfedale owners thread. I can't speak about the improvement of these Russian PIOs over new polypropylene caps in the W90s. What I can say with very very little time spent in front of them they sound incredibly smooth and musical. I LOVE this sound! I will provide more info as I have it in a different thread as I want to leave this thread to discuss L-Pad replacement.

Thanks for that link Brad. Looks like those mono Lpads will be the ones I get. Unless I hear differently.
Anxious to hear what happens when you re wire yours.

So this evening I rewired the stereo L-Pads in one speaker to use only one set of terminals. I think it sounds better this way, especially in the highs. I took lots of pics and will add them to this thread once I get back to a real PC.

So, I can say with conviction that if you are going to replace the L-Pads definitely go with the mono ones. I made a mistake with the stereo ones.