Advent experiment - mod - much better sound IMO

[Pete B]

Hi Ken,

That's a good amount of power so that's good. Thanks for the tweeter info. I've seen the R come before the L before and it usually helps raise the input impedance in the tweeter range, it also makes the rolloff heavily damped. I've actually simulated a very similar design and this configuration usually provides a very over damped response, at least -6 dB at the crossover point, perhaps more. This helps but even -6 dB is not that much. I'll try to simulate the actual Advent configuration sometime soon.

Looking at one of the orange tweeters the dome is very far forward relative to the magnet top plate, there's probably a long aluminum former that serves as a heat sink, very curious to find out the VC winding height, I'd bet that it's much greater than most tweeters providing much more Xmax. The diameter is about 1 3/8" inches using one half of the roll as is suggested for woofers so it's also got more surface area than most tweeters. Interesting design.

Anybody have a fried orange tweeter to disect and measure the voice coil height?

The orange tweeters I have are dated Nov 1, 1972 and they also look like prototypes. The suspension may be stiff, but that large roll should give it long throw, stiff with a low Fs means that the moving mass is fairly high.

Thanks for all the foam replacement info, the old one here looks like it was done correctly. I assume you do yours with the roll inverted as it was in the original? I'll be getting the ones you suggest.

I was looking at your crossover upgrade and I'd guess that the DC resistance of the coils is lower. The woofer coil will tighten up the bass a bit which is fine especially with a tube amp. I'd expect that the Erse inductors have decent distortion characteristics have you seen any measurements?

I just measured the old tweeter shunt coil at about 2.2 ohms and the new lower resistance coil will alter the Q of the network. It's good that it's air core, and some series R could be added so that the total resistance matches the old inductor if one wants to copy the old tonal balance with the advantage of lower distortion. It's a minor point.

[Guest Ken Perkins]

Now you have my curiousity up. I've wondered about the consistency of the parts used in these speakers over the years they were available. My shunt coils measure about .5 ohms, which as you say will underdamp the highpass causing a slight peak (ringing) at Fc but with a steepish rolloff. The high DCR you measure would overdamp the ringing, or eliminate it altogether, and yield a smoother rolloff. I've seen a small resistor put in series with shunt coils for just this purpose. You can to the same thing to a capacitor in a woofer's lowpass to soften the knee, as I call it, around Fc as well.

I've read that the early first gen. Advents used a 16uf cap as the bypass for the "increase" postition which was later lowered to 8uf like mine have, leaving the main cap at 16uf alone. I wonder if this could have been a part of any other changes, including a shunt coil change, as well. I've even read that some of the last of the first generation had the second generation 12" steel frame woofers instead of the masonite ringed ones as well. Too bad there's no one from the old Advent around to ask these questions... As I understand it, Andy Petit has his hands in the Small Advent as well as the voicing for the second gen. Large Advent so maybe he was "playing" with the first gen.

Now, I'm going to be compelled to open mine back up...again...to try adding a damping resistor to the highpass shunt to see if it makes an audible difference, eventually!

Out of curiousity, what do the woofer's coil you have measure? Mine are 1.5mH/.35 ohms DCR. The Erse replacements I use measure .32 ohms.

[Pete B]

The crossover design looks to be exactly the same configuration as the one shown at this site, however yes this system (1972 time frame) has a 16 uF capacitor where the 8 uF "increase" cap is shown. I'm positive that the system is stock. The tweeter shunt inductor is definitely 2.2 ohms, I measured both systems, and this system has never been stressed too badly, never had any tweeter failures. A low reading could be due to burnt and shorted insulation, these inductors are not going to handle much power at all. It's physically .5" in diameter painted red on top and the wire is VERY light gauge.

The lower DCR, assuming it is correct, will help LF rejection and power handling. I doubt it will change the voicing very much since this is mainly below the tweeter passband. I prefer the newer 8 uF for the "increase" cap. Actually, I'd put 4 uF across the 3 ohm directly to compensate for the 15 kHz rolloff, then an additional 4 uF when in the increase position - a minor point.

The other "decrease" inductor measures .6 ohms DCR, same diameter and is painted white. I've not put the system on the bench so I've not yet measured inductances and transfer functions.

The woofer inductor DCR is the same as you measured. The woofer inductor is nearly falling off the back and the other system has a loud buzz coming from the back when just the right mid bass note plays. These just need to be remounted probably with screws and hot glue.

I wasn't aware that you matched the coil resistances, so the only thing I'd check is that the old inductor does not have physical damage.

So are you going to try the BSC Ken? It should work fine with the newer XO since their very similar especially in the "normal" position and none of the systems seem to have BSC compensation.

[Pete B]

Hi Ken, Just wondering what you used for dust caps?

[Guest Ken Perkins]

Hey Pete...

I need to shout out a big thanks for your post regarding the DCR of the highpass shunt. As it turns out, BOTH of my original coils are deteriorating to the point they're practically a dead short. Apparently, the copper has oxidized to the point that the enamel insulation has began to turn to dust and flake off, and is causing the laminations to seperate as well. I can probe the coils at ANY point and get a different reading. In all the years I've worked with old speakers, this is the first time I've ever seen this.

As a fix to my upgrade crossovers, I've found that a 1.5 to 1.8 ohm resistor, in series with the shunt coil, will restore the DCR to 2.2 ohms as per the original. To think since July when I got these, I've been listening to them, first with bad coils and then with the wrong NEW coils!

The sound is quite different with the proper DCR. It's more laid back and relaxed sounding whereas the smaller DCR coils yield a more "west coast sound" upfront midrange, which might appeal to some. I'll keep the original voicing and will start to recommend this fix. There's no choice BUT to use this as I've never otherwise seen a .43mH/2.2 ohm DCR coil, although someone could probably custom wind one.

As for the dustcaps, I never cut the dustcaps when I do a refoam. I use a 15 hz sine wave pulse at about 1/3 xmax to pump the vc up and down in the field and force it to stay centered. I've used this method on several woofers and have never had one rub or buzz.

Also, I ordered the parts for the BSC circuit on Friday and they should be here tomorrow for me to try this weekend. I'm going to build the tape monitor version so it can be switched in or out.

[Pete B]

Hi Ken,

I'd guess that those inductors were overheated at some point and that lead to the deterioration of the insulation. I've never seen such small inductors in a speaker. Hope the inductance value is correct, yours agrees with the schematic on this site so it's probably fine. The air core inductor plus resistor is fine to retain the original transfer function, it's good that air core coils do not saturate.

I noticed that you measured the woofer in box, I was wondering if you could measure Qms in box to determine how much it is lowered by the damping material if it's not too much trouble. I expect it to be a fairly significant amount.

Anxious to hear what you think of the BSC!

[Guest Ken Perkins]

I got the parts for the BSC circuit today, will try it and report back. I'll get you the inbox Qms measurement as well. Also, I have an extra tweeter (old with a crushed dome) that volunteered its life to science and will post the dimensions you requested. I have to say, the tweeter is more robust that I though it would be. It has a full aluminum former, rather long, with the dome/donut assembly glued directly to it. I has a large diameter spider around the voicecoil as well, which I was not expecting, and actually looks like a little woofer. The space underneath behind the cone assembly is rather like a small enclosure.

[Guest Ken Perkins]

Here are the measurements for each speaker...

Fb - 43.0201/43.0204 hz

Qtc - .90/.91

"Qes" - 1.168/1.189

"Qms" is 3.948/3.966

All of these are so close, I have to say I'm impressed with these 28 year old woofers, not to mention the structural integrity of the boxes!

Here are the dimensions for the sacrifical tweeter. They are in mm since they are so small...

vc dia - 20mm

vc former len - 13mm

coil len - 3mm

top plate - 3mm

spider - 39mm

cone dia - 50mm

"Enclosure" dimensions are 10 mm X 50mm with the cone attached to the masonite baffle. The enclosure could benefit from some damping but who knows?

[Pete B]

Thanks Ken, very, very much for all this information. When I looked at that tweeter years ago I thought it must be fragile with that small voice coil and I didn't know at the time that it was crossed over so low. Recently, as I've been stating here I thought that it's probably long throw or at least fairly robust and thanks for confirming that.

The thing that jumps out is that the gap height and coil height are equal which means that the theoretical Xmax is zero. There will be some fairly linear displacement as a result of the fringe field which makes it an underhung coil in a sense and that the BL reduction is proportional to the fraction of the coil that's out of the gap. It is therefore slow and progressive. If we assume no fringe field as an approximation and allow a 50% reduction in BL then this results in an Xmax50 of 1.5 mm and from here we can calculate a VD for this imperfect case which can be compared to other tweeters. Many Morel tweeters also have a linear Xmax of zero and I've never used them for this reason, most others North, Scan, Vifa, Seas most have .2 to .5 mm theoretically linear Xmax. Let's take the North for example with an 1.8 mm underhung coil and a 2.8 mm gap height which results in a linear Xmax of .5 mm and an Xmax50 of 1.4 mm. This is close but the dome area and therefore VD are also lower than the original Advent. Still all these numbers are theoretical and the NorthD25 test data looks very good so it still may be an excellent replacement, at least it has a theoretically linear region.

I've also recently noticed that the Parts Express (DAYTON DC28F-8) 28 mm dome tweeter is going for only $12.50:

http://www.partsexpress.com/pe/pshowdetl.c...r=275-070&DID=7

It's been noted on the web that this is a sort of hybrid copy of the Morel tweeters, a Morel replacement dome even fits it. It probably has a zero theoretical Xmax but then so does the original Advent tweeter so perhaps this would work well also. It would be interesting to test these bargain tweeters that seem to have potential as replacements.

[Guest Ken Perkins]

That Dayton tweeter is not what you're looking for. I tried to use it three years ago in a sort of Dynaco A-25 clone with a Dayton 10" woofer. The woofer held up fine to well above 1200 hz but the tweeter was very strained. Granted, I was using a first order (electrical) series crossover, but I wanted to keep the crossover simple based on the A-25's simplicity. A better tweeter for low crossovers is the SEAS 27TFFC or one of its newer brothers. I've used it extensively and it's built like a tank and eats up a low crossover, even shallow ones. It's the "official" SEAS replacement for the tweeter in the A-25, per a discussion I had years ago with a rep from SEAS. Others have used the Morel MDT-20 and 30 as replacements for low crossovers. BTW, the SEAS woofer for the A-25 is still available from Madisound.

Regarding the Advent tweeter, I noted a while back that it has little or no "give" when pushed in, indicating a pretty stiff suspension and this would seem to agree with a tight xmax.

[Pete B]

Your observations on the Dayton make sense since it probably has low Xmax but then so does the Advent. I was thinking that the Dayton might need some mods and since the price is so good it looks interesting. Then I looked at the review and noticed that the response has gotten worse on the latest version when I thought I read at another moder's page that it had gotten better. I think it might need more damping in the pole vent, but who knows probably not worth the time and there's not much that can be done about Xmax.

I agree about the SEAS, I've not used that particular model but have used several others and they are very good, the TFFC did happen to be my next pick. It has the same .5mm one way Xmax as the North. I also noticed that the Advent tweeter suspension was stiff but as I mentioned it's required to get the correct Fs with a highish moving mass. As long as the compliance and Bl are constant then the driver is linear, but with an equal hung coil it will most likely soft compress with more excursion. Some drivers do very well exceeding the theoretical Xmax and it's hard to predict without Bl curves or distortion tests. I agree that it might be interesting to put some damping in the chamber that you mention. Did you notice if the pole piece is extended in the Advent tweeter?

Anyone have specs on the Layne black dome replacement tweeters, or have a dead one to disect?

[Pete B]

A-25s - I was given a pair many years ago and IIRC there was just an 8 uF cap to a switched pad for the tweeter, I think the woofer was directly wired, very simple. They are very good considering how simple they are. Yes, I also think about building the old designs and have noticed that Madisound has a replacement woofer. I've also noticed those Morels being suggested for low XOs and I have to wonder if they really do that well at higher listening levels, I prefer the SEAS as you mentioned. I was always impressed by how smooth that SEAS 10" was in the A-25 but it doesn't have much Xmax. The SEAS parts to build an A-25 are rather expensive to make it worth while today, but it is on my list to take a closer look at. I wonder how the Peerless CSX with 9 mm Xmax and smooth response would do in it's place?

[Pete B]

Some asked for component values for other BSC step sizes, here they are:

I also simulated the design taking into account the load impedance and the values are slightly different. I just used standard values in the early prototype and the BSC center frequency was slightly higher than the original target. These values are for a BSC center of 400 Hz:

IN O--------- R1 --------------O OUT

|--- C1 ---| |

|

C2

| ----------> RL

|

|

R2

|

GND O---------------------------------O GND

These values are for RL = 22K:

R1 = 2.2 K, C1 = .0047

C2 R2

1dB .027 15K

2dB .047 7K

3dB .082 4.7K

4dB .1 3.5K

5dB .12 2.6K

6dB .016 2K

These values are for RL = 47K:

R1 = 4.7 K, C1 = .01

C2 R2

1dB .012 33K

2dB .022 15K

3dB .039 10K

4dB .047 7.5K

5dB .056 5.6K

6dB .068 4.3K

Caps should be film type, mylar, poly, etc.

[Guest Ski Peru]

Pete, big thanks to you (and russwollman as well for his persistance) for this thread.

I recently re-furbed two pair of LA, each pair circa '75 based on the tweeter stamps and serials. One pair I've owned for many years and that pair (sadly) had the woofers replaced years ago when I was too stupid to know that all I needed was new surrounds, and the audio shop was too greedy to tell me as much. The second pair, recently acquired, has the masonite ring woofer, to which I've applied new surrounds. I replaced the caps in all.

Particularly after the cap-job I began to notice the midrange coloration you mention, more so than before (whether that was real, or driven by power of suggestion, we may never know. My ears tell me it was real). Long story short, I built your circuit, installed it in the tape loop, and I like what I hear.

I have a ton of questions though, especially as I've pored over the thread again and again, hoping to _understand_ the electronics. (Unfortunately, all of Mr. MacDonald's efforts to teach me the nature of such things was long ago left behind in that 12th grade physics classroom! I'm lucky to remember his name!)

One item I noted after building the circuit was very last sentence of your original post:

"Pre should have < 100 ohm output Z, power am > 22k input Z"

Comparing these values to the spec pages of my equipment, I'm now wondering what effect the differences have (or if I should immediately purchase fire insurance).

Pre amp: I'm using pre-out of NAD-3130. The spec sheet tells me that Line level outputs have output impedance (pre-amp = 800 ohms) (tape = Source Z + 1k ohms). Now, I'm in the tape loop, and my Source here is CD, which lists Output load impedance "over 10 kilohms". So as far as the pre-amp goes, I don't have a clue what I should be measuring.

Amp: Crown 460csl Input Impedance - 10k ohms, unbalanced.

So I guess my first question is: do the differences in values instruct a differently configured circuit?

Second question would be: can you suggest a good text that might get me grounded in the electronics???

(There was a third question, but I've forgotten it already...)

Thanks a ton for taking the time...

[Pete B]

Hi Ski,

Sorry I missed your post here for a while, good to hear that you tried it. I'm wondering which circuit you built, the 4.7K or 2.2K version or one with less than 6 dB of taper?

Basically, to make the calculations simple we'd like to ignore the source impedance and load impedance, and if they're 10X the circuit level impedance they can usually be ignored. So the 2.2K design wants to have a load of 22K or higher. The simulated designs take the load into account and therefore it should be close, but it is not critical since it is already much higher than the circuit level impdances. It will not blow up, with the wrong load or source impedance. However, a 10K load is rather low, it will reduce the number of dB in the correction. I said 6dB was probably too much so I think you'll be fine with the 10K load, I'd guess you'll get about 3-4 dB for the 2.2K ohm circuit.

The 800 ohm source impedance is a bit high but if we take a look at the circuit we see that the pre amp output impedance is in series with the first resistor R1 in the latest schematic. You can subtract the Pre Amp output impedance from R1 to and use the new value for R1. For 800, and the 2.2K circuit the new value for R1 is 2200-800=1400 ohms or 1.4K.

The book I usually recommend is Horowitz and Hill: The Art of Electronics, it's expensive so you might want to take a look at your library first. The very simple AC analysis is short caps, open inductors at high frequency (HF), short inductors, open caps at low frequencies (LF). Try redrawing the circuit, once for LF again for HF and compare.

I'm very curious to hear your description of the change in sound once you get the circuit sorted out.

Pete B.

[Pete B]

I made a few typos when I wrote this up, here are the corrected values:

C1 was swapped between the 2.2K and 4.7K version, and the C2=.016 uF in the 6dB case should be .16 uF.

Some asked for component values for other BSC step sizes, here

they are:

I also simulated the design taking into account the load

impedance and the values are slightly different. I just used

standard values in the early prototype and the BSC center

frequency was slightly higher than the original target.

These values are for a BSC center of 400 Hz:

IN O--------- R1 --------------O OUT

|--- C1 ---| |

|

C2

| ----------> RL

|

|

R2

|

GND O---------------------------------O GND

2.2K Version, these values are for RL = 22K:

R1 = 2.2 K, C1 = .01

C2 R2

1dB .027 15K

2dB .047 7K

3dB .082 4.7K

4dB .1 3.5K

5dB .12 2.6K

6dB .16 2K

4.7K Version, these values are for RL = 47K:

R1 = 4.7 K, C1 = .0047

C2 R2

1dB .012 33K

2dB .022 15K

3dB .039 10K

4dB .047 7.5K

5dB .056 5.6K

6dB .068 4.3K

Caps should be film type, mylar, poly, etc.

Pete B.

>Some asked for component values for other BSC step sizes,

>here they are:

>I also simulated the design taking into account the load

>impedance and the values are slightly different. I just used

>standard values in the early prototype and the BSC center

>frequency was slightly higher than the original target. These

>values are for a BSC center of 400 Hz:

>

>IN O--------- R1 --------------O OUT

> |--- C1 ---| |

> |

> C2

> | ----------> RL

> |

> |

> R2

> |

>GND O---------------------------------O GND

>

>These values are for RL = 22K:

>R1 = 2.2 K, C1 = .0047

> C2 R2

>1dB .027 15K

>2dB .047 7K

>3dB .082 4.7K

>4dB .1 3.5K

>5dB .12 2.6K

>6dB .016 2K

>

>These values are for RL = 47K:

>R1 = 4.7 K, C1 = .01

> C2 R2

>1dB .012 33K

>2dB .022 15K

>3dB .039 10K

>4dB .047 7.5K

>5dB .056 5.6K

>6dB .068 4.3K

>

>Caps should be film type, mylar, poly, etc.

[Guest esmachers]

Thread #377 from Pete begins:

>I posted this to another list, for what it's worth, be

>interested to hear from others if they try it:

>

>There was talk sometime back about large Advent speakers and

>I'm always surprised when people comment about how good they

>are, I suppose they might be good for their day or good for

>the low price point. I noticed fairly serious midrange

>coloration from the first listen.........

Hi Pete,

I had to write you to let you know the results I had with your circuit and to thank you for your good work. The results are amazing!

Since the parts were so cheap I decided to build every step from 1dB to 6dB so I could try them all. I figured this would be a good test for my hearing as well, i.e., to see if I could hear the difference in each of the steps.

What a blast. I tried them all and could tell the difference. I actually settled on the 4dB step. I guess I like a little more mid-range than you. (Perhaps Henry Kloss and I have a little mid-range deficiency in common). My system is so much more enjoyable to listen to. I truly cannot get over it. I’m listening to Van Morrison as I type and he has never sounded better.

I’ve owned my Advent large loudspeakers since 1974. I bought my Sony TA-1150 Integrated Ampifier at the same time. The speakers and amp spent a little time stored in the basement now and then depending on where I was living and my interest in setting everything up. For a while I had even given them to my son. He used them until the surrounds rotted out. I recovered them from him before he threw them out and had the surrounds redone for the second time. Thank goodness!

Last year I decided to set them up in my 12 x 14 office rather than resign them back to storage in the basement. They overwhelm the space a little but my amplifier isn’t real powerful anyway so it’s a good match.

I’ve always had a tough time getting the speakers to sound the way I wanted. Usually this amounted to using/not using the loudness control and adjusting the bass and treble settings. Bottom line, it generally was a compromise. Now, thanks to you and your circuit that compromise is a thing of the past.

I still can’t believe it.

Thank you again!

Steve

[Pete B]

Thanks for the feedback Steve and the email.

I'm going to set up the A/B again soon to demo it to some friends.

Did you happen to notice if your Advents are the early ones with two 16 uF caps in the crossover? Later ones had 16 and 8 uF, and even later had a 13 uF IIRC.

Pete B.

[Guest esmachers]

>Thanks for the feedback Steve and the email.

>

>I'm going to set up the A/B again soon to demo it to some

>friends.

>

>Did you happen to notice if your Advents are the early ones

>with two 16 uF caps in the crossover? Later ones had 16 and 8

>uF, and even later had a 13 uF IIRC.

>

>Pete B.

Pete,

Mine have two 16uF caps in each crossover. I was considering replacing these with poly caps but I'm concerned about changing the voice. I figured these were voiced with the electrolytics so I'd just stick with them. Any thoughts you have on this changeout would be appreciated.

Happy New Year,

Steve

PS: My Advents are the walnut veneer versions.

[Pete B]

I've put a lot of thought into this and considering that it is established that electrolytic caps do not age well, and after measuring several that did not meet their voltage specs and in one case had highly increased capacitance, I now suggest always replacing electrolytic caps that are more than 10 or 20 years old. The exception to be considered on a case by case basis is the large computer grade caps found in some systems, and perhaps some of the more exotic types. But always the electrolytic caps to the mid and tweeters which are more likely to fail due to a leaky cap:

http://www.classicspeakerpages.net/dc/dcbo..._id=7195&page=4

http://www.classicspeakerpages.net/dc/dcbo..._id=&page=#7710

http://www.classicspeakerpages.net/dc/dcbo..._id=&page=#7728

http://www.classicspeakerpages.net/dc/dcbo..._id=&page=#7713

I measured the electrical transfer function of the large Advent tweeter crossover and the Q is on the high side, somewhat over 1 if I remember correctly. I was surprised to find this and it does make the circuit more sensitive to ESR, however the shunt inductor has a high resistance, around 2 ohms from memory, and this should lessen the sensitivity to ESR. I suggest replacing the caps with reasonably priced film caps, Mylar or poly are fine. I'd go with 15 uF which is within the 10% tolerance of the original cap but will lower the Q of the circuit just a bit. You might also want to lower the cap across the increase switch to 8 uF since this was a good refinement to the design. I plan to look at this a bit more but I don't know how soon that will be.

It's also suggested that you measure the DC resistance of the shunt inductor as it was mentioned earlier in the thread that it cannot handle much power and turns shorted in one poster's system. I'd actually replace this inductor with a low cost air core type, then add a resistor in series to provide a total DCR equal to the original. This will lower the distortion at high levels in the tweeter circuit.

Speaking of this distortion, I always noticed distortion in the mids/highs when turning up the Large Advents, harshess or a sort of crying quality, it adds to our perception of loudness and tells us to turn it down. I tend to wonder if this was deliberate by Henry Kloss to save drivers from overload. I'm not sure if it's due to the very small iron core inductor, or the tweeter having zero Xmax. It is worst at fairly high levels and not much of an issue for normal listening but does take away from the transparency of the system at moderate-high levels.

Thanks again for your feedback Steve, it's always nice to hear.

All the best to you in the New Year!

Pete B.

>Pete,

>

>Mine have two 16uF caps in each crossover. I was considering

>replacing these with poly caps but I'm concerned about

>changing the voice. I figured these were voiced with the

>electrolytics so I'd just stick with them. Any thoughts you

>have on this changeout would be appreciated.

>

>Happy New Year,

>Steve

>

>PS: My Advents are the walnut veneer versions.

>

[Guest esmachers]

Thanks for the information Pete. I'll order some caps and give it a try. I'll also check the shunt inductors for a short and replace them if needed.

I'll post my results.

This has been fun.

Thanks again,

Steve

>I've put a lot of thought into this and considering that it

>is established that electrolytic caps do not age well, and

>after measuring several that did not meet their voltage specs

>and in one case had highly increased capacitance, I now

>suggest always replacing electrolytic caps that are more than

>10 or 20 years old. The exception to be considered on a case

>by case basis is the large computer grade caps found in some

>systems, and perhaps some of the more exotic types. But

>always the electrolytic caps to the mid and tweeters which are

>more likely to fail due to a leaky cap:

>

>http://www.classicspeakerpages.net/dc/dcbo..._id=7195&page=4

>

>http://www.classicspeakerpages.net/dc/dcbo..._id=&page=#7710

>

>

>http://www.classicspeakerpages.net/dc/dcbo..._id=&page=#7728

>

>http://www.classicspeakerpages.net/dc/dcbo..._id=&page=#7713

>

>I measured the electrical transfer function of the large

>Advent tweeter crossover and the Q is on the high side,

>somewhat over 1 if I remember correctly. I was surprised to

>find this and it does make the circuit more sensitive to ESR,

>however the shunt inductor has a high resistance, around 2

>ohms from memory, and this should lessen the sensitivity to

>ESR. I suggest replacing the caps with reasonably priced film

>caps, Mylar or poly are fine. I'd go with 15 uF which is

>within the 10% tolerance of the original cap but will lower

>the Q of the circuit just a bit. You might also want to lower

>the cap across the increase switch to 8 uF since this was a

>good refinement to the design. I plan to look at this a bit

>more but I don't know how soon that will be.

>

>It's also suggested that you measure the DC resistance of the

>shunt inductor as it was mentioned earlier in the thread that

>it cannot handle much power and turns shorted in one poster's

>system. I'd actually replace this inductor with a low cost

>air core type, then add a resistor in series to provide a

>total DCR equal to the original. This will lower the

>distortion at high levels in the tweeter circuit.

>

>Speaking of this distortion, I always noticed distortion in

>the mids/highs when turning up the Large Advents, harshess or

>a sort of crying quality, it adds to our perception of

>loudness and tells us to turn it down. I tend to wonder if

>this was deliberate by Henry Kloss to save drivers from

>overload. I'm not sure if it's due to the very small iron

>core inductor, or the tweeter having zero Xmax. It is worst at

>fairly high levels and not much of an issue for normal

>listening but does take away from the transparency of the

>system at moderate-high levels.

>

>Thanks again for your feedback Steve, it's always nice to

>hear.

>

>All the best to you in the New Year!

>Pete B.

>

>

>>Pete,

>>

>>Mine have two 16uF caps in each crossover. I was considering

>>replacing these with poly caps but I'm concerned about

>>changing the voice. I figured these were voiced with the

>>electrolytics so I'd just stick with them. Any thoughts you

>>have on this changeout would be appreciated.

>>

>>Happy New Year,

>>Steve

>>

>>PS: My Advents are the walnut veneer versions.

>>

>

[Pete B]

Hi Steve,

I've added some comments about the woofer inductor at the thread below since you seem to be open to mods. I also comment about some minor differences between the 16/16 and 16/8 not noted above in our discussion:

http://www.classicspeakerpages.net/dc/dcbo...d=689&page=#700

Pete B.

[Guest daveshel]

>I posted this yestersay on the Parts Express forum. It's a

>performance upgrade for the original Advent Loudspeaker. It

>does not address the baffle step but it does improve detail

>resolution and imaging and gives them that "disappearing"

>quality mentioned earlier that they lack stock. I've compared

>my modification before and after and it will not affect or

>alter the original voicing.

>

>

>

>http://www.pesupport.com/cgi-bin/config.pl?read=189156

>

>

>

Say Ken, this link seems to have expired. I would like to check out your performance upgrade.

Pete, your baffle mod sounds interesting, and I my have to experiment with that. My preamp has an EPL that needs something to do. Although I may have accidentally achieved good baffle with my setup. My Advents (4 larges is 2 stacks) sit on stands that are 6" off the floor in the front and sloping down toward the back so that the speakers are at a few degrees off from vertical. And they are placed roughly 20" from the wall. I have always loved their sound and was amazed at the synergistic effect when I added the second pair. Not boxy at all.

Thanks, guys.

[Guest Ken Perkins]

Hi Dave,

Unfortunately, Parts Express no longer has a good archive. A couple of years ago they did but for some reason they no longer keep old posts.

Regardless, the upgrades I'm talking about involved completely bypassing the stock crossover in favor of one specifically parted and wired to a particular position of the contour switch on the back. I used the "normal" position in this case as this position has the best balance to me. High quality parts are involved and includes replacing the woofer's lowpass coil with a heavier duty coil of the same inductance and DCR (1.5 mh and @.3 ohms). I used a Jantzen air core.

The highpass uses very high quality, though not overly expensive caps available from GR-Research and Sonicraft called Sonicaps. Any good poly cap of the Dayton/Bennic and Solen variety will suffice, just get rid of the 16 uf electrolytic cap. You do not need expensive "boutique" caps in this speaker. I used a 3 ohm Mills resistor to replace the sandcast stock one but this part is not really critical to replace as long as it measures correctly, I just like Mills resistors. The shunt coil in the highpass is a 20 gauge Jantzen. If you have the earlier version of the crossover with the two 16 uf caps, you should put a 2 ohm resistor in series with this shunt coil and together they will be wired into the crossover in place of the original "button" coil.

I also replaced the foam blocks in mine with real fiberglass bats. I used the "pink stuff" you can get from Home Depot in 18"x48x2" bats rolled up for about $4 a package. Approx. one and an half of these loosely stuffed with the glass pushed away from the back of the woofer (make a small bowl-shaped recess for the driver displacement).

Reseal the drivers down with new mortite rope or similiar and make new screw holes for the woofer by rotating the woofer 1" in either direction to get a better grip and seal between the baffle and the woofer. It is very important that when you are finished, if you push on the woofer cone it should move in with great resistance and move back out very slowly. If it pops in and right back out, you have a air leak.

Last, I originally cut some dense, 1/2" small foam sheets to line the baffle and fill in the gap caused by the grill and the baffle. Since then, I have removed the foam sheets and replaced them with 1/2" thick felt from McMaster-Carr.

Also, if you refoam, DO NOT use generic 10" woofer foams. You can find the proper size from rssound.com and it's the correct 17mm wide ring instead of the typical generic 14mm and is very thin. This is VERY important to maintain excursion as the smaller ring will restrict cone motion.

Internal wire was replaced with plain old 16 gauge zip cord. All the parts can be bought from Parts Express. You can get the coils anywhere just make sure they are matched as close to the originals as possible.

[Guest esmachers]

>Hi Steve,

>

>I've added some comments about the woofer inductor at the

>thread below since you seem to be open to mods. I also

>comment about some minor differences between the 16/16 and

>16/8 not noted above in our discussion:

>

>http://www.classicspeakerpages.net/dc/dcbo...d=689&page=#700

>

>Pete B.

Hi Pete,

I replaced the capacitors in my large Advents with Bennic polys from Madisound: 16uF for the C1 capacitor and 8uF for the C2 “increase” capacitor that was previously 16uF. While I was in there I disconnected the tweeter and measured the DCR of the L2 shunt inductor. It read 2.2 ohms in each speaker. Note: I don’t have the most accurate DMM so that could be off, but L2 is definitely not shorted.

I replaced the caps in one speaker first and thought I liked the sound so I did the other speaker. After that is when my ears started to hurt. The speakers were incredibly harsh in all 3 switch positions. This setup truly sounded like a transistor radio with a subwoofer. And, if I was listening to a weak FM station, i.e., one with a little background static, it was unbearable.

Undaunted, I left the caps in place over the weekend to see if it was just me being overly sensitive. By last night my soldering iron couldn’t heat up fast enough. I put my original 16uF electrolytics back in. I left the 8uF caps in place for now since I usually listen to these speakers in the “normal” position.

Anyway, I’m at a loss. I don’t have a capacitance tester so I can’t verify the Bennics but they are marked as 16uF and physically they are about twice the size of the 8uFs. Further, after heating up the electrolytics twice now to desolder/solder them I’m really concerned about their reliability.

Ideas and comments are appreciated.

Thanks,

Steve