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Old 12th September 2017, 02:53 AM   #1801
dgta is offline dgta  United States
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Originally Posted by AcoustatAnswerMan View Post
An owner's manual for the Spectra 1100 was recently posted ...
Yes, I have the owner's manual. It has some very basic assembly instructions on how to bolt the upper panel to the woofer box. I also have the interface schematic. But I believe there was a Service Manual that has information on taking apart the upper (ES) portion and servicing it. Do you know where I can find a copy?
Thanks
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Old 12th September 2017, 07:03 PM   #1802
jkasperows is offline jkasperows
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Default Acoustat Spectra 3

I have just acquired a set of Acoustat Spectra 3 speakers and have no idea how to use. anything I should check before plugging them in? what are the switches and connection for? Don't know if it matters but I plan to drive them with a Denon PMA-920 amplifier.


thank you


R
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Old 13th September 2017, 01:17 AM   #1803
charlesp210 is offline charlesp210  United States
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Default Suspect VR flyback

I've been using Acoustat 1+1 with a Krell FPB 300 amplifier since 2008, and I've posted in this thread before.

In the last few months, my amp has been intermittantly shutting down, and I've been going through a long process of "elimination" to find out what's wrong.

The shutdowns do not necessarily occur at high output levels.

This started when I was trying a tweako DAC (I'm back using a good DAC now) which created an unexpected high power blast that blew the Acoustat fuses (I was using 5A at the time, I've now switched to 3A as recommended by Roy). The shutdowns started later that same day and I started doing (at first not very well planned) elimination tests to determine what was wrong.

I first feared damaging the speakers, perhaps creating a HF transformer short (I cross the Acoustats at 100hz, so there's not much bass). But I still got shutdowns playing only one speaker at a time with the HF transformer disconnected.

Another test showed that I could consistently get either speaker to shut down the right channel of the amplifier, but not the left channel.

So I sent the amplifier back to Krell (who had just done full capacitor service on my unit a few months earlier). They found a fault in the left channel, and repaired it and returned it to me for free because of the earlier service done. They explained that a fault in the left channel could cause shutdown to occur in right channel.

Well, now I can get either channel of the amplifier to shut down, and with either speaker. I think the repair essentially restored the correct operation of the protection system. And correct operation is to shut down instantly when the signature of an electrical short appears. (A 6800 class computer in each channel figures this out looking at voltage, current, offset, and rail voltage regulator margin. It would be interesting to know what makes it decide "short", and even if that is what it is deciding now. On shutdown you can get one or two lights remaining on, and the "1 light" condition includes short, heat, and insufficient AC. I'd like a display panel telling me what the situation is in more detail...some very high priced amplifiers do that now.)

My thinking NOW is that it was actually the speakers all along. Since the problem started after a particular incident, that incident changed something in the speakers. I have already "eliminated" the HF transformer as a potential cause.

That leaves various things, the variable resistor and LF transformer among them. I am now strongly suspecting that the variable resistors in my factory C mod interfaces have a problem.

There had always been considerable green corrosion around (and probably under) the wipers on the resistors. I've been too lazy to clean that off, knowing I'd have to do it completely or not at all. I now have a fresh bottle of deoxit and this is now my plan for this coming weekend.

I'm thinking that if the wiper is sufficiently corroded, there may be intermittent dropouts in connection, or slight rectification even. This could, I think, produce a flyback voltage from the energy stored in the HF transformer when the connection is resumed, and this flyback voltage, though brief, could be what is causing the Krell to believe there is a short. (BTW, my Aragon amplifier has a much simpler protection system, and it just plays along fine, although I like the Krell better. I did see shutdowns with a newly purchased Eagle 2 amplifier, but I figured that was because it simply wasn't up to the task, but perhaps it had the same issue as with the Krell. I know from many years use that the Krell can play these speakers just fine, and you would think so also.)

If mere cleaning doesn't fix the problem, or even if it does, I'm also thinking of replacing the variable resistor with fixed resistors anyway. I intend to measure both of my VR's first however, to make sure I am not changing that. I find the high frequencies to be plenty strong up and measurably flat up to their limit at 19kHz now. I still use supertweeters just so I'm not missing 19-40kHz, in case it makes a difference (in sighted testing, it always seems to, even though I can't hear anything coming out of them, I can measure it). I find the Acoustat 1+1's slightly too strong in the 3-10kHz region (I make an intentional dip there using DSP EQ roughly following recommendations by Linkwitz).

So I'm not interested in boosting the highs by reducing the resistance from input to HF transformer (aka 'air mod' if I understand that correctly). The highs are just fine.

I might be interested in lowering the LF cutoff point in the interface. The region 100Hz to 300Hz has some broad depressions I've never fully worked out.

I don't think it would be a problem to use the entire 16 ohm variable resistor as the load for the capacitor to do that, with no wiper, then add an additional 1-6 ohms to feed the HF transformer as needed to get the best balance in extreme highs. This is sort of like replacing the VR with a slightly bigger VR and moving everything up.

From where I was reading a few years ago, the air mod does that also, by adding 10ohm below the VR. I would be using the entire VR as a fixed resistor, and adding more resistor(s) at the top.

Any fixed resistors should be low inductance, right? Replacing the big VR with a low inductance fixed resistor would be expensive, and would require holes in the box for chassis mounting to dissipate heat. So I'd avoid that, unless additional evidence points to the VR having internal damage.
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Old 13th September 2017, 11:14 PM   #1804
AcoustatAnswerMan is offline AcoustatAnswerMan  United States
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Quote:
Originally Posted by dgta View Post
Yes, I have the owner's manual. It has some very basic assembly instructions on how to bolt the upper panel to the woofer box. I also have the interface schematic. But I believe there was a Service Manual that has information on taking apart the upper (ES) portion and servicing it. Do you know where I can find a copy?
Thanks

There is no service document other than the owner's manual. There are no serviceable parts inside the panel structure (other than cleaning perhaps), so unless you want to change the grille sock, there is no reason to disassemble the panel.


Disassembly is difficult, and reassembly is even harder. Begin by removing the wooden trim on the sides of the panel. These are held on with pin nails, and can be pried off. Next remove the metal top plate and the bottom plastic piece. This will reveal the many staples that hold the sock in place, top and bottom.


The difficult part is reattaching the wooden trim strips, because the nail heads are hidden beneath the brass trim, which is held on with adhesive tape. You can remove the brass, but it will almost certainly be damaged in the process. Then the pin nails can be hammered out or ground off. You can reattach the trim with similar nails, and throw away the brass trim. That's what I had to do when I replaced the socks on my Spectras, and I have yet to find a suitable replacement for the brass inlays.


If you do open up the panels, it's a good idea to (gently) blow out both sides of the panel with compressed air, and make sure the felt blocks on the rear of the panel are secure. But unless you are having trouble with the panel, or want to change the grille sock, I would leave it alone.

Last edited by AcoustatAnswerMan; 13th September 2017 at 11:35 PM. Reason: edit
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Old 13th September 2017, 11:34 PM   #1805
AcoustatAnswerMan is offline AcoustatAnswerMan  United States
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Quote:
Originally Posted by charlesp210 View Post
I've been using Acoustat 1+1 with a Krell FPB 300 amplifier since 2008, and I've posted in this thread before.

In the last few months, my amp has been intermittantly shutting down, and I've been going through a long process of "elimination" to find out what's wrong.

The shutdowns do not necessarily occur at high output levels.

This started when I was trying a tweako DAC (I'm back using a good DAC now) which created an unexpected high power blast that blew the Acoustat fuses (I was using 5A at the time, I've now switched to 3A as recommended by Roy). The shutdowns started later that same day and I started doing (at first not very well planned) elimination tests to determine what was wrong.

I first feared damaging the speakers, perhaps creating a HF transformer short (I cross the Acoustats at 100hz, so there's not much bass). But I still got shutdowns playing only one speaker at a time with the HF transformer disconnected.

Another test showed that I could consistently get either speaker to shut down the right channel of the amplifier, but not the left channel.

So I sent the amplifier back to Krell (who had just done full capacitor service on my unit a few months earlier). They found a fault in the left channel, and repaired it and returned it to me for free because of the earlier service done. They explained that a fault in the left channel could cause shutdown to occur in right channel.

Well, now I can get either channel of the amplifier to shut down, and with either speaker. I think the repair essentially restored the correct operation of the protection system. And correct operation is to shut down instantly when the signature of an electrical short appears. (A 6800 class computer in each channel figures this out looking at voltage, current, offset, and rail voltage regulator margin. It would be interesting to know what makes it decide "short", and even if that is what it is deciding now. On shutdown you can get one or two lights remaining on, and the "1 light" condition includes short, heat, and insufficient AC. I'd like a display panel telling me what the situation is in more detail...some very high priced amplifiers do that now.)

My thinking NOW is that it was actually the speakers all along. Since the problem started after a particular incident, that incident changed something in the speakers. I have already "eliminated" the HF transformer as a potential cause.

That leaves various things, the variable resistor and LF transformer among them. I am now strongly suspecting that the variable resistors in my factory C mod interfaces have a problem.

There had always been considerable green corrosion around (and probably under) the wipers on the resistors. I've been too lazy to clean that off, knowing I'd have to do it completely or not at all. I now have a fresh bottle of deoxit and this is now my plan for this coming weekend.

I'm thinking that if the wiper is sufficiently corroded, there may be intermittent dropouts in connection, or slight rectification even. This could, I think, produce a flyback voltage from the energy stored in the HF transformer when the connection is resumed, and this flyback voltage, though brief, could be what is causing the Krell to believe there is a short. (BTW, my Aragon amplifier has a much simpler protection system, and it just plays along fine, although I like the Krell better. I did see shutdowns with a newly purchased Eagle 2 amplifier, but I figured that was because it simply wasn't up to the task, but perhaps it had the same issue as with the Krell. I know from many years use that the Krell can play these speakers just fine, and you would think so also.)

If mere cleaning doesn't fix the problem, or even if it does, I'm also thinking of replacing the variable resistor with fixed resistors anyway. I intend to measure both of my VR's first however, to make sure I am not changing that. I find the high frequencies to be plenty strong up and measurably flat up to their limit at 19kHz now. I still use supertweeters just so I'm not missing 19-40kHz, in case it makes a difference (in sighted testing, it always seems to, even though I can't hear anything coming out of them, I can measure it). I find the Acoustat 1+1's slightly too strong in the 3-10kHz region (I make an intentional dip there using DSP EQ roughly following recommendations by Linkwitz).

So I'm not interested in boosting the highs by reducing the resistance from input to HF transformer (aka 'air mod' if I understand that correctly). The highs are just fine.

I might be interested in lowering the LF cutoff point in the interface. The region 100Hz to 300Hz has some broad depressions I've never fully worked out.

I don't think it would be a problem to use the entire 16 ohm variable resistor as the load for the capacitor to do that, with no wiper, then add an additional 1-6 ohms to feed the HF transformer as needed to get the best balance in extreme highs. This is sort of like replacing the VR with a slightly bigger VR and moving everything up.

From where I was reading a few years ago, the air mod does that also, by adding 10ohm below the VR. I would be using the entire VR as a fixed resistor, and adding more resistor(s) at the top.

Any fixed resistors should be low inductance, right? Replacing the big VR with a low inductance fixed resistor would be expensive, and would require holes in the box for chassis mounting to dissipate heat. So I'd avoid that, unless additional evidence points to the VR having internal damage.

It's not impossible that the HF balance resistors are damaged, or that the slider is corroded and making a bad connection, but I seriously doubt the resistors have been damaged or that a corroded slider could cause an amp shutdown.


My first suspicion would be the LF transformer. It is susceptible to high-voltage breakdown. After a damaging incident such as you experienced, the transformer can play fine up to a certain level, and then arc-over and present a short circuit. You can test this theory by temporarily disconnecting the LF transformer tap and see if the problem continues. Of course, you won't get much sound from the speaker under these conditions.


I also do not suspect the HF transformer. They are quite rugged, are not exposed to the same high voltage levels as the LF transformer, and historically have been pretty reliable.


BTW, you can't modify the signal going to the LF transformer. It's driven directly from the amplifier (through a 1-ohm resistor). You can modify the step-up ratio of the LF transformer by trying a different LF transformer tap, which may or may not address your issue with the frequency response.


Remember that the LF and HF transformers overlap considerably in their range of operation. There is no crossover feeding the LF transformer, it just rolls off naturally. The HF transformer does have a crossover, and it gradually rolls in as the LF transformer rolls off.
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Old 14th September 2017, 03:23 AM   #1806
tyu is online now tyu  United States
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Quote:
Originally Posted by charlesp210 View Post
I've been using Acoustat 1+1 with a Krell FPB 300 amplifier since 2008, and I've posted in this thread before.

In the last few months, my amp has been intermittantly shutting down, and I've been going through a long process of "elimination" to find out what's wrong.

The shutdowns do not necessarily occur at high output levels.

This started when I was trying a tweako DAC (I'm back using a good DAC now) which created an unexpected high power blast that blew the Acoustat fuses (I was using 5A at the time, I've now switched to 3A as recommended by Roy). The shutdowns started later that same day and I started doing (at first not very well planned) elimination tests to determine what was wrong.

I first feared damaging the speakers, perhaps creating a HF transformer short (I cross the Acoustats at 100hz, so there's not much bass). But I still got shutdowns playing only one speaker at a time with the HF transformer disconnected.

Another test showed that I could consistently get either speaker to shut down the right channel of the amplifier, but not the left channel.

So I sent the amplifier back to Krell (who had just done full capacitor service on my unit a few months earlier). They found a fault in the left channel, and repaired it and returned it to me for free because of the earlier service done. They explained that a fault in the left channel could cause shutdown to occur in right channel.

Well, now I can get either channel of the amplifier to shut down, and with either speaker. I think the repair essentially restored the correct operation of the protection system. And correct operation is to shut down instantly when the signature of an electrical short appears. (A 6800 class computer in each channel figures this out looking at voltage, current, offset, and rail voltage regulator margin. It would be interesting to know what makes it decide "short", and even if that is what it is deciding now. On shutdown you can get one or two lights remaining on, and the "1 light" condition includes short, heat, and insufficient AC. I'd like a display panel telling me what the situation is in more detail...some very high priced amplifiers do that now.)

My thinking NOW is that it was actually the speakers all along. Since the problem started after a particular incident, that incident changed something in the speakers. I have already "eliminated" the HF transformer as a potential cause.

That leaves various things, the variable resistor and LF transformer among them. I am now strongly suspecting that the variable resistors in my factory C mod interfaces have a problem.

There had always been considerable green corrosion around (and probably under) the wipers on the resistors. I've been too lazy to clean that off, knowing I'd have to do it completely or not at all. I now have a fresh bottle of deoxit and this is now my plan for this coming weekend.

I'm thinking that if the wiper is sufficiently corroded, there may be intermittent dropouts in connection, or slight rectification even. This could, I think, produce a flyback voltage from the energy stored in the HF transformer when the connection is resumed, and this flyback voltage, though brief, could be what is causing the Krell to believe there is a short. (BTW, my Aragon amplifier has a much simpler protection system, and it just plays along fine, although I like the Krell better. I did see shutdowns with a newly purchased Eagle 2 amplifier, but I figured that was because it simply wasn't up to the task, but perhaps it had the same issue as with the Krell. I know from many years use that the Krell can play these speakers just fine, and you would think so also.)

If mere cleaning doesn't fix the problem, or even if it does, I'm also thinking of replacing the variable resistor with fixed resistors anyway. I intend to measure both of my VR's first however, to make sure I am not changing that. I find the high frequencies to be plenty strong up and measurably flat up to their limit at 19kHz now. I still use supertweeters just so I'm not missing 19-40kHz, in case it makes a difference (in sighted testing, it always seems to, even though I can't hear anything coming out of them, I can measure it). I find the Acoustat 1+1's slightly too strong in the 3-10kHz region (I make an intentional dip there using DSP EQ roughly following recommendations by Linkwitz).

So I'm not interested in boosting the highs by reducing the resistance from input to HF transformer (aka 'air mod' if I understand that correctly). The highs are just fine.

I might be interested in lowering the LF cutoff point in the interface. The region 100Hz to 300Hz has some broad depressions I've never fully worked out.

I don't think it would be a problem to use the entire 16 ohm variable resistor as the load for the capacitor to do that, with no wiper, then add an additional 1-6 ohms to feed the HF transformer as needed to get the best balance in extreme highs. This is sort of like replacing the VR with a slightly bigger VR and moving everything up.

From where I was reading a few years ago, the air mod does that also, by adding 10ohm below the VR. I would be using the entire VR as a fixed resistor, and adding more resistor(s) at the top.

Any fixed resistors should be low inductance, right? Replacing the big VR with a low inductance fixed resistor would be expensive, and would require holes in the box for chassis mounting to dissipate heat. So I'd avoid that, unless additional evidence points to the VR having internal damage.
Sounds like low bias....low bias can kill parts in the mixer an the low fr transfourmer as Andy I never seen.... a dead high fr transfourmer

If you can do the work your self....put new diodes an caps in the 30 years 24/7 on all the time......... old bias....
I buy a lot of used Acoustat...1+1 2+2 ,M3,M4,with MK121interfaces......first thing I do is this $50 in parts for the pr... If you cant do the work get a tec...may be $100ea....thats were I would start.
9 times out of ten....if the trans are not dead....new bias parts get the bias back up to 5k....work like new...

This is the first thing Roy E will do with any interfaces.....even the 500 meg panel feeder res..I have some his work here...but I find the stock 500meg is fine a sound great..

With new bias ...I can run 2+2 M3-M4s with a 60 watt tubs amp...loud...your amp fine.
good luck have fun
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Old 14th September 2017, 03:38 AM   #1807
charlesp210 is offline charlesp210  United States
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Default OK, thanks

Quote:
Originally Posted by AcoustatAnswerMan View Post
It's not impossible that the HF balance resistors are damaged, or that the slider is corroded and making a bad connection, but I seriously doubt the resistors have been damaged or that a corroded slider could cause an amp shutdown.


My first suspicion would be the LF transformer. It is susceptible to high-voltage breakdown. After a damaging incident such as you experienced, the transformer can play fine up to a certain level, and then arc-over and present a short circuit. You can test this theory by temporarily disconnecting the LF transformer tap and see if the problem continues. Of course, you won't get much sound from the speaker under these conditions.
Thanks Andy! That sounds quite reasonable and you are probably correct.

One curious thing, however, is how the shut downs are not correlated at all with the level currently playing. It seems to take 60 minutes at medium level, and then it goes. It's as if something is heating up, and goes through some kind of change at a particular temperature. "heating up" made me think of the power resistor. I had previously thought transformer damage would show up at a particular instantaneous voltage, and as the damage gets worse the failure voltage would get lower, and not be affected so much by heating up beforehand.

However, the LF transformer will heat up also. And since it doesn't have very good HF response, the energy in that range will be converted to heat. (Since my speakers are highpassed at 100 Hz, the big bass voltage swings aren't there.) And there could be a particular temperature where things are stressed to the exact point which realigns the damaged windings so the short can occur again.

The most curious thing of all is how that once it has heated up, it will just play very loud for hours without a problem. Presumably this is because it has passed some critical temperature range.

At least that's the way it has seemed many times so far. Which is another thing, it's hard to make generalizations about intermittent problems.

The LF transformer could have been damaged by DC. My highpass filtering is done in DSP, which the midrange DAC converts to analog for the power amp. Normally there is no signal below 100 Hz going to the speakers. However, if the DAC fails, it may well output enough DC to cause damage--and in fact, that was one problem with the DAC, the servo failed and it started outputting DC.
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Old 14th September 2017, 03:46 AM   #1808
tyu is online now tyu  United States
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I almost forgot.....with the bias up....even with the green wire a res still work fine..
this not to say new ones are not better....but thay work!
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Old 14th September 2017, 03:47 AM   #1809
tyu is online now tyu  United States
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nuts.....
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Old 14th September 2017, 03:56 AM   #1810
charlesp210 is offline charlesp210  United States
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Originally Posted by tyu View Post
Sounds like low bias....low bias can kill parts in the mixer an the low fr transfourmer as Andy I never seen.... a dead high fr transfourmer

With new bias ...I can run 2+2 M3-M4s with a 60 watt tubs amp...loud...your amp fine.
good luck have fun
One of my interfaces was a NOS unit I bought in 2010, never before used. The other was the original that came with the speakers (which I purchased from previous owner in 2008). Both of these interfaces produce exactly the same speaker output level, and the same level as the damaged one (still working until the short occurs) I put in storage in 2010 (but brought back out recently for re-testing). So I have 3 interfaces with very different usage histories with exactly the same level. That leads me to believe the bias levels are correct.

Rather than go through rebuilding, something that doesn't come easy to me, is there something I can just measure? I do have the 40kV probe for my fluke.

Your experience with 60W tube amp leads me to believe my 120W Eagle 2 should have been OK also. However, with such an old amplifier, never serviced, I don't know whether the amplifier itself has an internal problem, or had its protection triggered by the same speaker fault as the Krell.

Now that I'm almost certain both speakers have a serious issue, it's more likely that the shutdowns in the Eagle 2 were happening because of the speaker issue than an internal one, though it could have both.
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