I lost my job so had to walk away from this problem again. But I'm back at work now and ready to throw some time and money at this problem.
Because of what I have read about the ADCOM power amp (555-II) and the fact that I spent almost $500 on it (well outside my budget), I'm going to replace it last.
First on the block is the preamp. I have been using a Carver HR-752 Receiver. I use the pre-amp outputs and set the receiver for CD direct mode (all processing bypassed). I wonder if there is an impedance mismatch or sensitivity issue between the Carver and the ADCOM. I'm thinking of replacing it with an ADCOM GTP-450 or similar ($300). My daughter needs a receiver so the Carver won't go to waste.
Next on the block is the CD player. I have a Pioneer PD-M426. I have no idea what to buy here....plan to spend ~$300.
Last on the block are the KEFs. I have been checking out JBL and Klipsch, as someone suggested and the Klipsch (SF-2, RF3-II) sounds like my kind of speaker (nice and bright).
Thanks for listening to me babble...and I could sure use some helpful advice along the way.
Before I spend any money I'm going to go back through this email and try some of the troubleshooting methods offered up (that is...after my KEFs come back again for the fifth time).
One last note....I think most of you would be very surprised at the volume at which these KEfs are blowing. It's loud, but not insanely loud. I've certainly never turned the volume past 4 (out of 10).
Because of what I have read about the ADCOM power amp (555-II) and the fact that I spent almost $500 on it (well outside my budget), I'm going to replace it last.
First on the block is the preamp. I have been using a Carver HR-752 Receiver. I use the pre-amp outputs and set the receiver for CD direct mode (all processing bypassed). I wonder if there is an impedance mismatch or sensitivity issue between the Carver and the ADCOM. I'm thinking of replacing it with an ADCOM GTP-450 or similar ($300). My daughter needs a receiver so the Carver won't go to waste.
Next on the block is the CD player. I have a Pioneer PD-M426. I have no idea what to buy here....plan to spend ~$300.
Last on the block are the KEFs. I have been checking out JBL and Klipsch, as someone suggested and the Klipsch (SF-2, RF3-II) sounds like my kind of speaker (nice and bright).
Thanks for listening to me babble...and I could sure use some helpful advice along the way.
Before I spend any money I'm going to go back through this email and try some of the troubleshooting methods offered up (that is...after my KEFs come back again for the fifth time).
One last note....I think most of you would be very surprised at the volume at which these KEfs are blowing. It's loud, but not insanely loud. I've certainly never turned the volume past 4 (out of 10).
I've gone back and looked at the previous postings in this thread. I'm not going to spend any more money until I am more clear on the problem (even though in the end I think the KEFs have to go).
I do have access to an oscope, and I want to measure clipping. So I have a couple questions about setting up:
1) Can I perfom the measurement at the speaker terminals or do I have to pull the drivers and look right at the tweeter?
2) Can I perform the measurement using a music source since I don't have access to a signal generator?
3) If I do observe clipping - is it most likely the power amp's fault?
4) If I do not observe clipping, then the preamp or cdp are to blame. Is that about right?
I do have access to an oscope, and I want to measure clipping. So I have a couple questions about setting up:
1) Can I perfom the measurement at the speaker terminals or do I have to pull the drivers and look right at the tweeter?
2) Can I perform the measurement using a music source since I don't have access to a signal generator?
3) If I do observe clipping - is it most likely the power amp's fault?
4) If I do not observe clipping, then the preamp or cdp are to blame. Is that about right?
lamepops said:
1) you can measure it right at the speaker terminals
2)excessive clipping in music can be seen on a scope but a sine wave is best, you can see as low as 1% distortion on the screen with a sine wave, buy a test cd with sine wave tones, most have at least 1khz at 0db (maximum level)
3) not necessiarly, it could be too high a level of signal overloading the input of the amp, or the source clipping the signal at it's outputs, or something else, use the scope to check the signal level side of things as well, then you'll find out exactly where the "weakest" link in the chain is.
Start at the top of the chain and work down, get a test cd with at least 1khz at 0db on it and see if the cd player clips it, if it doesn't then we know it'll play anything without clipping, then hook up the pre amp and test it's output, then connect the amp and using high power resistors (not the speakers) test the amp.
Of course if you see clipping further up the chain you address that first before testing anything further down the line because it's pointless untill the problem higher up is fixed.
Lamepops:
Wanna have some fun cheap?
Make your own test CD. Have a burner?
Here are two freeware tone generators. There are others if these are not satisfactory.
Here is one I just found, but it sure looks good:
www.satsignal.com
Here is a demo model, you have to pay for it after a month, but very useful until then. You might even decide to pay for it:
http://www.nch.com.au/tonegen/
The good part about making you own test record is that you can use the tracks for different frequencies.
Like, Track 1=20 Hz
Track 2=25 Hz
Track 3=30 Hz
Track 3=35 Hz
etc. etc. until
Track 30 =5,000 Hz
Track 31=6,000 Hz
Track 32=7000 Hz
And so on. Of course, you can select your own frequencies for the Tracks.
Then you can use a multimeter-highly borrowable, available for less than $20 if you want to buy-and/or oscilloscope to conduct the tests.
Allow me to compliment you on deciding to find the root of the problem before you start laying out money for new
Wanna have some fun cheap?
Make your own test CD. Have a burner?
Here are two freeware tone generators. There are others if these are not satisfactory.
Here is one I just found, but it sure looks good:
www.satsignal.com
Here is a demo model, you have to pay for it after a month, but very useful until then. You might even decide to pay for it:
http://www.nch.com.au/tonegen/
The good part about making you own test record is that you can use the tracks for different frequencies.
Like, Track 1=20 Hz
Track 2=25 Hz
Track 3=30 Hz
Track 3=35 Hz
etc. etc. until
Track 30 =5,000 Hz
Track 31=6,000 Hz
Track 32=7000 Hz
And so on. Of course, you can select your own frequencies for the Tracks.
Then you can use a multimeter-highly borrowable, available for less than $20 if you want to buy-and/or oscilloscope to conduct the tests.
Allow me to compliment you on deciding to find the root of the problem before you start laying out money for new
Blowing Drivers
Maybe I am a complete idiot but the length of the speaker cable isnot going to blow a driver.....correct me if I am wrong, I am new to HI_FI stuff. I know in PA rigs I used to run some of the spaeker runs were well over 100ft. Another thing to consider is the power ratings of the amplifier as compared to the cabinets. If the amp is clipping at all: Square waves at a speakers maximum power rating will blow drivers easily. (Maximum outward to inward excursion for speaker)
Maybe I am a complete idiot but the length of the speaker cable isnot going to blow a driver.....correct me if I am wrong, I am new to HI_FI stuff. I know in PA rigs I used to run some of the spaeker runs were well over 100ft. Another thing to consider is the power ratings of the amplifier as compared to the cabinets. If the amp is clipping at all: Square waves at a speakers maximum power rating will blow drivers easily. (Maximum outward to inward excursion for speaker)
Update - building dummy load
I've acquired an oscilloscope and probes (borrowed), and I'm building a dummy-load module. I have (4) 16-ohm 100-Watt aluminum-housed resistors (freebies) and plan to wire them for (2) channels of 8-ohms @ 200W. I really feel that if I'm going to the trouble of debugging my system, it should be under load condition. I plan not to overwork my amp and risk damage.
I purchased a test cd on Ebay for $12.95 (too lazy to make my own), and should have everything by the weekend.
I have one more question. Other than clipping, what kinds of artifacts am I looking for in the waveform? Am I just looking for symmetry and comparison to the input signal?
Happy New Year to all and
I've acquired an oscilloscope and probes (borrowed), and I'm building a dummy-load module. I have (4) 16-ohm 100-Watt aluminum-housed resistors (freebies) and plan to wire them for (2) channels of 8-ohms @ 200W. I really feel that if I'm going to the trouble of debugging my system, it should be under load condition. I plan not to overwork my amp and risk damage.
I purchased a test cd on Ebay for $12.95 (too lazy to make my own), and should have everything by the weekend.
I have one more question. Other than clipping, what kinds of artifacts am I looking for in the waveform? Am I just looking for symmetry and comparison to the input signal?
Happy New Year to all and
Amplifiers Behaving Badly.............
You are looking for clean output sinewave up to clipping.
When driving into clipping, good amplifier behaviour just cleanly flattens the peaks of the waveform without other artifacts.
Bad amplifier overload behaviour can cause ringing on the leading part of the clipped section.
Another majorly bad behaviour is "sticktion" immediately coming out of overload.
This causes a vertical transient (often with some associated post ringing) coming back from clipping, and may or may not occur on both waveform polarities.
This behaviour is the speaker (tweeter) and ear killer bigtime.
Just about any amplifier will look fine into a purely resistive load, so a simulated speaker dummy load may be required to show up load dependant instabilities.- I have seen different schematics for reactive load circuit - somebody ?.
Even better is to look at your amplifier output waveform into your speakers with your kind of music driven into overload and have a look at what's happening.
You can then switch to a resistive at the same level load and look for differences.
This testing might reveal that you just need a bigger amplifier, or it might point to problems with the loading caused by your speakers and/or cables.
Eric.
Big caution - if you are running sine wave tests do NOT try full power at mids and highs frequencies - this will burn mids and tweeters quicksmart.
You are looking for clean output sinewave up to clipping.
When driving into clipping, good amplifier behaviour just cleanly flattens the peaks of the waveform without other artifacts.
Bad amplifier overload behaviour can cause ringing on the leading part of the clipped section.
Another majorly bad behaviour is "sticktion" immediately coming out of overload.
This causes a vertical transient (often with some associated post ringing) coming back from clipping, and may or may not occur on both waveform polarities.
This behaviour is the speaker (tweeter) and ear killer bigtime.
Just about any amplifier will look fine into a purely resistive load, so a simulated speaker dummy load may be required to show up load dependant instabilities.- I have seen different schematics for reactive load circuit - somebody ?.
Even better is to look at your amplifier output waveform into your speakers with your kind of music driven into overload and have a look at what's happening.
You can then switch to a resistive at the same level load and look for differences.
This testing might reveal that you just need a bigger amplifier, or it might point to problems with the loading caused by your speakers and/or cables.
Eric.
Big caution - if you are running sine wave tests do NOT try full power at mids and highs frequencies - this will burn mids and tweeters quicksmart.
Thanks for the info Eric. I have a couple days before I get started so I''ll look around for a reactive circuit schematic.
I also talked to my dealer who has sent the KEFs out for repair (again). He wants me to bring my entre setup in when the KEFs come back, and he is going to help me figure out a solution. They have really been terrific through the process (Hifi House in Shrewbury, Mass). He's going to do some side-by-side comparisons of my components to other quality components.
Once we figure out which component(s) are to blame, I'll have no problem purchasing from this dealer and paying the extra for the fantastic service I've been getting.
I also talked to my dealer who has sent the KEFs out for repair (again). He wants me to bring my entre setup in when the KEFs come back, and he is going to help me figure out a solution. They have really been terrific through the process (Hifi House in Shrewbury, Mass). He's going to do some side-by-side comparisons of my components to other quality components.
Once we figure out which component(s) are to blame, I'll have no problem purchasing from this dealer and paying the extra for the fantastic service I've been getting.
~10:00-11:00 is full output from CD sources with most amps/receivers I have owned. With my current onkyo receiver, level 14 (of 40 marked) is full power out. If you are anywhere near this, you are overdriving your amp with most CD sources. All that extra volume control range is for much lower output sources than CD players.
Just because speakers are rated to handle 150Watts doesn't mean they are capable of handling 100Watts continuously in a party situation. You are lucky to have an understanding dealer.
You need to buy Klipsch, JBL or Cerwin-Vega or some other high-sensitivity brand if you want high output speakers.
Just because speakers are rated to handle 150Watts doesn't mean they are capable of handling 100Watts continuously in a party situation. You are lucky to have an understanding dealer.
You need to buy Klipsch, JBL or Cerwin-Vega or some other high-sensitivity brand if you want high output speakers.
I can get the volume to about 2 o clock bfore I get clipping, but then again the whole lot is fully active, so at a 10 o clock position the amps are not having to work as hard as a full range. Either way I have NEVER destroyed a driver, well appart from the time I took a 50p one and blew it on purpose for fun
Caught on fire an all, very good bit of fun
Anyway, I would doubt that the CD player is at fault and its just a basic lack of power. Remember a 200 watt amp over a 50 watt will only provide you with 6db more gain, which as the human ear percieves things, is not very much.
Also I have hear a review of the original Q55's unfortuantly not the .2's, but I doubt that much would change. Anyway with it comes Noel Keywood's lab report. This speaker has a sens of 90db so is quite high, and a low(ish) avg impedance of 5.3 ohms. Through the mid and trebble, the imp is high so no hard load there, except at about 10k where it dips to about 3.5 ohms.
Having read all the other posts it does seem that you are trying to get too much out of these speakers. Not that it would make a huge amount of difference but those UniQ tweets are 19mm and sit on the mids pole piece and dont have a chamber to lower fs.
Basically put, 19mm = less voice coil area to dissipate heat. Being on top of pole piece of the mids will make the tweet get even hotter due to heating from the mids voice coil at high volumes.
No chamber to lower fs? maybe not as much of a problem if the tweet is crossed well, but still a 19mm prolly has a res of 1800hz(??), none of this will contribute to good heat dissipation and high power handling.
Dont get another amp, that wont solve the problem or might do at the levels you listen to, but if it will go louder, with the new amp, I dont doubt that you'll crank it up more if you can. I feel sorry for your ears, but its your health and not mine. I think your only answer is more sens speakers. Getting a 1000 watt amp only gives you 7db more output then your 200 watt. 90db on the kefs aint bad for cone drivers so you must really be playing it loud. Anyway I second the rest here get horns or some big PA things.
Caught on fire an all, very good bit of fun Anyway, I would doubt that the CD player is at fault and its just a basic lack of power. Remember a 200 watt amp over a 50 watt will only provide you with 6db more gain, which as the human ear percieves things, is not very much.
Also I have hear a review of the original Q55's unfortuantly not the .2's, but I doubt that much would change. Anyway with it comes Noel Keywood's lab report. This speaker has a sens of 90db so is quite high, and a low(ish) avg impedance of 5.3 ohms. Through the mid and trebble, the imp is high so no hard load there, except at about 10k where it dips to about 3.5 ohms.
Having read all the other posts it does seem that you are trying to get too much out of these speakers. Not that it would make a huge amount of difference but those UniQ tweets are 19mm and sit on the mids pole piece and dont have a chamber to lower fs.
Basically put, 19mm = less voice coil area to dissipate heat. Being on top of pole piece of the mids will make the tweet get even hotter due to heating from the mids voice coil at high volumes.
No chamber to lower fs? maybe not as much of a problem if the tweet is crossed well, but still a 19mm prolly has a res of 1800hz(??), none of this will contribute to good heat dissipation and high power handling.
Dont get another amp, that wont solve the problem or might do at the levels you listen to, but if it will go louder, with the new amp, I dont doubt that you'll crank it up more if you can. I feel sorry for your ears, but its your health and not mine. I think your only answer is more sens speakers. Getting a 1000 watt amp only gives you 7db more output then your 200 watt. 90db on the kefs aint bad for cone drivers so you must really be playing it loud. Anyway I second the rest here get horns or some big PA things.
Great Expectations.........
I went to the Kef site to refresh on your speakers.
I see 6.5" speakers, and in my experience if you want music big and loud you are not going to do it reliably with these Kefs.
You are pushing your amp too hard into overload and those tweeters will not cope with that, especially on music with sustained high level HF content.
If you want more 'power' in your sound you need to go to bigger bass drivers plus mids.
I know a pair of speakers with double 10", double 5", and 1" and with 200W/Ch these go as big, loud and deep as you could ever want, and stay dead clean.
Eric.
I went to the Kef site to refresh on your speakers.
I see 6.5" speakers, and in my experience if you want music big and loud you are not going to do it reliably with these Kefs.
You are pushing your amp too hard into overload and those tweeters will not cope with that, especially on music with sustained high level HF content.
If you want more 'power' in your sound you need to go to bigger bass drivers plus mids.
I know a pair of speakers with double 10", double 5", and 1" and with 200W/Ch these go as big, loud and deep as you could ever want, and stay dead clean.
Eric.
Attachments
The 1st time that I had my KEFs repaired at the dealer, he connected them to a Mcintosh system (400W/ch) and played them for several minutes at volumes that I have personally never heard before out of any loudspeakers, and a lot louder than I have ever played the KEFs. I understand this is subjective....size of room, location of speakers, etc. But this proved to me that the speakers can handle a lot of power...as long as it's clean and ample and extremely expensive.
I really do understand the concept of clean power and what an amp does to its output when it can't provide that, but I cannot afford a Mcintosh system, or anything close in terms of cost.
Regardless, I'm committed to finishing the project and learning something about my amp/preamp performance. I have everything I need....test cd, dummy load, and oscilloscope. With 25 years of electronics experience, I am pretty clear on the setup and what I am looking for in terms of input and output signals.
I'll hopefully report back on Sunday after I've run some tests and maybe post some pics of some meaningful waveforms.
Have a great weekend y'all.
I really do understand the concept of clean power and what an amp does to its output when it can't provide that, but I cannot afford a Mcintosh system, or anything close in terms of cost.
Regardless, I'm committed to finishing the project and learning something about my amp/preamp performance. I have everything I need....test cd, dummy load, and oscilloscope. With 25 years of electronics experience, I am pretty clear on the setup and what I am looking for in terms of input and output signals.
I'll hopefully report back on Sunday after I've run some tests and maybe post some pics of some meaningful waveforms.
Have a great weekend y'all.
A slight delay
I'm having trouble with the oscilloscope I borrowed. At certain frequencies, there are double waveforms...180 degrees out of phase. I can sort of make it go away by changing the trigger level. It's a pretty old scope, so I'm going to give it back and try to get hooked up with a newer and better model. Of course it's possible the amp is really putting this out, which would be a bad thing.
Also - I'm having trouble locating a decent mount for my power resistors. I located a couple of large heatsinks online that should do the trick.
I'm having trouble with the oscilloscope I borrowed. At certain frequencies, there are double waveforms...180 degrees out of phase. I can sort of make it go away by changing the trigger level. It's a pretty old scope, so I'm going to give it back and try to get hooked up with a newer and better model. Of course it's possible the amp is really putting this out, which would be a bad thing.
Also - I'm having trouble locating a decent mount for my power resistors. I located a couple of large heatsinks online that should do the trick.
Unbelievable
After a 5th repair of my KEF loudspeakers, I was asked to bring my system in for evaluation to hopefully understand where my problem is. As a reminder, here's my setup:
Pioneer MD-426 CD Player, Adcom 555-II Preamp, Adcom 555-II Amp, Kef Q55.2 Loudspeakers
First, the dealer connected my KEFs to his Mcintosh system and demonstrated 40-400 Watts operation with no noticeable distortion. Then, he connected the KEFs to a Pyramid system (125 Watts/Ch), and cranked up the volume until we heard distortion (at about 12:00 on the dial). Then we set up my system, and cranked it up, and it performed slightly better than the Pyramid, but not as good as the Mcintosh. Just what I expected.
After the dealer convinced me to replace all my cables with Nordost cables ($250), I took the system home and set it up. I allowed a few minutes for warmup and then cranked the volume up to about 9:30. After listening to a couple songs, I noticed a problem. The left speaker had no high freqs. It happened again. This had happened at about 1/4 volume.
At this point, the only reasonable conclusion is the home environment (noise on the AC). I have been using a surge protector from very early on, but perhaps that's not enough.
I know that some of you are thinking - "STOP THE INSANITY, AND FIX THE PROBLEM!" I have been working on my dummy load and have an oscope in hand along with a audio test cd, so I hope to get that all together soon. Unfortunately my new job leaves very little time to tinker.
Unbelievable.
After a 5th repair of my KEF loudspeakers, I was asked to bring my system in for evaluation to hopefully understand where my problem is. As a reminder, here's my setup:
Pioneer MD-426 CD Player, Adcom 555-II Preamp, Adcom 555-II Amp, Kef Q55.2 Loudspeakers
First, the dealer connected my KEFs to his Mcintosh system and demonstrated 40-400 Watts operation with no noticeable distortion. Then, he connected the KEFs to a Pyramid system (125 Watts/Ch), and cranked up the volume until we heard distortion (at about 12:00 on the dial). Then we set up my system, and cranked it up, and it performed slightly better than the Pyramid, but not as good as the Mcintosh. Just what I expected.
After the dealer convinced me to replace all my cables with Nordost cables ($250), I took the system home and set it up. I allowed a few minutes for warmup and then cranked the volume up to about 9:30. After listening to a couple songs, I noticed a problem. The left speaker had no high freqs. It happened again. This had happened at about 1/4 volume.
At this point, the only reasonable conclusion is the home environment (noise on the AC). I have been using a surge protector from very early on, but perhaps that's not enough.
I know that some of you are thinking - "STOP THE INSANITY, AND FIX THE PROBLEM!" I have been working on my dummy load and have an oscope in hand along with a audio test cd, so I hope to get that all together soon. Unfortunately my new job leaves very little time to tinker.
Unbelievable.
Sorry if this gets double-posted - I closed my window prematurely.
I am inclined to agree with you....that the cables have made the KEFs more susceptible to the problem. Previously I was using monster cables for the speakers and AR patch cables for the RCA connections. I assume the AR RCA cables were shielded whereas the Nordost cables speaker cables and interconnect cables are not.
Anyway, I just got a call from the dealer, and they have convinced KEF to replace my speakers with a newer model/year. This does not fix the problem, but certainly demonstrates the dealers willingness to go over the top in trying to help me. Sorry for the shameless plug but The HiFi house in Shrewsbury, Mass has done everything they can to help and they have invested at least 2X what I paid for the KEFs in repairs and support.
While I am waiting to get my new speakers, I am going to try some simple tests with my audio test cd and oscilloscope (no load) just to see if I can see some noise on the outputs of the amp). I have a nice 350 MHz TEK scope for a couple weeks, so should be able to see any artifacts in the signal.
Hopefully I can find some time to finish the dummy load (heat sink and power resistors have arrived).
I find it amazing that my system performed flawlessly in their store and broke immediately in my house. It's a fundamental problem that I have to be able to solve with some basic measurements, right?
I am inclined to agree with you....that the cables have made the KEFs more susceptible to the problem. Previously I was using monster cables for the speakers and AR patch cables for the RCA connections. I assume the AR RCA cables were shielded whereas the Nordost cables speaker cables and interconnect cables are not.
Anyway, I just got a call from the dealer, and they have convinced KEF to replace my speakers with a newer model/year. This does not fix the problem, but certainly demonstrates the dealers willingness to go over the top in trying to help me. Sorry for the shameless plug but The HiFi house in Shrewsbury, Mass has done everything they can to help and they have invested at least 2X what I paid for the KEFs in repairs and support.
While I am waiting to get my new speakers, I am going to try some simple tests with my audio test cd and oscilloscope (no load) just to see if I can see some noise on the outputs of the amp). I have a nice 350 MHz TEK scope for a couple weeks, so should be able to see any artifacts in the signal.
Hopefully I can find some time to finish the dummy load (heat sink and power resistors have arrived).
I find it amazing that my system performed flawlessly in their store and broke immediately in my house. It's a fundamental problem that I have to be able to solve with some basic measurements, right?
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