NOSValves Posted February 24, 2004 Share Posted February 24, 2004 What a sweet 7189/EL84 power amp ! After checking the unit out I called Allan to see what he wanted to do with it as far as updates. His reply was "do what you would do to it if it was yours" I always like to hear that ! It is now outfitted with Auricaps , New beefier B+ power supply, Cathode bypass and bias supply filtering , Percision resistors for bias measuring. This amp is setup great nice simple circuit with DC bias adjust , DC bias balance and Ac balance everything I like to see in a good amplifier. In the 20 watt and below range this is one fine power amp that I would be proud to own. I told Allan to put his MC-30 up for auction and he just chuckled Evendently my hand isn;t to steady today the pictures blurred on me I also tried the scope pictures in the dark this time and they may have something to do with the blurring. Sfogg ...... yes these are with the scope DC coupled I wouldn't want to mislead the world here !! 20HZ 100HZ 2Khz 10Khz 15Khz 20Khz Quote Link to comment Share on other sites More sharing options...
sfogg Posted February 24, 2004 Share Posted February 24, 2004 " ...... yes these are with the scope DC coupled I wouldn't want to mislead the world here" So, in other words contrary to your claims earlier about not seeing any difference between AC/DC coupling when you tried it you obviously did see the difference? Shawn Quote Link to comment Share on other sites More sharing options...
TBrennan Posted February 24, 2004 Share Posted February 24, 2004 Yeah, I used to have a couple of those, used 'em to drive compression drivers above 500-800hz when I bi-amped, used 'em fullrange at times too. Great amps. IMO Fisher stuff sounds MUCH better than Scott, I really dinna ken the Scott (pun intended) fixation around here. 80-AZs sound great too. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted February 24, 2004 Author Share Posted February 24, 2004 Your unfreakin believable dude ! Yes there is a difference but there is nothing devious about it when you show what the scope see's it like going in and coming out of the amp ! The difference between the input and output is the entire point of doing these tests. Craig Quote Link to comment Share on other sites More sharing options...
NOSValves Posted February 24, 2004 Author Share Posted February 24, 2004 Tom, I won't go as far as to say Fisher is better then Scott but I will say its every bit as good especially the early models. I've been saying it around here for ages "there are many vintage amps that sound and work wonderfully" You do not have to buy a Scott. Craig Quote Link to comment Share on other sites More sharing options...
Audio Flynn Posted February 24, 2004 Share Posted February 24, 2004 I saw Alan's amp in a visit to Craig's last weekend. It looks like fine transformer heft. Always a good foundation. Quote Link to comment Share on other sites More sharing options...
garymd Posted February 24, 2004 Share Posted February 24, 2004 ---------------- On 2/24/2004 3:20:12 PM TBrennan wrote: Yeah, I used to have a couple of those, used 'em to drive compression drivers above 500-800hz when I bi-amped, used 'em fullrange at times too. Great amps. IMO Fisher stuff sounds MUCH better than Scott, I really dinna ken the Scott (pun intended) fixation around here. 80-AZs sound great too. ---------------- I own both a fisher and a scott. Similiar models as far as power and vintage and both recently rebuilt by highly qualified technicians. Maybe it's due to the rebuilder, but the scott blows away the fisher IMO. Not that the fisher sounds bad. Quite the opposite. I do ken the scott fixation around here based on my limited experience and the fact that this is the only fisher I've heard since the 70s. One plus regarding fishers is that they aren't all the rage right now and can still be had for very reasonable prices on ebay. Quote Link to comment Share on other sites More sharing options...
sfogg Posted February 24, 2004 Share Posted February 24, 2004 Craig, " Yes there is a difference but there is nothing devious about it when you show what the scope see's it like going in and coming out of the amp !" But how can that be? You said you were going to show me that there was no difference? " The difference between the input and output is the entire point of doing these tests." Agreed, however that isn't what you were showing previously. Again that is because you weren't showing what was input into the amp. Hint: Your amp doesn't have the same filtering that is in your scope when you set your scope to AC coupling. It was passed a signal from your function generator without additional filtering added to it. As such when you add a filter to what is being fed to your scope you are not showing the difference between what was input into the amp and what is coming out of the amp. "there is nothing devious about it" If you make your scope distort the signals so that the input and output look the same (becaue of the scopes distortion) that is hiding the distortion of the amp and is misleading. Maybe you didn't intend to do that but hiding distortion was the end result. When you instead remove the scopes filtering (distortion) and show the actual signal input into the amp (without the additional filtering/distortion of the scope) and then show the actual signal coming out of the amp (without additional filtering in the scope) you see the distortion introduced by the amp itself. Obviously, this is the case since you already confirmed this above by admitting you saw a difference between AC and DC coupling. That demostrates that by AC coupling you are hiding some of the distortion of the amp at lower frequencies. If you were to do the tests comparing AC/DC coupling at say 1kHz you wouldn't see any difference because now you are well above the filtering/distortion within your scope. But down below the level of the filtering in your scope you will see differences between AC and DC coupling. Shawn Quote Link to comment Share on other sites More sharing options...
NOSValves Posted February 24, 2004 Author Share Posted February 24, 2004 Shawn, I have no clue why you have such a hard on these day's but why don't we just drop this before it gets ugly ! Craig Quote Link to comment Share on other sites More sharing options...
Tom Mobley Posted February 24, 2004 Share Posted February 24, 2004 Good idea. We don't need another of those flame wars, they are completely useless. everybody leaves thinking the same as they came in and everybody is the poorer for the mud-slinging. If it produced anything worthwhile it might be different, but it doesn't. Quote Link to comment Share on other sites More sharing options...
mobile homeless Posted February 24, 2004 Share Posted February 24, 2004 I dont even see why it should turn into a flame war at all. Although I am no expert in scope use by any mean, the posts made sense to me and it seemed like the typical debate we see in this forum all the time, not the least from Craig, who would question this guy in a second if he thought he was putting out scope shots using a method that was not revealing all the potential data. I didnt see any REAL ugly language until this last post from Craig. Although I think Shawn could have been more tactful in his presentation of the disagreement. I see nothing wrong with debate or questioning if both people keep an open mind. Why should it get ugly really? kh Quote Link to comment Share on other sites More sharing options...
mike stehr Posted February 24, 2004 Share Posted February 24, 2004 I think Shawn should just buy Craig a top-notch frequency generator, and end the debate. Whaddya think shawn? I'm sure Craig won't mind. Quote Link to comment Share on other sites More sharing options...
sfogg Posted February 24, 2004 Share Posted February 24, 2004 Mike, From the posts above Craig's function generator does fine at 20hz, I was mistaken about that. It was the AC coupling in his 'scope that was throwing me off as it is at a much higher frequency then what is in my scope. That is what was distorting the square waves. Shawn Quote Link to comment Share on other sites More sharing options...
NOSValves Posted February 24, 2004 Author Share Posted February 24, 2004 All I was saying was that if I display what the scope does at the input and output then I am not decieving anyone. Shawn accused me of being dishonnest nothing more and nothing less to me that IS NASTY I am not dishonnest in anyway. I never meant to say the AC coupling does not change what the signal looks like I just said if shown going in and coming out there is nothing dishonnest about it. The difference between what goes in and what comes out is THE ENTIRE POINT. Craig Quote Link to comment Share on other sites More sharing options...
ben. Posted February 24, 2004 Share Posted February 24, 2004 ---------------- On 2/24/2004 5:43:01 PM NOSValves wrote: Shawn, I have no clue why you have such a hard on these day's but why don't we just drop this before it gets ugly ! ---------------- Have you seen his lab assistant? Quote Link to comment Share on other sites More sharing options...
NOSValves Posted February 24, 2004 Author Share Posted February 24, 2004 Geezz don't send her over here I'd never get anything done Quote Link to comment Share on other sites More sharing options...
sfogg Posted February 24, 2004 Share Posted February 24, 2004 Craig, "Shawn accused me of being dishonnest nothing more and nothing less to me that IS NASTY" That is wrong Craig, I never said or intended any such thing. You misinterpreted what I was trying to saying. "All I was saying was that if I display what the scope does at the input and output then I am not decieving anyone. " Yeah you are, including yourself. I never said you were doing it on purpose... IOW being dishonest, you were just measuring wrong. Now that the error in your measurements has been pointed out to you if you continue to use that method then I'd start to wonder about your intentions behind it. "The difference between what goes in and what comes out is THE ENTIRE POINT." One last try..... since you obviously haven't grasped this yet.... Just to keep things simple say the square wave is a vertical line at 90 degrees we will ignore the horizontal component for this. That is what is coming out of your function generator. You split that two ways. One goes to your scope, the other to your amp. You AC couple your scope. That applies a high pass filter to the signal entering the scope. The signal going to your amp has no such filter. Right there you already aren't looking at what is actually going to the input of your amplifier. What the amp is trying to reproduce and what the scope is displaying is DIFFERENT. All you need do is use both channels of your scope on the input of your amp one AC coupled the other DC coupled to verify this. The amp receives that 90 degree signal. The high pass filtering in your scope is turning that into a 45 degree line. So at best your scope will display a wave at a 45 degree angle but *no* higher. Now you take the output of the amp (which was fed a true 90 degree sine wave) into the other channel of your scope. It too is high passed in the scope so at best it will display a 45 degree line. If the amp perfectly reproduced the 90 degree square wave fed to it you would see it as a 45 degree line on your scope because of your second channels high pass filtering which can't do better then 45 degrees. In this case the amp had perfect square wave reproduction. If the amp distorted the square wave to make it an 80 degree line you would see it as a 45 degree line on your scope because of your second channels high pass filtering which can't do better then 45 degrees. In this case the amp distorted the square wave by 10 degrees but that distortion is hidden in the measurements. If the amp distorted the square wave to make it an 70 degree line you would see it as a 45 degree line on your scope because of your second channels high pass filtering which can't do better then 45 degrees. In this case the amp distorted the square wave by 20 degrees but that distortion is hidden in the measurements. If the amp distorted the square wave to make it an 60 degree line you would see it as a 45 degree line on your scope because of your second channels high pass filtering which can't do better then 45 degrees. In this case the amp distorted the square wave by 30 degrees but that distortion is hidden in the measurements. If the amp distorted the square wave to make it an 50 degree line you would see it as a 45 degree line on your scope because of your second channels high pass filtering which can't do better then 45 degrees. In this case the amp distorted the square wave by 40 degrees but that distortion is hidden in the measurements. If the amp distorted the square wave to make it an 45 degree line you would see it as a 45 degree line on your scope because of your second channels high pass filtering which can't do better then 45 degrees. In this case the amp distorted the square wave by 45 degrees but that distortion is hidden in the measurements and looks no differently then when the amp actually had perfect square wave response. Only until the amp distorts the output more then 45 degrees would you see any difference between input and output using your scopes AC coupling on a low frequency square wave. As has been said this measurement is hiding the distortion of the amp and is misleading about the square wave response of the amplifier under test. I'm guessing the problem you are having comprehending this is you incorrectly assumed the amps distortion would ride on top of the distortion added by the AC coupling. That is not the case as you have now seen with your own eyes when you compared the 20hz signal with input/output AC coupled vs DC coupled. There is no shame in learning something new. Shawn Quote Link to comment Share on other sites More sharing options...
sfogg Posted February 24, 2004 Share Posted February 24, 2004 BTW, the 90 degree and 45 degrees above are just arbitrary values to try and get the point across.... Quote Link to comment Share on other sites More sharing options...
ben. Posted February 24, 2004 Share Posted February 24, 2004 Good explanation. I think I even get it now! Quote Link to comment Share on other sites More sharing options...
NOSValves Posted February 24, 2004 Author Share Posted February 24, 2004 I am going down later and showing you that the difference or amount of lost response using AC is indeed the same as DC the scope does not add a filter it just see's the square wave differently. I bet its Identical % difference input to output. When someone say's I'm being decieving/misleading to me that is the same as being dishonest. Maybe this is all a misunderstanding but just the same I didn't appreciate it. Quote Link to comment Share on other sites More sharing options...
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