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Old 9th February 2012, 03:36 AM   #41
AmCan is offline AmCan  Canada
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The technical manual is too big to attach but this is a Harman Kardon Citation 19 Power Amplifier and the manual can be found here Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics.
But like I said, it is part of the HK design philosophy so .....http://www.3dsi.co.za/HarmanKardon/A...0Bandwidth.pdf Its obvious that I don't understand the circuit design and I shouldn't have messed with it. I will know better than to mess with a circuit design again in the future. I doubt I did any damage but it was foolish to think I was going to make the amp perform better than the engineer who designed it.
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Old 9th February 2012, 07:45 AM   #42
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"The schematic is really hard to see though so I may have missed something. "

The only thing I see is a 20K+100pF load to ground on the Vas stage, and the 0.1F+5Ω on the output to ground.
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Old 9th February 2012, 10:10 AM   #43
AmCan is offline AmCan  Canada
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Originally Posted by djk View Post
"The schematic is really hard to see though so I may have missed something. "

The only thing I see is a 20K+100pF load to ground on the Vas stage, and the 0.1F+5Ω on the output to ground.
Thanks for trying to help. This is only the schematic for the driver board and output transistors. There is a main capacitor bank and the assay board for the zener capacitor as well. I don't know what we are looking for and the only way to see the whole schematic is to downloaded from the link I provided, unless someone knows how I can post the file somewhere else.
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Old 9th February 2012, 11:12 AM   #44
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Originally Posted by AmCan View Post
Dirk, I found a good website here on circuits. Here is a review article on input coupling Input and output coupling : BIPOLAR JUNCTION TRANSISTORS and Feedback Feedback : BIPOLAR JUNCTION TRANSISTORS It gives nice simple explanations of some basic things which I need, but I am still going to look into the books you suggested as well. Thanks.

Godfrey, Thanks for explaining the low frequency roll off. Now that I understand that C1 & C6 define the bandwidth I just remembered that this was part of the manufacturer's design philosophy - "Ultrawide Bandwidth". Should I be concerned that I increased the capacitance of C1 from 100uf to 220uf under the assumption that it would increase the bass response or is it just basically over kill. I certainly wouldn't want to do any harm from increasing the bandwidth even further but I am thinking I should return it back to spec.
Using a 220uf is a little of an overkill if youre using high quality electrolytics, 22uF to 100uf are good values. HH were aware of capactor distortion which when care is not taken could cause higher distortion than the inputstage and the vas combined at the low frequencies (100hz and lower). Often one sees cap values of 1uF or 4.7uf used, there is no problem concerning bandwith but THD could be if electrolytics are used. Using film types drastically improves this and in this case much smaller values could be used according to frequency rollof theory.
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Old 9th February 2012, 12:01 PM   #45
AmCan is offline AmCan  Canada
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Using a 220uf is a little of an overkill if youre using high quality electrolytics, 22uF to 100uf are good values. HH were aware of capactor distortion which when care is not taken could cause higher distortion than the inputstage and the vas combined at the low frequencies (100hz and lower). Often one sees cap values of 1uF or 4.7uf used, there is no problem concerning bandwith but THD could be if electrolytics are used. Using film types drastically improves this and in this case much smaller values could be used according to frequency rollof theory.
Thanks for putting my mind at ease. I used an audiophile quality axial Jensen electrolytic because the 220 was cheaper at this value on close out. I just wouldn't want to inadvertently over stress the transistors from having increasing the Bandwidth too much and create some weird oscillation or something (not knowing what I am doing). So as long as it is safe I will leave it but I would have never known to upgrade by decreasing the capacitance all the way down to a value where I could fit a film cap. Whereas the tendency is for most novices to automatically think bigger is better. Perhaps I will look at changing this to a smaller lytic with a film bypass cap.
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