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Hafler SE 120 Schmatic Explanation
Hafler SE 120 Schmatic Explanation
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Old 15th May 2018, 09:37 PM   #11
llwhtt is offline llwhtt  United States
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The bias pot, P1, controls the conduction of Q8. The more Q8 conducts the colder the bias, lower idle current and vice versa. In most BJT output amplifiers the bias xsistor is mounted on the heatsink so as to track the heat of the heatsink. The hotter the heatsink the more Q8 conducts and tries to lower the bias to avoid thermal runaway. Certain MOSFET output stages are immune to thermal runaway, not sure about this Hafler.

Craig
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Old 16th May 2018, 12:47 AM   #12
Marksd is offline Marksd  United States
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Default Hafler se120

Rayma, thanks for your help again and the reading web page.

Mark
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Old 16th May 2018, 12:50 AM   #13
Marksd is offline Marksd  United States
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llwht, This now explains why a low VCE 2n2222 is used. The rest of this amplifier is 2n5550 and 2n5401 transistors. I appreciate everyone helping me "understand". I have had many questions on the DIY Audio and the help is amazing. thanks. Mark
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Old 16th May 2018, 12:54 AM   #14
rayma is offline rayma  United States
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Quote:
Originally Posted by Marksd View Post
llwht, This now explains why a low VCE 2N2222 is used.
The 2N2222A is a better version, usually preferred.

Last edited by rayma; 16th May 2018 at 01:05 AM.
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Old 16th May 2018, 02:22 AM   #15
PRR is offline PRR  United States
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Quote:
Originally Posted by Marksd View Post
...What exactly is the 2n2222 doing...
2N2222(A) was EXTREMELY popular at one point in e-history. We used it for "everything". It was an early Silicon device with much lower leakage than Germanium devices. It had an EIA number and second-sources, unlike the TI house-number Silicon jellybeans. Its family (includes 2N2219) was heavily promoted; my father had a gift-pack of '2219 from a sales-rep.
2N2222 The Most Successful and Widely Used Transistor Ever Developed
It had a name so memorable that a small MOSFET was named after it (VL2222).

While other later parts had "better" specs, there were still many jobs the '2222 was totally fine for, and we all had half a box of '2222s left over from when they were new.


Quote:
Originally Posted by Marksd View Post
...I never know what the "line voltage will be day to day. Today was a steady 121.7 VAC. .... This past weekend it was 120 VAC.
So? 1.4% shift of line voltage is "nothing". 5% shift leads to about 10% shift of brightness on incandescent lamps, which is barely noticeable (much like the 1dB threshold on the ear for change of loudness). Your 1.4% shift is 5% on lamp brightness which is hard to see in A/B test, impossible to detect from one day to the next. That's plenty good for almost anything.
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Last edited by PRR; 16th May 2018 at 02:27 AM.
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Old 16th May 2018, 03:45 PM   #16
Marksd is offline Marksd  United States
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PRR, thanks for the information. I read everything DIY folks send me. Mark
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Old 16th May 2018, 03:50 PM   #17
Marksd is offline Marksd  United States
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llwht, i forgot to say this 2n2222 is not mounted on the heat sink. It is in the middle of the circuit board. This amplifier has on circuit board with both right and left channels on it. The users manual lists all parts, voltages and schematic. The voltages on the transistor pages are mixed up. I had to go item by item to correct the page. This amp sounds great. I am using it and have a Hafler DH200 also. Mark
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