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Old 13th November 2012, 10:16 PM   #861
a.wayne is offline a.wayne  United States
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Will the badger operate with 40 volt rails ...?
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Old 14th November 2012, 03:49 PM   #862
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Default Re: Will the badger operate with 40 volt rails ...?


The only concern of lowering the voltage from +/- 60V to +/- 40V is biasing the BJT. With lower bias, BJT (transistor) may not be operated at the point as the original designer intended.

Since the differential pair and VAS stage has current source, as long as the current source is maintained, you should be fine.
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Old 16th November 2012, 01:55 AM   #863
toufu is offline toufu  United States
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Hi guys, for a balanced version, can I add -IN to Q2? Thanks.
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Old 20th November 2012, 12:55 PM   #864
chunek is offline chunek  Singapore
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Hi All,

I did a bulb test on HoneyBadger on 1 channel. Without initial R30 set near to 500ohms, The light bulb is off. But when tune the TP1 to TP2 to ~35mV, The bulb started to light up. Just would like to know whether this is normal or not. Anything needs to check??

Click the image to open in full size.

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Old 21st November 2012, 01:20 PM   #865
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James, to be a bit pedantic maybe this needs to be in the "build" thread. The bulb test is meant for first switch on where we can see that nothing is overheating, fuse blowing or worse. Not certain if you are adjusting output DC offset or bias current. If the latter the amplifier will draw more power from the mains as Iq is raised and the bulb will glow more brightly. Is this a gradual increase with adjustment or does it suddenly take more power when a threshold is reached?

If the former you can dispense with the bulb and run on full voltage. If the latter you may be having instability problems. Without an oscilloscope one indication of instability could be overheating of the output Zobel resistor. Good luck with your project.

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Old 21st November 2012, 03:12 PM   #866
chunek is offline chunek  Singapore
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Keith, thanks for your advice! When I adjusted DC offset and CCS, the bulb still remained no light. Once I adjusted bias current to 10mV and above, the light started to glow gradually as increasing the voltage across 2X 0R22 Re. Currently I put it at 30mV and the brightness of light remains the same for an hour. Is this considered as formal case? I will try to dispense the bulb and try it tomorrow night again.

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Old 21st November 2012, 11:01 PM   #867
chunek is offline chunek  Singapore
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Keith, I just removed the bulb. Now my speaker is singing with dc bias set to 40mV on 1 ch. The sound is warm and rich.

Just share the experience what I have. It is not advisible to tune bias current in bulb test as it is really not accurate. I did it with 35mV with bulb. However, when I removed the bulb and connect directly, it shoot up more than that and continue increasing. Luckily I offed it immediately and tuned to Rmax again, removed bulb, turn on, and adjust to 20mV. Then, adjust it every 1/2 hrs. Now it is set to 40mV.

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Old 22nd November 2012, 12:35 PM   #868
AndrewT is offline AndrewT  Scotland
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Originally Posted by chunek View Post
I just removed the bulb..................... It is not advisible to tune bias current in bulb test as it is really not accurate. ...........
Yes, that is what is advised in many previous replies.
But, too many refuse to read !
regards Andrew T.
Sent from my desktop computer using a keyboard
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Old 27th November 2012, 01:36 AM   #869
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Default Burned out Power transistor


I am having issues of burned out power transistor.

After adjusting the offset to near 0V (+/-5mv) and bias to 15mv (between TP1 and TP2, and wait for few minutes), I started the music listening on one channel.

Everything is fine for few minutes, the heat sink is not hot, output is no more than 3V RMS.

Suddently, the transformer fuse (4A) at 120V side blown and sound stop.

After debug, found out that only Q17's and Q19's Collector and Emitter shorted, thus cause fuse blow. Other 4 power transistors are fine.

Since the heat sink is not hot at all and only one bias controls 6 power transistor, I have to assume the bias setting is as good as it can be.

I am guessing that the three transistors in parallel may fight with each other.
Transistor with higher hfe may try to charge transistors with lower hfe ??

To allow hfe difference among transistors, my understanding is to use R37 - R42 to minimize the hfe difference.

While looking at other similar design with parallel transistor, they were using 100-470 ohms as the base resistor.

If my understanding is correct, my question is how is the value of 2.2 ohms be determined ? Is it too small ? Or it requires very tight hfe matching ?

I do not believe matching hfe can be done just by using a multi-meter. Hfe will shift based on bias and frequency (thus called beta instead of hfe).

If anyone do not have burned out issue yet, it may simply indicating that those three transistors are not fighting hard enough yet.

I also remember someone else has the similar issue immediately after building the amp.

Any thought ? Any input is appreciated.
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Old 27th November 2012, 02:09 AM   #870
Art M is offline Art M  United States
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Default Performance measurements

Originally Posted by ingo50 View Post
Hi all, I am new at the forum.Watching this thread I wonder about the specifications of this amp. Only given the sup.voltage, but never read about THD or risetime or
F u to Fo etc. Can one help me ? thanks all
Ingo at the center of Berlin
This is the only "Test" information I have ever seen:

The MONGREL (supersym II)
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