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Old 27th March 2011, 09:07 AM   #1411
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Oh and ohh... I didn't realize that it is the worst position. Thought the space is open in front and have enough distance (15cm) from the wall will make the listening well already.
I arranged this position because of the size of my room (2.8m x 3.0m) and hoped this was appropriate. You know that is a student's room and moving something big requires quite a messy arrangement.
I will try to bring them to the living room and persuade my friends to share the test. I know I must put them back here in my room then but I will do some research about best postion in small room first.

Thanks a lot, lohk and uriah.
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Old 30th March 2011, 06:22 AM   #1412
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Peter,

I wonder if I can power your GC with battery (car or motobike battery for example)? What should I do? Any performance affection?

As back to my country, the main power is not stable and sometime it is cut for even a whole day or more, I am considering the battery instead. Read about this in Mother-of-Tone with BYOB amp and DAC but still doubt it is applicable for GC LM3875.

Any suggestion?

Thanks,
HT
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Old 30th March 2011, 06:33 AM   #1413
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Quote:
Originally Posted by deepblue2010 View Post
Peter,

I wonder if I can power your GC with battery (car or motobike battery for example)? What should I do? Any performance affection?

As back to my country, the main power is not stable and sometime it is cut for even a whole day or more, I am considering the battery instead. Read about this in Mother-of-Tone with BYOB amp and DAC but still doubt it is applicable for GC LM3875.

Any suggestion?

Thanks,
HT
Thats an interesting thought!!
Building a GC for car !!.
Any plans somewhere for that kind of power supply?

Nick
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Old 30th March 2011, 09:06 AM   #1414
lohk is offline lohk  Europe
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I have poewered a gainclone with four 12V batteries (+/- 24V) with very good effect - I still believe it maybe sounded better than with mains power. But it was only temporary.
The SLA batteries were used ones from alarm lights and gave plenty of power. I think car batteries would also be sufficient.

Powering a gainclone with a LM3875 from a single 12V battery (like in a car) is IMO only possible with a voltage converter (like in most higher powered car amps), with a lot of effort and very unpredictable side effects to the amplifier's sound.
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Old 30th March 2011, 02:25 PM   #1415
udailey is offline udailey  United States
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In the datasheet there is a diagram for single supply ie. +12V/0V. Its meant for cars. Its more complicated but should work fine and sound good.
For LM3886 datasheet is saying must have 20V or more but then the graphs are showing operating conditions with ~10V and up.
Will check LM3875..
Ah, okay looked at the graph again, its the one showing supply current vs supply voltage and even though it shows supply voltage as being at a min of ~10V that means +/- 10V so really you do need ~20V all together. I just wonder if that is necessary in the single supply configuration. Maybe there is more info in some app note. Will look around a bit.
Uriah
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Last edited by udailey; 30th March 2011 at 02:35 PM.
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Old 30th March 2011, 02:52 PM   #1416
udailey is offline udailey  United States
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Thought for sure I would find an automotive app note for something in OVERTURE series that would talk about 12V operation. From not finding anything I am thinking you must use min 18-20V/0V for single supply. The two car batteries in +-+- configuration will give you what you need for dual supply and would be easier than the single supply circuit.
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Old 30th March 2011, 05:08 PM   #1417
AndrewT is offline AndrewT  Scotland
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Hi,
in addition to the >=20Vdc between the supply rails, while there is PSU ripple and while the PSU has sagged due to high current demand, one must also ensure firstly that the >=9Vdc is adhered to and secondly that the mute current is adequate at the lower operating voltages.
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Old 6th April 2011, 11:48 PM   #1418
ss007 is offline ss007  United States
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Well lets see if I can Get some help with this one.

I'm finally getting around to putting my amp in a nice case. I built up a separate psu with a new transformer from Antek and the extra power supply board. It's all neatly installed in a box along with a +/-15 supply for the phono pre [see attached pic]. I have a four conductor connector handling just the GC supply which is +/- 35vdc at the output of the psu. There is a 3 ft cord connected to the GC temporary enclosure. I also have +/- 35vdc at the connector coming in. So everything appears to be right on so far. Now when I hook up the amp boards I pop fuses. Out of the 100 times I've traced the wires from the connector to the board I've found nothing wrong or different than the way the last supply was hooked up.

If I detach the purple wires [see pic]that carry the PG- wires to the star ground I can hook up the +/- vcd without a problem.

If I have the PG- wires attached and try to touch either of the +/- vdc wires from the amp boards to the appropriate pin on the connector it will spark

Anybody got any suggestions?
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File Type: jpg gc.jpg (349.2 KB, 340 views)
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Old 7th April 2011, 01:37 AM   #1419
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I am building a pair of gain clone mono's. and have a pair of 25v 25v 300va avel lundy transformers i'd like to use. Most of the gain clones are using 22v transformers. The original humpties use a 23.6 volt tranny don't they? Can i use these 25 volt ones? should i worry about the extra voltage? Can i make use of the xtra voltage to improve the performance? What values would you recommend for some induction post transformer to soothe the peaks a bit? I also have a pair of air gap 3 henry inductors, wouldn't these reduce the PS output voltage and smooth it?
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Old 7th April 2011, 03:53 AM   #1420
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anystereo,

I personally use 300, 25x2 and it's perfect for my GC. I got some level-0 questions here (Commercial Gainclone kit- building instructions and Commercial Gainclone kit- building instructions) and they were all solved. I even remember Peter has suggested that with high power toroid (>300VA) the sound is stronger but no need for more than 400VA (Commercial Gainclone kit- building instructions)

HT
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