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Old 11th February 2009, 02:19 PM   #2821
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The On state of a bipolar transistor is defined as 640mV at 10uA and 300K degrees.
But a BJT is not a diode, there's current flowing from the base to emitter at lower Vbe values, also depending on leakage values.
But who gives a hoot about Ib and Ic values in the nano-Amps order, starting at a Vbe of 0.4V and above ?
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Old 11th February 2009, 02:28 PM   #2822
sekess is offline sekess  United States
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Default transformer secondary voltage

I think at least initially I'll go with an unregulated supply and then possibly try a regulated one down the road.

I have a question on the transformer secondary voltage. I had built an unregulated supply for an Aleph J a little while ago. I used 330VA Avel Lindberg transformers with 18 volt secondaries. My line voltage is on the high side at 125V most of the time. I ended up with rail voltages of 22.5 -- a little low.

I was going to try 400VA Antek transformers this time. They have them in both 18v and 20v secondaries. Should I go with 20volt secondaries this time? Or, would that make my rails too high?


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Steve
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Old 11th February 2009, 02:54 PM   #2823
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sekess -

Did you have any type of resistive element in that passive supply, like a resistor or inductor? If so, it would help to have that info from you, and then we could always try using Ohm's Suggestion to figure out the voltage drop. - Pat
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Old 11th February 2009, 03:17 PM   #2824
vonfilm is offline vonfilm  United States
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Peter,
What parts did you leave out to eliminate current limiting circuitry?
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Old 11th February 2009, 03:44 PM   #2825
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It would look like this: http://www.diyaudio.com/forums/showt...67#post1724767
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Old 11th February 2009, 03:44 PM   #2826
sekess is offline sekess  United States
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Default supply

Hey Pat,
I use the recommended unregulated supply. The only difference is that I went dual mono. For each channel, I have a seperate supply. Each supply has it's own transformer, 2 rectifier bridges. The bridges feed CRC (capacitors - resistors - capacitors).

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Steve
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Old 11th February 2009, 03:53 PM   #2827
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Default supply

Each channel's supply has 120,000uF of capacitance and I used .2 ohms for the CRC resistors.

On this supply, the resistance will be a little less - I was planning on using 4 parallel .47ohm resistors (like Nelson uses in his amps) instead of the .2 ohm that I used the last time. But, I think the small difference will be insignificant with respect to the rail voltages.
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Old 11th February 2009, 03:55 PM   #2828
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Quote:
Originally posted by Peter Daniel
I completed my new monoblocks as well, and I'm very happy with the amp; connected directly to a source (no line stage, no attenuator) this is probably the best amp I had in this system.

Disregard AC power connection, it's only temporary.

Nice work. I have been contemplating vertically oriented monoblocks myself. Less floor space, and maybe easier layout of parts inside with respect to connections to PCB, especially if separate input and output supplies are used (in a different amp). I think the top plate may look better rebated into top edge of heat sink, though. Also, you may consider raising the sinks off the footers to get better air flow through the fins, especially over the footers. Don't know about Plitron, but SumR has cans for their transformers with leads that come out on the top. If turned over, they can feed right through the top plate. Have you ever tried SumR toroids? Put some legs on the heat sinks, and a cased transformer, and give R2D2 a woody! Twins!
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Old 11th February 2009, 04:51 PM   #2829
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My interest for vertical amp chassis was certainly stimulated by that site: http://www.marklevinson.com/image_li...6&productID=12

I've heard about SumR but never used his products. A friend of mine does and seems to be happy.

I could trim the chassis details, but the idea was to build everything in one weekend. Besides, the amps will be sitting behind the wall, so I was not concerned with aesthetics that much.
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Old 11th February 2009, 05:04 PM   #2830
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Have you ever considered using XLRs instead of RCAs?
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