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Old 15th May 2012, 01:20 AM   #41
kp93300 is offline kp93300  Malaysia
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Quote:
Originally Posted by rjm View Post
To check a few things, I'm building a second set with an experimental BOM, BOMX below.
  1. Emitter resistors R3,4 lowered to 1k to increase the bias current.
  2. Emitter resistors R7,8 lowered to 1R, which raises the bias current in the output stage to more closely match the driver stage, at the expense of stability and increased likelihood of thermal runaway.
  3. Ceramic bypass caps added in parallel to the four electrolytics after the Z-reg. If there is any high frequency stability issues, this should quiet things down.
Hi RJM
Any follow up in your experiment for items 1 and 2 when you lowered the resistor value?
What is the effect on the sound ?

thanks
kp93300
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Old 15th May 2012, 02:20 AM   #42
kp93300 is offline kp93300  Malaysia
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Hi RJM
One more thing .
Have you compered the sound difference with buffer build with BC and BD transistor?
Which is more transparent ?
thanks again
kp93300
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Old 15th May 2012, 02:50 AM   #43
rjm is offline rjm  Japan
Richard Murdey
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@dimkasta

For the input resistor use whatever you have it's just a non-critical part, with no power draw.

@kp93300

Most of the changes came from the ceramic bypass caps. Changing the resistor values didn't make much difference, or at least not enough for me to get a handle on. All things considered, I should probably update the BOM values to the BOMX values. The extra current doesn't cost much from a design perspective.

I haven't played around with alternate transistors, of course just about anything can be used if you want to experiment...
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Old 18th May 2012, 12:29 AM   #44
kp93300 is offline kp93300  Malaysia
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Default questions from electronic illiterate

Hi Richard,
i am going to build this buffer with BD devices and compare to B1 from NP.
I am using it as a line level buffer after the LDR volume control and there is an output caps in the dac before the LDR
Hope you can clarify a few points for a electronic illiterate like me.

1)What is the current draw?
2)What is the dc voltage range usable for the buffer? My transformer is 18 0 and 18 0 ac.

3) If i use +/- 24 V dc before the Z reg, do i need a 1W zener in stead of 1/2 w ?

4) Will help it in lowering power supply noise by using LED for voltage regulation in place of zener?

5) Are the values of the cap critical?

6)How to match the transistor to get lowest dc offset ? What are the variables that determine the dc offset?


thanks for sharing your project

kp93300
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Old 18th May 2012, 04:35 AM   #45
rjm is offline rjm  Japan
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Quote:
Originally Posted by kp93300 View Post
i am going to build this buffer with BD devices and compare to B1 from NP.
That should be interesting. Just remember to have the ceramic bypass caps installed before you run off and start making comparisons.

1)What is the current draw?

Kit BOM runs at about 12 mA per channel.

2)What is the dc voltage range usable for the buffer?

Kit BOM has 25 V capacitors. That's your upper limit. 18 VAC secondaries will blow the caps, but if you are dead set and you are sourcing your own parts anyway the BOM can be changed to operate at considerably higher voltages. I can provide the modified BOM. Email me.

3) If i use +/- 24 V dc before the Z reg, do i need a 1W zener in stead of 1/2 w ?

No, the Zener is running near its minimum current. Even with 24 V V++ the power dissipation does not increase significantly.

4) Will help it in lowering power supply noise by using LED for voltage regulation in place of zener?

I can't imagine it would be worth the trouble. R12, C7 are very effective at filtering out the Zener noise.

5) Are the values of the cap critical?

No, not at all. You can move a factor of 2 either way.

6)How to match the transistor to get lowest dc offset ? What are the variables that determine the dc offset?

I'm not sure as I haven't tried. I would assume matching hfe would do the trick. What you really want for low offset though is identical Vbe for a given static current and temperature.
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Last edited by rjm; 18th May 2012 at 04:44 AM.
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Old 18th May 2012, 07:40 AM   #46
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In the buffered VSPS/Phonoclone scenario, if we ommit the Z-reg parts, where do we connect the common X-reg psu output? On the power pads on the buffer side?

Oh and have you noticed a difference connecting the buffer before (replacing R6/R8) and after the coupling cap (C3) ?

Dimitri
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Old 18th May 2012, 10:24 AM   #47
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Haven't tried the latter, I've only had the B-board after the phonoclone C3.

For the former, and I admit I hadn't considered it before you asked, V+ and V- connect back to the B-board from the Phonoclone, but on the B-board neither the COM not the GND need be connected to anything. The common path is already made by the phonoclone's OUT-. In principle... I may be mistaken; you'll have to feel it out as you go along.
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Old 18th May 2012, 11:39 AM   #48
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And where do we connect the V+ and V- on the b-boards? on the buffer side power pads?
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Old 18th May 2012, 11:46 AM   #49
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Yes, the ones labelled +,-, as opposed to ++,--.
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File Type: png b-board GZ 10e board.png (7.4 KB, 163 views)
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Old 22nd May 2012, 10:22 AM   #50
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About BOMX, any comments on the increased bias changes?
Have you decided to make this the standard bom?
I am asking because you mentioned some possible instabilities and thermal drifting.
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