Mirko
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Posts posted by Mirko
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I built that one, Dukei is my handle on hf. 47uF cap is installed on the backside on the smd position.
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Another CFA is alive and well. Sorted out the issue with the bias when using the SS/ZF switch by doing the following (board rev 1.2):
- Remove the 4 ZF jumpers near the 600pF
- Increase R44/R49 to 50K
- Increase R50/R51 to 4.2K
- Remove C9/C10
Set at 190mA, plays beautifly in both modes. A must-have as reference in the amp collection. Thanks to KG for developing this amazing circuit!
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Thanks KG, will try it out.
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Maybe my post was a little ambiguous. Right now have it at 200mA in ZF. I shut it down and "jump" the amp to SS. When I power it up I get something like ~300mA bias.
My ultimate question is: should it act like this? Seems cumbersome adjusting bias up and down between the different modes.
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Have the V1.2 boards so they should be good?
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Running my CFA at 200mA bias in ZF mode, works perfectly but when I try to go over to SS mode it acts funny.
Bias jumps up way high when only the SS jumpers are engaged, is this normal behaviour? Using the latest boards.
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@RudeWolf Nice build! What transistors are using instead of that340?
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@jamesmking is the heater from pin 7 on el34 connected correctly on your schematic? Seems that it's connected to the junction of r28/29 on the original schematic?
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What do we think of SBCP56-16T1G and SBCP53-16T1G as replacement for pzta06/pzta56?
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5 hours ago, mdr30 said:
Gonna start Dynahi next, on board heatsinks and double mono in two boxes, and wonder if anyone konows where I can source two SJ109 jfets to go with the SK389s I got.
SJ109 (and sk389) are extinct for ages...Your best shot is to find linear systems parts, lsj689. But it is pricey
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@spritzer Did you listen to it, how does it sound?
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now that is what I call a mini, well done JoaMat!
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how big are the size of the boards? Looks like there are some space that can be further shaved off...
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Hi guys, quick question; what´s the current draw of the VAS transistors on the dynahi?
Measuring the R17-R20 resistors gives me 4,6V (15mA). Is this the correct value?
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3 hours ago, MLA said:
So, I would start with reflowing all solder joints and also double check that your R8 actually is 860R. Pic of the board would help trouble shooting.
My bad the R8 is 820R and not 860R, as I did not have 750R at hand for the desired 15V. Checked the solder joints and everything seems fine.
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Hi guys, just built the GRLV plus version but I have encountered some problems.
It is configured R8=860R, R7=1500R which would give me roughly 15,4V. But here is the problem VAC is 16 and im getting 17.8V DC..
Red led D1 is not lit but D9 is. Checked the leds and transistors, everything seems to be working.
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On 2016-01-20 at 3:00 PM, kevin gilmore said:
the opamp blows up at +/-40V would have to check the other parts, but +/-30V should absolutely work
speaking of power...
unbalanced/balanced/cast to balanced input block for all sorts of things, but mainly the uberamp, just need to find a way to get it into the box will probably involve splitting off the driver section. Uses GR power supply +/-30V for the front end and another GR power supply +/-40V to run the regulated output voltages to the output amp. If i add zeners to the servo amp, can easily go to +/-50V and as shown, its 100 watts of pure class A, and something north of 225 watts A/B
front end NO feedback of any kind, .0025% thd at 20khz, 2nd harmonic. 3rd harmonic not measurable. output amps are current feedback.
i think i have created a monster
What size of capcitor would be suitable, 47000uF or more?
~1000VA transformer ok?
Also where can I find the pdf or gerber for this?
and now for something completely different part 3
in Do It Yourself
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That's correct. R50/R51 on cfa3productionss.pdf
There is none but you can do it like I did and use relays to short/open the positions.