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Old 7th February 2010, 03:49 AM   #41
DiyFan is offline DiyFan  United States
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Quote:
Originally Posted by opc View Post
Hi Pidesd,


You are absolutely correct about the transconductance of the fet dropping drastically at low current, and after quite a few simulations, it looks like the fet plays a smaller role than I initially assumed. I need to verify this with real tests, so I'll be doing that over next week. If anyone has any favorites, let me know and I'll include them in the test. Here's the short list:


Cheers,
Owen
How about the Lovoltech LU1014D Jfet, I've been interested in trying this for a while?

Thanks
Sean
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Old 7th February 2010, 04:50 AM   #42
sergery is offline sergery  United States
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Nice looking layout. I will want to give this a shot. So with the on-board regs just provide filtered DC at what, 25-30ish volts?
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Old 7th February 2010, 08:08 AM   #43
qusp is offline qusp  Australia
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wow, so after I go ahead and sort out another output stage and buy PCBs this becomes an option again. I had all but written you off mate. hope you managed to come through whatever was taking your time well and without too many bruises. man, now I gotta make some hard decisions

Last edited by qusp; 7th February 2010 at 08:18 AM.
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Old 7th February 2010, 08:15 AM   #44
qusp is offline qusp  Australia
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oh and SMD all the way except for main films, perhaps we could get a GB together for some high quality R's from elfa or firstronics? yeah stuff it, i'm gonna build this up as well. ok mate bring it on!! :evil: (<~dont know if thats gonna work) at least I have pretty much got enough films already for the job.

LOL, that took me all of 7 mins to convince myself I needed to build both up and use my favorite for the ackodac and the other for my workshop rig driving active monitors from a PCM1794A dac. this stuff is truly like a drug

Last edited by qusp; 7th February 2010 at 08:22 AM.
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Old 7th February 2010, 05:10 PM   #45
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Hi Owen, thanks for the reply.

I actually scan a few mosfet listed in Farnell and looking at the transconductance curve trying to find the highest Gfs around 10mA. But only few datasheet show the curve and even fewer show value at 10mA.
Here is a few I found and I actually order a couple to try.

2sk2989 Toshiba
ssm3k02t
cph3430 Sanyo
irfl014n
fqp2n60c
irlml2803
zxm61n03f

Some of those is smd, but the D1 bias current is only around 10mA.

BTW, I tried the 2sk216 and irf610, both sound very good.
...chuck
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Old 13th February 2010, 05:06 PM   #46
qusp is offline qusp  Australia
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Hi Owen, any more movement mate?? sounding like I'll have to build up the QVR08's first and hope you get this done sometime soon. was hoping to get the parts with my next digikey order this week to save on shipping. i'll just wait for the official BOM though. suppose I could get some of the likely subjects while i'm there, though without knowing whether i'm ordering for throughhole or SMD complicates matters. any chance yo could incorporate pads for both in some positions for flexibility? I know peranders of sjostromaudio does this with most of his projects and I have found it to be very useful.
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Old 17th February 2010, 12:56 PM   #47
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Originally Posted by opc View Post
Hi Regal,

Sorry for the late response. I've attached a schematic that will work well with DAC's requiring 2.5V at the output.

Ignore the 33k3 value for R11 and R12, what you need there is a 50k pot. Start about midway (25K) and adjust to obtain 2.5VDC at the source of the fet. When that is set, you should see very close to 9VDC at the drain.

I'm not sure how much gain you need, but if you tell me what DAC and what configuration you plan to run, then I can dial in R1, R2, R3 and R4 to get you whatever you want voltage-wise at the output.

This project has been put aside for the past few months, but I should be getting back to it shortly.

Cheers,
Owen
Hi

would you please confirm that this schematic work with IRF610
I will use It with pcm63
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Old 5th March 2010, 03:27 AM   #48
pidesd is offline pidesd  Canada
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any news OPC?

how is this project going?
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Old 6th March 2010, 12:21 PM   #49
qusp is offline qusp  Australia
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who knows, cant wait around for it though. i'm sure when/if it eventually gets finished it will be very good, but to this point the stuttered development/ scarce communication leaves something to be desired.
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Old 6th March 2010, 12:54 PM   #50
regal is offline regal  United States
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who knows, cant wait around for it though. i'm sure when/if it eventually gets finished it will be very good, but to this point the stuttered development/ scarce communication leaves something to be desired.
Patience, this is a hobby. I'm sure the designer has a life, give him a break.
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