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Old 25th March 2012, 01:32 PM   #801
generg is offline generg  Germany
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Chris Goldring......

Here.... L'Amp: A simple SIT Amp

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Old 25th March 2012, 04:24 PM   #802
protos is offline protos  Greece
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Quote:
Originally Posted by generg View Post
@protos

here you can see the safe area for the Sony Mike calculated, it is the zone below the bend doted red line.....
Click the image to open in full size.


L’Amp: A Simple SIT Amp: Part 1

is the complete article...

sorry the picture got a bit big.....and I do not know why.... first time such a monster picture....
Ok it does not look linear at high voltages.
However I tested one kd-33 with my lab ps as ccs and with source 1ohm 2amp -2v bias I was only getting like 6v Vds-only half what the graph suggests.
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Old 25th March 2012, 04:41 PM   #803
generg is offline generg  Germany
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Did you set test equipment like Mike in Fig 1....?

In the article....
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Old 25th March 2012, 07:15 PM   #804
protos is offline protos  Greece
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Very bad news.
The 8 kd-33 I bought from Acronman-circuitdiy have huge variations.
I tested with 3ohm source resistor and lab ps as ccs set at 1.2A for 30 secs (clamp to heatsink not ideal). 47K gate to ground.
The variation in Vds was peppered from 3.75V to 11.5V.
That is more than 300% variation!!!
There are a couple that are close but I am now not sure if they are all rejects and should not be used at all.
Should I ask for refund and try and buy from somewhere else or is this normal?
It is a lot of money for rejects!
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Old 25th March 2012, 07:34 PM   #805
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I would not think of them as rejects. What is the gain and distortion
performance when they are biased and heat sinked correctly?

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Old 25th March 2012, 07:47 PM   #806
protos is offline protos  Greece
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I did not get that far yet. I was curious why my vfets were not operating according to Michaels graph. So I did a basic "matching" circuit test on the fly to see how close they are.
If the variation is so great it means the gain between two very different umatcheable transistors is unequal or am I analyzing incorrectly?
Or do I just try and match operating points by varying Vgs?
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Last edited by protos; 25th March 2012 at 07:50 PM.
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Old 25th March 2012, 08:06 PM   #807
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A particular Vgs isn't especially important unless you plan to build the self-biased version. In that case, your selection is more narrow. Since we have no definitive information on the various grades we have to improvise and adapt.

I suggest trying the version with the negative bias supply posted near the begining of the thread. Shoot for the same operating point (Vds and Id) and don't worry so much about the actual Vgs. Then look at the gain and distortion (or listen) as NP suggests.
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Old 25th March 2012, 08:19 PM   #808
Vix is offline Vix  Yugoslavia
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Protos, I am using the F3 (or more correctly, ZEN V9) without feedback, with "ordinary" CCS-no Aleph modulation), driving a pair of Visaton B200 above 150 Hz on Open baffle. If you can't do L'amp, play with the F3, its a heck of a good amp
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Old 25th March 2012, 10:14 PM   #809
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Or, maybe we could help him get his SIT amp working...
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Old 26th March 2012, 05:36 AM   #810
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Quote:
Originally Posted by protos View Post
Very bad news.
The 8 kd-33 I bought from Acronman-circuitdiy have huge variations.
I tested with 3ohm source resistor and lab ps as ccs set at 1.2A for 30 secs (clamp to heatsink not ideal). 47K gate to ground.
The variation in Vds was peppered from 3.75V to 11.5V.
That is more than 300% variation!!!
There are a couple that are close but I am now not sure if they are all rejects and should not be used at all.
Should I ask for refund and try and buy from somewhere else or is this normal?
It is a lot of money for rejects!

you must hve something wrong, i have put same batch of acronman KD33 and have between 4V and 4,2 v with 2,5 ohm source . look at your source , drain resistor resistor and power supply it must be there ( i use 25K gate to ground) ..

good luck
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