questions:
1. the pricing according to your list regarding A,B.C versions has the pricing going down for the higher gain versions. This is in comparison to spec sheet.
If this is so, would it not be better to order the higher gain versions?
Is there any downside to the higher gain versions? One can always lower the gain with source resistance which I believe may lead to less noise,
2. Luvdunhill: are you still planning on consolidating orders across types? especially applicable to 170 as the total is almost 3000 for lsk170
SheldonD
1. the pricing according to your list regarding A,B.C versions has the pricing going down for the higher gain versions. This is in comparison to spec sheet.
If this is so, would it not be better to order the higher gain versions?
Is there any downside to the higher gain versions? One can always lower the gain with source resistance which I believe may lead to less noise,
2. Luvdunhill: are you still planning on consolidating orders across types? especially applicable to 170 as the total is almost 3000 for lsk170
SheldonD
one thing I get to do as group buy leader is ask questions to my customers 
This question is actually on topic. I'd like to match my K170 by Vgs at a predetermined current and have this circuit on my breadboard:
however, I cannot get it to work. I'm getting around 1.4-1.5v across the 39 ohm resistor and Vgs for the BF246A is zero, so it's drawing its Idss.. obviously, everything is nice and toasty. Adjusting the pot doesn't seem to do much and inserting a larger pot doesn't seem to do much either. I've double checked the circuit, and all seems good. Since the above circuit was used to match K369, do I need to make a change somewhere in the circuit (like the 39 ohm resistor) to support matching lower current devices?
Thanks!
This question is actually on topic. I'd like to match my K170 by Vgs at a predetermined current and have this circuit on my breadboard:An externally hosted image should be here but it was not working when we last tested it.
however, I cannot get it to work. I'm getting around 1.4-1.5v across the 39 ohm resistor and Vgs for the BF246A is zero, so it's drawing its Idss.. obviously, everything is nice and toasty. Adjusting the pot doesn't seem to do much and inserting a larger pot doesn't seem to do much either. I've double checked the circuit, and all seems good. Since the above circuit was used to match K369, do I need to make a change somewhere in the circuit (like the 39 ohm resistor) to support matching lower current devices?
Thanks!
luv,
your circuit does not measure balance/matching very well.
V at gate is equal.
You should be able to set up the current in each FET drain resistor to match exactly. When you measure the voltages at the sources you will find they are all different. i.e. Vgs is different.
I suspect the jig was set up for the reversed pins of the 389 have you reversed some of the DUTs to match or remade the jig?
How do you keep the thermal matching of the devices?
I find that holding the DUT 1 second longer as I insert it into the jig affects the result. This ambient temperature variation must be compensated for.
But, you can adapt the method to find matches.
keep one FET unchanged. use this as the master.
inset DUTs into the other positions and read off Vgs. set aside all DUTs sorted by Vgs.
Now go back and insert loosely matched DUTs and see how well they track.
I would use a common source voltage with just one CCS and a common gate voltage. Then select for equal currents (Idss). Then adjust CCS over a range to find how well the matched pairs track at different currents (matching of transconductance).
your circuit does not measure balance/matching very well.
V at gate is equal.
You should be able to set up the current in each FET drain resistor to match exactly. When you measure the voltages at the sources you will find they are all different. i.e. Vgs is different.
I suspect the jig was set up for the reversed pins of the 389 have you reversed some of the DUTs to match or remade the jig?
How do you keep the thermal matching of the devices?
I find that holding the DUT 1 second longer as I insert it into the jig affects the result. This ambient temperature variation must be compensated for.
But, you can adapt the method to find matches.
keep one FET unchanged. use this as the master.
inset DUTs into the other positions and read off Vgs. set aside all DUTs sorted by Vgs.
Now go back and insert loosely matched DUTs and see how well they track.
I would use a common source voltage with just one CCS and a common gate voltage. Then select for equal currents (Idss). Then adjust CCS over a range to find how well the matched pairs track at different currents (matching of transconductance).
Hello luvdunhill,
I'm no expert, but regarding your Vgs measuring circuit, the fact that "Vgs for the BF246A is zero" is a worry - I wonder if you can separately check that the current source is working correctly by for example replacing an upper K170 with a resistor or milliamp meter, and varying the pot to make sure the current can be moved below the BF246A Idss. If not, I'm stumped!
Secondly, is there any chance the circuit is oscillating? Maybe some bypass caps on the rails are needed?
I'm no expert, but regarding your Vgs measuring circuit, the fact that "Vgs for the BF246A is zero" is a worry - I wonder if you can separately check that the current source is working correctly by for example replacing an upper K170 with a resistor or milliamp meter, and varying the pot to make sure the current can be moved below the BF246A Idss. If not, I'm stumped!
Secondly, is there any chance the circuit is oscillating? Maybe some bypass caps on the rails are needed?
Deek:
yup, I isolated the CCS and it didn't work.. varying the pot did nothing, and the BF246A didn't move less than Idss... oscillating with batteries would be a new one to me guess it's time to ditch this circuit.
AndrewT:
thanks for your comments. I like you approach with the "master" device. Perhaps you could draw up a circuit that I could test
yup, I isolated the CCS and it didn't work.. varying the pot did nothing, and the BF246A didn't move less than Idss... oscillating with batteries would be a new one to me
guess it's time to ditch this circuit. AndrewT:
thanks for your comments. I like you approach with the "master" device. Perhaps you could draw up a circuit that I could test
Anatech posted a circuit for matching BJTs. Base your FET jig on this.luvdunhill said:Deek:
yup, I isolated the CCS and it didn't work.. varying the pot did nothing, and the BF246A didn't move less than Idss... oscillating with batteries would be a new one to me
AndrewT:
thanks for your comments. I like you approach with the "master" device. Perhaps you could draw up a circuit that I could test
update:
The following people have paid:
coloradosound
shallbehealed
mlloyd1
ken.berg
TS Lo
jimt
Jim Hamley
hayenc
npapp
spind
JoeyDD
claudio
sonidos
wct
jonclancy
Conrad Hoffman
len_scanlan
ZUM911
Looneytunes
agent.5
mako1138
bobgroger
chertk
bkisiel
walt h
dankop
leadfinger
jims
finneybear
sidiy
pilli
Scott Wurcer
The following people haven't paid:
AndrewT
stoolpigeon
rolandong
tritosine
jpo
metalman
mikewong
cobra2
rjay
christer
genome
audiotony
EDDELARUE
kraljmatjaz
Scott Stansbury
flg
RogerGustavsson
klm1
pingrs
damohpi
jeje
Deek
I have no way to contact the following people:
pencoat
LarryNicks
relder
Rambi
We're over the minimums needed to get the various price breaks in all format except for the LSK389 SOIC-A at the moment.
Furthermore, we have payment for 48.04% of the devices that were spoken for.
If you're no longer interested in this group buy, do the right thing and just let us know!
The following people have paid:
coloradosound
shallbehealed
mlloyd1
ken.berg
TS Lo
jimt
Jim Hamley
hayenc
npapp
spind
JoeyDD
claudio
sonidos
wct
jonclancy
Conrad Hoffman
len_scanlan
ZUM911
Looneytunes
agent.5
mako1138
bobgroger
chertk
bkisiel
walt h
dankop
leadfinger
jims
finneybear
sidiy
pilli
Scott Wurcer
The following people haven't paid:
AndrewT
stoolpigeon
rolandong
tritosine
jpo
metalman
mikewong
cobra2
rjay
christer
genome
audiotony
EDDELARUE
kraljmatjaz
Scott Stansbury
flg
RogerGustavsson
klm1
pingrs
damohpi
jeje
Deek
I have no way to contact the following people:
pencoat
LarryNicks
relder
Rambi
We're over the minimums needed to get the various price breaks in all format except for the LSK389 SOIC-A at the moment.
Furthermore, we have payment for 48.04% of the devices that were spoken for.
If you're no longer interested in this group buy, do the right thing and just let us know!
one other question, perhaps Scott can answer as I know he's planning on using the LSK389 SOIC devices as well. What are you going to do with pins 3 and 7 (I'm assuming they are tied to the substrate), are they just not connected? Also, are you planning doing anything special under the device itself, such as pouring a small heatsink or anything?
AndrewT:
I cannot seem to find the post from Anatech that you referenced. I searched for Anatech as poster and BJT as a key word. Any ideas?
AndrewT:
I cannot seem to find the post from Anatech that you referenced. I searched for Anatech as poster and BJT as a key word. Any ideas?