ZM - you should start a new thread on this. I'd be interested in likely Edcor / Jensen / Cinemag candidates...
Many thanks,
BK
what's in F6 ?
besides , do not shun Edcors , just because they're cheapest
I think the problem here, is people don't think dumb enough.
Ya gotta get the dumb brain waves flowing then it all makes sense.
Hehehe
Ok, if we''re not starting a new thread... ZM, in your IronPre, are you using a standard isolation transformer wired as an autotransformer? It looks like it to me, but it's not clear. This is in contrast to using a purposely wound autotransformer.
From memory (potentially very faulty) the M2 uses an Encore wired as an autotransformer, and the F6 uses a Jensen transformer used in a standard way.
Steve Eddy on this site has this similar concept: Electro Magnetic Amplifier Co. Model 535SE Headphone Amplifier/Line Preamplifier ? The Audio Guild, Inc.
I think like the autotransformer better for a few reasons, but of course it lacks the isolation of a normal transformer, which can be an advantage in some cases.
From memory (potentially very faulty) the M2 uses an Encore wired as an autotransformer, and the F6 uses a Jensen transformer used in a standard way.
Steve Eddy on this site has this similar concept: Electro Magnetic Amplifier Co. Model 535SE Headphone Amplifier/Line Preamplifier ? The Audio Guild, Inc.
I think like the autotransformer better for a few reasons, but of course it lacks the isolation of a normal transformer, which can be an advantage in some cases.
there is no need (for me) to start new thread , and I believe everything is clear from basic schematic and explanation I gave in my blog post
use whatever you have,can find ........ that's just buffer in front of autoformer
nothing more , nothing less - concept known from days of triode birth
use whatever you have,can find ........ that's just buffer in front of autoformer
nothing more , nothing less - concept known from days of triode birth
Need help to figure out what went wrong.
I tested channel B and all good, I was able to adjust it.
When got to channel A something went wrong. First I was using a Variac and the bias was like 0.5V with the rails at 1.7V. So, I disconnected the Mosfets and tried again. Went with voltage half way and the LSJ74 popped with smoke.
I bought them paired from the DIY Audio Store. Just ordered more pairs.
What can I do to make sure that will not burn them out again.
Thanks,
Radu
I tested channel B and all good, I was able to adjust it.
When got to channel A something went wrong. First I was using a Variac and the bias was like 0.5V with the rails at 1.7V. So, I disconnected the Mosfets and tried again. Went with voltage half way and the LSJ74 popped with smoke.
I bought them paired from the DIY Audio Store. Just ordered more pairs.
What can I do to make sure that will not burn them out again.
Thanks,
Radu
if they were mounted as prescribed ,and everything else connected as well, sole possibility is dud LSJ
but - observe that as plenty of if's
but - observe that as plenty of if's
"First I was using a Variac and the bias was like 0.5V with the rails at 1.7V"
Is the bias pot completely in the wrong direction?
Is the bias pot completely in the wrong direction?
Thank you all for your help.
and:
- no, the bias pot was preset for 4V
- I didn't think that matched pairs from this store would cause a problem
and:
- no, the bias pot was preset for 4V
- I didn't think that matched pairs from this store would cause a problem
Were jfets labelled with idss value on them?
With biasing, assuming Zeners used in your circuit are between 5V and 7V, I set trimpots to midpoint and start from there (around 3V). It's the dumb mans approach. Set at midpoint and adjust from there and you should have no issues.
The biasing issue has nothing to do with jfets going poof and vice versa. Totally unrelated to each other. Seems a strange coincidence.
What are your dc powersupply voltages?
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Hold on.
Ok ok.
When using variac there will not be adequate voltage on rails to turn on Zener so what you are seeing is the voltage across resistors.
Depending on your feed resistor zeners won't turn on till you have 12V on power rails.
Ok ok.
When using variac there will not be adequate voltage on rails to turn on Zener so what you are seeing is the voltage across resistors.
Depending on your feed resistor zeners won't turn on till you have 12V on power rails.
Yes, I already did and all looks good.
I have to wait a few days for new pairs of JFETs.
Would these steps avoid future mistakes:
1. No Jfets and Mosfets installed, measure and set the bias at 3V
2. Measure Jfets Idss and make sure is under 9 mA and maybe add 10 ohms on the source.
3. Install Jfets and Mosfets
4. Powr up and adjust bias and DC output.
There is another schematics where the 1000uF caps are connected to the output and respectively to the minus rail. Would that make a difference?
I have to wait a few days for new pairs of JFETs.
Would these steps avoid future mistakes:
1. No Jfets and Mosfets installed, measure and set the bias at 3V
2. Measure Jfets Idss and make sure is under 9 mA and maybe add 10 ohms on the source.
3. Install Jfets and Mosfets
4. Powr up and adjust bias and DC output.
There is another schematics where the 1000uF caps are connected to the output and respectively to the minus rail. Would that make a difference?