The lead free purchase was a mistake, but it's here so I'll make the most of it. Waiting on delivery of leaded solder paste.
I add the paste first, then stick the component into the paste, that generally holds it in place. Sometimes you need to use some tweezers or similar to hold while the solder flows.
I may try your hot plate and skillet idea, it sure as heck looks easy and inexpensive enough to give it a go.
I add the paste first, then stick the component into the paste, that generally holds it in place. Sometimes you need to use some tweezers or similar to hold while the solder flows.
I may try your hot plate and skillet idea, it sure as heck looks easy and inexpensive enough to give it a go.
When I measured the first few batches of jfets I put them into these smd storage bins:
http://a.co/1wy30mZ
I bought 4 of those bins, labeled them, then as I measured (IDSS) I could record the measurement and toss each one into it's own bin. I'll consolidate groups of similar IDSS as a starting point to match them where needed.
I figure I can use the bins to stash smd components in my akro-mills bin drawer organizer things as well. Really handy how you can attach these little bins to eachother.
http://a.co/1wy30mZ
I bought 4 of those bins, labeled them, then as I measured (IDSS) I could record the measurement and toss each one into it's own bin. I'll consolidate groups of similar IDSS as a starting point to match them where needed.
I figure I can use the bins to stash smd components in my akro-mills bin drawer organizer things as well. Really handy how you can attach these little bins to eachother.
Attachments
Last edited:
That does look very handy - I may have to get some. Here is my method, it's cheap and very easy to see what values I need to match. I tape down the parts once labeled. Then when I find two that I need, I use an xacto to cut a slit in the tape and pull it out with tweezers. I always wear ESD wriststrap.
Attachments
I've been swamped with work the last few weeks, I think I'll get some time tomorrow evening or Sunday to get first sound. Hopefully!
I confess that I usually drive them directly off of the speaker taps of a full-size amp.
I have several easier-to-drive headphones, so I'm sure I'll fine a good pairing for this little Class A. Thanks for setting expectations, X!
I confess that I usually drive them directly off of the speaker taps of a full-size amp.
I have several easier-to-drive headphones, so I'm sure I'll fine a good pairing for this little Class A. Thanks for setting expectations, X!
However, I am working on another version that can potentially handle a monster can like this one.
I was thinking Nelson Pass ACA might be what you use to drive them?
Sorry to hear about the problems. We should be able to fix this.
Can you take a DVM and measure voltages at gate of mosfet and source of mosfet (output DC level). That voltage divided by R7 equivalent of 117.5R is the bias current. Should be in 50mA range. Also what is current going through the R3 1k resistor feeding the JFET? Measure on good side and bad side and compare. But please show us what you get. Wear antistatic ground strap when doing measurements probing around.
Are you sure your resistor values around the JFET (R2/R3/R4/R5) are correct? Make sure R1 is 100k and not some really low value. Look for solder bridges and shorts. If transistors are hot that may be normal as this is class A (but left should be pretty hot too).
A high resolution closeup photo of both sides would be very helpful. Make sure I can read resistor values.
Last edited:
Finished mine this morning, listening to it on the bench now.
R7A - 7.05v / 117.5R = .06, so ~60mA
R7B - 7.09v / 117.5R = .063, so also ~60mA
I haven't plugged in my DT770 PRO 250's yet, but I'm planning to listen on them later this evening.
Setup is MacBook Pro Retina, Tidal -> optical out -> SMSL SD-793ii DAC -> X's HA
R7A - 7.05v / 117.5R = .06, so ~60mA
R7B - 7.09v / 117.5R = .063, so also ~60mA
I haven't plugged in my DT770 PRO 250's yet, but I'm planning to listen on them later this evening.
Setup is MacBook Pro Retina, Tidal -> optical out -> SMSL SD-793ii DAC -> X's HA
no need to be sorry, it's just my lack of soldering skills. to answer your questions, i'm pretty sure about the resistor values, because i compared the codes with the pictures you posted. i was concerned about R7 because your code is 471 and mine is 4700 but i checked and both codes mean 470Ω.
R1 is 100k (code 1003).
mosfet voltage left side = ~7.2V, right side = ~0.27V, so i guess thats the issue. i did do a lousy job with the right mosfet, i'm going to remove it and try again.
voltage across R3: left side = ~6.76V, right side = ~8,3V
thanks for your help!
Nicely built !!
Perfectly matched FETs for channel balance.
Glad you like the sound.
Btw, driving with a nice DAC and high Rez flac files on your Beyerdynamic DTs will knock your socks off. Be prepared to love it even more.
Last edited: