*** The DIY Audio Thread ***

[adamau5]

have you got a pot connected? if not then you need one. That could be an issue, but this sounds a tad more serious.

does one side of the amp function ok? or do both channels drop to 10v?

which heatsinks get hot?

go through the schemetic step by step, check the orientations of everything against the datasheet (not the silkscreen)

 

[gurusan]

Well I had the jfets backwards, Q17 and Q18....swapped them around yet am getting -8Vdc on the right channel. argh

I went over the rest of the amp and am pretty sure everything is in the right orientation.

 

[adamau5]

ok, you now no there is a fault. Those fets are dead if they were in the wrong way round. I suggest you check the other fets for shorts and replace as necessary. do this whilst the amp is off.

This is good though - first step of troubleshooting is finding the issue.

 

[-Ad-]

ok, you now no there is a fault. Those fets are dead if they were in the wrong way round. I suggest you check the other fets for shorts and replace as necessary. do this whilst the amp is off.

This is good though - first step of troubleshooting is finding the issue.

And great experience too. Put some transistors in the wrong way round when I first powered up my Millett Max. One chaannel didn't work properly, but soon found the fault after some guidance and all worked perfectly.

But damn that's a lot of components on that headphone amp

 

[adamau5]

ok, looking at the schematic, i guess that if you replace the fets 17 and 18 you may be lucky. they are both common parts which you can get from farnell / maybe rapid or cpc.

however, the next candidates to be blown by the error are 15 and 16. IF these have gone too (check they are not shorted) then just keep working yourself backwards. 13 and 14 should survive...

and by the way - you are in the perfect situation of havig a working channel as reference. ohm things out to start with (everything off). This should tell you what to replace

 

[gurusan]

Thanks for all the help, really appreciate it. I've just ordered replacement FETs...rsonline had them. I ordered some of the other little transistors (MPS8099 and MPS8599) just in case as well, they were harder to find but got some in the end.

As for potentiometer impedance, how do I go about choosing this? I have a 50k Alps RK09 that I was going to use...any potential problems with that?

 

[Mr. Brightside]

Anybody started work on their BantamDACs yet?

I'm going to wait until term finishes and I'm home - a) I basically have no free time here and b) My smaller soldering iron for SMD work is at home

 

[adamau5]

finished mine the night i got it. only took an hour and half.

plugged it in and..... nothing. reflowed the 3.3 reg and it sprang into life. needs casing up now!

 

[ChrissyT88]

No, i need to find some flux cleaner/IPA, plus get some wire and rca jacks for mine yet... Looking forward to it though!

 

[Founder_film]

was going to suggest the lm338T

how about this

Been looking at this PSU circuit and trying to understand it but I am stuck on exactly what he is saying in his notes about putting caps on the chips PSU pins. I assume these are V+ and V-? Is the 100nF in parallel with the 2,200uF from V+ to GND and V- to GND or series? Also I am confused about the 3.3uF cap and the 0.1R/1W 3.3nF snubber, where do they go?

If anyone was kind enough to draw a quick circuit diagram that would be great! I am planning to use this PSU with the LM3875.

Finally should I go with the regulated version or this unregulated one?

 

[adamau5]

I assume he means directly attached to the where the ps connects to the ampflier chip.

 

[ChrissyT88]

Bantam Pics!

Its not finished - i dont have everything i need to get it done (no casework yet either), but all of the parts with the exception of the USB connector are on there. I dont thinks its awful, particularly as its my first SMT project (so go easy!). I have noticed a few bits on the pics that could use a touch up (namely c15), and the underside needs a clean, but hopefully its all made contact and will work. I am also well aware that the green caps are a little on the wonky side! I'll do the rest/more checks in daylight methinks.

Btw Adam, your comment on it being a half hour job was very misleading! The chip took me ages, and i made so many bridges! I got the hang of it in the end, just as i finished - frequent applications of flux is definately the key, whereas i was only using a little every now and then. I would like to do another really, so i need another project that involves a mouser order! I can only hope the chip hasnt burned out, but hopefully the applied heat was not that high.

Sorry about the poor pics - i have never really used the camera and the light in here is awful!

 

[adamau5]

looks like a good job to me!

I bridged to the pins on the ground plain (the two on each side furthest away in your pics), but i dont care as they shorted anyway by the ground.

told you not to go easy on the flux... the magic source.

 

[Mundu]

Some stuff I needed arrived today but I still need some flux. Hopefully I'll have some time on the weekend!

 

[adamau5]

oh yes, forgot to say chris.... solder the connector on and plug it in you big jessy!

 

[ChrissyT88]

Thanks Adam. I just hope all of the chip's pins are in contact properly... Theres not really much i can do now other than wait for a few extra bits. I also completely forgot about the trace bug... thats something i will have to attempt to do later on, which wont be much fun!

EDIT: A ninja post! This will sound pretty stupid... but i dont have a USB cable! All the ones i have are minis, and i cant really cut any of them up. I also need some RCAs or similar, plus an old PC to test the thing on (i dont trust my soldering.... at all!).

 

[Yaka]

nice build !


also here are some snaps on the starving student proto board i just did

the pot had a broken leg, i manged to work round it by soldering the remaining legs, sticking the broken in the hole and soldered the broken bit the the other end

easier than the p2p one i made, now the hard bit which i the case work

 

[adamau5]

case work is the fun bit. Get a step drill bit, some digital calipers and its fun from there on.

Although i did just put an order in at shaeffer for this....

its a remote controlled buffered preamp i am working on. 4 inputs, R2R relay controlled attenuator, pedja rogic buffers off a dual 15v supply.

Chris: I just plugged mine straight into my best pc. lifes too short.

 

[ChrissyT88]

Chris: I just plugged mine straight into my best pc. lifes too short.

This is true, but the lack of a USB cable is slightly more of a concern! I should have one tomorrow, but im headed home for the weekend so will not be able to make any headway. I have some RCAs etc at home that i will bring back, so i should be able to finnish soon.

Nice SS - i may have to look into the PCBs when they get a proper release.

Adam, can i ask what kit if any you are using for the buffered preamp?

 

[adamau5]

yes, i am using a volume/input kit from a chap called bbp on diyaudio .

seems extremely cheap ($65 for relay board and volume, lcd, reciever, handset, rotary encoders and wires.... there is no way on earth i could build it for that!)

I built my own 5vdc reg supply for the vol control.

the buffers... i am going to try the pedja rogic buffers, bought some obselete parts from a chap called justblair. buffers are powered by a shunt regulated cheapish chinese power supply.