Mini-A PCB finished... Some questions on it ;)

Xandrell · 21st February 2011, 07:29 PM

Hi folks...

Finally finished my layout of Grey´s "Mini-A-Schematic". Didn´t manage to make it one-sided

The schematic can be found here in the forum.

So... Are the trays thick enough? the "small" ones are 0,7 inch and the "big" ones are 1.5 inch.

Greetz...

Xandrell · 22nd February 2011, 05:32 PM

Sorry... I mean traces, not trays

gruni · 22nd February 2011, 05:35 PM

also, your traces arent .7 and 1.5 inch. that would be roughly 1.8 and 3.8 centimeters.

BobEllis · 06:34 PM

Small signal traces don't need to be anywhere near that big. You can go smaller than shown for all traces except the ones carrying power in the output. Might even allow you to make it single sided, it you really need to. The feedback trace can be small, just the output trace needs to be anywhere near that big. Same for R18 to C2, etc.

Move R16 much closer to the Gate of Q5 - like R14 and Q4.

Try rearranging so the input differential can be back to back - good thermal contact promotes offset stability. BrianGT's board used a chunk of aluminum between teh devices but if you can get them connected (with an isolator and Isolated screws) it would be helpful.

I don't have Grey's schematic, but I'll bet that there was a cap bypassing D1. A 1 uf film cap would be good, but you can go with a 10 uf electrolytic.

Why the fish hooks around R20 and R21?

Verify that the pads for your resistors are big enough to pass a lead through and still have something to solder to.

Xandrell · 23rd February 2011, 03:09 PM

@gruni: You´re right

I´m using Eagle. The traces are 0.07mil and 1.5mil.

@Bob: Done

Have a look at it...

Moved R16, added C4 for bypassing D1, reworked some traces to delete those fish hooks. Thermal contact will be established bay using a 3mm thick copper bar and good thermal greese (about 7.2W/m*K). Think that shall work

BobEllis · 23rd February 2011, 05:54 PM

You mean 70 mil and 150 mil or 0.070" and 0.150"

Looks better. I'm guessing that you plan to use the top of the board as a ground plane.

You have plenty of room if you want to make it a bit more compact. The feedback trace R21 to R8 should be 70 mil. Same with the trace R21 to C2.

I'm curious. Why did you choose to make R12 variable? Leave a pad to place a fixed resistor once you find a gain that works for you. It sets the active current gain. R11 sets bias. That's more often variable.

There's still a fish hook at R9 R11. No big deal, but you could run the trace from C2 diagonally to R10 then up.

Be sure that the holes and pads for resistors are large enough. Eagle defaults to some really small holes and very little pad around the hole. I've had troubles with resistor leads barely fitting, some brands have larger leads than the default holes. this means you'll end up editing your components, but you're in it to learn, right?

Another thing that would make the board interesting would be to add pads for external output devices so you can make a larger Aleph if you want later.

Xandrell · 23rd February 2011, 06:30 PM

Guess what... ^^

I´ll drill the holes for the parts min. +1/10mm everytime. That saves some room for changes with parts. And yes i´m still learning

R12 is variable for setting DC-offset. Or am i wrong? Could bet i´ve seen this here around...

I´ll first try this one as-is, experimenting around with some parts (capacitors, resistors and transistors from different manufacturers). When done testing and fooling around, i´ll maybe go on and make a design on an Aleph 30 (think this was the next "stage"). I don´t pay anything for the PCBs. So if i mind to change something, i´ll make it^^

Luckily the postman delivered some "presents" for me

25xIRF9610, 10xIRFP150 and a handful BC550C. Everthing for free. Did i mentioned that i´m also able to become some parts as "samples"? ^^ I´m in heaven for DIY XD

BobEllis · 23rd February 2011, 06:45 PM

R11 is what you'd make variable for a little bit of offset control. R12 doesn't make a difference in offset.

We each make our own decisions about samples. I don't take them because I am not going to make a production item, just like I won't test drive a Ferrari as much as I would love to see what it feels like. For $100 or so I can get a decent selection of devices to match...

Xandrell · 23rd February 2011, 07:12 PM

No^^

I mean i get some "samples" out of our stock

We produce sensors and bus-systems for automation industries. All parts which i declare as "samples" are parts from running systems

Xandrell · 14th March 2011, 08:23 PM

Well... Back again

First channel wired and what shall i say: It works^^ Runs @1A and gets hot (~50-60°C). Think that´s class a^^

Got some hum at the output... Very silent but it is there...

21st February 2011, 07:29 PM	#1
Xandrell diyAudio Member Join Date: Sep 2009 Location: Dortmund	Mini-A PCB finished... Some questions on it ;) Hi folks... Finally finished my layout of Grey´s "Mini-A-Schematic". Didn´t manage to make it one-sided The schematic can be found here in the forum. So... Are the trays thick enough? the "small" ones are 0,7 inch and the "big" ones are 1.5 inch. Greetz...

22nd February 2011, 06:16 PM	#4
BobEllis diyAudio Member Join Date: Sep 2003 Location: Upstate NY	Small signal traces don't need to be anywhere near that big. You can go smaller than shown for all traces except the ones carrying power in the output. Might even allow you to make it single sided, it you really need to. The feedback trace can be small, just the output trace needs to be anywhere near that big. Same for R18 to C2, etc. Move R16 much closer to the Gate of Q5 - like R14 and Q4. Try rearranging so the input differential can be back to back - good thermal contact promotes offset stability. BrianGT's board used a chunk of aluminum between teh devices but if you can get them connected (with an isolator and Isolated screws) it would be helpful. I don't have Grey's schematic, but I'll bet that there was a cap bypassing D1. A 1 uf film cap would be good, but you can go with a 10 uf electrolytic. Why the fish hooks around R20 and R21? Verify that the pads for your resistors are big enough to pass a lead through and still have something to solder to. Last edited by BobEllis; 22nd February 2011 at 06:34 PM.

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22nd February 2011, 05:32 PM	#2
Xandrell diyAudio Member Join Date: Sep 2009 Location: Dortmund	Sorry... I mean traces, not trays

22nd February 2011, 05:35 PM	#3
gruni diyAudio Member Join Date: Feb 2008	also, your traces arent .7 and 1.5 inch. that would be roughly 1.8 and 3.8 centimeters.

23rd February 2011, 03:09 PM	#5
Xandrell diyAudio Member Join Date: Sep 2009 Location: Dortmund	@gruni: You´re right I´m using Eagle. The traces are 0.07mil and 1.5mil. @Bob: Done Have a look at it... Moved R16, added C4 for bypassing D1, reworked some traces to delete those fish hooks. Thermal contact will be established bay using a 3mm thick copper bar and good thermal greese (about 7.2W/m*K). Think that shall work

23rd February 2011, 05:54 PM	#6
BobEllis diyAudio Member Join Date: Sep 2003 Location: Upstate NY	You mean 70 mil and 150 mil or 0.070" and 0.150" Looks better. I'm guessing that you plan to use the top of the board as a ground plane. You have plenty of room if you want to make it a bit more compact. The feedback trace R21 to R8 should be 70 mil. Same with the trace R21 to C2. I'm curious. Why did you choose to make R12 variable? Leave a pad to place a fixed resistor once you find a gain that works for you. It sets the active current gain. R11 sets bias. That's more often variable. There's still a fish hook at R9 R11. No big deal, but you could run the trace from C2 diagonally to R10 then up. Be sure that the holes and pads for resistors are large enough. Eagle defaults to some really small holes and very little pad around the hole. I've had troubles with resistor leads barely fitting, some brands have larger leads than the default holes. this means you'll end up editing your components, but you're in it to learn, right? Another thing that would make the board interesting would be to add pads for external output devices so you can make a larger Aleph if you want later.

23rd February 2011, 06:30 PM	#7
Xandrell diyAudio Member Join Date: Sep 2009 Location: Dortmund	Guess what... ^^ I´ll drill the holes for the parts min. +1/10mm everytime. That saves some room for changes with parts. And yes i´m still learning R12 is variable for setting DC-offset. Or am i wrong? Could bet i´ve seen this here around... I´ll first try this one as-is, experimenting around with some parts (capacitors, resistors and transistors from different manufacturers). When done testing and fooling around, i´ll maybe go on and make a design on an Aleph 30 (think this was the next "stage"). I don´t pay anything for the PCBs. So if i mind to change something, i´ll make it^^ Luckily the postman delivered some "presents" for me 25xIRF9610, 10xIRFP150 and a handful BC550C. Everthing for free. Did i mentioned that i´m also able to become some parts as "samples"? ^^ I´m in heaven for DIY XD

23rd February 2011, 06:45 PM	#8
BobEllis diyAudio Member Join Date: Sep 2003 Location: Upstate NY	R11 is what you'd make variable for a little bit of offset control. R12 doesn't make a difference in offset. We each make our own decisions about samples. I don't take them because I am not going to make a production item, just like I won't test drive a Ferrari as much as I would love to see what it feels like. For $100 or so I can get a decent selection of devices to match...

23rd February 2011, 07:12 PM	#9
Xandrell diyAudio Member Join Date: Sep 2009 Location: Dortmund	No^^ I mean i get some "samples" out of our stock We produce sensors and bus-systems for automation industries. All parts which i declare as "samples" are parts from running systems

14th March 2011, 08:23 PM	#10
Xandrell diyAudio Member Join Date: Sep 2009 Location: Dortmund	Well... Back again First channel wired and what shall i say: It works^^ Runs @1A and gets hot (~50-60°C). Think that´s class a^^ Got some hum at the output... Very silent but it is there...