So it is...

http://b.j4cbo.com/temp/gbf2-brd.png

http://b.j4cbo.com/temp/gbf2-sch.png

So it is...

http://b.j4cbo.com/temp/gbf2-brd.png

http://b.j4cbo.com/temp/gbf2-sch.png

cool, a thing of beauty!

the input JFETs are not correct. They should be layed out just like the 7-zip packages.

So it is...

http://b.j4cbo.com/temp/gbf2-brd.png

http://b.j4cbo.com/temp/gbf2-sch.png

you really should move the feedback loop trace and connect it exactly to the output pad. same thing w/ servo although that's not as critical. id also add a LPF on the inputs, it was beneficial on the dynahi

Edited February 9, 200917 yr by justin

Basically, the input JFETs need to be just like the Vas duals, except the 4-pin side needa to be placed back to back (i.e. one rotated 90 degrees) and the pins 5mm away from each other. Like this:

-0-0-0-

0-0-0-0

--------

0-0-0-0

-0-0-0-

where the distance between the second row of text and the fourth row is 5mm.

you really should move the feedback loop trace and connect it exactly to the output pad. same thing w/ servo although that's not as critical. id also add a LPF on the inputs, it was beneficial on the dynahi

a LPF would also require recalculating the global compensation cap, right?

maybe but that would be also be a good reason to change all the labels to R1, R2, etc, or at least label the parts that could be changed that way

maybe but that would be also be a good reason to change all the labels to R1, R2, etc, or at least label the parts that could be changed that way

I think it would.

At least that was the case when I played with it on a design I've been working on. I found a good write up somewhere in the documentation for the Leech amp I'll find and post. I pretty much followed the concepts like a recipe and it worked perfectly. Also accounts for phase issues, though in a slightly less elegant way.

OK, board and schematic updated (same URL) with all the suggestions so far. I removed the part labels until I get around to fixing up the numbers and changing the labels to display part number rather than value.

I also changed the power rails on the bottom to be large copper planes, rather than wide-ish traces.

Looks good. I assume that is ground plane (top) that is not rendered?

What are the resistor package sizes? I guess I assumed when Marc (luvdunhill) asked for the 0.200" and 0805 SMD, that these would be in addition to an RN60D type footprint... guess not. That's alot of money to Texas Components...

My only other comment at this point would be that it is my preference for an input connector that it be a Molex KK 0.100 rather than the Phoenix blocks, but that is minor.

I would assume that the mounting holes match a Dynahi board, as well as the output device mounting holes? I measured 0.45" c-to-c on the output devices on a Dynahi board I had. Mounting holes were 4 9/16" and 3.5" c-to-c.

You're pretty fast with Eagle, aren't you I was trying to recreate your previous layout this weekend and only got about halfway done with it. And was glad I didn't have to determine component placement...

Just noticed a problem on the schematic. Per post 72 in the headwize thread, only one of the two FB points for should be used. On the schematic here, both are being used. I would think using the point between the two 5k resistors would be best?

[url=http://headwize.com/ubb/showpost.php?fnum=3&tid=6584&pid=59968&fpage=4]HeadWize: View Post [DIY Workshop

Hmm, now I'm trying to be sure of Kevin's intent for the feedback setup. The original HeadWize post discusses optional multiloop feedback, which would explain having the intermediate feedback point as well. I don't remember if I'd forgotten one of the two at first, and I don't have old versions of the layout on hand.

That said, it looks like Kevin's own version of the layout doesn't connect the intermediate point...

Kevin, can you clarify how things are supposed to be wired up? Should I add in a jumper so that the board can be used in different configurations, or is the multiloop feedback not to be used at all?

i havent seen the latest schematic but why would a jumper be needed? can you put in the resistors/caps for both feedback methods and then allow the builder to choose which to populate?

If I'm reading Kevin's board layout right, there's supposed to be 10k resistance between the inputs of the diamond buffers even if that's not used as a feedback point; in other words, on this, R24 and R25 (just left of center) should be present and in series together even if their midpoint isn't connected to the rest of the feedback loop. As I said, though, I'm not entirely sure what the intent was...

The feedback is EITHER from the output stage, or stage 2. Not correct as shown

in jacob's schematic above.

Or in multiloop, a resistor from the output stage to input- AND a resistor from

stage 2 to input-. Plus compensation cap on the output stage, and possibly

the second stage.

I never messed with the multi-loop, and the prototypes have feedback from the

outstage only.

Edited February 9, 200917 yr by kevin gilmore

for the 0.200" and 0805 SMD, that these would be in addition to an RN60D type footprint... guess not. That's alot of money to Texas Components...

heh. There are a lot of other (reasonable) 0.200" options out there, like the Phoenix 0.6W MRS (I think?) series and the blue Vishay series. You can also tombstone larger resistors. If this isn't all that interesting to people, now's the time to speak up.

Jacob: Can we remove the ground plane from around the output pad and up, so there isn't any chance of the L-bracket scratching through the solder resist layer?

For the large output resistors, I like the Panasonic ERX series, which are available in 1W-3W.

http://www.panasonic.com/industrial/components/pdf/AOA0000CE18.pdf

What are you thinking for the caps? Something like Nichicon UHE 50V, perhaps?

http://products.nichicon.co.jp/en/pdf/XJA043/e-he.pdf

I'd also add some film bypasses, something like Wima FKP2. There is a 10nF/63 DCWV that is PCM 5mm 5.5mmx7.2mm that might work well

heh. There are a lot of other (reasonable) 0.200" options out there, like the Phoenix 0.6W MRS (I think?) series and the blue Vishay series. You can also tombstone larger resistors. If this isn't all that interesting to people, now's the time to speak up.

Jacob: Can we remove the ground plane from around the output pad and up, so there isn't any chance of the L-bracket scratching through the solder resist layer?

For the large output resistors, I like the Panasonic ERX series, which are available in 1W-3W.

http://www.panasonic.com/industrial/components/pdf/AOA0000CE18.pdf

What are you thinking for the caps? Something like Nichicon UHE 50V, perhaps?

http://products.nichicon.co.jp/en/pdf/XJA043/e-he.pdf

I'd also add some film bypasses, something like Wima FKP2. There is a 10nF/63 DCWV that is PCM 5mm 5.5mmx7.2mm that might work well

I would favor RN60D footprint capability (mostly out of familiarity, but sonically also they are a known quantity).

heh. There are a lot of other (reasonable) 0.200" options out there, like the Phoenix 0.6W MRS (I think?) series and the blue Vishay series. You can also tombstone larger resistors. If this isn't all that interesting to people, now's the time to speak up.

DIYHiFi.org • View topic - Distortion in resistors

Might be pertinent to the discussion.

I would favor RN60D footprint capability (mostly out of familiarity, but sonically also they are a known quantity).

would tombstoning these resistors be acceptable?

I think this was mentioned before but how about a larger output pad?

heh. There are a lot of other (reasonable) 0.200" options out there, like the Phoenix 0.6W MRS (I think?) series and the blue Vishay series. You can also tombstone larger resistors. If this isn't all that interesting to people, now's the time to speak up.

I was planning on Roedersteins MK3s, and PRPs. I've always liked the BC (now Phoenix/Vishay) MRS and SFR series (0.4W and 0.6W), but only the 0.4W would fit a 0.2" spacing. I just replaced a pair of 100 ohm MRS on an I/V board with PRPs and could hear the difference (PRPs were better). So, being time to speak up, I am less than thrilled with this option. I know it tightens the layout up alot, but the tradeoffs are unacceptable to me. Tombstoning is not really acceptable either.

Do you know of any really good 0805 resistors that aren't an arm and a leg pricewise? I know that some of the stepped atten. manufacturers think the resistors they are using are better than the leaded ones they used to use, but I haven't seen anyone identify what they are using.

Do you know of any really good 0805 resistors that aren't an arm and a leg pricewise? I know that some of the stepped atten. manufacturers think the resistors they are using are better than the leaded ones they used to use, but I haven't seen anyone identify what they are using.

I like Susumu and the KOA RK73A. I believe both DACT and Goldpoint use KOA resistors.

I like Susumu and the KOA RK73A. I believe both DACT and Goldpoint use KOA resistors.

The PRPs we used on the Pearl sound good too!

I guess whatever sounds good, is easy to source, works with the board layout, and is not outrageously priced is ok with me.

Looking again, it seems like adding 0.3" spacing as well wouldn't be too hard, which would allow most 1/4w resistors to fit. RN60 would still be out, but RN55s should fit fine.

That said, I'd still recommend surface mount

Looking again, it seems like adding 0.3" spacing as well wouldn't be too hard, which would allow most 1/4w resistors to fit. RN60 would still be out, but RN55s should fit fine.

That said, I'd still recommend surface mount

Showing my ignorance: would the surface mount resistors be something that can be soldered by us, or come already machine soldered on the board?