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Old 14th December 2008, 08:53 AM   #21
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You know I have read that but I guess it didn't really stick. The reason is he goes into detail about how adding caps after the rail splitter can have adverse affects. Then generally says not to do it. Thats right after he said that he had to do it in the MINT.

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An active virtual ground circuit has some "bandwidth": that is, it will be effective over some range of frequencies. If you put capacitors across its output, that lowers its bandwidth: as frequency goes up, the capacitors are "in charge" to a greater and greater extent. If the caps are large enough, the virtual ground circuit's bandwidth is completely swamped. It could end up being good for no more than maintaining the DC level of virtual ground.
I thought that was the point anyway?

He cautions about it possibly causing the TLE to become unstable.

Quote:
Another potential problem with big caps on the output of a virtual ground splitter has to do with stability. Some circuits will become very stable in this situation: no bandwidth and no gain, hence no oscillation. Most circuits aren't made to cope with capacitive loads, however. They become less stable when driving a capacitive load. Study the datasheets for the ICs you will be using. Unless they specifically tout the fact that they can drive large capacitive loads, beware of using them in virtual ground circuits.
He doesn't really say what kind if capacitive load the TLE2426 can handle. However, in the MINT amp he has 330uf caps after the splitter. I had planned on using 100uf caps. Should those be sufficient to keep the TLE2426 in the safe zone in this circuit?

I had planned to use OPA2132 and OPA2227. The latter possibly consuming more current.
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Old 14th December 2008, 09:19 AM   #22
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Those comments don't apply specifically to the TLE2426 - generally, it's fine about driving a capacitive load. He's saying that it can be an issue when "rolling your own" with a buffered resistive divider using certain opamps.

Actually, I'm sure the TLE doesn't mind the capacitive load, the PIMETA is set up with the caps after the splitter, and I've got one here with 4 x 470uF, 2 in parallel on each rail.

100uF is probably sufficient to handle transient current demand, but if you can fit 330 in the required footprint, I'd go for it.
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Old 18th December 2008, 12:06 AM   #23
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I made a few changes to the ground trace. I'm not really sure if this is better than it was before. It seems to me like it would be, but I'm no expert. Now the IG, OG, TLE, and rail caps have a dedicated trace. The caps are connected to the ground plane via thermal.

I haven't bothered trying to jump the gun on ordering these things. It's not like if I ordered tomorrow I would get them any time soon due to the holidays. Batch PCB isn't exactly the fastest as it is.

If you guys see any potential problem let the critique fly and I'll get back to work.
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Old 18th December 2008, 03:26 AM   #24
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Hmmm....if you're going to follow that path, maybe only have the trace connect to the plane at a single point, so it all sort of forms a star ground - I'd suggest the input ground pad as the place to do it.
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Old 18th December 2008, 12:41 PM   #25
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I'm pretty sure this is what you meant. Now I have moved the thermal connection to the IG point only.

I want to thank you guys for all your help. I have learned a lot since I began this endeavor.
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Old 18th December 2008, 06:05 PM   #26
gfiandy is offline gfiandy  United Kingdom
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Hi,

With the connection you currently have the input groung and the output ground share a track back to your star point (the pin on the ground splitter).

You want the output ground to have its own track to the pin on the ground splitter and the input gound plane to have a seperate track to the pin on the ground splitter. So no copper is shared by the ground return currents from the output and the input signal grounds.

Regards,
Andrew
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Old 19th December 2008, 12:09 PM   #27
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OK, I removed the trace from IG to OG and added a thermal connection to IG. I added a 20mil thermal connection to the ground pad of the TLE. Now the two ground should have a separate route to the Voltage divider.
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Old 22nd September 2011, 11:39 AM   #28
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How did this go?
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Old 22nd September 2011, 11:25 PM   #29
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It went fine magnum. I had four of these made and built them all.

What I learned.
1. The rail splitter is a bad idea. Real ground is best.
2. Air wired in/out and pot is absolutely the way to go. After trying to case up some JDS boards recently, I knew I had made the right decision with my design. You DON'T want board mounted connectors for an amp designed to be cased in a mint tin. Save that for your CNC routed front panels for real amps.
3. I guess everyone builds a C-moy as a first project. It was actually my second. I built a headbanger as a first project and I feel that is is actually the better amp in many ways. Its clarity and presentation can't compete with the C-moy, but it's usability far outweighs that.

There is basically no opamp on the planet that can do what a C-moy asks of it. The C-moy is a preamp. You can make it drive phones if you want. It will never be right for that. It is an excellent gain stage. It will require a buffer to drive anything substantial. You see people telling me exactly that throughout this thread and in others of the same subject matter.

My head is hard. I'm telling anyone willing to listen. Don't build a C-moy as your first project. Build some version of an A47 and you'll be way better off. It's just as easy as a C-moy and miles ahead.
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Old 23rd September 2011, 12:40 AM   #30
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Rail splitter ICs like TLE2426 are best used just to create a reference, midpoint voltage, like in a Pimeta where your ground return is a separate channel, or A47 where there's still a buffered ground.

Opinions will vary but I see no reason to build an A47 unless someone has extra opamps lying around. I mean, it is a significant step better than a CMOY, but skip the 2nd opamp in A47 and put a push pull discrete buffer within the feedback loop. It's not many more parts, about same, sometimes less expensive than a 2nd *good* opamp, and IMO, sounds better as well as greatly increasing current capability (depending on transistors chosen), giving bass an effortless appearance and treble more definition.

Last edited by !; 23rd September 2011 at 12:48 AM.
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