the Pimeta-V2 thread

[linuxworks]

obligatory update pics

yes, its funny looking.

you got a problem with that??

it sounds quite nice. I like it a lot. even on a single 9v battery (which is what its running on now, inside the lower box) its great.

 

[tangent]

Quote:

Originally Posted by joneeboi /img/forum/go_quote.gif Wow, I can get used to this much bass.

Yeah, there's something very clean about this style of bass boost, as compared to other implementations. (A typical graphic EQ or tone knob, for instance.) These new buffers help a lot, too, I think.

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The bass sounds great to me, so I have little impetus to get it "just right."

What cap value did you use || R4?

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R4 is absent. I have the amp set up in unity boost.

You certainly should have an R4. Unity boost needs it. If you're misspeaking and what you've left out is the equivalent of the PPA's R7, that's fine, but R4 isn't optional. If you really did leave it out, that would explain the DC offset, because you would then have no DC feedback path when bass boost is engaged.

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LM7818. Here's the different part for me....I don't know if tangent plans on incorporating this into the next design, but it can be done with this revision of board if you so desire.

It's not clear to me what you're doing with this.

The LM317 in the PIMETA v2 is officially only for charging a NiMH battery, as it's configured as a constant current source. Since I've not heard of using an LM78xx as a CCS, I'm guessing you're using it for its intended purpose, a voltage regulator. I don't immediately see how you're doing that, so if you could post a hacked copy of the PIMETA v2 schematic showing your connection changes and any trace breaks...?

One of the things I have tried to work out is a way to change the LM317 from a CCS into a voltage regulator with the same board design. I haven't figured that out yet, but may revisit it before the final design push.

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Thanks, tangent, for including me in the proto group. I really liked the card. Classy.

You're welcome, and thank you, too.

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Originally Posted by linuxworks /img/forum/go_quote.gif r7 goes from old of 10k to new of 100 r4g goes from old of 4.7k to new of 4.32k c6g goes from old of 10pf to new of 4.7pf (I have not done this one yet)

Yes, those are the important ones.

The R11 calculation changed since the 2.00 days, though the schematic doesn't show it.

RBIAS changed from an unrealistic 3K to 5K. 2.5K can work, but doesn't give you as much adjustment range as you might want. RBLIM changed at the same time for related reasons, though there's no reason to change yours if your class A is adjusted the way you want now.

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lesson: don't get power supply problems and you won't have to fix circuits downstream of them!

Yes. A berserk power supply can ruin your whole day.

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Originally Posted by joneeboi /img/forum/go_quote.gif Where was R4G mentioned? Why was it changed?

Don't worry about it. The new value is just slightly more correct. It won't really affect anything.

Quote:

Originally Posted by linuxworks yes, its funny looking.

I made a double-decker amp once, not entirely unlike that. Two mint tins glued back-to-back so I could have a spacious amp circuit in one and 2 x 9V in theother.

 

[joneeboi]

I have 0.1uF and 0.22uF paralleled with 50K for my bass boost. I was misspeaking earlier: you can't call my implementation unity boost. I left out R4, but I still don't see any DC. There was DC before I installed BB, so I will have to run some more tests later.

For the power supply, I did use the LM7818 as a voltage regulator. I had to add two jumpers, but for the most part, it's a simple change. I hope the schematic is clear.

 

[tangent]

Quote:

Originally Posted by joneeboi /img/forum/go_quote.gif I left out R4

I still don't see how you can get away with that. That opens the op-amp feedback loop at DC. You still have feedback for music, since the caps are kicking in. Also, R4 is a fundamental part of the bass boost filter equation: no R in parallel with the C == no boost.

Or am I still just misunderstanding what it is you're doing?

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For the power supply, I did use the LM7818 as a voltage regulator. I had to add two jumpers, but for the most part, it's a simple change. I hope the schematic is clear.

Yes. It tells me that this really isn't something we can just offer via a jumper or something on the existing board. I may document something like this in the tweaks section, but what I was hoping for is that someone could solder an LM317 in the IC1 position, and with just a jumper or two on the board, reconfigure it as a voltage regulator instead of a current regulator.


By the way, I finally got the benchmark pages up:

RMAA tests
square wave tests

Whew! Lot of work in those pages.

This puts us very near the end of the development process. This was the last major thing left to-do, along with deciding about the vreg issue. Is my TODO list missing something, or am I pressing the button on Monday, after spending the weekend staring at Gerbers?

 

[joneeboi]

Quote:

Originally Posted by tangent /img/forum/go_quote.gif I still don't see how you can get away with that. That opens the op-amp feedback loop at DC. You still have feedback for music, since the caps are kicking in. Also, R4 is a fundamental part of the bass boost filter equation: no R in parallel with the C == no boost. Or am I still just misunderstanding what it is you're doing?

The caps are paralleled with the potentiometer.

edit: I'm so sorry, I was talking about the PPAv2's R4. I don't have that R4, but I do have the PIMETAv2 R4 as the potentiometer.

 

[cobaltmute]

Ok after many weeks, I've finally been able to spend some time working on the Pimeta2 and my biasing issue.

Replaced all the CCS transisitors and replaced R7 as 100Ohms as tangent suggested. Significantly improved the situtation. I am now able to run at 20V supply and have the bias up into the fairly deep rang (~11mA) with no issues. I can still reach a runaway point if I keep biasing, but I think I should be fine where I am

Now on to building the battery pack and casing.

 

[sandbasser]

joneeboi -

Is there any chance you could post a photo or two of your board??? I like the idea of the LM78xx; but I couldn't figure out how to implement it.

Many thanks,

 

[tangent]

v2.01 final?

Changes since the v2.00 prototypes:

- Changed RBIAS part to one with centered pins instead of offset

- Inserted a pair of wire pads in series with RBLIM to make switching bias on and off easy. The pads are inline so you can just jump over this with the resistor leads if you don't want this feature.

- Labelled B+ pad between C2 caps

- Several minor value changes on the schematic, described above

I expect to send this off for manufacturing tomorrow, barring any last-minute changes. This will take about a month, barely letting me slide under my "summer" deadline.

Thanks to everyone for participating in this development process. The PIMETA v2 is better for it!

 

[cobaltmute]

Pimeta1 on the left and Pimeta2 on the right. They are variations on a theme - 12x AAA in the case with the power for the trickle chargers coming out of the right side of the case.

v1 is running OPA2107/OPA227 with Monofied Sijosae buffers in LR and Buf634 in G. Bias is 3-4 mA if I remember correctly.
V2 is running OPA2107/OPA602 with spec buffers. Bias is 11mA.

Both sound very good. When switching back and forth between the two, I notice that the v2 is slightly brighter in the mid to high end. It is not fatiguing, and I have been listening to it for a while now.

Took me a while, but I got there in the end. Thanks Tangent.

 

[tangent]

Still about two weeks of summer left!

 

[funch]

Slightly off-topic, but why does Internet Explorer abort my attempt

to go to his store page?

 

[Reima]

Quote:

Originally Posted by funch /img/forum/go_quote.gif Slightly off-topic, but why does Internet Explorer abort my attempt to go to his store page?

It does the same thing to me.
RC

 

[tangent]

EDIT: It turned out to be an IE6/7 bug. IE8 and all other non-IE browsers coped with the new image popup feature on the shop page just fine. I've changed it to work on all browsers. But y'all might want to upgrade, too.

 

[cobaltmute]

Ctrl+Shift+F5 will force the browser to reload the page skipping the cache.

Congrats on finally getting the boards into the shop.

 

[Juaquin]

Quote:

Originally Posted by tangent /img/forum/go_quote.gif EDIT: It turned out to be an IE6/7 bug. IE8 and all other non-IE browsers coped with the new image popup feature on the shop page just fine. I've changed it to work on all browsers. But y'all might want to upgrade, too.

Might I suggest the Kill IE6 information bar?

I'm only half kidding. While that's a bit extreme (I use it on my site, but that might drive some people away...) there are serious security risks when using IE6 and IE7, people. Especially when using those browsers to process transactions and credit card info. Upgrade to IE8, or better yet, Firefox or Chrome.

Back on topic, the new board looks awesome and I'm doing one as soon as I finish the other couple projects I'm working on.