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| Using a rotary switch for crossfeed will reduce real estate and multiple switches. |
The issue isn't "rotary vs. toggle", it's "crossfeed on the board or not". Among the current PPA team, the consensus is "not". Therefore, the current idea is to maybe have a META42-like situation where there's a daughterboard you mount on the PPA board that adds crossfeed. I had in mind to float it over the input pads at the rear of the board, so the RCA jacks go instead to the crossfeed board, then make a short trip through the crossfeed and then down to the PPA's input pads.
I still like the modified Linkwitz crossfeed design, and you can use rotary switches with it if you want, as discovered by Scott Lindeman. I'm considering making a new modified Linkwitz board especially for the PPA to allow boutique caps and with wire pads labelled to use one of Scott's rotary switch schemes, probably the simplified one. (See the
META42 crossfeed page if you don't know what I'm talking about.)
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| The thought of multilayer PCB. (this is leaving the realm of DIY) |
Since the idea is for me to have the boards manufactured, and not to provide files for people to etch their own boards, what does it matter how many layers there are, from the DIYer's perpective? You still plug components into holes and solder to pads on the outside layers, just as with the META42. What's the difficulty?
The real issue is whether it's worth the cost or not. It means we have to buy 4-layer CAD packages for all those hacking on the board, and it means the cost of the board goes up by at least 2x, and more if we get the boards tested. Automated testing of the boards is very tempting for 4-layer boards since you can't just look at them and tell that there are shorts or breaks.
The benefit is that we could add better shielding and such to the board, so channel separation would be better.
So given all that, would you be willing to pay 2 or maybe 3x more per PPA board if it were 4-layer vs. 2-layer? We're happy to consider the idea if people think it will be worth the cost.
One thing to note, though: we already have a working design on 2 layers with no vias so far. We don't absolutely
need 4 layers to succeed.
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| The use of Elna Caps, They are extremely difficult to obtain. |
We're not telling you to use ELNAs. We're telling you that they fit, if you want to use them. Use Black Gates, Nichicons, Panasonics, whatever strikes your fancy.
What we may say "no" to is designing the board so that only one particular rare cap makes sense in the board. We'd have to have a compelling reason to use that cap, like C4 on the META42. And if we do that, I'll again provide access to the part, just as with the META42. This isn't to say that people should feel free to request any strange part they might want and know that Tangent Will Provide, but we will at least consider the merits of rare parts.
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| Incorporate Hi Z and Lo Z output jacks. |
Several thoughts on that:
1. None of the current PPA team members are in favor of anything but 0 ohm output impedance, for most headphones. The only argument in favor of a nonzero output impedance that I can get behind is a 75 ohm jack for Ety-4P users who want their phones to sound like 4Ses.
2. If you just want a single nonzero Z output jack, you can easily wire the extra resistors inline with the wires going from the board to the jack.
3. If you want two output jacks with different impedances, it's the same situation, but you jumper from one jack to the other at the panel, adding resistors as necessary.
4. You'd have to use a smaller jack than the ones we have in mind (Neutrik NJ3FP6C) in order to fit both jacks on the panel of a Eurocard-size enclosure.
The thread running through all these points is that this is a nonstandard configuration. We won't try to stop you from doing one of these setups, but we aren't going to add stuff to the board to make it easier to add these features, either. It's easy enough as it is, given how rarely we expect these features to be used.
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| Do you intend this design to be less user-configurable than the META42? |
Nothing's stopping you from populating a PPA with wildly different configurations, just as you could with the META42. I'd say they're similarly configurable. But, what we do intend to do is make it clear in the docs that certain configurations were arrived at with painstaking research and that you should stray from them only at your own peril. At the same time, I don't want to be in a position to say, "that's not a PPA you've built because it doesn't use our exact resistor values".
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Why not? Since it's finely tunable if you like the idea and 100% defeatable if you don't, there's little reason not to add it, since we have the space.
The idea is for the bass boost to compensate for bass-weak headphones or bass-weak recordings. It's not to pull a Sony move and get throbbing bass from a violin concerto.
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| Tangent is selling the Alps Blue |
Ummmm, sort of. I have surplus and I have been known to sell a few on the side, but I'm not providing them explicitly on my orders page. Until I do that, you can't really say the question of availability is answered, since I don't currently want to be in the pot distribution business. (Hah ha!) Seriously, these little things are too expensive and too hard to get for me to go offering them on a high-volume basis.
We should indeed consider alternate volume controls for this design. I think low-end pots like the Panasonic EVJ are totally out of the question for this amp. What does the Head-Fi public think of the idea of using the Nobel 25mm pot from Michael Percy, or perhaps adding pads for one of the cheaper stepped attenuators? (DACT, TKD...)
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| Maybe all that matters is that it's easy to carry around, not that it will run on rechargable batteries. |
I for one intend to build a PPA with a rechargeable battery setup, and live with the size of the amp. I will also be building at least a few wall-only ones. That's what I like about the PPA design as it currently is: the ability to have excellent sound on the go if you want, yet not be limited w.r.t. sound quality when you don't mind being tied to a wall outlet.
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| I guess I'm a little disappointed that there has to be such compromises in the design. |
From one who has actually listened to the PPA: it ain't too shabby already! Sure, it could be even more over-the-top, but the PPA's place in the world will be useful anyway. The impetus behind the PPA is all these people making META42s that push that design so hard that they're deep into diminishing-returns territory. What you really need instead is a new design, not to keep putting ever more exotic components into such a small, portable board. The PPA is that new design.
After the PPA gets going we can talk about a completely unportable design. I still wouldn't presume to say that such a thing could be made without compromises. Morsel's right -- no amp design is without compromises.
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Not at all. I'm sure a great many PPAs will be used as wall-powered amps. Remember, it's about the size of a large brick, if not quite as heavy. Not everyone will be willing to lug that big an amp around. So, imagine that you're sitting in your listening room, rockin' out to some great tunes on some great, comfortable headphones, the phone rings, and you unthinkingly get up to answer it, yank on the cord, pull it out halfway, curse, have to go answer the phone anyway and tell the caller to hang on, then get back to the amp to either unplug the phones or plug them back in. This whole sequence has taken long enough that the buffers could be killed.
Jan Meier chose to go with 1/8" jacks in his HA-1 to solve this problem, but that was an unpopular decision. People want 1/4" jacks on higher-end amps. Thus the choice: add output protection, current-limit the power supply, use locking output jacks, or none of the above and laugh cruelly at those who burn their buffers?
....i have the feeling they are already changing their mind about portability..
