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M³ Project Announcement - Page 12

post #166 of 565
9/9/04 at 1:32pm
Thread Starter 
DACT CT2 are $51 each for 100. This eliminates Elma as a contender.



TKD 2CP-2500 are ¥3000 or $27 each for 100. These are not stepped attenuators, but are perhaps the finest pots in the world, with true log, 90dB cutoff, laser trimmed conductive plastic tapers. See the picture below and read the THEL Audio World description for more detail. (edited: CP-2500 is single gang)

THEL Audio World Pots (in German)
THEL Audio World Pots (Babel Fish translation)



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post #167 of 565
9/9/04 at 2:03pm
Quote:
Originally Posted by morsel
DACT CT2 are $51 each for 100. This eliminates Elma as a contender.
That's a great price.

For the amp, I'm liking the TKDs. Is that price for a dual?

I don't think you can go wrong with either choice.
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post #168 of 565
9/9/04 at 6:48pm
Quote:
Originally Posted by morsel
DACT CT2 are $51 each for 100. This eliminates Elma as a contender.
That sounds very interesting, Morsel. If you want I'll go and pick them up after the order is placed


/U.
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post #169 of 565
9/10/04 at 9:39am
That's an amazing price. Although it represents a $5K plus outlay, I have a feeling that 100 people would be willing to spend $50 on an attenuator that normally sells for $150-$180. Considering the switch alone is $38-$50, then you need to buy a pile of resistors and solder them, it's even a good alternative to building one.

This is really more a topic for a seperate thread, I think. What a good price though. Look at how many people chipped in on silver wire- that order was significantly larger than this one would be. /hmmmm
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post #170 of 565
9/10/04 at 9:59am
At this price, I don't think selling 100 would be much of a problem


/U.
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post #171 of 565
9/10/04 at 12:59pm
Thread Starter 
Andrew: You were right, I did not specify stereo to TKD. I edited the previous post to correct the model number and price.

VC: Actually this directly relates to M³ as AMB will have to provide stepped attenuators with the board if we are going to incorporate them. Also keep in mind the prices I was quoted do not include shipping, handling, insurance, and other fees either from the manufacturer to AMB or from AMB to the end user.
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post #172 of 565
9/10/04 at 2:06pm
I realize that... I meant that you would likely have more than enough interest even outside the scope of this project to be able to move 100 attenuators- even if they were $60 or $65 each. I can't stop smiling when I think about it!
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post #173 of 565
9/10/04 at 5:47pm
Quote:
The resistors were added to the PPA to shorten the high frequency current loop to keep it confined within the smalest area around the op amp power rails. Do not confuse power supply decoupling as we are doing hear with the simple Bypassing used in PPA version 1.0. with just simple Bypassing the actual PCB foils can become inductors and actualy hearting stability by creating a high impedence L/c Tank circuit tuned well up into the RF range and probaly lower in frequency than the unity gain bandwidth of your chosen op amp thus allowing the entire circuit to oscilate at the Tuned L/c frequency. Simply adding this small resistor kills the "q" Factor of any possible L/c tank and maintains stability. Granted quality RF grade capacitors of at least 0.1uF is min and bigger would be evean better. The Wima and BC component polypropylene types have less than 10 nH of inductence and this is added to any PCB foil's inductence.

True the JFET isolation technique is more effective up to the point that Criss takes over however this is still farly high in frequency. My Battery operated reference trravaler that the PPA style isolation technique was first used on employed all three methods of isolation the two used on PPA v 1.1 in addition to a Capacitence multiplier.
I almost never disagree with you but I do on this point. Adding that resistor will increase the output resistance of the opamp and what's worse, it would inject the signal into the rails at the opamp (as the variable current will modulate the rail voltage through that large resistor (10 Ohm is large in this case)). It may not make much difference in this case as they don't drive a low impedance load but still. True, it would insulate the big capacitor(s) (since on the schematics you have a big cap before the resistor, then "small" cap at the opamp after the resistor)from the possible parasitic RLC loop, but my understanding is that the big capacitor is never the problem anyway - it would create resonance at relatively low frequencies, and there the small capacitor (film, ceramic) would have much lower impedance anyway (big ones usually have comparatively large resistance), so the loop would close through the small one instead. That's one of the reasons two caps are used. Now if you add resistor BEFORE the bypass capacitors, then it all acts as a filter, just like what FET does but less efficient.
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post #174 of 565
9/17/04 at 3:50pm
Thread Starter 

Bay area Grado and Sony lovers wanted for M³ testing

Team M³ seeks high end Grado and Sony 32 Ohm headphone lovers for listening tests. We are looking for people with outstanding hearing (hopefully still in your 20s) to visit us in Sunnyvale, California. Bring your headphones, favorite amplifiers, and music. Send amb or morsel an email if you are interested.
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post #175 of 565
9/17/04 at 7:24pm
That almost makes me want to cry. My Grados and I are in cloudy southern Idaho

-Drew
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post #176 of 565
9/18/04 at 2:17pm
Are there any interim updates, with potential decisions (P/s, casing, pseudo parts listing)?
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post #177 of 565
9/18/04 at 3:07pm
Thread Starter 
We are busy testing various aspects of the prototype, conducting listening tests, and drawing draft layouts.

I created a DACT CT2 part and discovered much to my dismay that when overlaid with an Alps Blue such that they are both flush with the panel, the Alps rear wiper pad overlaps the front DACT wiper pad, so only one of them can have mounting holes for board mounting without a shaft extender. It would be too wasteful of space to have them side by side.

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post #178 of 565
9/18/04 at 3:46pm
Quote:
Originally Posted by morsel
I created a DACT CT2 part and discovered much to my dismay that when overlaid with an Alps Blue such that they are both flush with the panel, the Alps rear wiper pad overlaps the front DACT wiper pad, so only one of them can have mounting holes for board mounting without a shaft extender. It would be too wasteful of space to have them side by side.
My feeling is that the ALPS blue will probably be the more popular choice amongst builders simply because the DACT is several times its cost (~$16 rather than ~$65+). As such, we should lay out the PCB for direct-mounting of the ALPS and provide a second set of pin headers not far from where the rear of the DACT would be (for hand wiring to a DACT or other models of pots or stepped attenuators). A short run of wires is easier to deal with shaft extenders, and should not adversely impact performance. I'd like to hear what your opinions are about this.

Moreover, the TKD 2CP2500 has large solder tabs which makes it incompatible for direct board-mounting (ExpressPCB does not allow flat slots, so we'd have to use some huge holes to clear those tabs, and soldering the tabs to such holes is not going to be pretty. I don't think Morsel has tried creating a part in ExpressPCB for the TKD yet, but my guess is that it might also conflict with the ALPS. Thus, having the pin headers will also allow the TKD to be hand-wired.
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post #179 of 565
9/19/04 at 2:54am
Thread Starter 
We are considering a smaller, cheaper heat sink, the Aavid 504222.

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post #180 of 565
9/19/04 at 1:26pm
This might have been mentioned already, but would the smaller CP601 work in the place of the CP2500? It appears to have leads that would enable it be mounted to the pcb more easily. Is this a possibility, or is the CP601 inferior to the CP2500?
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