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M³ Project Announcement - Page 22

post #316 of 565
12/29/04 at 3:00pm
Quote:
Originally Posted by z2trillion
I'm just wondering, if you only used the pot for the bass boost, wouldn't bad things happen if the wiper on the pot lifts?
With a semi-decent pot like the Alps Blue, how often does that happen?
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post #317 of 565
12/29/04 at 3:45pm
I have no idea, but tangent mentions the possibility several times on his page. If it does lift, wouldn't it lead to a headphone frying dc offset?
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post #318 of 565
12/29/04 at 3:58pm
Thread Starter 
Quote:
I'm just wondering, if you only used the pot for the bass boost, wouldn't bad things happen if the wiper on the pot lifts?
No. Look at the schematic, or the layout for that matter, and you will see that the pot is wired end to end with the wiper shorted to one end, so if the wiper should lose contact, the pot is still in series with the circuit, resulting in maximum bass boost, but no DC offset problems.
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post #319 of 565
12/29/04 at 4:16pm
Indeed, I should pay more attention to such things. Thanks for your help.
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post #320 of 565
12/31/04 at 7:31am
Just wanted to say that it's looking really good!

One question - how hard is it to implement an additional treble boost option, just like the bass boost option? Will it be very difficult? Looks like there's enough space on the board for an extra Alps Blue.

I feel like for some phones - in my case, the HD650s - would benefit greatly from some sort of a variable treble boost instead of bass boost. Simply boosting the treble by a bit on my PC with software EQ makes the cans really shine, so I was sort of missing that feature on my PPA with only an adjustable bass boost.

I've been dreaming of someting like Meier Audio's implementation of treble and bass boost on their Prehead MKII for a while now...

(sorry if this has been asked before)
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post #321 of 565
12/31/04 at 7:57am
Quote:
Originally Posted by doobooloo
One question - how hard is it to implement an additional treble boost option, just like the bass boost option? Will it be very difficult? Looks like there's enough space on the board for an extra Alps Blue.
That would require more parts and traces in the amp's feedback loops. We can't fit that into the current pcb layout without major restructuring and increasing the board size. Moreover there isn't enough space for another Alps Blue. The "empty" area by the M³ logo is a "no-fly zone" to clear headphone jack(s). The bass boost option is very simple so we threw it in there, but I feel that adding treble boost would compromise the quality of the amp.

I dunno, I have a pair of HD600s, and agree that they aren't as bright and sparkly as, say, the Grados; but I think the sonics of the Senns are actually very natural and fatigue-free to listen to for a long time.
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post #322 of 565
1/1/05 at 9:52pm
Is it just possible then to just create optional pads to connect an Alps Blue externally (or just resistor pads like on the PPA) but be able to mount caps on board?
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post #323 of 565
1/2/05 at 8:37pm
Quote:
Originally Posted by doobooloo
Is it just possible then to just create optional pads to connect an Alps Blue externally (or just resistor pads like on the PPA) but be able to mount caps on board?
At this point we're not going to cram any more parts and traces onto the pcb for treble boost. I suggets waiting until this amp reaches "production" and listen to one before wanting treble boost. With AD8610 opamps it might be just right. If you still want more treble I think the best thing to do is to use a good preamp with tone controls.

We are taking a "purist" and KISS approach with this amp, in that the focus is on quality rather than loading it up with features. The bass boost option is there only because it adds very few parts and some headphones do need a bit of help at the low end. If I were building this amp for my own use I'd actually skip the bass boost feature because I find it unnecessary with the HD600s.
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post #324 of 565
1/2/05 at 8:49pm
OK. Thanks for the response amb!

I can't wait to hear the amp!
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post #325 of 565
1/4/05 at 3:02am
Thread Starter 
We ordered prototype pcbs, they should arrive by the end of the week.
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post #326 of 565
1/4/05 at 6:10pm
Congraduations, very exciting!
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post #327 of 565
1/11/05 at 4:29am
Thread Starter 
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post #328 of 565
1/11/05 at 4:30am
Thread Starter 
M³ v022
removed test pads
enlarged output resistors to 200×600mils
removed extra output pads
moved D1 to make room for Molex power connector
rearranged capacitance multiplier away from input pads
reoriented labels

The prototypes arrived. The only mechanical issue was output resistor fit, which has been addressed in v022. It will take us a while to assemble the prototypes and conduct electrical and listening tests. We will let you know when we have news to report.
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post #329 of 565
1/12/05 at 6:36am
Could you post a picture of how the physical PCB turned out?
Was it 0.18 that you made for prototype?
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post #330 of 565
1/12/05 at 6:51am
Quote:
Originally Posted by morsel
M³ v022

reoriented labels
I was just going to tell you that it's smart if you can see the labels when the parts are there. Don't forget to have polarity signs also visible. This will be a good help when checking the pcb and that parts are located right.

Otherwise it looks good, Morsel.


The picture below is just an example of what I mean. Check the LED, and the big caps for instance. I have also marked interesting nets like C, A, R in my case. This just for making it easier if an another refrence is used.

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