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Part Sourcing Assistance/Advice Thread


n_maher

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Had an interesting convo with a luthier who is friends with Sam Zygmuntowicz (the most famous still living luthier in the US and the creator of the strad3d project). He asked if it was possible to design a piezoelectric setup to monitor pressure from the sound post to top plate and I said I don't see why not. I think I can implement a version of what I've been developing in my take on Krell autobias to forward to Sam for his measurements, so he can monitor in real time from anywhere. Anyone have any suggestions on a nice piezo resistor strain gauge for this purpose?

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1 hour ago, cspirou said:

I found a site that has some surprisingly affordable stainless steel CNC. I know that most enclosures use aluminum, but is there any particular reason why I shouldn't use stainless steel?

SS should be a bit more ridged but it's much more about the design of the mill than just the materials

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15 minutes ago, Kerry said:

SS should be a bit more ridged but it's much more about the design of the mill than just the materials

It's actually not milled but laser cut. I want to try to do something using T-slots

biased-box-corner-with-pettis-joints.png

It's at lasergist.com and they have 3 mm stainless steel available. 3 mm is also a common thickness for lasercutting wood so I could do wood first for prototyping before doing steel.

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On 9/18/2016 at 8:25 AM, DefQon said:

Here's what it costs from my source:

2SJ74-BL @ $0.90 each 
2SJ74-V @ $0.90 each 
2SK170-BL @ $0.90 each 

GR grades are a bit harder to get in bulk at an appropriate price but I'm trying to haggle another supplier for roughly the same as the above.

Anything going on with this? I would take 20 2SJ74BLs...

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9 hours ago, Craig Sawyers said:

Haven't heard anything since that post; but yes like you I'd be up for a bunch (provided they are genuine new old stock).

They are genuine, I've linked Justin, Kevin Gilmore to the seller but not sure if Justin ordered any lot from him. Two other hc'ers and 5 people from diyaudio have ordered from him and confirmed testing and working fine, excluding myself.

PM me for details because I don't want shit bag unregistered lurkers or somebody from China buying the entire lot if I post the link here.

Edited by DefQon
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BTW, I was curious as to why the BL grade of FETs seems to be more popular than the V grade, which has a higher Idss range? People seem to prefer BJTs with higher Hfe...


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Not sure what happened to the other post I wrote (on Tapatalk).
Why is the BL grade favored over the V grade (higher Idss). In BJTs it seems as though the higher the Hfe the better...


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The reason is power dissipation. Folks run the devices at full Idss and when you do that and look at the range of rails required to stay under SOAR curve, the V devices aren't preferred.



You can use V devices, but need to add degeneration resistors (which reduce voltage swing), which your design / layout might not have locations for.
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Yes, I obviously hadn't considered that aspect.

My main use would be in front-end stages (Dynalo Mk2 mainly, maybe Dynahi as well). Those seem to have enough emitter/collector resistors / current sources that it shouldn't be a problem, particularly if the V devices were in the BL/V overlap range (high end of BL Idss). I'll look at things some more before I decide whether to get some or not.

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In that case, you are loosing a ton of transconductance with that configuration in order to gain Vds. The question is whether the resulting Vds puts the device in is linear range (I assume so with KG's designs).



TL;DR A super high Idss puts Vds around 5V to stay within power dissipation limits which isn't a all that linear operating point for these devices. Adding degeneration resistors adds noise and reduces voltage swing.
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Yes, those were my target cap for the GRLV... and they have some in either 50V or 63V that will be perfect. Thanks!

EDIT: Noticed they have a $50 min order. I was only going  order up to 6 caps, ~$22. Hopefully I can come up with enough that they stock to fill out the balance.

Edited by Pars
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Placed an order with online components today.
Also noticed they have the MeanWell IRM-15-24 PSUs for the mini Dynalo2 for ~$8.50@, or $7.06@ in qty of 10-24. Considerably cheaper than Mouser, if someone wanted to do a group buy.


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