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New DIY Altoids Tin Amp - The Pocket Class A "Wintergreen Handwarmer" by xrk971
Jul 28, 2017 at 12:17 PM Post #421 of 468
stellarelephant said:
Yeah, great review Sodacose. It reads as very balanced, and full of useful descriptions and comparisons. Glad you agree that this amp rocks. Why isn't the link working anymore?
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Weird, I don't know what happened with the link but I just fixed it. Might have been an edit that screwed with the address or something.
 
Jul 28, 2017 at 1:49 PM Post #422 of 468
Ok, ok, ok... I just built up a new amp with FR 1000uF 25v outputs - no film bypass. On inputs I am using 10uF 35v Silmic II no film bypass. I wonder if this will color the sound signature to that of Silmic? Listening right now - no problems driving my 16ohm KZ ZS5 IEM's (106dB). Bass is full and deep for 1000uF. I am trying to see if I can hear a difference in treble detail. Hard to tell. May have to get out my A/B switch box. The sound is very nice overall though. I am pretty convinced that film bypasses are not really audible now when using good electrolytics to start with. Running 62mA bias current, source is just my phone at present. So real test will be FLAC running 192kHz 24bit files with A/B switch box. More to come....
SN022-FR-Caps.jpg
 
Jul 28, 2017 at 6:19 PM Post #423 of 468
Man, that one looks snazzy.^ Wish I'd bought a white LED for mine! X, if I had to pick one word to describe you, it'd be "prolific."

I imagine you will hear a significant difference, especially with those supertweeter-equipped IEMs you just picked up!
Still, the overall result ought to differ some from what I'm hearing, since my latest impressions are based on the amp with PPS input caps. I feel these add significant treble transparency themselves.
 
Jul 28, 2017 at 10:55 PM Post #425 of 468
xrk971 said:
What's the Mouser/Digikey part number for the PPS stack you made?
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Haha, I was hoping you'd ask!
SMDIC03680TB00KQ00

Heads up: When soldered in, my pair of PPS stacks extend about 2mm past the pot housing, towards the center of the board. Fitting 10mm rail caps and 10mm output caps is no sweat, but 10mm + 12.5mm pushes my rail cap slightly over the board's long edge. I think fitting batteries in the tin will be a little harder.

I thought of a way to save about 1mm of space by soldering two leads on with an offset:
Top is what I did. Bottom is what I'll do next time. :)
Screen shot 2017-07-28 at 10.50.36 PM.png

Oh yeah, and if you use these, be sure to take some sandpaper to the inside plastic edge of the input jack housing so that the caps can slide in there.
 
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Jul 29, 2017 at 12:14 PM Post #427 of 468
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Jul 29, 2017 at 2:26 PM Post #429 of 468
xrk971 said:
Ok $6 per cap is better but cost of those caps is more than half the BOM:)
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Yeah if you like the sound, you may have to introduce the (totally) TNHB model lol.

I wonder if there is any wiggle room in the 47K value of the R2 local feedback resistor? If a larger resistor could be substituted without issue, then a smaller value cap could be used. Maybe an off-the-shelf through-hole PPS solution. I really like the sound of the Kemet SMR series too, but they aren't as compact as the stack I made.
 
Jul 29, 2017 at 3:14 PM Post #430 of 468
Making R2 100k is possible but you tradeoff resolution. Sometimes I like making it 22k even in which case a 4.7uF is needed.

Those PPS's you linked are presently out of stock at Mouser.
 
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Jul 30, 2017 at 1:01 PM Post #431 of 468
That's fascinating. Can you elaborate on how local feedback resistor value affects the resolution???

If you don't want to wait for those SMD-PPS parts, you could try the 1uF KEMET SMR and get essentially the same bass (better than -0.1dB at 20Hz). Or raise R2 to 56K if you want it "perfect." But probably not worth raising it if resolution is at stake. I doubt even Quincy Jones could hear a 0.1dB difference at 20Hz lol.

Grrr...Why didn't I think to try them out when testing input caps??? They might actually sound better than my stacks since they are internally wound, not stacked construction. I did try them at the PCA output the other day, to couple to my boombox, and was blown away at the SMR's crystal transparency and immediacy...the bass was lacking of course in that scenario. But I think they have potential here.

Looking at my pair of SMRs next to the board, I'd say you'll have to do even more sanding on the input jack than I did, but they should fit just fine, and actually be less work than my stack. They'll also not have the problem of protruding into the board past the pot...
If you don't try it, I will!!!
 
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