Post by Owen Y on Aug 30, 2020 12:05:23 GMT 12
The volume pot is an interesting one - a TKD CP600 series, 50k, plastic film, only 16mm square, US$30. (I've used ALPS myself (OK) & Noble (better I think), but not TKD.) My initial impression is that this TKD sounded pretty good.  The interesting part is how it's designed to achieve a 'Log' or 'audio' taper.... 
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Post by colinf on Sept 1, 2020 18:16:50 GMT 12
On these pots it’s good not to load down the output with a parallel resistor. I use circuits with high input impedance with them. The bigger TKD has similar construction but with more separate resistive elements to achieve even more stable contact resistance. The 601 has a nice warm sound, perfect for SS gear. I find the Alps RK27 slightly grainy by comparison. The TKD 2500 series is more neutral and clearer.
AMR-iFi R&D
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Post by Owen Y on Sept 1, 2020 18:52:38 GMT 12
Hi Colin - I haven't spent any more time auditioning J's amp, but the 'taper' of this vol control seems VERY gentle at first (much moreso than typical 'log' pots which, from my measurements once, may not closely resemble a log curve). So, J finds himself disconcertingly with this ~45Wpc amp wound up on the vol control to around 1 o'clock, driving my 87dB/W Spendors. Back on the bench, some pics with the shaft extensions installed on the Input Selector switch & Volume pot.  (Not sure if the knobs will be painted & there will be dial rings around them.)  (Rectifier board on RHS.)  (Close-up of the LM3875s with heatsink off.)
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Post by sadface on Sept 1, 2020 21:52:47 GMT 12
Dayum,That is a stunning looking build.
Up to your usual standards.
I'm glad you like you're gainclone, I've been very impressed with them so far in my experiments.
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Post by Owen Y on Sept 1, 2020 21:58:33 GMT 12
Jeremy's build, not mine! I try to stick with wood & hand tools 
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Post by colinf on Sept 2, 2020 2:22:39 GMT 12
Nice machining! Be sure to use heatsink grease on the LMs, otherwise you get localised hot spots on the plastic IC case. What resistor is J using to ground after the pot? Lower than 50k would distort the log curve on the 601. But if the wiper loses contact even briefly while turning the pot, you don’t want too much DC offset reaching the speaker with too high a resistance.
AMR-iFi R&D
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Post by Owen Y on Sept 2, 2020 22:11:37 GMT 12
First listen, a couple of quick videos, straight off the iphone (I need to add a decent mic):
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Post by Owen Y on Sept 3, 2020 14:22:01 GMT 12
Can anyone manage to view either or both of the above videos? (It seems I have music copyright claims on them & they are blocked or blocked in some regions.) 
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Member
Post by snewt on Sept 3, 2020 16:07:22 GMT 12
The 2nd one played, but not the first. Good music btw 😎
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Post by Owen Y on Nov 14, 2020 13:39:00 GMT 12
An update: Jeremy's finished article....  
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Post by sadface on Nov 14, 2020 15:01:51 GMT 12
That is an inspiring build!
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Post by Owen Y on Nov 16, 2020 19:41:23 GMT 12
Now being fed some decent FM radio signal:  
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Post by Owen Y on Nov 17, 2020 9:52:22 GMT 12
The impression I'm getting is - 'neutrality', 'effortless' clarity, no discernable 'hifi-ness'. The slight cabinet resonance-warmth of the Spendors is still present, reassuringly. Also the tubed McIntosh tuner. The TKD 'log' vol control is taking some getting used to, though. Usable volume can range from 7:30 through to say 2 o'clock! (Amp output is 45-50Wpc & the Spendors are 87dB/W sensitive, 8 Ohms nom..) The LM3875 output power is shown below in this graph from the Texas Instruments LM3875 datasheet: Impressive, from a chip measuring just 2cm square x 0.5cm thick 
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Post by Owen Y on Nov 26, 2020 13:03:42 GMT 12
The wee LM3875 Gainclone takes on the main system...   (Sitting atop my usual tube amps.)
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Post by cartridgeguyonline on Nov 26, 2020 17:40:52 GMT 12
All beautifully finished Owen, lovely job
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Post by Owen Y on Nov 26, 2020 21:06:56 GMT 12
(The Gainclone is Jeremy's handiwork of course - his standards are more exacting  ).
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Post by Owen Y on Nov 27, 2020 8:33:42 GMT 12
(Apparently, the music violates copyright, but hopefully this link will work 'privately'.)
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).