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New active speaker on order from Taobao

Posted 26th September 2014 at 02:49 AM by abraxalito
Updated 6th October 2014 at 02:44 AM by abraxalito

This one has dual TDA7265 chipamps and a nice 60VA toroidal trafo which should give better regulation than the normal EI type. Four electrolytics for the main PSU is encouraging. The opamps are socketed so opamp rolling is on the cards...

Update - received the speakers now. A quick listen showed the typical lack of dynamics opamp sound. After all they're only NJM4558s in there. So I shall re-jig the XO for TL082s by scaling up all the impedances and biassing the opamps into classA. Already all the through-hole caps have come out ready to be replaced by SMT types. The topology tends to suggest this may well be a clone of the D1010 which I'm already familiar with.

Update2 - modded the XO board but so far left the amp board 'as stock'. Mods are 11k resistors to VEE for classA bias, opamps swapped to TL082s, TL431 shunts installed to give +/-5V (from the regulated +/- 12V), plenty of 3,300uF caps across the supplies, 220uH inductors filtering from the shunts, impedances scaled up by a factor 10 to 20 to lighten the loading on the opamps. Slight tweaks to the filter shapes which didn't look optimized. Result - wow! I'll have to order another pair in order to post pictures of the modded board as these are staying on now. Dynamics in spades from such diminutive boxes....

The component cost of the mods so far is probably a couple of dollars. Oh I forgot to mention I extracted the boutique input coupling caps (mounted under the board) and replaced them with X7Rs to give a bit more space for supply caps I'd hazard a guess that those yellow boxes on the amp board might eventually suffer the same fate.

I've uploaded the outline filter schematic - eagle eyed readers will notice how similar it is to the D1080 XO....

Update3 - the yellow boxes came out, not because I've an aversion to such caps but because they obstructed access to the chipamp pins on the topside of the board. Extra supply capacitance (4 * 6800uF) with a couple of no.28 chokes (17mm dia) between. This improved dynamics but still the HF would have me tensing up so I've now separated the power wiring to the two chipamps, adding extra decoupling to the tweeter one. I was surprised to discover they're using one 7265 for the LF, the other for HF - this makes adding only tweeter decoupling that much easier, I was expecting they'd have tweeter and bass allocated to one chip for thermal reasons. I've now added 1500uF/50V locally and a couple of paralleled 220uH chokes. The cringe factor on HF has gone away on most recordings, there are still one or two though that are inviting me to add more uF.....
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Comments

  1. Old Comment
    Seems as if you can't put a foot wrong at the moment, Richard ... ;)
    permalink
    Posted 29th September 2014 at 11:27 PM by fas42 fas42 is offline
  2. Old Comment
    abraxalito's Avatar
    Well that's bad news for learning, big mistakes spawn major lessons
    permalink
    Posted 30th September 2014 at 12:43 AM by abraxalito abraxalito is offline
 

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