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BT928
Feb 11, 2006 21:52:37 GMT
Post by nastyrox on Feb 11, 2006 21:52:37 GMT
Have just found your upgraded components page for the B-Tech BT928. Having not soldered before, how difficult would this be for a novice? I guess the Caps and resistors have to be soldered in a particular direction (+ & -) Also have looked at the component list image and tracked stuff down at Maplins. They seem to have a few different makes / quality for some of the components - anything I should or shouldn't go for? Thanks for any advice - love Flat Eric BTW He looks happy in his variety of cans! ;D
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BT928
Feb 12, 2006 14:36:34 GMT
Post by PinkFloyd on Feb 12, 2006 14:36:34 GMT
Have just found your upgraded components page for the B-Tech BT928. Having not soldered before, how difficult would this be for a novice? I guess the Caps and resistors have to be soldered in a particular direction (+ & -) Also have looked at the component list image and tracked stuff down at Maplins. They seem to have a few different makes / quality for some of the components - anything I should or shouldn't go for? Thanks for any advice - love Flat Eric BTW He looks happy in his variety of cans! ;D Ok let me see if I can remember......... A novice should be able to undertake the work but the pads on the BT-928 are pretty "delicate" (especially those around the opamp) so it's probably a good idea to practice desoldering on an old board.. you can get plenty of old boards out of radios etc. at your local skip. When you're confident in your soldering skills then you can start work on the BT-928. The resistors are omnidirectional (can be soldered in any way round) the caps, however, are directional and you need to observe polarity when fitting them. If you look at the board you will see "+" markings. The positive leg of the capacitor must face the plus marking and the negative lead should face the other way (there is always a band on the side of the capacitor which denotes negative) as long as you carefully note which way they go round "before" you remove them then you'll be fine. As to components you are looking for 1% metal film resistors (0.6W) and some good low ESR type capacitor (not sure if Maplin sells them) such as the Panasonic FC. I've got most of the parts and will be happy to send them to you if you can't get hold of them so just send me a PM and I'll see what I can come up with. Thanks for the Flat Eric compliments, nice isn't he?
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BT928
Feb 12, 2006 14:37:02 GMT
Post by PinkFloyd on Feb 12, 2006 14:37:02 GMT
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BT928
Feb 12, 2006 15:18:53 GMT
Post by nastyrox on Feb 12, 2006 15:18:53 GMT
Thanks for the Flat Eric compliments, nice isn't he? He's the dog's ! Have seen across at the 'other' forum too! We even have his single. May have a go at the BT928, not sure if I'll screw it up but they're only £30 anyway. Might be fun. Cheers.
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BT928
Feb 12, 2006 22:45:49 GMT
Post by PinkFloyd on Feb 12, 2006 22:45:49 GMT
May have a go at the BT928, not sure if I'll screw it up but they're only £30 anyway. Might be fun. Cheers. That's not the attitude, you "won't" screw it up. if you do I'll unscrew it up for you no worries
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BT928
Feb 13, 2006 13:36:01 GMT
Post by nastyrox on Feb 13, 2006 13:36:01 GMT
That's not the attitude, you "won't" screw it up. if you do I'll unscrew it up for you no worries Sorry Teacher I'm always a bit negative and unwilling to take "risks" not too much of a gambler. On the subject of components can you suggestion somewhere else other than Maplins? Have looked at RS but they've got so much stuff it's difficult to see the wood from the trees. Anywhere else that springs to mind? Thanks again for your info. ;D
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BT928
Feb 13, 2006 13:45:35 GMT
Post by PinkFloyd on Feb 13, 2006 13:45:35 GMT
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BT928
Jan 17, 2007 15:59:17 GMT
Post by mayday on Jan 17, 2007 15:59:17 GMT
I've gone one step further in modifying my BT928: Capacitors are Black Gate, resistors are Kiwame karbonfilm, op-amp is AD827 and the pot is an ALPS Blue Velvet. But I'm not done yet, I've got some new connectors, silverwire and different op-amps I'm going to try out. And also I've yet to put decoupling caps on the BG's and the op-amp and I'm going to try with an increased bias (6,8mA) on the op-amp and put a small heatsink on it if I have to.
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BT928
Feb 23, 2007 20:41:20 GMT
Post by mayday on Feb 23, 2007 20:41:20 GMT
I've raised the bias current in the AD827 to 6,8mA using 2,2Kohm 1% metalfilm resistors. The result is even better than I expected. Instead of soldering the resistors under the PCB, I carved som plastic out of an IC-socket to make room for them. Resistors connected like this: pin 1 -> pin 4, Pin 4 -> pin 7 Mounted it like this: Added a heatsink:
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BT928
Feb 23, 2007 21:30:22 GMT
Post by mayday on Feb 23, 2007 21:30:22 GMT
Next step is to build a stabilised 15V supply using a 2x15V~ 20VA transformer, 2x2200uF/35V low impedance capasitors and a LM350T regulator.
Some changes: I'll be using BC low ESR caps 2200uF/35V 105 Degr. C. and An LM317T regulator, decoupling the BC's with Wimas.
I've also ordered a few 470uF/50V BC's in case I wan't to change the 47uF BG's in the B-Tech as PinkFloyd did.
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BT928
Jul 25, 2007 9:07:42 GMT
Post by dynoPort on Jul 25, 2007 9:07:42 GMT
Is there a consensus as to which op-amp is the best for a replacement -the OPA2134PA-? (I can’t seem to source the AD827) and as I asked in another thread, would a lead-acid 12v battery be too low a voltage? Clean power tho!
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Deleted
Deleted Member
Posts: 0
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BT928
Jul 25, 2007 9:51:35 GMT
Post by Deleted on Jul 25, 2007 9:51:35 GMT
Mayday Probably a stupid question, but are you using the 2 x 15V windings in parallel ?Are the 2 x 2200uF in parallel too? Both regulators you mention are +VE regulators. Or are you talking about a dual polarity supply? e.g. + and -15VDC. If so, you will need LM317T and LM337T and a couple of 10uF electros (NOT tantalum) for the "adjust" terminals,as well as ,for example, 2 x 100uF for the output of the voltage regulators.Anything much bigger there, will slow down the regulators' response. SandyK
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BT928
Jul 31, 2007 17:06:38 GMT
Post by dynoPort on Jul 31, 2007 17:06:38 GMT
Please correct me if I’m wrong but if you don’t need the tone control, the second headphone socket (e.g. 6.3mm) & the phono out loop you’d only need the components marked with the black blob in my photo. You’d need all the caps but could do without 6 resistors and perhaps afford to put in some more expensive ones since you wouldn’t need so many! If I don’t get howls of derision I’ll try it and let you know if it still operates. PS once the board is free of the metal case, hold it up to the light and you can easily follow the circuit. Cant seem to load the picture
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BT928
Apr 22, 2008 11:20:45 GMT
Post by andy on Apr 22, 2008 11:20:45 GMT
Have now owned one of these for a couple of months and have replaced/upgraded all the components. Using my At W1000's and the sound is prety remarkable for a cheep amp with some expensive components in!
I do run the amp from a 12V 7AH battery and the sound difference from this to the mains adaptor is huge, would realy recomend the battery, though my cans are easy to drive.
Andy
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Deleted
Deleted Member
Posts: 0
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BT928
Apr 22, 2008 11:51:55 GMT
Post by Deleted on Apr 22, 2008 11:51:55 GMT
Andy
SLA batteries, like normal lead acid batteries, have a very low impedance, and in fact, act very much like a HUGE capacitor. This will also result in a more neutral sound. (balanced) as well as lower noise.
SandyK
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