My B-tech BT928 a bit modified... - diyAudio
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Old 17th January 2007, 09:46 PM   #1
Mayday is offline Mayday  Sweden
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Default My B-tech BT928 a bit modified...

Some time ago I heard about this cheap headphone amp that could be modded to sound good. So I bought one and ordered some components. In its original state it sounds crappy to say the least.

What I've done:
* Capacitors are now all Black Gate
* resistors are now all Kiwame carbonfilm.
* Op-amp is at the moment AD827, but can easily be changed since I've soldered on a socket on the PCB.
* Volyme pot is now ALPS Blue Velvet.
* the tone control and components around it has been put where they belong, the trash bin.
* Diode is now BYV27-200 decoupled with a 0,1uF Wima capacitor.

Click the image to open in full size.

What I'm going to do:
* Put decoupling caps on all BG's
* Put decoupling cap on the op-amp.
* Put in better RCA's
* Use teflontube insulated silverwire as internal cable.
* Raise bias to about 6,8mA and put a small heatsink on the op-amp if needed.
* try a few other op-amps, I've got AD8066 and an adapterplate.

Any input? I think that's all I can do to tweak this headphone amplifier.

BTW, not sure if this is the right part of the forum to post this, if not a moderator could please move it.

Sorry about the crappy english
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Old 18th January 2007, 12:28 AM   #2
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I've got a broom. I've had it for years and years. It's had four handles and three heads. Its the best broom I've ever owned.

BT928? A bit modified? You've kept the PCB and the connectors...

My friend gave me a Ferrari once. Well, it was a Renault, but he'd pinched the fuses from a Ferrari...

Sorry if this comes across as negative, but really!
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Old 18th January 2007, 12:32 AM   #3
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I really don't get the point of that post?!? What is it that you wish to say with it?
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Old 18th January 2007, 12:48 AM   #4
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As I said, it may seem negative (damn, it IS negative!) but, like you, I don't see the point.
You haven't, in any real sense, tweaked this amplifier - you've rebuilt it!
I'm sure if you started from fresh, and looked around, you could build a better amplifier from scratch. Why start with a cheap-and-cheerful amplifier and then replace everything that made it cheap - IE almost everything?
The whole point of finding cheap-and-cheerful pearls is to (maybe) give them a little polish, and then sit back and enjoy.
Making the pearls into a diamond is pointless IMHO - why not buy (or build) a diamond from the beginning?
You've put a lot of work into your amplifier, and I'm sure you're enjoying it - but I don't see the point. Sorry.
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Old 18th January 2007, 12:53 AM   #5
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That's ok, everyone has their own opinion, no need to be sorry.
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Old 18th January 2007, 12:58 AM   #6
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I hope my negativity isn't catching - You continue doing what you enjoy doing.
I'll continue collecting schematics, ordering bits and pieces, and changing my mind before I actually build anything at all...
I'm glad I've not upset you too much - as you say, our opinions are just that - and all have equal validity.

Happy building/tweaking.

Steve.
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Old 18th January 2007, 06:35 PM   #7
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I decided to try the AD8066AR op-amp, so I soldered it on to the adapter:

Click the image to open in full size.


Put a heatsink on top for future bias adjustements and this is how it looks in the box:

Click the image to open in full size.

I think I prefer the AD8066AR, at least with headphones i use at the moment. Thinking of buying new ones though.
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