What's the best 78xx/79xx and B649/D669 replacement? - diyAudio
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Old 2nd August 2009, 02:54 PM   #1
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Default What's the best 78xx/79xx and B649/D669 replacement?

Can anyone help me upgrade my headphone amp? The power supply uses Fairchild 7812/7912 and 7805/7905 voltage regulators, and I'm wondering if there are premium low-noise versions of these chips that can just drop-in? I don't think I can stick in an adjustable voltage regulator circuit due to space-concerns.

The amp also uses B649/D669 transistors in the output stage. Are there premium versions or equivalents that can drop in as well?

thanks! any help from the chip gurus would be much appreciated.
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Old 2nd August 2009, 03:14 PM   #2
AndrewT is offline AndrewT  Scotland
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the 2sb649/d669 are very good driver transistors.
They are difficult to even match their performance never mind improve on it. But, there are some expensive difficult to source equivalents that spec better.

Read Jbau's thread and the links to alternative topologies.
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Old 3rd August 2009, 03:33 PM   #3
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Quote:
Originally posted by AndrewT
[B]the 2sb649/d669 are very good driver transistors.
They are difficult to even match their performance never mind improve on it. But, there are some expensive difficult to source equivalents that spec better.
Oh, that's good. Are there particular manufacturers that make better performing B649/D669's (or is it not worth the trouble of swapping out)?
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Old 3rd August 2009, 03:54 PM   #4
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http://www.profusionplc.com/

These guys carry it.

As for the 78xx/79xx regulators, there are discrete replacements developed by DIY'ers, that have all around better specs, but that can be directly replaced with the originals.

http://cgi.ebay.com.my/Audiocom-SUPE...mZ250454393583

I remember finding different ones though on another site...

- keantoken
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Old 3rd August 2009, 09:19 PM   #5
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Just looked at the specs for those regulator replacements. Max output current is only 100mA (although they say surge handling is good). I'll bet using lower power output transistors makes very good performance possible.

But I still remember seeing the same thing on another site which could handle the full voltage and current specs of the actual devices.

- keantoken
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Old 3rd August 2009, 09:29 PM   #6
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Quote:
Originally posted by keantoken
http://www.profusionplc.com/

These guys carry it.

As for the 78xx/79xx regulators, there are discrete replacements developed by DIY'ers, that have all around better specs, but that can be directly replaced with the originals.

http://cgi.ebay.com.my/Audiocom-SUPE...mZ250454393583

I remember finding different ones though on another site...

- keantoken
WOW, those are perfect! I'll look into them. If they're inexpensive enough, I might just start using them in say...everything! Thanks!!
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Old 3rd August 2009, 09:38 PM   #7
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Originally posted by smellygas


WOW, those are perfect! I'll look into them. If they're inexpensive enough, I might just start using them in say...everything! Thanks!!
I share your ambition!!!

But being the perfectionist I am, I have some ideas myself and want to try my own hand on designing something similar. My trump card is equal performance between + and - supplies.

Also, what application are the 669/649 for? it would be easier to suggest a substitute if we knew our margins.

- keantoken
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Old 3rd August 2009, 11:49 PM   #8
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Originally posted by keantoken


Also, what application are the 669/649 for? it would be easier to suggest a substitute if we knew our margins.

- keantoken
Output transistors for a dual op-amp headphone amplifier.
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Old 4th August 2009, 01:03 AM   #9
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smellygas,
take a look at 2SC5171/2SA1930, maybe you want to increase the quiescent current and the heatsink size, otherwise you won`t gain much just by shifting 2SD669/2SB649.
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Old 4th August 2009, 02:34 AM   #10
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I looked into the BD787/788 as replacements, but they are pretty inferior even though they have higher max current (no need for that in a headphone amp anyways).

- keantoken
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