What's the best 78xx/79xx and B649/D669 replacement?

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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.
 
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.
 
AndrewT said:
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)?
 
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
 
keantoken said:
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-SUP...805-LM317_W0QQcmdZViewItemQQitemZ250454393583

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!!
 
smellygas said:


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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Joined 2006
Its pretty easy to find transistors that better the d669/b649 combination. If you are going to order from profusion take a look at 2sb1144 and compliment, for higher voltages try 2sa1249 and comliment as well as 2sa1507.

I would keep away from the profusion d669/b649 combination, simply because they are chinese made copies of the original hitachi devices. Specs are never upto the standards of the original devices although they will always quote the original device specs.
 
Hi,
none of the transistors can get anywhere close to the SOA of the b649/d669
@ 50Vce, the 1144 does 0.08A, the 1249 does 0.15A, the 1507 does 0.2A, the 649 does 0.3A.
All are of similar speed.
All can just about drive a 100W into 8ohm amplifier.
Only the latter two can drive a 180W into 4ohm amplifier.

The 649/669 has the lowest hFE.

For headphone amp any would do the job but so would bd139/140
 
AndrewT said:
Hi,
none of the transistors can get anywhere close to the SOA of the b649/d669
@ 50Vce, the 1144 does 0.08A, the 1249 does 0.15A, the 1507 does 0.2A, the 649 does 0.3A.
All are of similar speed.
All can just about drive a 100W into 8ohm amplifier.
Only the latter two can drive a 180W into 4ohm amplifier.

The 649/669 has the lowest hFE.

For headphone amp any would do the job but so would bd139/140

I see.

I was going to suggest the BD139/140 but I forgot and he beat me to it.

The BD139/140 are a very good pair and come in 3 Hfe classes. I suggest you look into them before going for more expensive japanese devices...

- keantoken
 
Disabled Account
Joined 2006
When looking at high performance in these positions one has to look at the cob and at the early voltage, much more relevant than speed aka FT, one has to stay in the SOA of the device as well offcourse. Keep in mind that a driver is used in common emitter and effectively the total capacitance is cob x HFE.

Keantoken, you have got it a bit wrong there, take a second look at the sanyo datasheets, AndrewT is spot on from what I can remember.
 
homemodder said:
When looking at high performance in these positions one has to look at the cob and at the early voltage, much more relevant than speed aka FT, one has to stay in the SOA of the device as well offcourse. Keep in mind that a driver is used in common emitter and effectively the total capacitance is cob x HFE.

Keantoken, you have got it a bit wrong there, take a second look at the sanyo datasheets, AndrewT is spot on from what I can remember.

I agree that Cob is much more relevant in the audio spectrum.

I was meaning they have the best SOA apart from the 649/669. Maybe I was mistaken.

The 1144/1648 can run at 1.5A until 7V Vce, much better than the others. But the 139/140 and 2690/1220 are close runners. I am looking at the DC SOA.

EDIT: Nevermind, the BD139/140 have the best DC SOA.

- keantoken
 
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