LM338 regulated snubberized PSU for audio amplifiers

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carlosfm

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Joined 2003
Re: MKT vs. Ceramic SMD

agent.5 said:
I am eagle-ing my LM4780 SuperSymmetry with LM338 snubber. For the 300nf (connecting V+ and V-) and the 100nf (bypassing V+ and V-), should I use 1210 ceramic smd chip capacitors on the pins of the LM4780, or should I stay with the MKT type capacitors?
Click to expand...

MKT.
100V rated for the 330nf (not 300).
The 100nf caps can be 63 or 100V MKT, which are small.
Put these as close as possible to the chip's PSU pins, as always.
 
S

slackman

Member
Joined 2005
Hi all,
some time ago i build the psu with TO3-regs, the only ones i could buy in germany (PSU with TO3 regs). Now i've got some TO220 types (one third of the TO3 price!) for my next project.
Thanks a lot, carlos, the psu runs really good, the LM4780 modules from peter couldn't run the psu to it's limit. ;)

Are there limitations i have to take care for? Thermal stability? Maximum current? In the datasheets i could find any diffs.

For the bridged version (not sure: one LM4780 or two LM3886), should i lower the voltage?

Michael
 
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Tor M

Member
Joined 2002
Hi!:)

I finally finished my new amp, wich is based on carlos`s ideas.
This is an dual mono integrated amp, with two lm3886 pr channel in paralell made as carlos suggested with low value resistors. The preamp section is made of opa627bp with a gain of 2,5.
The powersupply is this lm338 snubberized.

This amp is truly exellent!:att'n: It`s the best amp I have ever had in my system.
The sound is detailed, dynamic and powerful and sounds more like 200W than 50W. It actually has much more bass power than my old Electrocompaniet ECI-1 wich is an true 100w (and costed atleast 2500 $ some years ago)

The amp sounds very "clean" and "uncolored", and seems to reveal everything in the recordings.

I`m very happy!:D

Thanks

Tor Martin:)

BTW my speakers are the old, but exellent epos ES 14.
 
jackinnj

jackinnj

Member
Joined 2002
tech-diy.com
slackman said:


Are there limitations i have to take care for? Thermal stability? Maximum current? In the datasheets i could find any diffs.

For the bridged version (not sure: one LM4780 or two LM3886), should i lower the voltage?

Michael
Click to expand...

The tradeoffs can be found using National's interactive web-tool, based upon Excel. When you download it you have to "enable macros".
http://www.national.com/appinfo/audio/files/Overture_Design_Guide15.xls
In the bridged version, PdMax is 4X that of one chip -- this is because each chip sees a complete swing from Vee to Vcc.

I use a whoppingly big heat sink on the Bridgeclone -- and can get distortion stats which are nothing short of sensational.

Because this is an opamp on steroids there is a tradeoff between running the chip hot (with very low distortion) and "mean time between failure".

Jack
 
C

carlosfm

Banned
Joined 2003
Tor M said:
[BThis amp is truly exellent!:att'n: It`s the best amp I have ever had in my system.
The sound is detailed, dynamic and powerful and sounds more like 200W than 50W. It actually has much more bass power than my old Electrocompaniet ECI-1 wich is an true 100w (and costed atleast 2500 $ some years ago)

The amp sounds very "clean" and "uncolored", and seems to reveal everything in the recordings.

I`m very happy!:D
Click to expand...

Thanks for reporting, Tor.
You description is quite accurate, that's it.

:cool:
 
A

Andy Bartha

Member
Joined 2004
This thread has wondered all over. The point needs to be made that the speaker will determine which GC version sounds the best. My experiance with unsnubberized andunregulated GC amps is they sound wonderful with easy to drive speakers. I used my simple GC amps with rear horn loaded Lowther PM2As. The sound was very good, amazed many friends with single ended amps. But when I used the GC amps with speaker that showed a more difficult load the sound wasn't nearly as good. I tried the GC amps on wide veriaty of speakers and the pattern was the same. Great sound on efficient simple loads and not so great on more difficult loads.
 
A

Andy Bartha

Member
Joined 2004
To continue, I hit the tab button and posted before I made my point.
The GC builder needs to aware of the the speaker load before deciding which version to build. If there is doubt then build the simple GC listen to the result. If the sound isn't what was expected then the snubbers and regulators can be added. As with everything there are no absoltes.
Just my opinoin.
 
C

carlosfm

Banned
Joined 2003
Andy Bartha said:
My experiance with unsnubberized andunregulated GC amps is they sound wonderful with easy to drive speakers. I used my simple GC amps with rear horn loaded Lowther PM2As. The sound was very good, amazed many friends with single ended amps. But when I used the GC amps with speaker that showed a more difficult load the sound wasn't nearly as good. I tried the GC amps on wide veriaty of speakers and the pattern was the same. Great sound on efficient simple loads and not so great on more difficult loads.
Click to expand...

That's correct.
The low capacitance GC is as picky with speakers as a SET amp.
Wich is obvious, no matter how big a trafo you use.
The 'juice' goes away fast with such small caps.
I test my amps with lots of speakers, I can only say they can drive most of them and they sound good practically everywhere.
The low capacitance GC is exactly the opposite: you struggle to find a speaker that matches it, or else you will have to make your own high sensitivity fullrange horn, which is not exactly the type of speakers I like.
Not that it will only work with this type of speakers, but the choice is very narrow.
It can sound good, yes, but only sometimes.:D
 
T

Tor M

Member
Joined 2002
Hi!:)

I agree with that. The last chipamp I had in my system was a VBIGC. This had wonderful midrange, and impressive holgraphic soundstage. But with my speakers the dynamics were slow and bass were "mucky".
The amp sounded very good with slow vocal jazz and that kind of music, but when things needed to speed up.....

Probably a terrific amp for the right speakers! ;)


Tor Martin:)
 
Vikash

Vikash

Ex-Moderator
Joined 2003
vikash.info/audio/
Peter Daniel said:
I noticed the same boards being sold on two other European sites, both of them run by diyAudio Moderators. I was never approached before those boards appeared there. Some of my UK clients were actually under impression that I have UK agent, which is not the case.
Click to expand...

Peter, I'm appalled to read this. I had assurances that you had no issue from me distributing some kits in the UK (and before I put them on madaboutsound.com). Granted, it didn't come from you directly but I took Brian's word as true. I'll remove them from the site.
 
C

carlosfm

Banned
Joined 2003
derekyu said:
dear carlos
i would like to know if i change it to voltage variable. what values should i change to to r3 and r5?
Click to expand...

What voltage do you need?
The formula is: 1.25 * (1 + R5/R3).

To make the PSU variable you could use 1K trimmers in series with 1.2k resistors in place of R5 and R6.
That would give you an adjustment between ~17.5V and 31V.
 

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