High-End Regulated Buffered Inverted GC

[digi01]

Hi carlosfm,always sweetness points.you are so happiness

My wife like listen to music and play musical instrument,but against digi01 take a lot of time in diy things ......


anyhow,your new gc looks very fine!congratulations!

[ebijma]

Hello everybody,

Got a question for CarlosFM.

You did a realy good job building your amp.
It looks very nice.

After allot of reading i made a plan for my amp.
You can see the circuit below.
Its based on Pedja regulated supply and Joe's vbnigc.

I want to build this Valve Bufferd Non Inverted Gainclone.
And ofcourse with the regulated supply.
I want to run the LM 3875 with 31 volts on each rail.

So my question is :
Can you tell me the value of the resistors in the LM338 ciruit?
And what kind of transformer can be used?

Hope you can help me out here.

[jackinnj]

Originally posted by ebijma

I want to build this Valve Bufferd Non Inverted Gainclone.
And ofcourse with the regulated supply.
I want to run the LM 3875 with 31 volts on each rail.

I(pk) with 31 V rails wll be 3.4 Amps according to the National Semi interactive chipamp tool. http://www.national.com/appinfo/audi...gn_Guide14.xls
At best this will cause the regulators to shutdown, at worst, it will blow your regulators.

There is no need for regulating the chipamp power supply.

[carlosfm]

Originally posted by jackinnj

At best this will cause the regulators to shutdown, at worst, it will blow your regulators.
There is no need for regulating the chipamp power supply.

Please go read the LM338 datasheet and come back later, ok?

[carlosfm]

Originally posted by ebijma
Hello everybody,
Got a question for CarlosFM.
You did a realy good job building your amp.
It looks very nice.
After allot of reading i made a plan for my amp.
You can see the circuit below.
Its based on Pedja regulated supply and Joe's vbnigc.
I want to build this Valve Bufferd Non Inverted Gainclone.
And ofcourse with the regulated supply.
I want to run the LM 3875 with 31 volts on each rail.
So my question is :
Can you tell me the value of the resistors in the LM338 ciruit?
And what kind of transformer can be used?
Hope you can help me out here.

Hi ebijma,

You didn't identify the resistors, but to make it simple and quick (this site si sooooo slooooooow now... )look at the LM338 datsheet and use 180 ohm resistors for R1 and 4.7k trim pots for R2.
Don't bother to use resistors for R2, even if you match them, the regs are not matched and you'll always have a small difference between the rails.
May be that I'm too picky, but I like to precisely adjust for the voltage I want.
Adjust to 30~31v, and you can use a 2x25v to 2x30v transformer.
My trafo was scavenged from an old amp, it has 2x33v , it's on the limits of the regs, but no problem, it works fine.
BTW, use around 33~47uf caps on the LM3875 chips, I found out to be an optimal value with these regs.

Thanks for your nice words and I hope to get feedback from you when it's done and singin'.

[Pedja]

Ebijma,

If a current set resitor stays 120R, then a voltage set resistor (2k2) should be about 3k (0.5W at least). Transformers with secondariy voltages of about 30V will be fine. Check the voltage rating of used diodes, SB560 might not be that safe in this case.

Pedja

EDIT: Carlos was faster... This post won't hurt anyway?

[jackinnj]

Originally posted by carlosfm



Please go read the LM338 datasheet and come back later, ok?

maybe if you are running only one amplifier, i.e. mono -- with the In-Out voltage differential you are bumping up against the limit of the LM338 for a pair of LM3886 devices -- yeah, it will work, for a time, but the MTBF will eventually kick in.

[carlosfm]

It's good for two chips.
Nominal current 5A.
Max current 12A.
Just use a good heatsink.

[tbla]

the In-Out voltage differential you are bumping up against the limit of the LM338 for a pair of LM3886 devices --

there'll be no problems as the "in/out" V for the 338 is 30-40 V and if you use a trafo with 25V primare gives 35 sec and regulate it down to 30 V.....a difference only at 5V......go ahead with it, it works very well.

[ebijma]

Thanks for all your reply's.
They are very usefull.
Hope to start building soon.

When im done you surely can read about it here on diyaudio.

Bye