LM338 regulated snubberized PSU for audio amplifiers

[carlosfm]

Here it is.
Results are impressive, this elevates the chipamp to a league of it's own.

Notice that I recommend 1,000~2,200uf caps on the chips, snubberized.
I'm using 2,200uf.

This regulated PSU is good for two chips (LM3886, etc.).

As a side note, this is not only a PSU for chip amps.
There are discrete class-A amps around that use the LM338 regs.
These amps will also benefit from the snubber.
No, let me put it this way: every regulated PSU benefits from a snubber.

The values for the snubber were calculated for the LM338's output impedance. Don't ask me how, I won't reveal it.

Enjoy.

[homer09]

I knew you wouldnt resist sharing your most recent recipe

how does this supply compare to non-regulated high-cap snubbed PSU?

Is this the new chip amp PSU king ?

[cjd]

Now, if I could run four chips off this... X-GC using a pair of LM4780's per side, you know? (the chips showed up today in the mail finally!)

Wonder what the flavor of the month will be next month. Discrete?

C

[carlosfm]

Originally posted by homer09
I knew you wouldnt resist sharing your most recent recipe
how does this supply compare to non-regulated high-cap snubbed PSU?
Is this the new chip amp PSU king ?

This is it.
I couldn't help but sharing...

Originally posted by cjd
Now, if I could run four chips off this... X-GC using a pair of LM4780's per side, you know? (the chips showed up today in the mail finally!)
Wonder what the flavor of the month will be next month. Discrete?
C

I was thinking in paralleling, but results are so impressive with this PSU and single chips that I'm not doing it.
Deam it, this stereo power amp sounds better with my speakers than a Krell integrated (used as a power amp) I had at home last week.
What's on my plans for soon is to make two small monoblocks with two chips each for bi-amping my Epos ES11 speakers.

[XELB]

I will tell a friend to try it on a stereo bridged LM4780 amp.
(my PSU is not regulated)

I hope to have news tomorrow.
Since you don't tell the miraculous formula, I will tell him to buy thousands of caps and resistors to find out the best combination LOL

[carlosfm]

Originally posted by XELB
I will tell a friend to try it on a stereo bridged LM4780 amp.
(my PSU is not regulated)

I hope to have news tomorrow.
Since you don't tell the miraculous formula, I will tell him to buy thousands of caps and resistors to find out the best combination LOL

You have a complete PSU schematic with the right values.
What do you want more?

[homer09]

Originally posted by carlosfm




You have a complete PSU schematic with the right values.
What do you want more?

i think he wants to check your math

[XELB]

You got me... I was with hope that you would tell! LOL

[inocent] [/inocent]




If you say that this one is much better, I will give it a try but I only have 8,600uF caps.


What electronic House you recommend in Lisboa ?
I will have to buy some parts.

[mateo88]

Originally posted by carlosfm
The values for the snubber were calculated for the LM338's output impedance. Don't ask me how, I won't reveal it.

[/B]

If you pretend the power supply is a speaker and calculate a zobel for it, that gets you in the general ballpark. Mess around with the values a little to see what works best.

[carlosfm]

Originally posted by XELB
If you say that this one is much better, I will give it a try but I only have 8,600uF caps.

That's not important, those are fine.
On this PSU you should have around 10V more voltage before the regs, so there's plenty of voltage to sag.
After the regs, the voltage is steady as a rock, of course.
Big capacitance is not needed, 4,700uf is fine, or up to 10,000uf.

Originally posted by XELB
What electronic House you recommend in Lisboa ?
I will have to buy some parts.

In Lisboa you have Dimofel and some others, but not too good for decent parts. Sometimes you find them, but you have to search.
There's a guy in Cacem that has Philips caps is almost all values, and 1% film resistors.
It's on the main street, on the Bons Amigos (I think it's called this way) shopping center.

[carlosfm]

Originally posted by mateo88
If you pretend the power supply is a speaker and calculate a zobel for it, that gets you in the general ballpark. Mess around with the values a little to see what works best.

I don't feel like messing around, it's fine as it is.
Try it with these values.
Then you can try other values, but I doubt you can improve this...

[mateo88]

I'm not saying the values aren't great as they are, I'm just saying that's how you can calculate the values. I don't know if you tried these values yet, but 1 ohm and .1 uf look like good values to correct the impedance issues above 1 mhz.

[XELB]

In Lisboa you have Dimofel and some others, but not too good for decent parts. Sometimes you find them, but you have to search.
There's a guy in Cacem that has Philips caps is almost all values, and 1% film resistors.
It's on the main street, on the Bons Amigos (I think it's called this way) shopping center.

At the beginning, I went to Dimofel but know I go to a small store between Areeiro and Alameda. They sell 4,700uF NA caps, 2.50€ each. ( I don't know if it's a nice price)

LM3886 costs 5€.

But the last time I went there I bought 6,800uF caps

[carlosfm]

Originally posted by mateo88
I'm not saying the values aren't great as they are, I'm just saying that's how you can calculate the values. I don't know if you tried these values yet, but 1 ohm and .1 uf look like good values to correct the impedance issues above 1 mhz.

I'm lowering the impedance at a much lower frequency.
1R+100nf is what I recommended for the unregulated PSU, and it's fine for that.

[carlosfm]

Originally posted by XELB
They sell 4,700uF NA caps, 2.50€ each. ( I don't know if it's a nice price)

Nice price, but toilet caps.

Originally posted by XELB
LM3886 costs 5€.

Do they sell them?

[mateo88]

That's cool, I'm not trying to say that you're wrong or anything. I'm just trying to say that you can calculate the snubber by calculating a zobel network based on the output impedance of a power supply.

Just letting people know how to calculate the snubber so they can do it on their own and experiment with values that their ears agree with.

[XELB]

Do they sell them?

Yes.
And normally they have a few different LM models in stock



This store was recommended form a friend specialized in electronic and HIFI techniques. ( He is now creating an High End HIFI chip (maximum THD 0,003%)
I have shared your snubber technique with him...

[carlosfm]

Originally posted by mateo88
Just letting people know how to calculate the snubber so they can do it on their own and experiment with values that their ears agree with.

Just try different cap values and keep the resistor at 0.47R.
But why bother?
Try this first, you will not want to touch it.

[metalman]

Hmmm ... Thanks for sharing Carlos. This should be pretty easy to add to my current PS setup (only missing the snubber caps and resistors). Let me see if the XGC likes it!

Cheers, Terry

[carlosfm]

Originally posted by metalman
Hmmm ... Thanks for sharing Carlos. This should be pretty easy to add to my current PS setup (only missing the snubber caps and resistors). Let me see if the XGC likes it!

Cheers, Terry

Do that, try it.

[XELB]

Carlos, you have 8 Ohms speakers. Don't you ?

Mine are 6 Ohms, and normally I test the amp with 4/2 Ohms speakers(this ones have 5 drivers but 98dB sensitivity).
Do you think 10,000uF per rail will work fine with this speakers?

[cjd]

Originally posted by metalman
Let me see if the XGC likes it!

Originally posted by carlosfm
Do that, try it.

The only reason I want to parallel before the X (SuSy) circuit is the speakers will be rather low impedance... between 2 and 3 ohm I think very likely. May dip below but I think I can keep it above 2. I also have a few of the LM3886 to mess with, and will likely wire up one with those before the LM4780's. There I can obviously go with this circuit as-is. Looking forward to it.

C

[neutron7]

carlos, why dont you try a tracking pre-regulator version . It is a cheap way to get quite improved noise performance. since the pre regulator is referenced to the output of the main regulator. the main regulators input also benefits from the regulation of its output,. (and who knows maybe the snubberization as well ) and the error amplifiers in those things need as much help as they can get, they are about the quality of a 741!

i hope that makes some kind of sense.

you need to have a bit more of a voltage drop though.

you just need another 338, a cap and 2 resistors per rail.

its on page 12 of here
http://www.national.com/ds/LM/LM138.pdf

[Mikett]

Try some LT1083s which have better HF impedance characteristics than the LM338 which are not as high performance. The snubber values will need to change I imagine. The LT1083 is unfortunately more expensive though.


Here's one example with no snubbers.
http://shine7.com/audio/gainclone.htm

[Alcaid]

Carlos

Secondary on T2 is shorted in the diagram.

[Nuuk]

Carlos, does the regulated 3886 still run hotter with your latest regulated supply?

[nina]

The LM338 reg Ic is more expensive than the LM3875 power IC !





Carlos,

Seems we also put the chipamp to its limitation now. Just wonder what next innovation you will contribute to this forum

How about this:

- Parallel chip amps with IC driver/buffer
- Chipamp as driver to Mosfet power stage
- Integrated (Chip)amp with NOS DAC
- Chipamp with High WAF ** Important*
( WAF = Wife Acceptance Factor )

Hee hee hee

[NealG]

Hey Carlos, thanks for sharing this!

It's been a while since I changed my clone, I will dust off the soldering iron and get to work!

All the best

NG

[Nuuk]

Yes, I'm going to try it as well. I'll sell the Krell to raise money for the extra parts! (Only joking Uncle Carlos but I will need to order the extra caps)

[shusha]

Originally posted by nina
The LM338 reg Ic is more expensive than the LM3875 power IC !

I don't know. LM338 cost me less then LM3886, while both of them cost practically as one LM3875. In my local store(s).


LM338 = 4,4€
LM3886 = 5,3€
LM3875 = 9,3€

[carlosfm]

Originally posted by NealG
Hey Carlos, thanks for sharing this!

It's been a while since I changed my clone, I will dust off the soldering iron and get to work!

All the best

NG

Welcome back, uncle Neal.
Long time no see.

PS: I will keep up with the thread tonight, I'm busy now with some SQL Server triggers.

[tiroth]

LM338T is only USD$1.50 in quantities of 25 at digikey. I'd shop around unless you only need a couple.

Thanks Carlos for the research! I have a pile of regulator boards here that will be built up according your design.

[carlosfm]

Originally posted by tiroth
LM338T is only USD$1.50 in quantities of 25 at digikey.

Originally posted by tiroth
LM338T is only USD$1.50 in quantities of 25 at digikey.

I pay around 1.5€ a piece here, but if I look next door they ask around 4€ each.
You guys have to look around for the best price, don't take for granted the first quote you get.
Sometimes to buy some parts I go to 3 different places.
The guys that have the LM338s at 4€ have some other parts that are cheaper than at other places.
Buying electronic parts is a science.

[carlosfm]

Originally posted by XELB
Carlos, you have 8 Ohms speakers. Don't you ?

Mine are 6 Ohms, and normally I test the amp with 4/2 Ohms speakers(this ones have 5 drivers but 98dB sensitivity).
Do you think 10,000uF per rail will work fine with this speakers?

I think 10,000uf will do, even for 4 ohm speakers.
Btw my speakers are 8hms, but not easy to drive.
You can ask to anyone who knows, has or sells Epos ES11 speakers (discontinued, ES12 later, M12 now) if it's easy to find a commercial amp that really makes them sing.
There are some, but $$$$$$.

Originally posted by Alcaid
Carlos
Secondary on T2 is shorted in the diagram.

No, it's not.
Go back to the first post again and check it out.
When I opened the thread and posted the schematic I saw that I had a reversed bridge (B2).
I corrected that and edited the post.
This was a question of minutes, maby you downloaded the first one.
The last think I want is to post a PSU that explodes in your faces.

Originally posted by Nuuk
Yes, I'm going to try it as well. I'll sell the Krell to raise money for the extra parts! (Only joking Uncle Carlos but I will need to order the extra caps)

Nuuk, you have to make some stock at home.
I'm in a creative mood.

[Nuuk]

Nuuk, you have to make some stock at home.

Well Carlos, I may be down on parts but a friend just dropped in with.......


Good friend eh?

[SvErD]

Originally posted by Alcaid
Carlos

Secondary on T2 is shorted in the diagram.

Carlos, it's still shorted.

[carlosfm]

Originally posted by SvErD
Carlos, it's still shorted.

You are right.
Who would spot that one?
Congratulations, you have just winned... an unshorted trafo.

PS: maby the moderators could replace the file on the first post?
Thanks.

[carlosfm]

Originally posted by Nuuk
Well Carlos, I may be down on parts but a friend just dropped in with.......
Good friend eh?

Are all those in working order?
Nevermind, either way, good friend.
Even if it's for recycling.

[Nuuk]

Are all those in working order?

He said that they all had both traces working so I hope to get at least one good one from the three. There is also a digital bench voltage tester.

[XELB]

I just finished my unregulaterd Snubberized PSU
Since here is 1:15 AM, I could not test it loud and clear…
I will let the amp burn this night on and, in the morning, I will wake up everyone in the building! AH AH AH LOL

I'am using an STK4152II chip for testing



Next step, regulated PSU



Carlos, I that small store an 340VA-35V Toroidal transformer costs 40€ ( with instalation parts ).

[carlosfm]

Originally posted by XELB
Carlos, I that small store an 340VA-35V Toroidal transformer costs 40€ ( with instalation parts ).

I know that store for many years but I don't go there for long years...
If it's the place I'm thinking, it's in Av. Madrid, right?
Are they open on saturday mornings?

Interesting.
Is that 2x35V?
That's too high, but the price is not bad at all.
2x30V at 250~300VA is what I need now...

[XELB]

It's in Almirante Reis. When you go from Areeiro to Alameda you cross a small garden. The shop is "in" the garden.
You can park the car in the garden and ask there for the shop.
(they don't have any outdors)
They still have a lot of prices in escudos and old things in stock. That's why some have really good prices


I saw 35V because a friend (expert in HIFI) tested LM's chips really hot. He said that they play better hot


I'am also awaiting for two STK401-290 chips(2x50W each 6/3 Ohms).
This one's I will bridge.
In the papper they look great, thats why I wont to test them with 2Ohm and 6Ohm speakers.



If I make an external regulated 35/33V PSU, I can use it for the two amps

[carlosfm]

Originally posted by XELB
It's in Almirante Reis. When you go from Areeiro to Alameda you cross a small garden. The shop is "in" the garden.
You can park the car in the garden and ask there for the shop.
(they don't have any outdors)

Aaahhhh...
I know that guy since I was a kid.
Forgot his name...
My father went there very often to buy parts.

[XELB]

We call him "o Barbas"




What do you think of an LM3886 with an 35V transformer ?
This will give (35x1.41) almost 50V

[Bob03]

[IMG]D:\Audio&Electronic\Snubb. Reg. power supply Ver. 1.GIF[/IMG]
[IMG]D:\Audio&Electronic\Non-inverting ML3886 PA ver. 3.GIF[/IMG]

[Bob03]

PS: maby the moderators could replace the file on the first post?

[Bob03]

Summary

[XELB]

I have tried the unregulated snubberized PSU loud and clear at lunch time

Differences :
- more detail in high frequencies(guitars, voices, hithat, etc... all got better)
- Backing vocals and supporting instruments more detailed
- Bass seemed equal

( I have a little problem with bass, I am using an 125VA transformer as an test transformer speakers only wake up when I give some "gas")


What I most enjoyed was discovering new sound that this amp couldn't reach.
I was listening and I was saying to my self, this instrument was not here…. Heheheh


Now a look forward to try the regulated

[carlosfm]

Well... I think a resistor and a cap must be one of the most cheap and effective tweaks ever.

Much better than speaker cable lifters and gold-plated volume knobs.

[Mikett]

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