Hybrid DIY cct of LM3886+6N11 - diyAudio
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Old 10th March 2012, 11:29 AM   #1
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Default Hybrid DIY cct of LM3886+6N11

Hi Everyone.
I'm building the above mentioned amplifier, and there are a few threads mentioning this exact project, but no note of anyone having completed it.
Mine arrived fully assembled; I just had to load the tube and mount the cct onto the heatsink.

Click the image to open in full size.

I then loaded into a scrap case...

Click the image to open in full size.

...and made a volume control.

Click the image to open in full size.

It's still running in, but sounding quite sophisticated at low-ish volumes.
I deffo need a better PSU (currently a 200VA/20-0-20 torroid feeding the on-board caps).

Anyone got a schematic for a 30-0-30@10A DC regulated PSU?

Zennered Darlingtons? Op-amp + Power-stage? AC by-pass caps? Has anyone ever built anything like this before? What's the best design philosophy?
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Old 13th March 2012, 11:56 PM   #2
Pemo is offline Pemo  Mexico
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I´m about to order this amp. What makes you think this needs a bigger trafo. The seller (along......) claims that a 150va 24-0-24 0-9 (that he also sells) is enough.

Do you have another gainclone to compare with?
Sound quality, detail, bass, etc.

RGDS

PEMO
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Old 14th March 2012, 03:29 AM   #3
Junm is online now Junm  Philippines
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schematics please?
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Old 21st March 2012, 09:15 PM   #4
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Is this worth buying?
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Old 23rd March 2012, 01:26 AM   #5
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Okay, so I was having some problems with the 20v transformer; all the expectable ones like no headroom and so on.

So I installed (with some trepidation) the 35v 5A transformer that resided on my test-bench. This had the immediate effect of pushing the speaker protection circuit straight out of it’s comfort zone and into latch-trip-off mode anytime it got pushed past a 6vRMS waveform. So Nurse, board surgery!

First job first, get rid of that awful latch. Option 1 would be to just link-out the output relay, but I kinda like the de-thump delay function, especially with that 6N tube warming-up. So, what controls it? There is a SIL UPC1237 right next door to the relay. The data sheet shows that the latch function is deactivated by an earth on pin three, so link-out C18.

That just left the laughably low level of the trigger. The cct is suppossed to be spec’ed for 68W/ch on a normal heatsink. Mine’s a bit bigger… So, I want to push this thing.

As a start on the trigger-level, with the two 56kRs monitoring the speaker channels summing into a 4u7F electrolytic, I tried a 25% reduction by discharging the 4u7 through a 100kR, but my eyes are getting so bad I got a 180kR instead. So I paralleled that up with another, but realised that it wasn’t transients setting it off, it was sustained bass power. That frequency-dependent characteristic is set by the 4u7.

Therefore, ultimate mod; stick a 10uF across that.

Job done. Now I can get 80w/ch out of it. Seriously, even the smoothing cans get warm. Never seen that before…
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Old 23rd March 2012, 01:33 AM   #6
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Quote:
Originally Posted by Pemo View Post
I´m about to order this amp. What makes you think this needs a bigger trafo. The seller (along......) claims that a 150va 24-0-24 0-9 (that he also sells) is enough.

Do you have another gainclone to compare with?
Sound quality, detail, bass, etc.

RGDS

PEMO
Hi Pemo.
It's Coke; I'm lovin it.
The bass is really good now; deep, tuneful. My mate Kev said it was " a thumpy piece of kit".
It really holds female vocals well; Eva Cassidy doing fields of gold had my friend Alison in floods of tears.
So, that's a 9 and a 9, and a 8.5 for stereo imaging. I still think it needs a firmer power supply (think; Point of Diminishing Returns).
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Old 23rd March 2012, 01:34 AM   #7
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Quote:
Originally Posted by Junm View Post
schematics please?
later
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Old 23rd March 2012, 01:36 AM   #8
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Quote:
Originally Posted by nullbyte View Post
Is this worth buying?
Yes.
My qualifications for saying that?
This is my company.
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Old 23rd March 2012, 01:46 AM   #9
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There are some further details of the build on there as well.
http://alacrityaudio.co.uk/2012/03/0...-project-pics/

Last edited by copperweed; 23rd March 2012 at 01:58 AM. Reason: added web address
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Old 23rd March 2012, 03:36 AM   #10
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Haha, sweet! Looking forward to seeing what else you do with it, the 10uF cap mod seems pretty great. What transformer do you think will work with a regular sized heatsink? I might have a larger one lying around too, so I might emulate your setup a little. Also, bought it!
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