First LM3886 Gainclone Build - Need Guidance/Suggestions

It plays fine at 50% volume but the SPL sags at 80% after a couple of minutes.
When I check DC at the speaker binding posts I get 70 mv & 116 mv on left and right channel respectively.
 
I've 2200uf x 2 per amp pcb and 10,000uf x 2 on rectifier pcb

capacitor bank per rail, is it the no. of capacitors on power suppy or capacitors on amp pcb or a total of both?
 
I've 2200uf x 2 per amp pcb and 10,000uf x 2 on rectifier pcb

capacitor bank per rail, is it the no. of capacitors on power suppy or capacitors on amp pcb or a total of both?

I was referring to PSU board capacitor bank.

20000 uF per rail would be good. So total 2 x 20000.

2 x 10000 uF is too low, I feel.

Your DC offsets are on higher side.
 
It plays fine at 50% volume but the SPL sags at 80% after a couple of minutes.
When I check DC at the speaker binding posts I get 70 mv & 116 mv on left and right channel respectively.

As others have pointed out earlier in the thread,the transformer looks suspect.
You would need at least 7-amps from the 18-0-18 transformer to power up two channels delivering around 40W each into 6 ohms.
Is the current rating mentioned on the transformer somewhere?

Try powering up only one channel and see if you can crank up the volume a bit more.

Have you checked the dc offset with input grounded(recommended) or left floating?
 
This scavenged transformer along with the LM3886 amp boards have been tortured enough.

I've decided to build a new amp with a suitable transformer preferably a toroid.

Now, I'll need help with these below.

A) I want to build a stereo amp for 6 ohm, Sensitivity: 86dB/2.83V/m speakers (wharfefdale 9.1)
B) I am aiming at a min of 50 watt / channel
C) Want to add this along with a line level input as well
D) Please advise if this kit is good enough and how much tweaking will be required to set the gain etc to achieve my goals.
E) Will I need a transformer with 22 0 22v x 1 (stereo amp boards) and 0 12 x 1 (BT decoder board)

Please confirm so I can order the amp boards.

BR,
Abhishek
 
Yes it is possible. Connect the extreme ends of the secondary winding (do not connect the centertap anywhere) to the a/c inputs of a bridge rectifier

But since the transformer rating is the same the current you can draw at 12V is half of what is rated at 6V
 
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OK, so an output rated at 6 0 6v with 1A will become 0 12v 500Ma

Also, after connecting the extreme ends of secondary to rectifier pcb AC input will we get 12v from joining V+ & V- together (6+6 =12v) and 0v from centre tap?
 
OK, so an output rated at 6 0 6v with 1A will become 0 12v 500Ma

Also, after connecting the extreme ends of secondary to rectifier pcb AC input will we get 12v from joining V+ & V- together (6+6 =12v) and 0v from centre tap?

I am not sure I understood you properly. What is your output voltage requirement ? What is the rectifier you are using ?

Please do not connect anything unless you are sure of it
 
This scavenged transformer along with the LM3886 amp boards have been tortured enough.

I've decided to build a new amp with a suitable transformer preferably a toroid.

Now, I'll need help with these below.

A) I want to build a stereo amp for 6 ohm, Sensitivity: 86dB/2.83V/m speakers (wharfefdale 9.1)
B) I am aiming at a min of 50 watt / channel
C) Want to add this along with a line level input as well
D) Please advise if this kit is good enough and how much tweaking will be required to set the gain etc to achieve my goals.
E) Will I need a transformer with 22 0 22v x 1 (stereo amp boards) and 0 12 x 1 (BT decoder board)

Please confirm so I can order the amp boards.

BR,
Abhishek

Why not seriously look at the MyRef LM3886 kit available from Linuxguru in Chennai? This board has a compensation scheme designed by the late Mauro Penasa, and tweaked to the max by various DIYers including Linuxguru. I have a feeling the MyRef boards will be way superior to the one you've linked.

For very detailed explanation of how to design your own LM3886 based amp, read and understand this article:

A Complete Guide to Design and Build a Hi-Fi LM3886 Amplifier - Circuit Basics

A Complete Guide to Design and Build a Hi-Fi LM3886 Amplifier - Circuit Basics

Also read this page:

https://www.neurochrome.com/taming-the-lm3886-chip-amplifier/

It's best to go with the recommended transformer configuration and PSU to achieve rated power without burning/blowing up something.

And here's an old but very long thread on the MyRef amp:

http://www.hifivision.com/diy/11495-group-buy-mauro-penasa-myref-rev-c-kit.html
 
This scavenged transformer along with the LM3886 amp boards have been tortured enough.

I've decided to build a new amp with a suitable transformer preferably a toroid.

Now, I'll need help with these below.

A) I want to build a stereo amp for 6 ohm, Sensitivity: 86dB/2.83V/m speakers (wharfefdale 9.1)
B) I am aiming at a min of 50 watt / channel
C) Want to add this along with a line level input as well
D) Please advise if this kit is good enough and how much tweaking will be required to set the gain etc to achieve my goals.
E) Will I need a transformer with 22 0 22v x 1 (stereo amp boards) and 0 12 x 1 (BT decoder board)

Please confirm so I can order the amp boards.

BR,
Abhishek
As "Jls001" pointed out Myref rev C will be all together at a different level of chip amp, the amplifier board you mentioned will not be able meet the SQ of Myref.

I think it is wrong idea to power lm3886 with 12-0-12, and also I would say avoid using same power supply for your amplifier board and music player.

You might go for a transformer with dual output voltages (24-0-24 and 12-0-12) which you can feed into respective rectifier and filter boards.

Other good option is PeeCeeBee Amp by FM "Shaan", you won't regret if you build PeeCeeBee, it is such a wonderful amplifier.


Regards
Bilal
 
So far what I've gathered is soldering parts on pcb is 10% of the build.
With my present skill level I'm only capable of soldering and follow wiring connections when explained at dummy level.
Most important for me at this stage is to understand and practically wire up everything successfully.
I understand the concept of working of an amplifier.

I need to learn how to wire everything up confidently to get an amplifier working.

ATM I'm struggling at the transformer and rectifier stage. Would love to build either PeeCeeBee or MyRef depending on availability.
 
ATM I'm struggling at the transformer and rectifier stage. Would love to build either PeeCeeBee or MyRef depending on availability.

If you are planning to build PeeCeeBee then you can use a power supply circuit as shown in below image. Additionally you will have to add fuse in this circuit.

If you are building Myref amp then it already comes with a power supply section on the same board, doesn't need a separate power supply.


When I started I didn't ask questions and made a lot of mistakes, Don't make the same mistake I did. Later realised "No question is stupid question".

Regards
2c6a755c207c0da5c861714bb410d4cc.jpg
03ce7a6a359f3e199d55bff4c1418769.jpg


Regards
Bilal
 
Hi All,

For the last 2 days, I've been pondering over a thought of building a LM1875 based GC and based on the info given here

I've done a few calculations with 15 0 15v transformer as a base, please double check them for me.

GOAL: 20W per channel

SPEAKERS: 6ohm

Would like to use a single transformer with a single bridge rectifier


15.49V - PEAK OUTPUT VOLTAGE
+/-22.72V - MAXIMUM SUPPLY VOLTAGE NEEDED BY THE AMPLIFIER
24.66V - MAXIMUM SUPPLY VOLTAGE OUTPUT BY A TRANSFORMER
24.51W - OUTPUT POWER FROM A TRANSFORMERS VOLTAGE RATING
61.65W - REQUIRED TRANSFORMER POWER
92.47W - REQUIRED TRANSFORMER POWER(multiplied it by a factor of 1.5)
184.95VA - Stereo amplifier powered by a single transformer.

From what I've gathered 15 0 15v CT (200VA) transformer should work, how many amps will it roughly be ?

BR,
Abhishek
 
Hi All,

For the last 2 days, I've been pondering over a thought of building a LM1875 based GC and based on the info given here

I've done a few calculations with 15 0 15v transformer as a base, please double check them for me.

GOAL: 20W per channel

SPEAKERS: 6ohm

Would like to use a single transformer with a single bridge rectifier


15.49V - PEAK OUTPUT VOLTAGE
+/-22.72V - MAXIMUM SUPPLY VOLTAGE NEEDED BY THE AMPLIFIER
24.66V - MAXIMUM SUPPLY VOLTAGE OUTPUT BY A TRANSFORMER
24.51W - OUTPUT POWER FROM A TRANSFORMERS VOLTAGE RATING
61.65W - REQUIRED TRANSFORMER POWER
92.47W - REQUIRED TRANSFORMER POWER(multiplied it by a factor of 1.5)
184.95VA - Stereo amplifier powered by a single transformer.

From what I've gathered 15 0 15v CT (200VA) transformer should work, how many amps will it roughly be ?

BR,
Abhishek
It will be around 6.6 Amps, here is a online calculator for converting VA to Amps.

http://www.rapidtables.com/calc/electric/va-to-amps-calculator.htm

The link you provided is for a LM3886 amp and you were referring LM1875, I'm little confused.

If you want to build something with LM1875, you can go with Miniref by Linuxguru which is a younger brother to Myref rev C. If you want to build it yourself, you might be able to find the schematic on diyaudio, or you can buy it as a kit from Linuxguru.

Myref/Miniref bring out best of LM3886/LM1875 chips, no other reason to emphasize on these design. By the way I have built 4-5 chip amps with lm3886.

Regards
Bilal
 
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I refered to that LM3886 build link for calculations only.
Which approach will give the most learning, building it myself or assembling a kit
The reason I'm looking at Lm1875 is because of fewer no. of pins as compared to Lm3886
Also, for some reason I believe that I'll be able to put LM1875 together with a few trials.

The calculator link you shared needs total no. of watts and max peak to peak line voltages, so 185W and about 49Vdc - correct?

All this is with LM1875 & 15 0 15v transformer with calculations based on formulas given in the 3886 build link
 
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