My LM3875 Amplifier

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bill6300gp

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Joined 2008
#1
My LM3875 Amplifier for TB4 Speaker.

Inner_1
An externally hosted image should be here but it was not working when we last tested it.

Inner_2
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Speak Protector
An externally hosted image should be here but it was not working when we last tested it.

LM3875 IC
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Outer_1, the main transformer for Amplifier.
An externally hosted image should be here but it was not working when we last tested it.

Outer_2
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Why do I add VR on this amplifier?
Because I don't have any preamplifier, I use them to adjust volume.

The following are wave-test(Square wave) measured by oscilloscope.
I use 8R resistor as load, and output Vp-p is set 20V(+/-10V)
100Hz
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1kHz
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20kHz
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50kHz
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100kHz
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Thanks for your reading.
 
#3
thomgun_lc said:
🙂 🙂 WOW Big Pictures, what about the sound?
Click to expand...

I feel not bad, but I can comfortably listen to music.
(It work about 50hrs)

Compared to LME49810 Amplifier which I made before.
(The article in LME49810 - a new cousin for LM4702 on Post #579 and Post #618)
1. The low frequency in music is not enough low. The speed of them is OK, I mean the sound of low frequency is "Q".
2. The median and high frequency in music has a little sound of tube and a little blur.
 
#7
Luck said:
Oh...Two power transformers are on the top of the case?Do you put a preamplifier IC inside?:smash: :smash:
Click to expand...

Because the case is too small to put The two transformers , supplying for LM3875 modules, outside.

I let this LM3875 as temporary amplifier for us because I have no preamplifier yet.
I give signal from DAC to the LM3875 amplifier, and only using VR to adjust volume.


The preamplifier and power amplifier is preparing...
The preamplifier: I want to try all transistors' amplifier circuits with remote control module.
The power amplifier: I want to try LME49830 circuits.
But I not sure what time to start.
 
#9
s800 said:
People rave about toroids for gainclones- curious if you have noticed any downsides with the traditional transformers?
Click to expand...
Downsides of "traditional transformers" are.
  • - They need more height.
    - They need more distance to the audio circuit, due to their wider stray magnetic field.
    - They are slightly less efficient.
    - They are getting ever harder to source, because of the hype around troroids.
But no shadow without light.
  • - They need less width and depth.
    - They usually have a higher saturation limit.
    - Their stray magnetic field is wider dispersed, thus weaker.
 
#10
If we only consider feel of hearing without other factors, EI- transformers(traditional transformers) and wreath-transformers(toroids) having some different feel.
Due to this, some of people still like to use EI-transformer.

But...
If I make power amplifier for us, LME49810 upto 300W for example, I will want to use wreath-transformers.
(The LME49810 amplifier,I made before, is for friends.)
When I make amplifier by tubes, I will only use EI-transformer because of feel of hearing.

Thanks for your suggestion.
 
#11
bill6300gp said:

I use DZ(diyzone) speaker protection, which is given from my friend. And it is already finished.

I can't find its circuit from www.diyzone.net now, so I have no circuit, sorry:dead: . I only find the circuit of LM3875 PCB out.
Click to expand...

hi bill6300gp,

I just bought the same speaker protection from a reseller on Ebay.

I am very pleased with the quality of the components: Holco resistors, Nichicon FW caps and some excellent 16A Omron relays. :bigeyes:

BUT, I only received all the parts + PCB, no schematics, no layout, no BOM. :cannotbe: Thanks to your photos above I was able to figure out how to place all the parts. :up:

Now, do you have info on the AC input requirements and limit? And/or, other usefull info?

Thanks a lot, berthej

BTW, a hard to read schematics can be found in this post: http://www.diyaudio.com/forums/showthread.php?postid=63212#post63212
 
#13
The heat sink a too large?, I use a computer(CPU) heatsink it is not even warm.

You don't really need a speaker protector for LM3875, when I turn ON or OFF the amp, there is a very small tut to the speakers.

You can mount the power transformer some distance away(that what I do) and the low ac voltage is carried via twisted wires and terminated on your amp chasis. The vision effect would improve.

Minimalist approach is always better(cleaner and sonic improvements). You can use the space for more channels and then make your speakers active, the sound will improve dramatically.

Just an opinion and past experience.

Cheers.
 
#14
ttan98 said:
The heat sink a too large?, I use a computer(CPU) heatsink it is not even warm.

You don't really need a speaker protector for LM3875, when I turn ON or OFF the amp, there is a very small tut to the speakers.

You can mount the power transformer some distance away(that what I do) and the low ac voltage is carried via twisted wires and terminated on your amp chasis. The vision effect would improve.

Minimalist approach is always better(cleaner and sonic improvements). You can use the space for more channels and then make your speakers active, the sound will improve dramatically.

Just an opinion and past experience.

Cheers.
Click to expand...

The heat sink is not hot indeed.
How big heat sink I used is because the case which is prepared before for another amplifier. But the original amplifier is given for my friend.
In the end, I decide to use this case for LM3875.

I test power amplifier form pre-amplifier that are usually tubes-amplifier, and I a little afraid that have the DC.
Due to this, when I make power amplifier will use speaker protectors.

The transformers and Minimalist approach I will reconsider when I make LM3875(or other amplifiers) next time.

Thanks for your suggestion.
 
#15
Bill,
please don't direct link those big pics to your post.
I have medium speed broadband and it took over three minutes to download this page.

Provide thumbnails to your pic server and we can choose to download if we want/need or compress to less than the Forum limit for attachments.

The down load speed peaked at 1.88Mbps and averaged ~50kbps with 34seconds completely idle while the pic server gave priority to some other downloads.
Please consider those that use dial up etc.
 
#16
berthej said:


hi bill6300gp,

I just bought the same speaker protection from a reseller on Ebay.

......... Thanks to your photos above I was able to figure out how to place all the parts. :up:

Now, do you have info on the AC input requirements and limit? And/or, other usefull info?
Click to expand...

Bill & Berthej-
Thanks for the info on the SP board.

I'm just putting together one of these speaker protection boards myself, and it caused a bit of 'head scratching' for a few minutes. It looks like ONLY the + output from amp and + to the speaker is connected to the SP board. (There are only two IN and two OUT pads on the board.) It took me a while to figure out that the GND connection is between the two AC terminal connectors.
(There is a 'competing' SP kit on eBay that has simpler IN/OUT connections, and I'd just put one of them together as well.)

BTW, the eBay ad listing for my SP kit mentioned that AC 10V-36V will work.
Quote:
FEATURES
‧Ultra High Speed Reacting
‧Independent Two Channel Design.
‧Trigger Voltage DC 0.5V
‧Military / Audio Grade Parts / OMRON High Current Relay
‧Suitable for 10W-250W Power Amplifiers
‧Delay Speaker Turn-On (Thump Killing Function)
‧DC Output Protection. Disconnects the loudspeaker when DC appears .
‧Wide Power Supply Range AC10V to 36V
‧Build-In Regulator System

Cheers
John
 
#17
Edit-
For others thinking of buying this style SP board....
I forgot to mention that it seems this SP board will work with 'stereo' amps with common ground at the outputs and also a CT-type AC supply. The SP board is looking for a common ground and AC-CT connection.

John
 
#19
berthej said:


hi bill6300gp,

I just bought the same speaker protection from a reseller on Ebay.

I am very pleased with the quality of the components: Holco resistors, Nichicon FW caps and some excellent 16A Omron relays. :bigeyes:

BUT, I only received all the parts + PCB, no schematics, no layout, no BOM. :cannotbe: Thanks to your photos above I was able to figure out how to place all the parts. :up:

Now, do you have info on the AC input requirements and limit? And/or, other usefull info?

Thanks a lot, berthej

BTW, a hard to read schematics can be found in this post: http://www.diyaudio.com/forums/showthread.php?postid=63212#post63212
Click to expand...

Sorry for seeing this reply now😱.

AC power input:12VAC-0-12VAC, current is about 0.5A~1A.

If speaker protection is not work and all parts is on the right place.
Try to use higher HFE transistors replace original transistors.

AndrewT said:
Bill,
please don't direct link those big pics to your post.
I have medium speed broadband and it took over three minutes to download this page.

Provide thumbnails to your pic server and we can choose to download if we want/need or compress to less than the Forum limit for attachments.

The down load speed peaked at 1.88Mbps and averaged ~50kbps with 34seconds completely idle while the pic server gave priority to some other downloads.
Please consider those that use dial up etc.
Click to expand...
Because I can't edit post when having reply.
So I only change pictures.

If someone want to see bigger one, try to change url like following:
Code: 
..../LM3875_01.jpg => ..../LM3875_01M.jpg
 
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