eBay mono LM1875 kit

Hi
compared to the Marantz PM6006 i try to list all components for a complete amp with single chip per channel to have a cost overview between DIY vs. commercial amp.
https://www.diyaudio.com/forums/chip-amps/341675-ebay-mono-lm1875-kit-43.html#post6009010
best parts amp:
https://www.diyaudio.com/forums/chip-amps/341675-ebay-mono-lm1875-kit-37.html#post5997205
cap bank version 2:
https://www.diyaudio.com/forums/chip-amps/341675-ebay-mono-lm1875-kit-39.html#post6002877
I found a lot of components in my work bench but i try to give you the price for each components.
attached the list --> 173 euros for a complete amp:)
chris
Merry Christmas and a happy new YEAR 2020 !!!


Super work, Chris and others.
Out of the 173 Eur, more than half is for an aesthetical wrapping (cabinet) which can be reduced somewhat for those who just want the mere basics. About one third is for a power supply with a transformer. The transformer can be found somewhat cheaper if salvaged from an old commercial amplifier (typically made in Japan, disregarding the brand, and of good quality).

Allow me to conclude for new DIY'ers who may read this thread, based on thorough and competent listening tests by Chris, rabbitz, fdenys and many more, that effort and skill in DIY work is rewarded by constructions that are often at least on level with high-class commercial products but at a fraction of the price. Not only do you learn a lot about electronics with DIY and know how to solve many problems yourself, you also get access to sound quality that could else be a load on your economy.
 
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Hi FF


Yes you are right - the housing is very expensive if we compare to the other parts.


yes a cheaper transformer and housing press down the total costs. never the less i forgot the 2nd board ...so here is the correct "luxury" version with +18,83€ for the other channel;)


chris
 

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...start to build a parallel LM1875 each channel..

Hi


i started in the "old year" :p with the parallel chip amp. i want to have a better 4ohm current capability and take the challenge to build the amp boards with my planned housing..:)


here some fresh pictures. the cap bank will not be installed and the naked pcb is for my fuse and terminal +V, GND, -V. i wish i have more room for that parallel amp :D;)



chris
 

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Some tips and hints for "LM1875t kit"

The cost issue discussed earlier inspired me to summarize my own experiences sofar.
I believe the cost can be reduced - while remaining high standards
Hopefully my remarks might add a bit to help others to start or conduct their own project.
It's fun to make!

I will discuss following issues:
1- My experience so far with the standard kit
2- which kit to buy
3- An inexpensive but quality low noise Audio SMPS as alternative Power Supply
4- An inexpensive compact housing

1- My experience with the LM1875 kit.
So far i built and tested a standard kit (2 x) with the following results after approx a week of testing:
- the sound is excellent with the delivered components. (only input cap replaced by 2.2 uF foil type cap)
- The amplifier is dead silent
- A stereo setup delivers more than sufficient power for my living room of over 50 m2
- In daily use - playing music (at moderate to loud level) the amplifier and power supply are not getting hot at all.
- No switching on- or off clicks with the standard boards (no additional delay circuitry etc)
- The LM1875 chip delivered is certainly a fake one. This is annoying because to tune the circuit you need to know with which chip you're dealing with.

In conclusion: even a standard board using the delivered components outclassed my vintage Marantz.
The fake chip delivered is most probably a TDA2050 kind of chip.
The TDA2050 no doubt is also an excellent chip, although the LM1875 is generally considered somewhat superior (if you can find genuine ones).

In my case, any fine tuning of the board had to be based on the TDA2050 datasheet characteristics.
Especially the supply voltage should be kept at about +/- 23 V dc. See the TDA2050 data sheet.
In access of about 24 V i noticed oscillations, most probably because the built-in protection starts to be triggered. Reducing the voltage to 23 V immediately re-established stable conditions.
I measured about 25 W of clean power at 8 Ohms.

2- Which kit to buy?
In the meantime i ordered several kits from different sources.
It looks like there are two kind of kits, lets call them "Set A" and "Set B"
At first sight they look identical.
But there are important differences!

In general SET "B" is preferred:
The PCB is superior (important!).
The PCB layout is identical, but the soldering "islands" are bigger. Also the board-holes are side-plated and on the top-side of the pcb there is another "soldering island", resulting in easier soldering and better contacts
Look at the annexed pictures comparing the boards.
Set "A" PCB
Set-A.jpg
Set "B" PCB
Set-B.jpg

Next the "LM1875" of set "B" could be a real chip (not tested yet), all my experiments sofar were on set "A".
There are no side notches (typically found for TDA20xx series)
Also characteristic of set "B" is, that a TO-220 silicone insulation set is included/supplied.

My suggestion is to go for set "B", look at Ebay etc and you will easily see the differences: particularly watch for the top layer of the PCB (soldering islands)
and the silicon insulator.

3- An audio quality SMPS, low noise +- 24 V (and 12 V). Supply spec is 600 W (6A)
I decided to follow a different route for the power supply and bought a SMPS (approx $24- excl $9 shipping).
see: SMPS

Advantages:
The output is regulated, adjustable between approx 21 and 29 V. This is important, because a genuine LM1875 can operate till 30 V, while a TDA2050 or other fakes, should not be operated above 25 V.
During my experiments i liked the flexibility of having a variable 21-29 V range!
Of course a regulated supply is advantageous and the ripple is max 150 mV.
The unit is very compact and of relatively light weight.
Under use it is not getting hot (or even warm).

Most important however: it greatly simplifies the project and allows a compact amplifier in comparison to a traditional transformer and rectifier/ caps.
Furthermore it reduces cost (approx $24 - excluding $9 shipping)

4- The casing
Of course that remains a personal matter, but my idea: the most beautiful power amplifier is an "invisible" one.
So i will simply place the finished amplifier somewhere hidden.
I decided to order a RND black aluminium (4 mm thickness) extruded case. Type RND 455-00758, cost about EUR 15 (another cost saver) .
see: Aluminium case
My present prototype with an oversized heatsink is not even getting "hand-warm", so i might try to use the 4mm aluminium case as heatsink.
Although the casing is rather compact, it will be housing the SMPS power supply - as well as 3 x LM1875 boards (the third board for two rear/surround effect speakers)

Fred
 
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That's a really good description with lots of useful advise to new DIY'ers. Personally, I appreciate your statement that 2x25W is sufficient at home even in a big living-room.
The LM1875 is very suited as a project also for less experienced DIY'ers because the costs are very moderate and the SQ amazingly good for the investment. Class AB amplifiers allow typically more "mods" and experiments than class D amplifiers because class D chips are optimized for a certain implementation (shown in the datasheet) and apart from using components of high quality, there are less hidden resources to reveal from a class D chip.
Class D chips can indeed be very good but working with a class AB chip may leave you a better idea of how an amplifier, as a regulated system, functions.
 
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Hi Fred


Very good example of "do it cheap". thanks for that.
about the PCB: yes i can agree the PCB are delivered in SET A and SET B i bought a lot of kits from the same seller but I get different pcb - SET B is with through hole connection and is better for soldering. be arew both pcb are not good for changing components more the 1 time :( - the solder dots getting loose!


finally this kit give everybody new DIY a fine result for Sound and a lot of fun to start and mod it:)



chris
 
Chris,
To avoid misunderstandings: my objective is not persé "making it cheap".
At the contrary, i simply want to finally get the maximum out of the box, regardless of cost.
However as a (retired) Philips manager and graduated electronics engineer, (by nature) i am cost conscious and critical.
After studying various possibilities (for instance) i simply believe the SMPT is technically superior today over a conventional PS. Of course provided you select a suitable one.
A side effect is, that it is also cost effective and more simple, but that was not my main objective.
This is all work in progress and a very first prototype. Just to see whether there is any potential and also as a hobby project for the dark season days...
In the meantime i found out that, yes..! - this simple circuit fully meets and exceeds my expectations. It fully justifies further efforts and time to explore and study.

Eventually i will most probably join FauxFrench' interesting efforts for a more advanced composite solution, but i will do that step by step.

Fred
 
Hi Fred
Sorry my internet was down up to now....


Sorry for my easy saying " do it cheap" - i do not want to blame you.;)


the only thing what i really give me goose pumps at such SMPS for DIY is the primary side is not protected against touching - so please be aware that the primary you have more then 230V ....look at the primary cap (3rd pic) ...400V


You are an EE- so you know that :)


chris
 
There is no real risk of touching a 300V dc point really. This potential is only at the downside of the board, which is completely screened from the "outside".
Of course you should never involve yourself with the internals/inside of the SMPS (unless you know very very well what you are doing).

The unit complies with the international Safety standards: GB4943, UL60950 and EN60950.
If it would be possible to simply touch 300V from the outside - of course it would never have complied to the international Safety qualifications.
 
The LM1875 Bigcap

Hi guys,

I figured I'd leave this here in case anybody is interested.

I've designed an LM1875 PCB. I call it the Bigcap.
It turned out halfway between the old schoolies amp and the datasheet implementation.

-I removed the 10R ground lift resistor. It doesn't feature on the datasheet and my understanding is that this is generally unnecessary.
-I added fuse rails back onto the board that were taken off the Ebay pcb when they ripped off the schoolies PCB design.
-I've changed the screw terminals for power connections and outputs to spade connections.
- Space has been allocated around the 22uF feedback cap to allow large sized film caps (up to 27mm pitch) instead of an electrolytic can.
- Space has been allocated between the power supply decoupling caps to allow a screw driver to access the IC.

IMG_1162.jpg
My board beside the ebay board

IMG_1163.jpg
Populated big cap pcb beside the ebay board.
IMG_1156.jpg
IMG_1157.jpg
IMG_1158.jpg

Attached are the gerber files if anybody feels like a JLCpcb order.

Given that the minimum order is 5 and these are typically used in pairs, I do have 1 spare board I could send for testing if somebody with test equipment is interested.

I could also provide something like a mouser BOM as thats where most of my parts have come from.
 

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Turns out a Mouser only BOM won't be possible.

Mouser doesn't stock the 1R resistor in a CMF65 or RN65, I got them from Element 14.

Mouser also doesn't have the best options for spade terminals or fuse rails, I purchased these from Element 14 also.

With name brand/quality parts throughout: total parts bill came to about $25 NZ per board (roughly $15 USD or Euro).

Wima film caps
Panasonic 10000hour electro caps
Vishay Monocap ceramics
Vishay/Dale RN/CMF resistors.

I do find it a bit amusing that the 22uF film cap is more expensive than a genuine LM1875 ($8.19to $4.69)
 
Thanks for sharing as it's nice to see another build and a different approach. Never seen a film cap for the 22uF bipolar as most of the builds I've seen use a Nichicon ES.

Any reason for using a film cap in this location?

Spades and fuse holders are also found at Altronics.
 
Hi guys.

I read it enough times on these forums that the feedback cap is the most important part in the circuit for sound quality.

My logic is that a film cap is generally better than an electrolytic. So that’s what I did.

I did notice that some recommend up to 100uf however my plan here was to work off the data sheet. It would surely be possible to find a larger value film cap with 27mm lead spacing.

Space was probably the biggest factor. I think my point was proven by the photos a page or 2 back of an eBay board with larger components stuffed into it.
 
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I ordered 2 of the eBay lm1875 mono boards as a first amp project. I’m looking for advice on kits for the power transformer, power supply, speaker protection board and transformers. I’m looking for pre existing kits to work from as I am very new to the diy audio hobby.

Some components I was considering:
- Antek AS-3225
- 120A Amplifier Rectifier Filter Power Supply from eBay
- UPC1237 Stereo Speaker Protection Board Delay Boot Circuit Module AC 12V-18V 5A from eBay (I think I need a separate transformer for this)