eBay mono LM1875 kit

[NareshBrd]

Instead of worrying about a 1kHz test, I would connect it to different speakers, and play a known piece of music through the amp, see how it actually sounds.
And through your headphones too.
The input and the speakers are important too....

Enjoy.

 

[JonesySA]

I just found two of these kits in my parts drawer. I'd like to populate with genuine components.
Does anyone have a suitable BOM / shopping cart for mouser/digikey?l etc?

I was overwhelmed by the options then discovered not all components are available in Australia.

 

[chermann]

Hi
here is my best parts list. the luxury housing and the bigger PSU is according to other members not relay needed.


rabbitz version is that( refered to Brain BEll)
Reference: Brian Bell (Chipamp.com) LM1875 (schematic unknown)
Default configuration [components used in rabbitz build 2019]
R1 - not used (optional resistor to ground before C1) [not used]
R2 - 22k (input to ground resistor) [0.5W MF] 0,5 WATT R3 - 1k (gain resistor , gain = 1 + R4/R [0.5W MF] 0,5 WATT R4 - 22k (nfb resistor - on bottom of pcb) [0.5W MF] 0,5 WATT R5 - 2.7 2w (optional - zobel network) [2R7 2W MF] 2,7R - 3W R6 - jumper (optional resistor between input ground and output ground) [not used, linked]
C1 - 2.2µF (optional input capacitor) [1uF MMK] MMK version C2 - 22µF bipolar (optional) [Nichicon ES 22uF 25V] just 22µF C3 - 0.1µF (power supply decoupling) [ceramic X7R Vishay BC] XR7 Temp class C4 - 47µF (power supply decoupling) [Nichicon KZ 47uF 50V] 47µ Nichicon KZ C5 - 0.1µF (power supply decoupling) [ceramic X7R Vishay BC] XR7 Temp class C6 - 47µF (power supply decoupling) [Nichicon KZ 47uF 50V] 47µ Nichicon KZ C7 - 0.1µF (optional - zobel network) [MKT]
Note: 1K resistor after input cap not listed above but installed [0.5W MF]

https://www.diyaudio.com/forums/chip-amps/341675-ebay-mono-lm1875-kit-40.html#post6006059
Finally made a LM1875 amp

enjoy this amp
chris

 

[rabbitz]

Does anyone have a suitable BOM / shopping cart for mouser/digikey?l etc?

I was overwhelmed by the options then discovered not all components are available in Australia.

It's easiest to stick with the values in the original SC article as that's what I mostly did on my final build. The only change I made was the zobel 2R7/100nF, 220pF in lieu of 330pF and a 1uF MMK (MKT also OK) input cap. Make sure you use monolithic X7R for the 100nF by-pass caps.

You should be able to get most parts from Altronics and better power supply caps from RS Components if desired. Digikey is also good if you are ordering other components as well to make up the A$60 free shipping.

If you are having difficulty in sourcing I can send you 2 Nichicon ES 22uF 25V and 4 Nichicon or Panasonic 220uF.

 

[chermann]

Hi rabbitz
thank you for your additionally inputs.


if you need ceramic isolation between the power chips. here i got some for my class A. watch out they are available with or without holes:
10pcs aluminium nitride ceramic substrate thermal conductive insulating ceramic TO 220/247/264/3P/3 aluminium nitride|Air Conditioner Parts| - AliExpress
chris

 

[motokok]

Hello guys, I'm thinking of using the LM1875 for my first DIY build. I'd like to use this with 84-85db 8ohm small desktop speakers.

Would this chip be OK with this kind of load at low-normal listening levels?

Assuming yes, it seems that the majority of the total build cost is the chassis and power supply, specifically the toroidal transformer.

Could you tell me what I would need there? I'm unclear if I need 1 transformer per channel or if I can run both channels off a single trafo?

On transformers, can anyone run me through the load requirements for a stereo amp to determine the secondary voltages and VA needed from the trafo?

Thanks!

 

[rabbitz]

The LM1875 would work fine with those speakers in a small to medium room at normal levels.

One transformer is ample and would suggest 15V-0-15V 80VA to 120VA. This will give around ±21-22VDC after rectification. You can use 18V-0-18V (±25-26VDC rails) but gets close to the limit of the chip especially with lower impedance speakers and the chip gets hotter with the higher rails. 4700uF caps per rail would be enough.

For some guidance on the LM1875, have a look at Rod Elliott's Project 72 as it gives some insight into the power supply.
Single Chip 25W Amplifier (Project 72)

I've added a pic for reference showing a power supply with a single transformer in the build.

 

[rabbitz]

I've added another pic of a power supply for my last build which is in it's own case and uses an umbilical cable to the power amp case.

 

[motokok]

Thanks a lot, rabbitz! The photo explains tons for me! So, this is great news it is possible to run 2 chips with 1 trafo and 1 rectifier, where you split the DC output to each LM1875 with that black cable. How did you do that, btw? Do you use a 6 conductor cable or special connector?

Regarding trafos, I have found Antek which seems much cheaper than anything else. They offer 100VA and then 200VA; nothing in between. Excluding cost and size, is 100VA less desirable than 200VA at all?

 

[rabbitz]

You have 2 DC outputs from each rail and PS ground. So you end up with Transformer > Bridge Recifier > Capacitors > 2 wires from each +ve, -ve and power ground. If you look at the Pic in post #847 there's a Molex with 6 leads and I've added a pic of a LM3875 where you can see it easier with different coloured wires. Red +ve, black -ve, green ground.

!00VA is fine and 200VA would be overkill.