eBay mono LM1875 kit

[rabbitz]

Originally Posted by chermann

Hi Rabbitz

I have the amp as you posted in #857

my uncoverd topics are: (from left to right)

the 10µF input cap is wrong polarized- but nevertheless we should use a foil cap.
the 47µF is the electrolytic cap for the PIN 2: at the other schematic´s its a 22µF non bolarized cap.
right/upper corner: the 3R3 is marked on the pcb but it should be a 1R resistor. 1W minimum
the supply electrolytic caps are not correct (100µF) because it should be 220µF at minimum on the supply
all other part i measured with my LCR meter and they are ok.

btw: at my kids the 1M and the 10R are missing - i claimed the seller....will see..
wating for power supply and then start with tests...


chris

Hi Chris

I've yet to decide what values I will end up using as still researching.

I'll be using a 1uF film cap on the input. I've seen various sizes for the feedback cap... TI has 22uF, P72 has 47uF, Gobo has 22uF BP, SC has 47uF. I've still looking at what I will use, but a lot recommend bipolar such as Nichicon ES or a very good Nichicon audio cap. For the zobel, TI and SC has 1R + 220nF, P72 has 10R + 100nF but I'll use 2R7 + 100nF as per my other Chipamps. Most LM1875 I've seen including TI have supply caps at 100uF but some do have 220uF. My power supply will be in a different case so I will add 2200uF caps in the amp case as that was recommendation from a previous build so I will use 100uF I think.

I still have to see if I need a Thiele network (L//R) on the output as have done that on most of my other amps.

[chermann]

Hi rabbitz
this is my first chip amp so i just compare the TI datasheet and the chinese "interpretation". so i have no experience and measurements....i read and learn
i will use the 3R3 at the output
as input cap i will use a 4,7 Wima MKS
the missing 1M and 10R i have on hand - the 220µF too
i will try the electrolytic 47µF at the feedback...first try...
we will see...

chris

[chermann]

Hi


The schematic of Gobo, schoolies ...are different to the TI datasheet at the inverted input of the amp....why is that "better?"


hmm. maybe the bipolar is the correct cap here...
chris

[blackdod]

My amp (with the same pcb´s as yours) came with a bipolar at the input. I am looking at the IT scheme and they also use a bipolar (1uF) here too.


http://www.ti.com/lit/ds/symlink/lm1875.pdf

[chermann]

Originally Posted by blackdod

My amp (with the same pcb´s as yours) came with a bipolar at the input. I am looking at the IT scheme and they also use a bipolar (1uF) here too.


http://www.ti.com/lit/ds/symlink/lm1875.pdf

yes. maybe i wrote it wrong. imean the NFB cap (the network for the pin 2 = inverted input). in the TI schematic is C2 22µF but its polarized.

chris

[rabbitz]

Originally Posted by chermann

Hi

The schematic of Gobo, schoolies ...are different to the TI datasheet at the inverted input of the amp....why is that "better?"

hmm. maybe the bipolar is the correct cap here...
chris

As far as I can see, electrically they are the same, just drawn differently.

Remember that Dunk02 (LM1875 layout thread) built it as per the listing and was happy with the end result.

[blackdod]

Originally Posted by chermann

yes. maybe i wrote it wrong. imean the NFB cap (the network for the pin 2 = inverted input). in the TI schematic is C2 22µF but its polarized.

chris

Sorry. I thought you mean the input capacitor.

[kurtvisti]

Originally Posted by rabbitz

R3 and the 1K are in the same place just before pin 1 on the chip. The location of the 330pF cap makes no difference for this resistor. The 10R is a ground lift resistor which sits between signal ground and power ground and can help reduce hum but have not seen it used on any of the Chipamps I've build but have on plenty of SS amps.

Thanx Rabbitz.
I now feel ready to have a go at testing both Daniels and the ESP P72 schematics on the ebay PCB.
How about the 15v dual power supply for preamp/active crossover at
LM1875_20W_diy_haoDIY?
Is it any good hifi wise?

[chermann]

Hi Kurtvisti

i personally think that your PSu from the link is not really suffiecient fo delivery enough power. just 2 4700µF is not enough - maybe its space to solder 2x 4700 caps per side, or smaller caps but 3pcs.- eg.g 3300µF . the diode are 1N5404 and the max current is 3Ampere so its ok.

at the big thread at the beginning there is a good proposal of a good psu:
Beginner's Gainclone, HiFi LM1875, The Amplifier Board

the idea of small VA for the transfomer to protect the LM1875 I not agree.
the a 160VA-250VA ( mono 100VA) sould be suffiecient


chris

[kurtvisti]

Hi Chris
I generally agree with your advice about the 25V POWERAMP LM1875 PSU, but my question was about the quality of the 15V PREAMP PSU-addition shown at LM1875_20W_diy_haoDIY.
Is that PSU-addition (used for powering a preamp) ok for hifi?