eBay mono LM1875 kit

[DaveFred]

NO! this is to less for 2 amp boards. its a 12V - 12VA transformer with 1amp current.
please us in minimum a 80VA transformer. so a rule of thumb.
one channel can deliver in 8R speakers about 30W so you have 60Watt total + factor 1,5"dynamic reserve".....--> so its about 90VA. so i found that a 100VA-120VA is the same price with more power reserves.


please look at transformer with 2 secondary windings- or use a dual rail SMPS- less work and same result as fred wrote.


chris

I was asking if that was the correct type of small transformer to power *JUST* the speaker protection board as it requires AC12V to AC24V.

The main amp boards would get a proper separate DC+-24v SMPS.

Thank you,

David.

 

[chermann]

hi david


oh...sorry...i over read this. yes its enough.
but if you use the smps like fred show us...then you have additionally some outputs for preamp etc..


chris

 

[kp93300]

Smps regulatedwith LM7818. 22 v smps power in.
Lm 7818 hardly warm at all. No obvious detriment to the sound at all.
Speaker is markaudio 12p

 

[rabbitz]

Hey.... they look like the modules I gave away.

 

[kp93300]

Rabbitz
Yes. This are your modules. I have a fun with them and enjoying Trisha Yarwood at this very moment. It is as entertaining as the supergainclone! Thanks for your generosity.

 

[rabbitz]

Good to see they are being used and enjoyed.

 

[DaveFred]

Is there any reason I couldn't use a Laminated Core transformer instead of a toroidal transformer to connect to the dual rail power supply board?

Specifically this one,

https://www.mouser.ca/ProductDetail/Hammond-Manufacturing/266P18?qs=BJ2NLfHFoSmTmieF1Zt%2BoA==

I know they are expensive, but I already have a couple from another project.

 

[asuslover]

They are perfect, use them.

 

[mjf]

18Vac (ct) @ 5A ........gives 90VA.
does that mean these are 2 x 9Vac ?

 

[asuslover]

You are right mjf, it looks like they are 2x9v 5amps=90va, so a little bit low voltage.

 

[DaveFred]

Would something like this be suitable?



Link to VPS16-8100 Transformer

VPS16-8100
Electrical Specifications (@25C)
1. Maximum Power: 130.0VA
2. Primary – Series: 230VAC, 50/60Hz; Parallel: 115VAC, 50/60Hz
3. Secondary: - Series: 16.0V CT@ 8.1A; Parallel: 8.0V @ 16.2A
4. Voltage Regulation: 25% TYP @ full load to no load
5. Temperature Rise: 30C TYP (45C MAX allowed)
6. Insulation Resistance: 100MΩ

And they are pretty cheap, $27.90.

 

[asuslover]

Still not good, only 2x8v secundaries, if you are looking for something cheap take a look at this:https://canada.newark.com/multicomp...ransformer/dp/38K4905?st=toroidal transformer

 

[DaveFred]

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.

View attachment 807347
My board beside the ebay board

View attachment 807348
Populated big cap pcb beside the ebay board.
View attachment 807343
View attachment 807344
View attachment 807345

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.

The $64,000 dollar question, has anyone ordered boards and built this version?

 

[Sadface]

I have built a pair and they work as they should.

I have not hooked them up to my main system for serious critical listening but the results have been great in the system they are in.

Chermann took my spare pair of boards month or two back so we might get some testing results at some stage.

 

[chermann]

Hi sadface


yes it was at the beginning of September and i am still waiting for the pcb. good knows when it will be delivered.


chris

 

[DaveFred]

Just for Yucks, I decided to translate the Chinese supplied instructions that came with an Ebay LM1875ST kit.



Parts list right of schematic,

Component name Quantity
LM1875T
1M resistance: brown black black yellow brown 1
22k resistance: red red black red brown 2
1k resistance: brown black black brown brown 2
10Ω resistance: brown black black gold brown 1
10Ω1W: brown black black silver brown 1
10uf electrolytic capacitor
330pf (331) monolithic capacitor 1
47uf electrolytic capacitor 1
22nf(224) monolithic capacitor
100nf (104) monolithic capacitor 2
100uf electrolytic capacitor 2
2p terminal block 1
3p terminal block 1
2.54 terminal block 1
PCB board

Description from bottom,

Performance parameters: output power: typical 20W maximum 30w); speaker impedance: 4Ω-8Ω; total harmonic distortion: <0.04%: signal-to-noise ratio: 105dB
Frequency response: 14Hz100kHz (the maximum range calculated by the RC high and low pass circuit is 3.29Hz-482. 29kHz, the power supply voltage: recommended ± 25V (the maximum voltage cannot exceed ± 30, AC 18V full
The bridge rectifier is 25) Note: The resistance and the monolithic capacitor are not divided into positive and negative electrodes. The resistance value should correspond to the welding of the board. The long leg of the electrolytic capacitor is the positive electrode.
Treasure picture. Our company has more than 100 electronic kits, teachers, students, and fans can consult if necessary, thank you!

I found it interesting anyway...

David.

 

[DaveFred]

I am new to building amplifiers, and I am unsure if I have picked the right parts.

If anyone is bored, can they double check my selections?

Sorry about the formatting, it was the best I could do with the forum software.



LM1875T Bill of Materials

Component # -- Value -- Brand -- Part # -- Description -- Each -- Mouser Link
R1 -- 1M Ω -- Vishay -- CMF551M0000FHBF -- Metal Film Resistors - Through Hole 1/2W 1Mohms 1% -- $0.56 https://www.mouser.ca/ProductDetail...elj5bFfk4FtAzIRqjwPRk%2Bt5HC7H2iipGp7KThMjQ==
R2 -- 22.1K Ω -- Vishay -- CMF5522R100FHEB -- Metal Film Resistors - Through Hole 1/2watt 22.1ohm 1% 50ppm -- $0.82 https://www.mouser.ca/ProductDetail...Tmhe1Q9BKbT4Syeb1Kol2J9HjrWHOaOkF0Fu2%2B4tQ==
R3 -- 22.1K Ω -- Vishay -- CMF5522R100FHEB -- Metal Film Resistors - Through Hole 1/2watt 22.1ohm 1% 50ppm -- $0.82 https://www.mouser.ca/ProductDetail...Tmhe1Q9BKbT4Syeb1Kol2J9HjrWHOaOkF0Fu2%2B4tQ==
R4 -- 1K Ω -- Vishay -- CMF551K0000FHEB -- Metal Film Resistors - Through Hole 1/2W 1Kohms 1% -- $0.82 https://www.mouser.ca/ProductDetail/Vishay-Dale/CMF551K0000FHEB?qs=LPGv226TKJI%2BJ6H0OWpwaw==
R5 -- 1K Ω -- Vishay -- CMF551K0000FHEB -- Metal Film Resistors - Through Hole 1/2W 1Kohms 1% -- $0.82 https://www.mouser.ca/ProductDetail/Vishay-Dale/CMF551K0000FHEB?qs=LPGv226TKJI%2BJ6H0OWpwaw==
R6 -- 10 Ω -- Vishay -- CMF5510R000FHEB -- Metal Film Resistors - Through Hole 1/2watt 10ohms 1% -- $0.82 https://www.mouser.ca/ProductDetail/Vishay-Dale/CMF5510R000FHEB?qs=LPGv226TKJLUYQ3M1pJCKA==
R7 -- 10 Ω -- Vishay -- CMF6010R000FHEK -- Metal Film Resistors - Through Hole 1W 10ohms 1% -- $0.39 https://www.mouser.ca/ProductDetail...%2B2aD51zgE2h8X1uoWMQSWUbH%2B1mgpnKPmLENnRw==
C1 -- 10 µF -- Nichicon -- UES1H100MPM -- Aluminum Electrolytic Capacitors - Radial Leaded 50volts 10uF 85c 8x11.5 3.5LS -- $0.72 https://www.mouser.ca/ProductDetail/Nichicon/UES1H100MPM?qs=kArNe9LFxXklZCpwKNvlZg==
C2 -- 330 pF -- Vishay -- K331J15C0GF5TH5 -- Multilayer Ceramic Capacitors MLCC - Leaded 330pF 50volts 5% C0G 5mm LS -- $0.30 https://www.mouser.ca/ProductDetail...jbQwRn0EbJl2ADjOGVXJdeyQ9gIGrIyUlLzFt0%2BMA==
C3 -- 47 µF -- Nichicon -- UES1H470MPM Aluminum Electrolytic Capacitors - Radial Leaded 50volts 47uF 85c 10x20 5LS -- $1.14 https://www.mouser.ca/ProductDetail/Nichicon/UES1H470MPM?qs=kArNe9LFxXllYp69T5X4iA==
C4 -- 220 nF -- Vishay -- MKT1817422065 Film Capacitors 0.22uF 63V 10% -- $0.97 https://www.mouser.ca/ProductDetail/Vishay-Roederstein/MKT1817422065?qs=gf7KboYS0C74bO0tSIYI5Q==
C5 -- 100 nf -- TDK -- FG28X7R1H104KNT00 -- Multilayer Ceramic Capacitors MLCC - Leaded RAD 50V 0.1uF X7R 10% LS:5mm -- $0.27 https://www.mouser.ca/ProductDetail/TDK/FG28X7R1H104KNT00?qs=vNwBHymccZ/wzEPXJYHH%2Bg==
C6 -- 100 nf -- TDK -- FG28X7R1H104KNT00 -- Multilayer Ceramic Capacitors MLCC - Leaded RAD 50V 0.1uF X7R 10% LS:5mm -- $0.27 https://www.mouser.ca/ProductDetail/TDK/FG28X7R1H104KNT00?qs=vNwBHymccZ/wzEPXJYHH%2Bg==
C7 -- 100 µF -- Nichicon -- UFG1H101MPM Aluminum Electrolytic Capacitors - Radial Leaded 50volts 100uF 85c 10x16 5LS -- $1.11 https://www.mouser.ca/ProductDetail/Nichicon/UFG1H101MPM?qs=kArNe9LFxXmKPf4cG1tgWA==
C8 -- 100 µF -- Nichicon -- UFG1H101MPM Aluminum Electrolytic Capacitors - Radial Leaded 50volts 100uF 85c 10x16 5LS -- $1.11 https://www.mouser.ca/ProductDetail/Nichicon/UFG1H101MPM?qs=kArNe9LFxXmKPf4cG1tgWA==
IC -- LM1875T -- Texas Instruments -- LM1875T -- Audio Amplifiers 20-W Audio pwr Amp -- $5.49 https://www.mouser.ca/ProductDetail/Texas-Instruments/LM1875T-LB03?qs=X1J7HmVL2ZFQRJTsZH2odA==

 

[rabbitz]

Just make sure the lead spacing suits the PCB as well as the cap diameter. C3 can be a tight fit on diameter depending on the size of C1, C7, C8.

C1 can be a film cap 1-2.2uF.

 

[chermann]

Hi David


As rabbitz wrote. film cap as C1 . C3 as big as possible but this depends on the size of the C7, C8.
If you are not soldering directly on the pcb then look good quality terminals for input, output and power supply. look maybe at Digikey to get the LM1875 cheaper.


for posting some lists:
i do very often use escel and then print to pdf. after this you can upload this pdf to us. advantage is that you have in excel a list which you can better cost calculate and make easy some updates or compare some comonents.


Chris

 

[DaveFred]

I changed a few things depending on PCB space and availability, as well as changing C1 to a film cap.

Here is a Mouser cart,

Mouser Electronics Canada

Just make sure the lead spacing suits the PCB as well as the cap diameter. C3 can be a tight fit on diameter depending on the size of C1, C7, C8.

C1 can be a film cap 1-2.2uF.

Hi David


As rabbitz wrote. film cap as C1 . C3 as big as possible but this depends on the size of the C7, C8.
If you are not soldering directly on the pcb then look good quality terminals for input, output and power supply. look maybe at Digikey to get the LM1875 cheaper.


for posting some lists:
i do very often use escel and then print to pdf. after this you can upload this pdf to us. advantage is that you have in excel a list which you can better cost calculate and make easy some updates or compare some comonents.


Chris