Hi
I have a 18v-0-18v 160va toroidal which i would like to use. Most of the amplifiers I have build of late are low power d-class using laptop SMPS and I have little knowledge of linear supplies.
My speakers range between 4 and 8ohms and what ever I build should be very good sounding and reasonably cheap.
I had considered an LM1875 but 160VA seems overkill or doesn't it matter?
This has received some favourable reviews for the price:
20W HIFI Mono Channel LM1875T Stereo Audio Amplifier Board Module DIY Kit 878881388223 | eBay
A step up would be the LM3886 however I don't know of any relatively complete cheap kits out of china that are worth building?
Also, would 18V be fine for 4-8ohm loads?
Would there be any suitable d-class amps that would benefit from a linear supply? i.e. ~25v after rectification?
Thank you
I have a 18v-0-18v 160va toroidal which i would like to use. Most of the amplifiers I have build of late are low power d-class using laptop SMPS and I have little knowledge of linear supplies.
My speakers range between 4 and 8ohms and what ever I build should be very good sounding and reasonably cheap.
I had considered an LM1875 but 160VA seems overkill or doesn't it matter?
This has received some favourable reviews for the price:
20W HIFI Mono Channel LM1875T Stereo Audio Amplifier Board Module DIY Kit 878881388223 | eBay
A step up would be the LM3886 however I don't know of any relatively complete cheap kits out of china that are worth building?
Also, would 18V be fine for 4-8ohm loads?
Would there be any suitable d-class amps that would benefit from a linear supply? i.e. ~25v after rectification?
Thank you
160VA is fine. No problem there.
The 18 volt rating should be OK, although at low loading the supply will rise a little and it is near the 'top end' of the LM1875's absolute maximum of 60 volts. How near depends on your mains voltage and the regulation of the transformer.
Remember the DC voltage is around 1.4 times the applied AC as an easy reckoner.
Less is often the better alternative for amplifiers like this and tbh a 15-0-15 would perhaps be a better option, and more so for 4 ohm loading.
No idea on Class D, sorry 🙂
The 18 volt rating should be OK, although at low loading the supply will rise a little and it is near the 'top end' of the LM1875's absolute maximum of 60 volts. How near depends on your mains voltage and the regulation of the transformer.
Remember the DC voltage is around 1.4 times the applied AC as an easy reckoner.
Less is often the better alternative for amplifiers like this and tbh a 15-0-15 would perhaps be a better option, and more so for 4 ohm loading.
No idea on Class D, sorry 🙂
The 2x25 Volt is very fine for LM1875 as Mooly concludes. 25V should leave you 30W in 8 Ohm and 60W in 4 Ohm. With 4 Ohm, it will be on the limit of 4 Amp for the LM1875 output so in 4 Ohm it may stop a little before. Anyway, with 60W for each channel you have 120W for two channels. Class AB has an efficiency approaching 70% at full output. Therefore, your 160VA available leaves about the right margins for amplifier losses. It is no overkill.
A good choice.
For class D, I have a TA2022 running on just 2X18V and it sounds great. With 2x25V it can only be better. I also tried a TDA8954 that will do fine with 2x25V. More possibilities.
You call it a "linear" supply. Linear often means you have a linear regulator inserted, which you hardly have voltage margins for.
Good luck with the project!
A good choice.
For class D, I have a TA2022 running on just 2X18V and it sounds great. With 2x25V it can only be better. I also tried a TDA8954 that will do fine with 2x25V. More possibilities.
You call it a "linear" supply. Linear often means you have a linear regulator inserted, which you hardly have voltage margins for.
Good luck with the project!
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Thank you for the responses this is very promising.
Is there a cheap generic power supply board that would be ideal or even gerbers to have printed?
I could whip one up on projects board but I prefer a proper printing.
Is there a cheap generic power supply board that would be ideal or even gerbers to have printed?
I could whip one up on projects board but I prefer a proper printing.
Sorry, I haven't got one. I always use these bread-board PCBs with a regular array of pads.
Unless you find it a challenge to mount the components for the power supply yourself, you may buy it at the same price ready-made:
Aiyima Dual Power Rectifier Filter Board 4700uf 35V Capacitance DC Dual Audio Power Supply For Amplifier Diy-in Amplifier from Consumer Electronics on Aliexpress.com | Alibaba Group
Aiyima Amplifier Rectifier Filter Board 4x10000UF Large capacitor Full Bridge Filter Subwoofer DC Amplifiers DIY KITS-in Amplifier from Consumer Electronics on Aliexpress.com | Alibaba Group
2017 NEW amplifier NOVER Electric Capacity Rectifier + Loudspeaker AIO Board-in Amplifier from Consumer Electronics on Aliexpress.com | Alibaba Group
3300uf 50V *8 PCS Filter Capacitor High voltage high power high capacity Amplifier Rectifier Filter power board finished board -in Amplifier from Consumer Electronics on Aliexpress.com | Alibaba Group
power supply board, rectifier filter circuit board, power amplifier PCB empty board, support multi foot capacitor, double bridge-in Double-Sided PCB from Electronic Components & Supplies on Aliexpress.com | Alibaba Group
Then you can focus on the amplifiers.
Unless you find it a challenge to mount the components for the power supply yourself, you may buy it at the same price ready-made:
Aiyima Dual Power Rectifier Filter Board 4700uf 35V Capacitance DC Dual Audio Power Supply For Amplifier Diy-in Amplifier from Consumer Electronics on Aliexpress.com | Alibaba Group
Aiyima Amplifier Rectifier Filter Board 4x10000UF Large capacitor Full Bridge Filter Subwoofer DC Amplifiers DIY KITS-in Amplifier from Consumer Electronics on Aliexpress.com | Alibaba Group
2017 NEW amplifier NOVER Electric Capacity Rectifier + Loudspeaker AIO Board-in Amplifier from Consumer Electronics on Aliexpress.com | Alibaba Group
3300uf 50V *8 PCS Filter Capacitor High voltage high power high capacity Amplifier Rectifier Filter power board finished board -in Amplifier from Consumer Electronics on Aliexpress.com | Alibaba Group
power supply board, rectifier filter circuit board, power amplifier PCB empty board, support multi foot capacitor, double bridge-in Double-Sided PCB from Electronic Components & Supplies on Aliexpress.com | Alibaba Group
Then you can focus on the amplifiers.
A chassis mounted bridge rectifier and two suitable reservoir caps (also chassis mounted in suitable clamps) is all you really need.
Is jumping up to the LM3886 in a presupplied board that much more expensive? IIRC it comes in a larger package (giving you a better chance at dumping the heat), and will easily take this PSU voltage. Minimum gain is the same as the 1875, so input sensitivity will be identical.
DPH is (once more) right, the LM3886 is a (slightly) better performer than the LM1875. However, LM1875 is still a high quality product. LM3886 is, as it could be expected, more expensive than the LM1875.
But, for me it is also a question about the purpose with this project: to build an amplifier that is as good as possible within a moderate budget (then LM3886) or to gain experience with class AB through designing and building an amplifier (then LM1875).
LM1875 has the advantage of being the closest you come to a power OP-AMP: the 5 basic pins only and there you go. Very simple in peripheral components, easy to include for instance in a composite amplifier, gain from 20dB......
For you to decide, JonesySA: The better performance but less experiments (LM3886) or amble potential for experiments but slightly inferior performance (LM1875)?
But, for me it is also a question about the purpose with this project: to build an amplifier that is as good as possible within a moderate budget (then LM3886) or to gain experience with class AB through designing and building an amplifier (then LM1875).
LM1875 has the advantage of being the closest you come to a power OP-AMP: the 5 basic pins only and there you go. Very simple in peripheral components, easy to include for instance in a composite amplifier, gain from 20dB......
For you to decide, JonesySA: The better performance but less experiments (LM3886) or amble potential for experiments but slightly inferior performance (LM1875)?
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It isn't overly more expensive if we compare similar boards. LM3886 kits start at ~$8. The issue is rather finding one that performs well. The 1785 I linked to has quite a good repoure for what it is whereas every lm3886 appears to have many faults.
A quick look in AliExpress shows many lm3886 boards ranging from simple mono through to combined stereo, power supply, speaker delay with an assortment of opamps.
None of them come with a circuit diagram from what I could see.
I would like to try both if I find a recommended 3886.
The LM1875 is *not* designed for 4ohm loads - 8ohms or larger only imho!
According to the spec sheet at max P out = 20W into 4ohms with +/- 25V supply.
Now, with P = 20W in 4ohms the Vout equals 12.6Vpeak. That leaves 12.3V over the output transistors in the LM1875. Result : a lot of heat dissipated in the IC.
So if 4ohms and the said tranny are requirements, then go for some other IC than LM1875. Having said that, it is supposed to be fine for 8ohm.
Regards
Lars
According to the spec sheet at max P out = 20W into 4ohms with +/- 25V supply.
Now, with P = 20W in 4ohms the Vout equals 12.6Vpeak. That leaves 12.3V over the output transistors in the LM1875. Result : a lot of heat dissipated in the IC.
So if 4ohms and the said tranny are requirements, then go for some other IC than LM1875. Having said that, it is supposed to be fine for 8ohm.
Regards
Lars
Alright, this is a double edged post:
LM3886 Chip Amp
Tom is an active member here and has written extensively on the 3886, in addition to providing extremely high quality kits, albeit at much higher cost to the Alibaba crowd. We all have to make decisions about value, so I'll leave it there. In any case, the link above gives a LOT of good information about what to think about when working with these chip amps. As an EE, even one that doesn't really do circuit design at all, it's an easy read for me, but I realize that it could be daunting for someone outside the field.
At the same time, a careful reading of what he writes could take an enterprising individual, even one that's a beginner, very far. And that's doing point-to-point (without a PCB). Does carry a lot of risks of screwing things up, too. So caveat emptor
I'm not thrilled with the layout of any of the inexpensive boards, but if you're trying to get something out the door, I don't really see much difference in quality between the board you linked (LM1875) and the cheaper LM3886 boards. Evaluations and reviews would only influence me so far as complaints about missing or defective parts being sold.
I hope this helps.
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LM3886 recommendation
I have built up 4 of the kits and found them to be quite satisfactory. I did find a peak in the response well above 150KHz which was taken out by adding a 100pFd silver mica cap across the feed back resistor. The corresponding 0dB crossing, slope at intercept, and phase margin all looked good.
This all originated as a basic 4-channel box project using pre-assembled switching amps but ran into several difficulties. They are fragile and readily fail if hot swapping inputs and outputs under power. Unfortunately they do not lend themselves to repair. A secondary issue is that there is NO speaker protection and these have floating outputs which are not compatible withe common protection schemes available. Also the floating outputs make it difficult to pick off the signals when routing to other system elements.
The LM3886 Kits are self contained with their own power supply and speaker protection circuits. They require a minimum of +/-24Vdc to work the relay section. The mute resistor was changed from 33k to 18k to get the assembly to work at lower DC rails.
The DC idle current runs at 30-40 mA (the + side uses another 20mA to energize the relay) so it is important to heat sink the LM3886'S prior to any testing to first determine if the heatsink is large enough under idle conditions. I ran each of the four overnight and you can see the idle draw move around as steady state (idle) conditions are met.
I have built up 4 of the kits and found them to be quite satisfactory. I did find a peak in the response well above 150KHz which was taken out by adding a 100pFd silver mica cap across the feed back resistor. The corresponding 0dB crossing, slope at intercept, and phase margin all looked good.
This all originated as a basic 4-channel box project using pre-assembled switching amps but ran into several difficulties. They are fragile and readily fail if hot swapping inputs and outputs under power. Unfortunately they do not lend themselves to repair. A secondary issue is that there is NO speaker protection and these have floating outputs which are not compatible withe common protection schemes available. Also the floating outputs make it difficult to pick off the signals when routing to other system elements.
The LM3886 Kits are self contained with their own power supply and speaker protection circuits. They require a minimum of +/-24Vdc to work the relay section. The mute resistor was changed from 33k to 18k to get the assembly to work at lower DC rails.
The DC idle current runs at 30-40 mA (the + side uses another 20mA to energize the relay) so it is important to heat sink the LM3886'S prior to any testing to first determine if the heatsink is large enough under idle conditions. I ran each of the four overnight and you can see the idle draw move around as steady state (idle) conditions are met.
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