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Old 10th July 2009, 03:49 PM   #1
pra3718 is offline pra3718  India
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Default 1875 v/s 1554

I have completed tda1554q multichannel system. It's car amp single power supply 16V. I used 4 Nos Ic i.e. 8 Channels 22 watt each. Overall it's sounding good for me. But I don't wish to stick with it. Looking for best.

I read good information here about gainclone. ( LM1875 OR TDA2050 ) I don't want loudness but looking for best quality sound than tda1554q. Is 1875/2050-PSU-25V would complete my requirement ? Is that worth to scrap 1554 ?
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Old 10th July 2009, 07:59 PM   #2
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It is worth to scrap the TDA1554,if you make a better planning this time.

PSU - 25 V what? Single supply? Split supply? 25 V transformer output or rail voltage? Which load impedance will be connected?
As long as you use the same uncoordinated approach as with your first project, forget it.
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Old 11th July 2009, 01:45 PM   #3
pra3718 is offline pra3718  India
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Quote:
PSU - 25 V what? Single supply? Split supply? 25 V transformer output or rail voltage? Which load impedance will be connected?
25V (+-) i.e. 18-0-18 3 amp transformer and Split supply. Should I develop ESP's Project 72. with 4 ohm speaker. As my previous project I will have to use 8 IC. ESP says 20watt for tda2050 and datasheet says 35 watt, I think this is due to GAIN (feedback resister) Right now I don't have (1875 OR 2050) let me find out it is available to my supplier.

Thanks for co-operation, pl. don't mind but are you confident it will improve the sound quality and my listening experience ?

Regards.
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Old 11th July 2009, 06:07 PM   #4
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25 V and 4 Ohm means 20 W output per channel. 8 x 20 W = 160 W. 2*18 V*3 A = 108 VA. You will need a bigger transformer, at least 4,5 A.

The different output power is due to the amount of distortion they allow during the test.
LM1875 acc. to datasheet 25 V 4 Ohm 20 W 1 kHz THD = 0,022 %
TDA2050 acc. to datasheet 25 V 4 Ohm 28 W 1 kHz THD = 0,5 %
TDA2050 acc. to datasheet 25 V 4 Ohm 35 W 1 kHz THD = 10 %
Those two ICs will perform very similar.

To compare that to your old TDA1554: 4 Ohm 5,5 W THD = 10%

The sound quality will improve, when you do it right.

Have a look at LM3875 or LM3886 as well. They will be a good choice for the subwoofers, because they have a higher current capability than the LM1875 or TDA2050. With that 18-0-18 V 3 A transformer you could drive up to four channels of LM3875 or LM3886. Start with two channels for the subwoofer and see, what it does for your sound. If you like, what you hear, you can upgrade the other channels later as well. You could e. g. use your old 12-0-12 V 5 A transformer for the remaining six channels with any of the LMs or the TDA2050 and convert your preamplifier/cross-over to split supply.
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Old 11th July 2009, 07:32 PM   #5
sangram is offline sangram  India
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Where are you getting the LM1875 from? RS?

The 3875/3886 will be better overall, more power for one, and that almost always help one play louder and cleaner. Unless your speakers are over 95dB efficient, I would build one of the above 2. I bought 10 LM3886 chips from D-K of which I have pressed 6 into service, and am pretty happy with the results. If not the absolute highest fidelity, they compete with amps upto the 50-60K range easily, though the output power is lower, *just* 50 watts a channel or so.

The 1875 is much lower power, and though it's a good chip, will require care to partner with the speakers of your choice.

I usually build with 22-0-22 transformers for ~30V rails, or 25-0-25 for ~35V rails. 5 amp secondaries for mono, and 11 amps for stereo, or 2 transformers (usually, I use 2 transformers). The voltage is not standard so I get them built to order. Anyone who supplies in your town locally should be able to build you some for a low cost. I pay about 225/750 for the above.

Listening experience depends strongly on your speakers. Low resolution speakers will not help you appreciate the differences. Locally available drivers cloud detail, and it is difficult to reliably distinguish between amplifiers with equipment of such quality.
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Old 13th July 2009, 05:21 PM   #6
pra3718 is offline pra3718  India
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Thank you.

I am going to focus on two major things.

1) Quality sound ( better than tda1554q )
2) Should be very silent when power ON/OFF ( Pl. find datasheet for TDA7265 [POP-FREE] )

I will be able to build tda2050,lm1875. But not confident for 3875/3886. Even I don't know is it available to my city. Please give me some time.

Before reading your post, I was planed for TDA2050 mono for satellite & TDA2050 BTL for subwoofer.

Thank you, Regards.
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Old 13th July 2009, 06:15 PM   #7
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Building 1875 and 3875 takes the same degree of difficulty. 3875 has a few more pins that are however not connected.

For pop-free operation 3886 is better, because it has a mute pin. It takes an additional resistor and a capacitor to use the mute function. Everything else is again the same as 1875 or 3875.
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Old 13th July 2009, 07:39 PM   #8
sangram is offline sangram  India
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I am pretty much sure that you will not find the 3875/3876/1875 in the country's retail markets, let alone the city. I know that there is a Panasonic/National distributor in India, but they don't do very much retail business because the mainstream market does not support the higher pricing carried by almost all National products, including Pana capacitors, Nat semi chips, etc. They're very tough to find - RS prices are exorbitant though they will supply you with the chips, but D-K works out cheaper, and needs only a valid Paypal account.

Pop-free operation requires correct DC balance on the output. In your case, you have a problematic single-supply preamp, IIRC, and no matter what you do, if the preamp is switched on after or with the amp you will have a thump in the speakers. You have to fix that issue first. I have built a few split-supply amplifiers with a few chips (TDA 2030, lots of different STKs, TDA 7294, LM3886 and 4780) and have no pop on the output at switch on, mute pin or no mute pin.

The TDA 7265 is used in some multimedia speakers, including the Altec Lansing MX5021. The sound is of reasonable quality, and is easily bettered. I would urge you to not get that chip unless you are totally desperate. The TDA7294 has a much better overall sound, but requires a better power supply and heatsinking, but gives you more power.

Watch for fake chips, the Indian retail market is littered with them. Ask your dealer to give you only originals (not that it helps), as the fakes don't sound very good and blow out at anything more than 30V power supplies. Fakes are a constant problem with all chips unless you buy direct from the distributor (and even then there's no guarantee), get samples from the manufacturer (safest) or use a reputed source like D-K or RS.

Good luck, let us know what you finally do.
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Old 14th July 2009, 03:25 PM   #9
pra3718 is offline pra3718  India
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Thanks, pacificblue & sangram

You are teaching me lot of electronics from last six months.

Quote:
Building 1875 and 3875 takes the same degree of difficulty
That's right, I read datasheet for 3875 it is similar to 1875 & deliver high power. i.e. 56 Watts. I would like to tell you complete story for what I did with tda1554q. Pl. give me time.

I am using two speakers for one satellite. i.e. MID & Tweeter. For that I am using two amplifiers with pre-filteration. If I use two 3875, I would have 112 Watts per satellite. I should post hear my present satellite photo. 112 Watts per satellite, is it reasonable? Infact, I choose 1875 because I would have 20+20 watts per satellite. As per your choise it is not sufficient.

Within 2-3 days I will try my level best to post photos.

Thanks again & Regards.
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Old 14th July 2009, 05:30 PM   #10
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The output power depends on the supply voltage. 56 W is, what you get into an 8 Ohm load with 35 V DC. With an 18-0-18 V transformer you can expect ~40 W into 4 Ohm from the LM3875. The LM1875 will only deliver 20 W, because its internal output limiting circuitry does not allow for more. The datasheets show how much power you can get with which supply voltage and load impedance.

Which amount of power is reasonable?
Don't confuse the power of an amplifier with the power of a light bulb. When you use a light bulb with more power, you get more light. When you use an amplifier with more power, you can listen louder, but you usually don't. There is a certain level at which you feel comfortable, and you will set your volume knob to that level, whether the amplifier can deliver 10, 100 or 1000 W. Most of the time people use less than 1 W of average power. That is understandable, because speakers deliver more than 80 dB with as little 1 W in a living room. In workplaces, when there is more than 80 dB of noise present, hearing protection is usually stipulated.

There is usually little need to worry about having too much power, because you never use it continuously. For the same reason compatibility between amplifier output power and speaker power rating is usually not an issue.
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