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Chip Amps Amplifiers based on integrated circuits

LM1875 in parallel configuration and used in a composite amplifier.
LM1875 in parallel configuration and used in a composite amplifier.
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Old 14th February 2020, 10:18 PM   #451
FauxFrench is offline FauxFrench  France
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Quote:
Originally Posted by maxhifi View Post
Here is the board of the Majik... wow those trimmers are small! It makes exactly 34W at clipping versus 33W like the spec says. It was sitting for years, I originally planned to somehow make it fully operational, but it was beyond any reasonable repair.

Listening is interesting, I have to get used to it a bit. It definitely sounds different from my tube amps, or my usual transistor amps. It makes me very interested to hear what a composite design can do!
Tube amps will almost always be different. Gentle and pleasant sound but no need to look at measurement results. Ideal for classical, jazz and folk music. Not at all suited for punchy bass. The sound of your usual transistor amps depend on the age. If of the elder type, modern chip-amps may be more transparent and with a more firm bass than your usual transistor amps. The TDA1514 was the best class AB chip from Philips/NXP and their chip designers were skilled.
For the composite amplifiers, it is mainly the OP-AMP that decides the sound. Expect even more transparency and precision in the sound, not tube sound.
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Old 14th February 2020, 10:44 PM   #452
maxhifi is offline maxhifi  Canada
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Quote:
Originally Posted by FauxFrench View Post
Tube amps will almost always be different. Gentle and pleasant sound but no need to look at measurement results. Ideal for classical, jazz and folk music. Not at all suited for punchy bass. The sound of your usual transistor amps depend on the age. If of the elder type, modern chip-amps may be more transparent and with a more firm bass than your usual transistor amps. The TDA1514 was the best class AB chip from Philips/NXP and their chip designers were skilled.
For the composite amplifiers, it is mainly the OP-AMP that decides the sound. Expect even more transparency and precision in the sound, not tube sound.
I think it is unfair to write off tubes like that, a big powerful tube amp with big sensitive speakers will do rock music, or orchestral music justice. A lot of tube amps in use suffer from bad design and low power though. That said, I'm somehow much less worried about a TDA1514 catching fire, it will never degrade over time. And what is life without trying new things? I've been listening to these paralleled ICs all afternoon and they seem to sound better and better.

Solid state amps have been many, mostly vintage stuff though. I repair equipment, and have had the opportunity to test a lot of it. I usually wrote off chip amps due to my distaste for Sanyo STK based amplifiers, but building an op-amp based preamplifier stimulated my interest.
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Old 15th February 2020, 12:08 AM   #453
FauxFrench is offline FauxFrench  France
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Quote:
Originally Posted by maxhifi View Post
I think it is unfair to write off tubes like that, a big powerful tube amp with big sensitive speakers will do rock music, or orchestral music justice. A lot of tube amps in use suffer from bad design and low power though. That said, I'm somehow much less worried about a TDA1514 catching fire, it will never degrade over time. And what is life without trying new things? I've been listening to these paralleled ICs all afternoon and they seem to sound better and better.

Solid state amps have been many, mostly vintage stuff though. I repair equipment, and have had the opportunity to test a lot of it. I usually wrote off chip amps due to my distaste for Sanyo STK based amplifiers, but building an op-amp based preamplifier stimulated my interest.
You are absolutely the reference on tube sound compared to me. I only have a very limited knowledge on tube-amps from my childhood where solid state technology had entered the electronic scene some years before I started. I still have a box in the basement with tubes I removed from radios and TVs at that time. When it comes to practicality and power efficiency (Greta ), the solid state technology scores high.
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Old 15th February 2020, 05:24 AM   #454
Turbowatch2 is offline Turbowatch2  Germany
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@Chris

Digikey did not sell you fake chips!

The data sheet claims 20W/4Ohm and 30W/8Ohm.

If you look at your spread sheet and use R=U/I you will see that the numbers you measured are perfectly in line with Ohms Law. It does not even matter if 1, 2 or n chips work in parallel, the Ohm, Volt, Ampere ratio will stay constant.

The claimed 4 A are an absolute maximum value that the chips can stand for a short while, depending on the heat sinking. If you want to see such high current, you have to go under the recommended load impedance of 4 Ohms, maybe 2.9 Ohms. But please, do not try without a proper heat sink.
The 4A get relevant, if you bridge two chips. Such an amp, with 4 Ohms load you will get near them.
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Old 15th February 2020, 08:48 AM   #455
FauxFrench is offline FauxFrench  France
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Good morning Chris,

A sound principle in testing an electronic item is to vary only one parameter at the time and keep all the other parameters fixed at values within specified operational limits meanwhile. As Turbowatch2 says, it is very unlikely that you got fake chips from Digikey. Worst case, some of the chips you have may have suffered damage from hard treatment - we will see.

So, a supply voltage of +/-20-25V. A good heatsink! No load for a start. 1KHz sine-wave. The chip should be able to clip at some 3V below the supply voltage. Until clipping, the sine-wave should look fine. At clipping, the flat tops should be rather clean without oscillation. If this test is passed well you continue.
Then, same setup but this time with a load of 8-10 Ohm. 8-10 Ohm with 25V supply will not reach the 4A limit of the LM1875 and not even the test limit of 3A due to the voltage drop in the output stage (2-5V depending on the current). So, clipping should happen near 4V below the supply voltage and the sine-wave look fine until then. A bit of "wool" at the flat tops. If still OK, you continue.
Now 4-5 Ohm loading. With 4 Ohm loading, the 3A test limit is reached at 12V peak and the 4A limit at 16V peak. We know up front that there will be problems at high amplitude. You increase the amplitude until it starts looking strange which should be from 15-16V peak. When the limit is reached you note the limit and lower the amplitude not to stress the chip from increased heating. Current limitation is activated so you cannot rely on nice flat tops.

If you successfully passed these tests, the IC is fine. Only the short-circuiting tests will decide if it is fake but I would be careful with those and only perform such with reduced supply voltage and for short moments.

The big mess starts when you use a load that you have used before but which will cause current limitation, you let the chip heat up significantly so you are not sure how it behaves, the unregulated supply voltage sags and it all looks weird for which reason you declare the chip "fake". You simply lost overview.

Ruhig - ruhig - ruhig.

After having concluded that the chip is OK, you can try with square-waves, increased frequency, changing the supply voltage etc. BUT only vary one parameter at the time.

In electronics, the principle apply that it is much easier to make the system work under gentle conditions and then harden the conditions until poor operation (seeking the limits of operation), than starting the system up under conditions where it performs poorly and try to bring it to proper operation.

Last edited by FauxFrench; 15th February 2020 at 09:03 AM.
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Old 15th February 2020, 12:37 PM   #456
FauxFrench is offline FauxFrench  France
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As suggested by Chris in posting #399, 2.7 Ohm in parallel with 100nF or 1uF.
Still my unregulated power supply with +/-24V.

Picture 1: 1KHz, 20Vpp, 2.7 Ohm in parallel with 100nF
Picture 2: 1KHz, clipping, 2.7 Ohm in parallel with 100nF
Picture 3: 1KHz, 20Vpp, 2.7 Ohm in parallel with 1uF
Picture 4: 1KHz, clipping, 2.7 Ohm in parallel with 1uF

In conclusion, the triple LM1875 is pretty unimpressed by capacitive loading.
Attached Images
File Type: jpg TripleLM1875_1KHz_20Vpp_2.7Ohm_100nF.jpg (127.9 KB, 77 views)
File Type: jpg TripleLM1875_1KHz_Clip_2.7Ohm_100nF.jpg (240.9 KB, 74 views)
File Type: jpg TripleLM1875_1KHz_20Vpp_2.7Ohm_1uF.jpg (98.6 KB, 74 views)
File Type: jpg TripleLM1875_1KHz_Clip_2.7Ohm_1uF.jpg (156.0 KB, 75 views)
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Old 15th February 2020, 02:58 PM   #457
maxhifi is offline maxhifi  Canada
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Quote:
Originally Posted by FauxFrench View Post
As suggested by Chris in posting #399, 2.7 Ohm in parallel with 100nF or 1uF.
Still my unregulated power supply with +/-24V.

Picture 1: 1KHz, 20Vpp, 2.7 Ohm in parallel with 100nF
Picture 2: 1KHz, clipping, 2.7 Ohm in parallel with 100nF
Picture 3: 1KHz, 20Vpp, 2.7 Ohm in parallel with 1uF
Picture 4: 1KHz, clipping, 2.7 Ohm in parallel with 1uF

In conclusion, the triple LM1875 is pretty unimpressed by capacitive loading.
Can you get any ringing on the square waves if you use, say, 1uF without parallel resistance? A pure capacitive load won't have a resistor to damp ringing and may provoke a square wave which looks a bit less textbook perfect.

With such nice behavior on the scope I bet it already sounds good.
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Old 15th February 2020, 03:12 PM   #458
maxhifi is offline maxhifi  Canada
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Quote:
Originally Posted by FauxFrench View Post
You are absolutely the reference on tube sound compared to me. I only have a very limited knowledge on tube-amps from my childhood where solid state technology had entered the electronic scene some years before I started. I still have a box in the basement with tubes I removed from radios and TVs at that time. When it comes to practicality and power efficiency (Greta ), the solid state technology scores high.
Ahh, some day you should listen to an expensive tube setup like ARC or something and hear what all the fuss is about. Aside from sounding good, they are very interesting to play with, although contrary to the concept of keeping a low hobby profile for your wife's sake!

Anyway, I've been working with tubes for years, so time for a change. I hope we can make these TDA2050 sound close to as good as the TDA1514A does, because after more time I still can't believe I'm hearing a chip amp. All it needs to be perfect is more power! As a vacuum tube enthusiast I am not surprised that Philips made some good ICs, after all they made some of the best tubes ever made as well.

Last edited by maxhifi; 15th February 2020 at 03:14 PM.
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Old 15th February 2020, 04:06 PM   #459
FauxFrench is offline FauxFrench  France
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I was asked about the -3dB bandwidth. I tested with two signal amplitudes (2.7 Ohm load / +/- 24V supply):
20Vpp gave 100KHz (slew-rate determined / triangular)
2Vpp gave 180Khz (slew-rate determined / triangular)

I also tested the slew-rate with 2.7 Ohm load and 20Vpp square-wave. I arrived at 3.3V/us. A "raw" LM1875 is specified to 8V/us but I have reduced the speed with the 100pF in the feedback.
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Old 15th February 2020, 05:04 PM   #460
FauxFrench is offline FauxFrench  France
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As requested, only 100nF or 1uF but no resistive loading. Actually, it does not change much.

Picture 1: 1KHz, 20Vpp, 100nF (no resistive load)
Picture 2: 1KHz, 20Vpp, 1uF (no resistive load)

NB: foil capacitors.
Attached Images
File Type: jpg TripleLM1875_1KHz_20Vpp_100nF.jpg (32.8 KB, 57 views)
File Type: jpg TripleLM1875_1KHz_20Vpp_1uF.jpg (39.7 KB, 12 views)

Last edited by FauxFrench; 15th February 2020 at 05:08 PM.
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