I have an LM3886 amp; transformer, rectifier, the 3886 with 2,200 uf + 0.1 uf in parallel and two resistors.
Idle searching for the LMxx series brought up the LM1875 which will also work into the 4 Ohms CHP70s I use. And then I found this http://www.ptpaudio.com/blok20 €2,250!
Hmmmm I thought and wondered if the LM1875 made up using the minimum of components as per my 3886 would actually sound any different to it? Soon find out though I've ordered couple of LM1875's, a 12 volt transformer and some ultra fast 3 pin Schottky diodes. Once finished I will do a proper subjective switched test from a sitting position of the LM3886 versus the LM1875.
More soon
Idle searching for the LMxx series brought up the LM1875 which will also work into the 4 Ohms CHP70s I use. And then I found this http://www.ptpaudio.com/blok20 €2,250!
Hmmmm I thought and wondered if the LM1875 made up using the minimum of components as per my 3886 would actually sound any different to it? Soon find out though I've ordered couple of LM1875's, a 12 volt transformer and some ultra fast 3 pin Schottky diodes. Once finished I will do a proper subjective switched test from a sitting position of the LM3886 versus the LM1875.
More soon
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A 12V transformer???????
We are starting with the wrong foot here.
Build a working amp first, and then start worrying about minor matters such as "sound".
We are starting with the wrong foot here.
Build a working amp first, and then start worrying about minor matters such as "sound".
But, but... You'll need that solid Corian housing for "resonance control" and tuning by Mr. Reinders himself to replicate the performance... 🙂
The LM1875 is a cool li'l amp. Should be a fun project. I suggest that you add 10-22 uF for local decoupling right by the LM1875 in addition to the 0.1 uF just to get a bit better decoupling in the 1-10 MHz range where the LM1875 runs out of loop gain.
Hopefully the "12 V transformer" is a 2x12 V type. Personally I'd probably aim for 2x18 VAC from the transformer.
Tom
The LM1875 is a cool li'l amp. Should be a fun project. I suggest that you add 10-22 uF for local decoupling right by the LM1875 in addition to the 0.1 uF just to get a bit better decoupling in the 1-10 MHz range where the LM1875 runs out of loop gain.
Hopefully the "12 V transformer" is a 2x12 V type. Personally I'd probably aim for 2x18 VAC from the transformer.
Tom
Errrrr Oh right,
Well checking the voltage input to my CHP70s with a sensitive analog voltmeter I get 0.5 Volts at a very loud listening level.
2.83 Volts into 4 Ohms = 2 Watts
2.83/0.5 = 5.66
2 Watts divided by 5.66 = 0.353 Watts
To check that, the db rating of the CHP70s is 85, also checking my small listening room with a db meter I get 70 to 80 db
For every 3db decrease in volume the power required is halved therefore.
85* db at 1 Watt
82db at 1/2 Watt
79db at 1/4 Watt
And a subjective switched test done properly from a listening position over a week or so is the final arbiter of any audio system. See John Linsley Hoods 1969 amplifier test from his article in Wireless World. Google will find it for you.
The 8 to 10 Watts that I will get from the 1875 with 12 Volts becomes more than ample.
Cheers both
*Do not listen at this level for more than 20 minutes and then leave off completely for 24 hours. Damaged hearing does not recover!
Well checking the voltage input to my CHP70s with a sensitive analog voltmeter I get 0.5 Volts at a very loud listening level.
2.83 Volts into 4 Ohms = 2 Watts
2.83/0.5 = 5.66
2 Watts divided by 5.66 = 0.353 Watts
To check that, the db rating of the CHP70s is 85, also checking my small listening room with a db meter I get 70 to 80 db
For every 3db decrease in volume the power required is halved therefore.
85* db at 1 Watt
82db at 1/2 Watt
79db at 1/4 Watt
And a subjective switched test done properly from a listening position over a week or so is the final arbiter of any audio system. See John Linsley Hoods 1969 amplifier test from his article in Wireless World. Google will find it for you.
The 8 to 10 Watts that I will get from the 1875 with 12 Volts becomes more than ample.
Cheers both
*Do not listen at this level for more than 20 minutes and then leave off completely for 24 hours. Damaged hearing does not recover!
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JLH's preamble to the tests he conducted. I was going to edit the above with it but by the time I'd found this the edit function had gone;
It would be convenient if the performance of an audio amplifier (or loudspeaker or any other similar piece of audio equipment) could be completely specified by frequency response and harmonic distortion characteristics.
Unfortunately, it is not possible to simulate under laboratory conditions the complex loads or intricate waveform structures presented to the amplifier when a loudspeaker system is employed to reproduce the everyday sounds of speech and music; so that although the square wave and low-distortion sine wave oscillators, the oscilloscope, and the harmonic distortion analyser are valuable tools in the design of audio circuits. The ultimate test of the final design must be the critical judgment of the listener under the most carefully chosen conditions his facilities and environment allow.
Cheers
It would be convenient if the performance of an audio amplifier (or loudspeaker or any other similar piece of audio equipment) could be completely specified by frequency response and harmonic distortion characteristics.
Unfortunately, it is not possible to simulate under laboratory conditions the complex loads or intricate waveform structures presented to the amplifier when a loudspeaker system is employed to reproduce the everyday sounds of speech and music; so that although the square wave and low-distortion sine wave oscillators, the oscilloscope, and the harmonic distortion analyser are valuable tools in the design of audio circuits. The ultimate test of the final design must be the critical judgment of the listener under the most carefully chosen conditions his facilities and environment allow.
Cheers
Is it peak-catching?
If you don't catch the peaks you want to add 14dB to 18dB to the average reading of speech/music to know the clipping level needed.
That is a 'Gainclone' version of the 1875, with short signal paths.
Bog common.
If you said 2250 Euro for one, I will ask you to seek medical treatment.
Or tell you that a working amp of that circuit is 15 Euros or less here in India, so 2250 / 15 is 150 pieces, or a gross, if you want to be old style.
Bog common.
If you said 2250 Euro for one, I will ask you to seek medical treatment.
Or tell you that a working amp of that circuit is 15 Euros or less here in India, so 2250 / 15 is 150 pieces, or a gross, if you want to be old style.
Hello PRR
An Android phone/tablet with a db app in it will sample and hold down to 0.1 of a second. The free program Audacity at its default setting will detect dynamic range to 0.03 of a second. Checking recordings with either will never result in 0db. Why, because recording engineers will tame any spikes before they get near to a CD.
Screenshot of Audacity with Hélène Vogelsinger's 'Contemplation' like most synth artists she records into the 'red'. But as you can see the resultant recording does not exceed the limits and is in fact well within them. Most CD's loudest sections will be just above the 0.5 mark, recording engineers are very careful about dynamic range.
Hello Haresh
May I suggest with great respect that you investigate the original Gain Card you will find that it bears no resemblance to the Chinese offerings.
Cheers both - J
An Android phone/tablet with a db app in it will sample and hold down to 0.1 of a second. The free program Audacity at its default setting will detect dynamic range to 0.03 of a second. Checking recordings with either will never result in 0db. Why, because recording engineers will tame any spikes before they get near to a CD.
Screenshot of Audacity with Hélène Vogelsinger's 'Contemplation' like most synth artists she records into the 'red'. But as you can see the resultant recording does not exceed the limits and is in fact well within them. Most CD's loudest sections will be just above the 0.5 mark, recording engineers are very careful about dynamic range.
Hello Haresh
May I suggest with great respect that you investigate the original Gain Card you will find that it bears no resemblance to the Chinese offerings.
Cheers both - J
I was referring to the unit in the photo at the start of the thread as a Gain implementation.
Sorry for the confusion.
The Chinese ones are not Gain versions, normal paths, and small PSU caps.
And the ones sold here are locally assembled with Indian PCB, and some with local Keltron (Sprague licensee) caps.
Sorry for the confusion.
The Chinese ones are not Gain versions, normal paths, and small PSU caps.
And the ones sold here are locally assembled with Indian PCB, and some with local Keltron (Sprague licensee) caps.
Sorry but your Math is wrong 🙁
Power is proportional to squared voltage.
So 2.83V into 4 ohm is 2W indeed.
But 0.5V into same load is 31.25 MILLI-watts, not "0.353 Watts"
PS: nice Electronic Music.
Hello JMF,
Many thanks for that I stand corrected 0.03125 Watts it can be, my goodness there's a lot of power 🙂 But hmmmm at 0.5 volts I was measuring nearly 80db and at the halving of the of the power for every 3db downwards it comes out at 79db?
I also must thank you for pointing the 12v power supply it is of course the 12-0, 0-12 of a toroid which means I will be getting about 20 to 25 watts out of it.
I'm glad you found Hélène's music she is something else! I've been following her career for a couple of years. She's got to the stage where the Eurorack synth module designers give her stuff, like the Strega she got a few months ago £529!
Just listened to Metaphysical Aleteration 2/4
downloaded the WAV and played it on my FHMk3's I could feel the bass in my chest. How she gets that out of an oscillator beats me. When she puts it on Bandcamp I'll buy the FLAC.
Cheers and thanks - J
Many thanks for that I stand corrected 0.03125 Watts it can be, my goodness there's a lot of power 🙂 But hmmmm at 0.5 volts I was measuring nearly 80db and at the halving of the of the power for every 3db downwards it comes out at 79db?
I also must thank you for pointing the 12v power supply it is of course the 12-0, 0-12 of a toroid which means I will be getting about 20 to 25 watts out of it.
I'm glad you found Hélène's music she is something else! I've been following her career for a couple of years. She's got to the stage where the Eurorack synth module designers give her stuff, like the Strega she got a few months ago £529!
Just listened to Metaphysical Aleteration 2/4
Cheers and thanks - J
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Hello PRR,
I was in error again apologies
Android db meter resting on some trestles at speaker height and quite close to them, this reading barely alters anywhere in my little room. And Hélène as above on my speakers very loudly!
Anyway onwards:-
85db at 1 volt and 1 Watt. my CHP70's
82 @ 0.5 Watts
79 @ 0.25
76 @ 0.125
73 @ 0.0625
70 @ 0.03125 Exactly as you predicted and checked out at 0.5 Volts I'll forgo the Volts in future and stick to the Watts 🙂
69 @ 0.01562
66 @ 0.00781 I won't take it down to the 47 db average I'd carried the meter around to the speakers while it was recording.
Astonishing stuff I am grateful to you, it just shows what Watts really are and shows up the charlatans who sell by Watts and flood the forums with the resulting snake oil. No wonder you can buy a 1 Watt amplifier in Japan! It's very similar to the photographic pixel caper. Thinking about some 97 db speakers the mind boggles at the actual amount of Watts, well, and the voltage.
Worra caper! Cheers - J
[edit] Even if there were an 18db transient say from a Class B amp at crossover it would barely exceed 1 Watt.
I was in error again apologies
Android db meter resting on some trestles at speaker height and quite close to them, this reading barely alters anywhere in my little room. And Hélène as above on my speakers very loudly!
Anyway onwards:-
85db at 1 volt and 1 Watt. my CHP70's
82 @ 0.5 Watts
79 @ 0.25
76 @ 0.125
73 @ 0.0625
70 @ 0.03125 Exactly as you predicted and checked out at 0.5 Volts I'll forgo the Volts in future and stick to the Watts 🙂
69 @ 0.01562
66 @ 0.00781 I won't take it down to the 47 db average I'd carried the meter around to the speakers while it was recording.
Astonishing stuff I am grateful to you, it just shows what Watts really are and shows up the charlatans who sell by Watts and flood the forums with the resulting snake oil. No wonder you can buy a 1 Watt amplifier in Japan! It's very similar to the photographic pixel caper. Thinking about some 97 db speakers the mind boggles at the actual amount of Watts, well, and the voltage.
Worra caper! Cheers - J
[edit] Even if there were an 18db transient say from a Class B amp at crossover it would barely exceed 1 Watt.
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Well... The LM1875 is specified to provide 25 W into 8 Ω (typical) at 1 % THD, i.e., at clipping on a ±25 V supply. The power into 4 Ω isn't specified in the spec table, but from Figure 3 in the data sheet it's pretty clear that you shouldn't expect more than a smidge over 20 W into 4 Ω. Maybe 25 W at 1% THD - for a typical part at room temperature operating on ±25 V.
I wouldn't count on more than ±13-14 V DC from a 2x12 V transformer under load. You'll get closer to ±16 V at idle. A 2x18 V transformer would be a better fit if you want the full output power.
Tom
Well, back in the Loudness Wars, commercial CDs maxed-out several times a second in the loud parts. Widely discussed here and elsewhere. Ricky Martin (C2/Columbia CK 69891) "Livin' La Vida Loca" is a much cited example. Have The Wars ended already?
Don't tell me what I will "never" see until you live a while.
Hello Tom,
Having already bought a 12v transformer (expected soon) may I with respect ask you to wait until I have finished the amp and done 5 to 7 days worth of switched comparisons with my LM3886.
Hello PRR,
Many thanks for your pleasant and kind message I must say that through your generosity of spirit you've been a great help to me.
Fancy that though a 'loudness war' over that recording I can scarcely believe it 🙂
Reminds of the 'great tea trolley disaster of '67' in the Bristow cartoon.
Hello there
The box is a die cast Hammond 1550G
The heat sinks are a cut down longer one, cheapo from eBay
The two LM1875's arrived just now other bits to follow.
The paper is the size of the transformer
And the Vitcas the paint I sprayed on, when it's dry, 60 minutes at 160c or gas mark 3 to bake it on. It makes a nice hard matt finish.
More soon
Having already bought a 12v transformer (expected soon) may I with respect ask you to wait until I have finished the amp and done 5 to 7 days worth of switched comparisons with my LM3886.
Hello PRR,
Many thanks for your pleasant and kind message I must say that through your generosity of spirit you've been a great help to me.
Fancy that though a 'loudness war' over that recording I can scarcely believe it 🙂
Reminds of the 'great tea trolley disaster of '67' in the Bristow cartoon.
Hello there
The box is a die cast Hammond 1550G
The heat sinks are a cut down longer one, cheapo from eBay
The two LM1875's arrived just now other bits to follow.
The paper is the size of the transformer
And the Vitcas the paint I sprayed on, when it's dry, 60 minutes at 160c or gas mark 3 to bake it on. It makes a nice hard matt finish.
More soon
I am 100% convinced that your chips are NOT authentic( If the chips from your picture are your lm1875), where did you buy them from?
Attachments
Make sure you're using genuine LM1875, otherwise it is waste of time and money!
Buy from authorised seller only.
Buy from authorised seller only.
Hello all,
I eventually bought two kits on eBay for £7 including the postage.
Fake chips, great PCB and a lot easier to assemble.
22k Resistor as indicated
820R in top 1k indicated position
220R in next 1k indicated position
10 uF position replaced by a link
47 uF position replaced by a link
The 2 - 1000 uF 25Vcapacitors fit nicely in the space above the power feed
I removed the pins from the audio in socket. Bent them in an L shape and soldered them in.
https://lm1875diyamplifier.blogspot.com/
Cheers - J
I eventually bought two kits on eBay for £7 including the postage.
Fake chips, great PCB and a lot easier to assemble.
22k Resistor as indicated
820R in top 1k indicated position
220R in next 1k indicated position
10 uF position replaced by a link
47 uF position replaced by a link
The 2 - 1000 uF 25Vcapacitors fit nicely in the space above the power feed
I removed the pins from the audio in socket. Bent them in an L shape and soldered them in.
https://lm1875diyamplifier.blogspot.com/
Cheers - J