Hi all,
I have following Tone control Module (Link) Which I would like to use along with separate MM Phono Board. My questions are
- Earlier I have made tone control and phono with dual supply and the 0V connection of both were made coomon ground to chassis. (Link) But this new project being different should i also connect Phono boards 0V reference to chassis along with 0v of Tone control board ?
thanks
I have following Tone control Module (Link) Which I would like to use along with separate MM Phono Board. My questions are
- The Tone control board requires 12-0-12v AC What should be current rating of transformer ?
- I also have SS Phono board which requires single supply 0-12V. Will it be ok if I share single Ac supply from 12-0-12v AC transformer or if separate transformer what current rating should phono preamplifier be ?
- Earlier I have made tone control and phono with dual supply and the 0V connection of both were made coomon ground to chassis. (Link) But this new project being different should i also connect Phono boards 0V reference to chassis along with 0v of Tone control board ?
thanks
Tone controls and preamaps generally only need a few ma, so a transformer of 3-5watts will be ample.
Yes, just use the 0 and one 12v ac output from the transformer. If the phono stage needs DC then you could take it from the tone control stage as it's running on + - 12v
Connect all 0vs to a common point
Yes, just use the 0 and one 12v ac output from the transformer. If the phono stage needs DC then you could take it from the tone control stage as it's running on + - 12v
Connect all 0vs to a common point
thanks
This board has two NE5532 opamps. The PS is regulated by L7912+L9812 Regulator with 4 small caps.
so....
asking as I have a friend who winds custom transformers so will have to give him general broad (with little more margin than regular) current values for the transformer windings. (Input ~230v AC, output 12-0-12V, current rating ?)
regards
This board has two NE5532 opamps. The PS is regulated by L7912+L9812 Regulator with 4 small caps.
so....
- Can I tap the rectified filtered DC out X-0v(for Phono board) from X-0-XV supply On this board ?
- Any broad generalized current drawn values for maximum hypothetical music peaks for both tone board and phono board event? Just to be sure components dont get hot during long working sessions
asking as I have a friend who winds custom transformers so will have to give him general broad (with little more margin than regular) current values for the transformer windings. (Input ~230v AC, output 12-0-12V, current rating ?)
regards
lets say for full bass+treble at maximum and volume full (Though not in reality) both Phono preamp and tone control running at same time, 100mA is enough ?
thanks
thanks
As they are class A amplifiers, the current drain is independent on pote settings.
If the cable joining pre and amp is a bit long, thus it has relatively large capacitance. It means more load for the tone stage opamp. In the other hand, trebble notes usually have less amplitude than bassier ones, so we can deduce rhet it is rougly independent of frequency too.
If the cable joining pre and amp is a bit long, thus it has relatively large capacitance. It means more load for the tone stage opamp. In the other hand, trebble notes usually have less amplitude than bassier ones, so we can deduce rhet it is rougly independent of frequency too.
My "practical rule" for general purpose dual Op Amps, thin k TL072 and similar, is 3.5mA per chip.
NE5532 atre b iased higher, about twice as much.
In any case, you see a 100mA trafo is ample, it would be good for some 60-70 mA total.
The chips he is using are class AB.
Hiten- NE5532 supply current per chip idle is 8mA typ 16mA max. (This can be found in the Datasheet which should be in your hand.)
Yes, the dynamic current can be higher. For full sine-tone at 30V supply and 600 Ohm load, another 8.3mA per channel, 16mA per chip.
But at-clipping speech/music has 12dB-18dB crest factor. Say 16dB or average power is 1/6th of sine-tone maximum power. So maybe 3mA dynamic current for hard-worked speech/music.
Home hi-fi do not run 600 Ohm loads. More like 5K, 10K, 22K. The dynamic current at 9Vrms output will be less than a half mA per channel, lost in chip tolerances. And home hi-fi signal levels are closer to 1V than 9V, so down in the tenths-mA.
Taking four chips at 16mA worst-case just hits JMF's prediction of 60-70mA for a 100mA transformer.
We really only have to account dynamic current if we are the BBC or other giant broadcast organization. For purchase acceptance, they like to drive ALL channels (sometimes hundreds of chips) with sine-tones at MAX level in 300r (can never happen in real life) to check for large distortion (or smoke).
Ok. I never had at hand those IC you mentioned. And sincerely they are of no personal taste. I used mostly TL JFET series and more recently TLC CMOS: it is an interesting version of TLC08x. And TLC 27x.
Generally speaken I dislike BJT alone or integrated. Note I don't say they are bad devices, simply I reject them as much as I can.
Generally speaken I dislike BJT alone or integrated. Note I don't say they are bad devices, simply I reject them as much as I can.
These all have class AB output stages. Their current "can" rise with large signals. The "fat" old BJT designs have so much idle current that the dynamic current is rarely a problem. But I was looking at fast micro-power amplifiers (both chip and discrete) and noticed significant power rise with large signal in low impedance.
Thanks all very much.
Good to know these things. My Phono board (Vintage Japan assembled) Has two AN360 ICs. Both tone board and phono will share same PS. So 0.5A transformer will do I guess. As transformer winders usually save copper. So this is what I will do.
transformer 12-0-12V Ac will be supplied to Tone Preamp Board which has on board rectifier and filter. Whatever dual DC comes on that board; a +Xv and 0v will be tapped to supply Phono board. Schematic of my Phono says transformer of 1.2A Secondary which is strange.
Regards
Good to know these things. My Phono board (Vintage Japan assembled) Has two AN360 ICs. Both tone board and phono will share same PS. So 0.5A transformer will do I guess. As transformer winders usually save copper. So this is what I will do.
transformer 12-0-12V Ac will be supplied to Tone Preamp Board which has on board rectifier and filter. Whatever dual DC comes on that board; a +Xv and 0v will be tapped to supply Phono board. Schematic of my Phono says transformer of 1.2A Secondary which is strange.
Regards
Hi,
purchased one transformer (from chinese Akai subwoofer) and lable on it says 12-0-12v (2.5A+2.5A) and has separate winding of 22-0v 300mA. Took it to my transformer winder and he says these are not 2.5A+2.5A transformer Maximum they may be 1A.
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So I will probably go for new transformer. the toneboard will have 12-0-12v 300mA BUT How much current rating should I have for LM1875 power amp. Voltages are AC 18-0-18V and PS supply rectifier+filter is single board which will provide DC to two separate boards.
thanks.
purchased one transformer (from chinese Akai subwoofer) and lable on it says 12-0-12v (2.5A+2.5A) and has separate winding of 22-0v 300mA. Took it to my transformer winder and he says these are not 2.5A+2.5A transformer Maximum they may be 1A.
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So I will probably go for new transformer. the toneboard will have 12-0-12v 300mA BUT How much current rating should I have for LM1875 power amp. Voltages are AC 18-0-18V and PS supply rectifier+filter is single board which will provide DC to two separate boards.
thanks.
some good guy posted power measurements of lm1875
so for my 18-0-18 (36v) the results say
impedance -- supply current -- rms current
2ohms -- 1.42a -- 3.15 (16-0-16v)
4ohms -- 1.42a -- 2.58
8ohms -- 0.67a -- 1.40
to average out and taking 4 ohms load I guess around 3 to 4A capable gauge copper wire for transformer would be more more than sufficient ?
impedance -- supply current -- rms current
2ohms -- 1.42a -- 3.15 (16-0-16v)
4ohms -- 1.42a -- 2.58
8ohms -- 0.67a -- 1.40
to average out and taking 4 ohms load I guess around 3 to 4A capable gauge copper wire for transformer would be more more than sufficient ?
For a good LM1875 stereo amplifier 150VA transformer is more than enough, even you can go lower. For a wide variety of load secondary voltage should be not more than 15-0-15~17-0-17.
From the PSU point of view, a just-reaching-clipping amplifier "looks" like a 2 Pi load equivalent resistor, connected from end to end rfails.
Meaning: your 18+18V AC transformer will give you raw +/-25V rails.
Load them with a 2*Pi*8 ohm so 50 ohm, from +25V to -25V and it will be doing the same job as feeding your "just clipping" amplifier.
So if you wish you CAN test your full power supply without amp, signal or speaker, go figure.
A perfect amp from a perfect supply would put out 40W RMS (compare that to the expected 50W "DC" pull caused by the 50 ohm resistor) but of course a real supply will sag by 15-20% under full load, plus semiconductors in power amp will at least rob you of 2V from each rail so in practice you will be closer to 20-25W RMS ... tops.
So for a single channel and an 8 ohm load you will need at least 50-70VA rating.
Double that for a Stereo amp.
I would not load an LM1875 with 4 ohm speakers under such supply voltages.
If you see figure 9, at +/-25vDC activation of current limiting circuitry is inevitable if you use 4ohm spkrs. So it is a wise decision to reduce the supply voltage to +/-20~22vDC. At this voltage lm1875 can comfortably deliver about 20-25 watts into both 4 and 8ohm load.
You can't expect extraordinary performance from this 5pin chipamp, so don't waste your precious time thinking too much about this simple little chipamp.
Regards
You can't expect extraordinary performance from this 5pin chipamp, so don't waste your precious time thinking too much about this simple little chipamp.
Regards
I am not wasting my time. As this is DIY mostly people within limits tend to have a little bit more of everything... good components, boards, PS, layouts etc. This is just hobby, learning and it keeps me busy in electronics.
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After Electricity Board changed cables in my area, I checked voltages whole day and they vary from ~197v to 230v. BUT 90% of time hover around 210v. Transformer winders need to know input voltages and it is 230V standard here. So for 230 V and 18-0-18v mostly I will be getting 15-0-15v at my home. A newbie attempt to have both power and non clipping small amplifier. Will do forum's 'Speaker voltage test' to stay within the amplifier wattage limit.
regards
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After Electricity Board changed cables in my area, I checked voltages whole day and they vary from ~197v to 230v. BUT 90% of time hover around 210v. Transformer winders need to know input voltages and it is 230V standard here. So for 230 V and 18-0-18v mostly I will be getting 15-0-15v at my home. A newbie attempt to have both power and non clipping small amplifier. Will do forum's 'Speaker voltage test' to stay within the amplifier wattage limit.
regards
LM 1875 you can safely run at +/- 24V, first decide how much output you want, and get proper transformer.
See graph for power vs. voltage.
https://www.instructables.com/Tales-From-the-Chip-LM1875-Audio-Amplifier/
Commercial amps use one tap of 12-0-12 to drive the tone circuit, on a 3 amp transformer it does not create sag, expected drain is less than 200 mA.
That is for 2030 and 2050 chips.
Philips used 0-14-28 windings, 14 for pre amp and 28 for power amp section on same transformer, in Power House series of cassette / radio /amplifiers.
You can put a separate transformer for pre amp section, 500 mA claimed is ample, and check regulation on load, may damage devices if it goes high.
Your choice, single or separate transformers.
See graph for power vs. voltage.
https://www.instructables.com/Tales-From-the-Chip-LM1875-Audio-Amplifier/
Commercial amps use one tap of 12-0-12 to drive the tone circuit, on a 3 amp transformer it does not create sag, expected drain is less than 200 mA.
That is for 2030 and 2050 chips.
Philips used 0-14-28 windings, 14 for pre amp and 28 for power amp section on same transformer, in Power House series of cassette / radio /amplifiers.
You can put a separate transformer for pre amp section, 500 mA claimed is ample, and check regulation on load, may damage devices if it goes high.
Your choice, single or separate transformers.