Hi, Im building a LM1875 chipamp (exact copy of the National datasheet typical operation circuit) however I am powering it with two SLA 12V batteries. So far it sounds good but...
I plan on also building a ESP automatic battery charger for it, does anybody know how much current the LM1875 draws when it is idle? Or how to measure this?
Basically, I want to set the circuit up so that the automatic charger turns itself on when the amp is idle (but not switched off) and off again when the amp is playing music, has anybody else done something like this? On another note, would I have to switch the pre-amp off to get this drop in current drawn or just the CD player? and would this drop be greater than the 10mA needed to activate the circuit?
Oh yeah, one final question, Should I put any big capacitors on the battery power supply, or is the 100uf by the chip enough for battery supply, I did put two 1250uf caps on the battery terminals when testing the circuit but couldn't hear a difference?
Cheers,
I plan on also building a ESP automatic battery charger for it, does anybody know how much current the LM1875 draws when it is idle? Or how to measure this?
Basically, I want to set the circuit up so that the automatic charger turns itself on when the amp is idle (but not switched off) and off again when the amp is playing music, has anybody else done something like this? On another note, would I have to switch the pre-amp off to get this drop in current drawn or just the CD player? and would this drop be greater than the 10mA needed to activate the circuit?
Oh yeah, one final question, Should I put any big capacitors on the battery power supply, or is the 100uf by the chip enough for battery supply, I did put two 1250uf caps on the battery terminals when testing the circuit but couldn't hear a difference?
Cheers,
[Oh yeah, one final question, Should I put any big capacitors on the battery power supply, or is the 100uf by the chip enough for battery supply, I did put two 1250uf caps on the battery terminals when testing the circuit but couldn't hear a difference?
/QUOTE]
Long-time battery user, Ron Clarke uses something like 6 uF on the rails of his battery driven Gainclones and finds it quite adequate (even preferable).
I have answered for Ron as he is in the process of moving home and may not see your post for a while.
Ron also states that he leaves his charger in circuit and charging 24/7 and does not notice any difference. This saves a lot of complication in designing an 'intelligent' charging system such as you have outlined above.
Fragen said:
I've started looking at this chip lately because CarlosFM has said it has particularly good sounding high frequency response. Also, my speakers are 98dB/8ohm, so I really only need a few good watts.
I'm glad to hear this because I've been eyeing that circuit for over a year. Unfortunately, I'm a complete newbie so I was waiting for someone with more experience to build it first.
You know, that was one of my biggest concerns. I could see my girlfriend turning on the amp(or system) and then going shopping after an hour or so. Or, listenign to some music before bed and forgettign turn it off. This would result in the amp drawing off the batteries until it reached it's minimum charge threshold.
Considering that this probably happen on a daily basis, I'd be going through batteries on a yearly basis - not cheap.
I wonder is there's a way to attatch the sensing circuit to amp's input signal w/o adding any noise? That way, when the amp receives an audio signal from the preamp or cd player, it would disconnect the charger.
That's the big question! Does the current drop enough when the cd stops spinning and no signal is sent or when the entire unit is turned off? The same would apply for a preamp, if used.
I'm guessing here, but couldn't we add a capacitor to store "x" amount of minutes worth of current? After "x" minutes of no signal, the relays would trip and the charger re-connect?
Perhaps I'm just a newbie freaming of things which would seriously complicate the already simple design.
Please let me know how things go with this charger,
victor
Sorry, I have almost no experience
So far I've built the ESP P88 preamp (with OPA627's instead of 2134's) and run it into the LM1875 circuit (I run the amp off batteries but have not completed the charger)The ESP site http://sound.westhost.com/project98.htm has a table for minimum current and resistor values, If I knew the value of what the LM1875 draws when idle and what it draws playing I could select a resistor that is above the minimum current of idle and below current drawn when playing. This would save me from having to add a power switch to each power amp, (which would ruin the look of my amps
) not to mention I hate having to turn equipment on and off.The LM1875's do sound great, I don't have very loud speakers (87db efficient bookshelf monitors) but when I hooked it up, it was loud and clear, best of all I only have two little 12V 1.3AH SLA batteries, wired to give -12V-0V-12V, Im very happy with the sound. Also, the 1875 chip only has 5-pins, a real bonus for careless people like me who don't check stuff before they solder.
I'll make the circuit charger tommorrow and post back if it works, trial and error should get the right resistor value.
This preamp/amp combo sounds great, I put the preamp into an old art-deco style silver cigar box, The amps are going into little die-cast boxes painted hamerite grey, the batteries and charger will also go into a bigger diecast box painted hamerite grey (it is also quite small though.)
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The LM1875 is a really good sounding chip.
Those who have very efficient and easy to drive speakers should give it a try.
The batteries can be charging permanently (24/7), at a current of up to 10x less than their nominal capacity.
With 7A batteries I would leave them permanently charging with a small 300~500ma trafo and LM317/337 adjusted for +/-13.8V.
You may switch the PSU off when listening, if you notice any difference in the sound.
No maintenance, no worries, easy, great.
Those who have very efficient and easy to drive speakers should give it a try.
The batteries can be charging permanently (24/7), at a current of up to 10x less than their nominal capacity.
With 7A batteries I would leave them permanently charging with a small 300~500ma trafo and LM317/337 adjusted for +/-13.8V.
You may switch the PSU off when listening, if you notice any difference in the sound.
No maintenance, no worries, easy, great.
It seems like batteries act as sort of buffer, preventing PS connected to it from degrading the sonics in big way. I noticed that in a DAC, and I have similar experience with GC.
Although alone (without charger connected), batteries still sound better, the influence on the sound of the charging circuit is not that pronounced (in my system it's more bright, not as smooth and coherent, with Velleman charger) and for less critical listening I don't bother to disconnect charger.
Although alone (without charger connected), batteries still sound better, the influence on the sound of the charging circuit is not that pronounced (in my system it's more bright, not as smooth and coherent, with Velleman charger) and for less critical listening I don't bother to disconnect charger.
Increased smoothness, more natural presentation, better defined bass.Pan said:
In those amps, for best performance, every component is important, as it brings it's signature influence on the sound.
I also think that LM3875 might be a better candidate, if you expect more "magic" from those amps.
I thought about using a LM3875 with batteries, but I thought it need more than 12V? With the 1875 running off 12V batteries you don't have to worry about anything like large voltage, big batteries, big caps, big heatsinks...
Its hard to imagine an easier amp to build for a beginner (like me).
As a beginner...
What is an ammmeter or DMM? and how would I hook it up?
Its hard to imagine an easier amp to build for a beginner (like me).
As a beginner...
What is an ammmeter or DMM? and how would I hook it up?
Fragen said:
DMM is a digital multimeter. It's used to measure voltage(mV-kV), current(mA to A), and resistance(mOhm to Mohms).
I bought a used Fluke 8050A bench DMM for $50 on eBay last year and it has become the single most important tool I have next to a good soldering station. After that, comes an oscilloscope.
An externally hosted image should be here but it was not working when we last tested it.
The 8050A also measures Conductance, voltage in decibels(dB), polarity, and input signal as an offset to a relative(stored) reference value.
A DMM is invaluable when you need help because it allows you to precisely follow values through your circuit at each and every component. Makes it much easier to find where something is going wrong or even fine-tune things. And also allows you to give the gurus around here a good idea of what exactly is happening in your circuit.
Save yourself a lot of headaches and get a good one
Fragen said:
... an ammeter measures current, which is measured in units called amps; or fractions of amps called milliamps. A multimeter also measures amps, as Darkmoebius told us. To measure current, the ammeter (or multimeter) must be part of the circuit, so in your case it would be fitted between the power supply (batteries) and the amplifier. The current flows through the meter which tells you how much the amplifier is drawing.
(By the way, don't confuse "amps" with "amps"!)
Cheers,
I'll try and measure it that way, I have a little digital multimeter. Thanks for all the input for my questions, the information on this site has been very helpful to a complete newbie like me.
Once I get this up and running Im going to try the same with a 3875 then Im going to bi-amp them.
Dan
I'll try and measure it that way, I have a little digital multimeter. Thanks for all the input for my questions, the information on this site has been very helpful to a complete newbie like me.
Once I get this up and running Im going to try the same with a 3875 then Im going to bi-amp them.
Dan
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