| Zero One |
Just for interest here is my latest clone module, hopefully optimised for tweeter use. It will be totally enclosed in a copper case around the circuitry tomorrow once tested, it is as small as I can make it, virtually all P2p SMDs, LM1875 chip, 12V battery supply, gain of 15, 47uf caps with a bank of 10 snubbered 10uf caps per rail, (off board and not shown).
The watch is shown for comparision.
Input/powerwiring is foil wrapped and earthed to the groundplane which is insulated from the heatsink, and the output runs under the heatsink and up through a hole just under the output tab on the chip. I am absolutely determined to kill any chance of oscillation in the search for the "tube clone sound". |
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| Zero One |
| Here is another pic a bit easier to see. |
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| Nuuk |
| What is that yellow cap ZO? :confused: |
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| Zero One |
Hi Nuuk
The yellow cap is a .1 uf bypass on the input 2.2uf input cap, to help keep the highs all sweet, the main input cap is SMD, I could have used a chip cap, however I,m a little dubious about using chip caps in the signal path, hence the MKT. |
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| Nuuk |
If you are going for the 'ultimate' tweeter amp, you can get away with a much lower value input DC blocker and go for a good quality polyprop, or even paper-in-oil type.
IMHO, polyester types in the signal path are lo-fi rather than hi-fi!
What's a chip cap? :confused: |
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| Zero One |
Hi Nuuk
Yep I agree entirely I will be using a better grade cap, this is a prototype to test a few things, in fact the final modules will only have a small blocking cap, and be fed via an active crossover, so only 6000 Hz and up will be going to the module.
Chip caps are non polarized SMD caps that look, well like a tiny tiny brick, pretty poor quality apparently.
Heres and update, I finsihed the module today with its little copper coffin all around the module and it is running right now, but in full range mode (ie driving my full range speaker set-up) with 3200uf off baord caps and the sound, very very nice, somewhat smoother than the other clone module on the other speaker, nicer mids/upper.
Currently its running on 12smps, but going on my expereince from a couple weeks back I feel the 18v battery set-up with the 100uf cap banks be nicer still once hooked up for tweeter use.
And thanks for your interest and comments, how low do you think I could go on the blocking cap value. |
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| Circlotron |
"that look, well like a tiny tiny brick,"
I think chip caps look like a little bed with a pillow at each end :clown: |
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| Zero One |
Yep and just about small enough for an errant flea to get a kip on when he gets a bit tired.
:) |
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| Nuuk |
| quote: | | And thanks for your interest and comments, how low do you think I could go on the blocking cap value. |
It takes two to Tango so it depends also on the resistor (input to ground) involved! I'm not sure if there are any other factors affecting how low you can go. But based purely on theory, you could go to something like 10 nF (with 51K). :att'n: |
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| Zero One |
The resistor to ground on the input is 1M does that help?
Just put the little fella to sleep after running for 7 hrs, not even warm to touch...lovely |
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| Nuuk |
| quote: | | The resistor to ground on the input is 1M does that help? |
According to my calculations, a 1 meg resistor with a 10n cap give a cut off frequency of around 16 Hz. |
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| Dag |
Excellent work!!! I want to do exactly the same.
Do you use 12V or +/- 12V??
I want to use the LM1875 for a small active speaker. Single 18V supply and 1xLM for the tweeter and 2xLM (bridged, 8ohm) below 3k. Is that a good idea?? Or are there better (bridged)18V chips for the bass?
:)
ps. You can use the coupling cap for a pole in your (active) filter if you want. |
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| Zero One |
I feel you would be better off to go for a dual rail supply, 12v works suprisingly well with these chips, I have used 18 as well and I'd say it is the pick of all the options as far as sound and power goes.
In my opinion if you are going with low voltage supplies then the 1875 chips are the best, they will produce slightly more power and in my opinion they sound more musical than the other chips, but others may feel differently of course.
Finding a circuit for bridged mode is not so easy, I had one but I don't know where it is now, but bridging will give useful power on low voltages. I'd say a bridged LM1875 on 12V will give somewhere around 20w equivalent, which would be very neat. You don't need much for tweeters of course and low V on the tweeters is very sweet indeed.
The trick for getting good bass is having plenty of capacitance, normally going over 1000uf degrades the highs (common wisdom anyway) but I have found that battery supply or smps with big caps works brilliantly and vastly superior to regular transformer supplies.
There is a dual chip version of the Nat Semi LM1875 available, I think its called a 1876, I do have some in my workshop but I have not yet tried them, this might suit your application better. |
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