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Old 9th February 2010, 05:55 PM   #11
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Quote:
Originally Posted by Mooly View Post
Why not germanium ?
You should be able to swing a slightly larger output voltage with Germanium transistors & given your low supply voltage that must be an advantage.

Yes i'm sure you could increase it & then use Silicon, but why not make use of something that'll be perfectly adequate & save leaving things on a shelf unused
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Old 9th February 2010, 06:18 PM   #12
Mooly is online now Mooly  United Kingdom
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It's just fun to work with old stuff sometimes...
You are right about the supply voltage, and germanium has a much higher conductivity than silicon at an atomic level... the energy required to "break free" the electrons is less than silicon. What's the word I'm looking for ? co valent bonds ?
Trying to remember the theory of all this it was a long time ago (ish)
Well germanium has it's advantages, biggest disadvantage is temperature... about 50 degrees C would be an upper limit I guess.

I'm going to use rechargeable batteries, a 9.6 volt pack so will hopefully come up with a "full" worked design in the next week or two including the PSU and charger.
Have ordered some of the bits... case etc today.
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Old 10th February 2010, 05:05 PM   #13
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PSU taking shape of sorts... hope to do the whole thing on one PCB. This gives a simple on/off from one push Tact switch. I have some great looking illuminated blue ones.
Bit of head scratching to get this to work, using a D flip flop as an "invertor"
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File Type: jpg PSU.JPG (243.2 KB, 1126 views)
File Type: jpg Tact.JPG (13.5 KB, 1026 views)
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Old 10th February 2010, 06:53 PM   #14
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Oy - no cheating!!!!

Those better be germanium gates I'm seeing there on the diagram!

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Old 11th February 2010, 06:26 AM   #15
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Quote:
Originally Posted by godfrey View Post
Oy - no cheating!!!!

Those better be germanium gates I'm seeing there on the diagram!

Would it sound better I could do a discrete one... better check what other size cases are available lol
Can't even use germanium for the switching transistor... to much leakage.
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Old 11th February 2010, 11:26 AM   #16
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The switching device in the above PSU is now an IFR630 Fet. This gives only 20 mv or so drop across it when on.
And an OpAmp has (will) appear in the final design. I am going to drive the blue LED on the tact switch from it, and use it to indicate low battery voltage by flashing when a predetermined level is reached. Have prototyped the circuit... it works well using a 1458 dual opamp. One half of the OpAmp drives the LED and is configured as a 1hz oscillator. This then enables/disables the oscillator. The other half is a window comparator monitoring the switched supply from the FET and taking a sample of the regulated supply as a reference.
The small mains transformer feeds a 7912 and from there via a 33 ohm (for now) feeding the battery pack. Have to use a 7912 to prevent damage in case the battery went OC and the 4013 saw to much volts. Regulation of the small tranny is around 58% but it's ideal for the job.
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Old 13th February 2010, 07:24 AM   #17
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The low battery indicator is taking shape.
The battery pack is 9.6 volts nominal. The regulator (7906) now has the voltage lifted by two 1N4148's to give -7.17 volts (measured) The input to the reg can approach -8 volts before any dropout is observed at these low currents. That gives a 1 volt per cell value for the battery when discharged... not sure if that is considered to low to discharge cells to... have to research that one.
Here is the basic indicator. A ten turn 100 k pot allows the trip point to be accurately set.
C1 ensures the circuit doesn't latch in the wrong state at power on. The 6M8 introduces a little hysteresis to ensure the opamp switches states cleanly. The oscillator is built around the second opamp and is "enabled" via D1.
So we have steady LED for normal and flashing LED for low battery.
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File Type: jpg Low Battery Indicator.JPG (271.3 KB, 962 views)
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Old 17th February 2010, 06:56 PM   #18
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The PCB is slowly taking shape... it's proving difficult fitting it all on.
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Old 17th February 2010, 07:02 PM   #19
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Looking good so far chap

I'd be joining you in a headphone amp but as i have absolutely no idea of the impedance of any headphones i'm likely to buy it's just a pipe dream at the moment.

Sennheiser are a good possibility though, i'm sure some of those are in the 300 ohm region though i could be wrong.

I think i need to get out more & at least audition some cans

Best of luck Mooly
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Old 18th February 2010, 06:13 AM   #20
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Thanks...
You can compare headphone specs here, and choose by impedance/make/type etc
Your Search Results | CPC
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