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Old 30th January 2006, 09:07 PM   #1
Bazukaz is offline Bazukaz  Lithuania
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Default ESL Headphone direct drive

Hi,
I am trying to design a simple transistor headphone direct drive amp.

Would this schematic work ?

Thanks in advance ,
Lukas.
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Old 30th January 2006, 11:04 PM   #2
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ESLs generally require balanced drive (i.e. push-pull) on two stators. How do you intend to connect this to an ESL driver?

You also need a HV bias source for the diaphragm...

Try something like this:

http://www.headwize.com/projects/sho...lmore2_prj.htm

Download a copy of SwitcherCAD and learn how to use it. You can simulate the circuit and get a pretty good idea what it will do.

I_F
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Old 31st January 2006, 01:33 AM   #3
Bazukaz is offline Bazukaz  Lithuania
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Thanks ,
I will try to learn SwitcherCAD.For now I can only get "Unknown subckt called in" error with it. I Can't find any tutorial in english on the net .
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Old 31st January 2006, 02:36 AM   #4
jcx is offline jcx  United States
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LT's Spice is great but not setup for learning Spice from, buy a book on learning electronics with Spice, LtSpice will be 99%+ compatable

you can download other, less capable, "Demo" versions of Spice from the big guys and just use the documentation with LtSpice

you have to join Yahoo to acess the really great LtSpice user's group, many example files, Spice experts and the main LtSpice programmer are there - just don't expect them to teach you Spice basics

the "uknown subcircuit" error means you are calling for devices that aren't in the supplied model libraries (\lib directory), adding spice models in LtSpice is easier than many other Spice programs but you do need to read the help - if you enter the schematic in the editor and select devices from the tool bar component pull down (the "and gate" symbol) you should have no probelms - don't expect to run any random netlist in any Spice without finding all of the required models/subcircuits and adding them to the library
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Old 2nd February 2006, 05:52 PM   #5
Bazukaz is offline Bazukaz  Lithuania
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Thanks a lot ,
LTSpice really helps.
I tried to simulate the following circuit.I built a prototype and tested it , but the distortion levels are around 0.2% from 50Hz to 20Khz.
What is the problem ? Circuit design flaws , or wrong type of transistor ?


Regards ,
Lukas
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Old 3rd February 2006, 01:57 AM   #6
jcx is offline jcx  United States
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in LtSpice the default setting is to compress the waveform data - this causes distortion in the analysis of the sim

add the spice directive:

.option plotwinsize=0

to the schematic with the ".op " button at the right of the toolbar

my sim of your circuit using the (inadequate V) mje340 which I think came with LtSpice and a higher gain, high speed Lt1115 op amp gives ~ -110 dB 2nd harmonic 140Vrms @10KHz

I couldn't find a 2sc3865/6 model with google - to share you can put the added models on the schematic with the .op button and post the .asc circuit file by changing the file extension to .txt and attaching to your post

please use .png or .gif for schematics, jpeg renders part # unreadable
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Old 3rd February 2006, 11:27 AM   #7
Bazukaz is offline Bazukaz  Lithuania
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Thanks for help ,
The problem is not LTSpice related , because i really built it.
I used NE5532 for a driver IC with 2SC3866 transistor.Sound card was used as both oscilloscope and signal generator(it produces ~0.03% THD from output to input).
For measuring i used SpectraPLUS program.
THD+N was around 0.06% at 1 khz but ~0.2% at 5 khz and higher.
I have also tried generating square wave , but it wasn't even close to it at any frequency.Probably sound card is not capable of generating square too.
The little amp produced ~85Vrms until distortion started to rise quickly.

Transistor's datasheet :
http://www.alldatasheet.com/datashee...I/2SC3866.html

I have also found one interesting direct drive schematic at www.shackman.de .Unfortunately , its description is in german .
I could share it if you are interested.

Regards ,
Lukas
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Old 3rd February 2006, 05:58 PM   #8
jcx is offline jcx  United States
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it's hard to say what the 2sc3866 is is capable of distortion-wise,

op amp open loop gain is falling with increasing frequency and output Q Zcb nonliear current is rising too, the distortion rise isn't too suprizing

Resistor bias causes the Q to work harder, maybe a ccs would help

often higher bias current reduces distortion, may speed up output Q too
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Old 4th February 2006, 06:37 AM   #9
Bazukaz is offline Bazukaz  Lithuania
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Hi,
Thanks for support,
I have tried increasing bias a bit , but problems did not solve.
The distortion is basically a 2nd harmonic.
What does a ccs mean ?

Regards ,
Lukas.
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Old 4th February 2006, 10:40 AM   #10
Calvin is offline Calvin  Germany
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Default ccs

Hi,

ccs means constant current source. Replacing R4 by a e.g. FET- or bipolar source gives the working Transistor Q1 much better conditions.

jauu
Calvin
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