Explendid amplifier designed by Michael Bittner, our MikeB

[MikeB]

??? Mosfets don't have hfe... You can measure Vgs (like Vbe) by placing the mosfet like a npn, b -> g, c -> d, e -> s. It might be necessary to increase voltage to 12v. Vgs is expected to be between 3v and 5v.

Mike

 

[MikeB]

Hi
finally my boards are ok and soon a new SYM will be born.......

Hi Spirtos, any news with your nice boards ? Just curious... 🙂

Mike

 

[Spirtos]

Hi Mike,
unfortunately I haven't finish the installation yet. Too much work and business trips...I hope that next week I'll finish the boards and power supply so I will be able to make some mesurements and a first listening test

 

[dytln_02]

@mikeb
can I remove Toshiba sc5200/sa1943.
see picture
how many power into 32 ohm impedance and how many gain from this amps ?
I'm looking mini version from this amps. I want use it as headamps

An externally hosted image should be here but it was not working when we last tested it.

edit: output after R 10 ohm

 

[MikeB]

Hi dytln, that should be possible, i guess you can reduce supply voltage to ~12v, use pure classA for the outputstage and reduce the overall gain and open loop gain. I will have a closer look later... (weekend)

Mike

 

[PMA]

Hi dytln_02,

you will have a plenty of gain with this amp as a headphone amp, and it is not necessarily what you need. The symasym is a pretty wild horse when you try to decrease its gain to a value raesonable for headphones. Think about it.

Regards,
Pavel

 

[MikeB]

Hi dytln_02, i played a bit with your suggestion in sims, it should work to create a headphone amp with this topology.

I choosed +/-16v as dc-source (from 12v AC rectified)

I have not build it, only sim'd, but should work quite good...
As you can see, i made some more changes.

Bias in outputstage is ~200ma.

Mike

 

[Chuck911]

Helo Mike. To comply with the conditions of competent standards you must connect a current limiting resistor in series with load (headphone). For small power amps it should be 100 ohm.

 

[00940]

"Standards" ask for an output impedance of 120Ohms. However most headphones (Sennheiser, Grado, Akg) are designed with an output impedance of 0Ohms in mind and sound best when driven that way. Iirc, only Beyerdynamic still designs with 120Ohms in mind.

 

[PMA]

In any case you should have a possibility of the series output resistor. You need not use it then, if you do not like it.

 

[dytln_02]

Hi dytln_02, i played a bit with your suggestion in sims, it should work to create a headphone amp with this topology.

I choosed +/-16v as dc-source (from 12v AC rectified)

I have not build it, only sim'd, but should work quite good...
As you can see, i made some more changes.

Bias in outputstage is ~200ma.

Mike

thanks mikeB

I Will Try this Headamps ......
I will report the result next week. 😀

 

[dytln_02]

@mike_B

Is 1/4 Watt Resistor enough for Resistor At Output (1.2, 47 and 32 Ohm) ?
Is Small Heatsink Enough for MJE 15030/15031 ?

 

[MikeB]

Hi dytln, these resistor should be ~2watts, but just for testing a 1/4 watt is ok. A simple U-shape will not be ok for the mje15030/31 they dissipate 3watts each, it should be enough to mount them to a metal case.

Mike

 

[dytln_02]

@mikeB
I have build PCB, i will start to make Symasym5 headamps
can you give spec from Symasym5 headamps (in sims).
THD: ?
Power into 32 ohm ?
Gain ?
Feedback ?
GainBandWidth ?
Slewrate ?
Frequency response ?
Phaseshift at 10khz ?

 

[MikeB]

Hi dytln, heare are your numbers:

---------------------------

THD at 20khz, 3.3v (~0.01%)
h2: -80db
h3: -90db
h4: -125db
h5: -133db
higher order below noise

Power into 32ohm: ~3watts

Gain: ~1:12 ~20db
Openloopgain: 1:1400, -3db at 48khz
Feedback: 41db
GainBandWidth: 61mhz
Unitygain at 6.5mhz 157° (unitygainstable)
Stable into capacitive loads

Phaseshift at 10khz: openloop 13°, closedloop 1.7°

Frequency response: -1db, 3.3hz to 150khz

Slewrate: ~14v/us (enough at these powerlevels)

---------------------------

I optimized the circuit for stability, not for impressive THD numbers.

Mike

 

[Archimedes]

😉
Hi Michael

Congratulations on a well designed amplifier and to all the fundis that assisted you here and there with some of the finer details. I have had the pleasure of building 4 of them for an in car 4 ch amplifier and have enjoyed every minute of listening to music on it
The treble clarity is amazing. The bass seems defined but does not dwarf the vocals or upper frequency instruments. Just my 2cents worth.

Attached is a photo of the configuration I have used. I have not built a cover for the case as I was to busy enjoying it in my car to care about the cosmetic side of things.

 

[dytln_02]

@mikeB
Can You give Voltage Measure Across Resistor, So I can debug it ?
I have finish build One Channel...
With Input Connected No Hum, Hiss Only AT 3/4 Volume, maybe from soundcard (Chaintech A7V)
I Can Say how it's sound because it's only One Channel
I will build another channel...

edit :
I Can not Say how it's sound because it's only One Channel
Is 1A +16 0 -16v PSU Enough for this Headamps ?

 

[MikeB]

Hi Archimedes, thanks, appreciated. You might be the first using symasyms as car amp... 🙂
I am glad that you enjoy symasym !

Dytln, 1A power supply should be sufficient.
Typically, if you can easily set bias in outputstage and DC-offset is low everything is right.

Mike

 

[anatech]

What a great idea, using Symasym as a car amp!

If I can find some old MGT 2100's .... Supplies were +- 33 VDC.

-Chris

 

[Ryssen]

Will a heatsink that´s 7x6x2 inch be enough for 2 channels?