Single gain stage transistor amplifier.

[rcollege]

Hi All,

Completely new here,
I've gotten hooked on this DIY audio amp building.
My goal is to replace a Marantz 2226B with a DIY integrated amp. So far I have had good results, but not enough to beat out the Marantz ( it may never happen). I have 90db speakers and can blow go too loud with 4-5 watts. Personally I like lower watts.

So I have tried the Chip amps...but I love the simplicity of a Single ended amp. To me there's no sense in creating a class A/B chip amp if I already have a Class A/B amp...that sounds good.

So I want to find/ develop a circuit that uses a single gain stage single ended transistor amplifier. I had a darlington amp work...but not enough volume. I'm trying to stay away from mosfets- I always come up with more distortion on the simulator with mosfets...and seems to give me a headache when played...awsome transparency though...just too sharp on the highs.

So am I trying to do the impossible? I don't want to rock the windows to a rattle...detail is more important.

Thanks for reading this and for any help you may have.

[paulb]

Yes.
Here are a couple of references for you to look at:
http://www.passdiy.com/pdf/zenamp.pdf
Death of Zen - A new Class-A power amp

[paulb]

And if you do want to pursue a bipolar transistor amp (and you'll end up with three stages), the design at this site is well regarded and there are many references to it on this forum:
The Class-A Amplifier Site
Or if you change your mind about FETs the passdiy site has many refinements to the Zen amp that you may find interesting.
Better start saving up for big heatsinks and transformers.

[rcollege]

Originally Posted by paulb

Better start saving up for big heatsinks and transformers.

This is the circuit I used for the mosfet amp- DIY Class-A 2SK1058 MOSFET Amplifier Project
I really do like the sound for what it is...I made some modifications and replaced the Pot with two resistors who's values were determined by my playing with the simulator.

Interestingly enough, I cheated and bought a $15 switching power supply. It powered one channel with this switching power supply- 24V 2.5 Amp. Amazingly, when I turned it up all the way with no music, you could here absolutely nothing from the speakers...zero hum. No filtering capacitors needed. Virtually no heat.
I ran two channels on a 24V .7 amp switching supply. Didn't sound bad with "how to Tame Your Dragon" movie...even though it does best with music.
I have a 24V 5 Amp switching supply if I can't get enough out of the 2.5amp supply. The heat is generated by the resistor in this circuit...and it runs HOT. after an hour of play, I could put my hand on the BUZ 11 mosfet- hot to the touch and a warm heatsink.

Luckily I got a ~30# heat sink out of a VFD that controled motors running off of 450V. I've been cutting it up into usable sizes so I wouldn't have to use a fan.

[picowallspeaker]

Strange that you say that .I haven't built any SE resistor loaded mosfet amp ,which is remarkable for its high 2nd harmonic distortion (should sound better on higher loads),but for the power supply usually I see often some very huge caps ,also with a 1-2 Ohm resistor or regulated .

[rcollege]

Originally Posted by picowallspeaker

Strange that you say that .I haven't built any SE resistor loaded mosfet amp ,which is remarkable for its high 2nd harmonic distortion (should sound better on higher loads),but for the power supply usually I see often some very huge caps ,also with a 1-2 Ohm resistor or regulated .

I know in multism spice simulator the distortions were 10- 15% at full volume. It came down to a more manageable .9% around 15%. The crazy thing is I couldn't get past 25% without good chance of waking the kids in the other room...so the design is for less 4.8watts I'm probably using 2 watts with a 2.5 amp source. The speakers are Boston Acoustics A100's - 2way 10" x 1" and 90db acoustic suspension. I wouldn't consider these the most sensitive speakers...but it does the job.

However, with a BJT darlington or BJT...I'll get the same voltages/ amps...but not near the volume. That was on a 89db speaker though.

[picowallspeaker]

wow ! you're deranging me from my 'audio beliefs'
Also a box containing a 10" woofer with a 1" dome tweeter !!!
quite difficult to have 'merging emissions' from two drivers with such different size -at least the tweeter needs a large mouth waveguide .
In hi-fi ,to avoid distortions and having the amplifiers never clipping ,it is better to have plentiful of Watts ...about 100-200 should be enough

[rcollege]

Originally Posted by picowallspeaker

wow ! you're deranging me from my 'audio beliefs'
Also a box containing a 10" woofer with a 1" dome tweeter !!!
quite difficult to have 'merging emissions' from two drivers with such different size -at least the tweeter needs a large mouth waveguide .
In hi-fi ,to avoid distortions and having the amplifiers never clipping ,it is better to have plentiful of Watts ...about 100-200 should be enough

Yes...10" x 1"...and I'm not sure how they did it, but it puts out full spectrum sound better than some other speakers I have thought about buying. Only the $3k each Martin Logan electrostatics came close...but had problems transitioning to the woofers for bass.
I know that this was Boston Acoustics "no comprimise" speaker. The larger baffle helps and plus it is an acoustic suspension- detail is more prominent than heavy bass and loudness. These are not "party" type speakers. You don't get as heavy bass as in a ported speaker.

This is one of the reasons I believe you can get great sound using lower watts. I used to think more watts was better...then my vintage 1977 25watt/channel Marantz blew away my 2006 80watt/channel Marantz receiver. Both in detail, full range and volume.

I truly believe in using less watts. If your speaker is rated at 90db...then 1 watt at 3ft = 90db of sound. Creating an amp that doesn't clip at these levels is doable...I just want to do it using a single stage...and BJT's will produce down to 1.79% THD full volume with no clipping...but .05% at 60%...I just need more power, 8 watts is more than enough.

[WuYit]

rcollege,
your amp hates that power supply immensely.

[rcollege]

Originally Posted by WuYit

rcollege,
your amp hates that power supply immensely.

Forgive my ignorance,
but may I ask why?
It swithces at MHZ...and handles 2.5 amps.
I also have one that is +12, -12 at 5 amps.