Hi all,
Does anyone know if someone has tried leveraging figure 1 of this design note into a headphone amp? It looks like it could work will with a high quality op amp.
http://www.ti.com/lit/an/snoa600b/snoa600b.pdf
I was bored so I started up a simple PCB layout, using Express PCB and their 3.8X2.5 proto-board size. No traces around the OA yet, just working out the output stage. I doubled up on the output transistors and I think the 2.5 ohm ballasting resistors should drop to about 1 ohm to suit. The green plane will be for audio, red will be for power rails and ground plane.
So, bad idea? Errors in the layout? Order parts, build it and report back?
-Brian
Does anyone know if someone has tried leveraging figure 1 of this design note into a headphone amp? It looks like it could work will with a high quality op amp.
http://www.ti.com/lit/an/snoa600b/snoa600b.pdf
I was bored so I started up a simple PCB layout, using Express PCB and their 3.8X2.5 proto-board size. No traces around the OA yet, just working out the output stage. I doubled up on the output transistors and I think the 2.5 ohm ballasting resistors should drop to about 1 ohm to suit. The green plane will be for audio, red will be for power rails and ground plane.
An externally hosted image should be here but it was not working when we last tested it.
[/URL]An externally hosted image should be here but it was not working when we last tested it.
[/URL]So, bad idea? Errors in the layout? Order parts, build it and report back?
-Brian
That circuit looks to be well thought-out and actually designed - not just presented as a textbook example of a concept. It offers a lot of possibility for learning and experimentation. I suspect you can find the same basic architecture in quite a few projects published on the 'net and elsewhere. For example,
Here on the DIYAudio Forum you can probably collect a few dozen suggestions for more modern, higher-performance substitutes for the LF35x family opamps. I'm partial to the TL07x family over the LF35x.
The 2N2219/2N2905 devices may be difficult to obtain from reliable sources. There are several current-production (at least as of June, 2014) devices in TO-126 or TO-225 packages that should be suitable substitutes.
If you can't find the solid tantalum bypass capacitors, a good quality (low ESR) electrolytic - perhaps with a film capacitor in parallel - should do the job. In fact, I'd probably park a pair of film caps right at the opamp power pins even with the tantalums on the power input lines.
Dale
- "Hi-Fi Headphone Amplifier" at http://www.amplifiercircuit.info/2014/03/hi-fi-headphone-amplifier.html#.U5UI2SimU40
- "Headphone Amplifier Circuit" at http://www.electroschematics.com/2882/hifi-headphone-amplifier/
- "Designing an Opamp Headphone Amplifier" (see Fig 11) at http://headwize.com/?page_id=147
Here on the DIYAudio Forum you can probably collect a few dozen suggestions for more modern, higher-performance substitutes for the LF35x family opamps. I'm partial to the TL07x family over the LF35x.
The 2N2219/2N2905 devices may be difficult to obtain from reliable sources. There are several current-production (at least as of June, 2014) devices in TO-126 or TO-225 packages that should be suitable substitutes.
If you can't find the solid tantalum bypass capacitors, a good quality (low ESR) electrolytic - perhaps with a film capacitor in parallel - should do the job. In fact, I'd probably park a pair of film caps right at the opamp power pins even with the tantalums on the power input lines.
Dale
don't use Ta electros - expensive and Al have more than caught up in performance compared to 30+ yrs ago when solid Ta were the datasheet standard - but unexamined even then suggestion
if boredom is the design criteria then its something to do
if performance is the desire then embrace surface mount, use last decade or so better op amps, can still use Scott Wurcer/Walt Jung multiloop topologies but with DSL driver op amps as high current, low audio distortion output stage if your headphone specs are fine with op amp voltages
if boredom is the design criteria then its something to do
if performance is the desire then embrace surface mount, use last decade or so better op amps, can still use Scott Wurcer/Walt Jung multiloop topologies but with DSL driver op amps as high current, low audio distortion output stage if your headphone specs are fine with op amp voltages
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Sure!
A couple of those circuits are right out of Walt Jung's IC Op-Amp Cookbook
OK, cool. Thanks, Fast Eddie D
That circuit looks to be well thought-out and actually designed - not just presented as a textbook example of a concept. It offers a lot of possibility for learning and experimentation. I suspect you can find the same basic architecture in quite a few projects published on the 'net and elsewhere. For example,
Great, those examples show that there is some precedent. I think the 3rd one I stumbled upon while googling. I'm sure the use of the LM334 is superior to resistors. Any idea why they would use 2 diodes per base and raise the idle dissipation of the output transistors?
The LM334, 2N2219 and 2N2905 all seem to be available from Mouser. I'm open to suggestions for replacements on the "2Ns"... maybe something in a beefier package or that takes a more space efficient heat sink?
Lower crossover distortion? Avoiding reduced Hfe (or lower Ft) at low collector currents? Class-A operation into moderate-resistance loads?. . . why they would use 2 diodes per base and raise the idle dissipation of the output transistors?
The old standbys would be MJE340/350, MJE172/182, and BD139/140. There are several threads on this Forum discussing possible, more modern, alternatives.. . . suggestions for replacements on the "2Ns"... maybe something in a beefier package or that takes a more space efficient heat sink?
Dale
I made an amp using similar topology and it worked great!!!
It can be found here,
http://www.diyaudio.com/forums/chip...own-supply-what-could-happen.html#post3695968
I have used several pieces of pro audio equipment that uses this topology as well.
jer
It can be found here,
http://www.diyaudio.com/forums/chip...own-supply-what-could-happen.html#post3695968
I have used several pieces of pro audio equipment that uses this topology as well.
jer
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