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2N3055 preamp\headphone amp

post #1 of 13
Thread Starter 

This is a preamp\headphone driver using a single 2N3055. An electronic friend of mine said that many times large power transistor are quieter than smaller transistors due to their large base. I took his advice and made this emitter follower preamp\headphone amp. You lose about 10% of the signal because of the emitter follower but it drives really well into low impedance loads. It drives my ATH700 Airs (33ohm 98db efficient) with ease and is dead quiet. Strange build with the 2N3055 bolted to a block of Merboo timber for resonance control. I call the preamp "Woody Pro".

 

Built in an attractive 19" 1U rack enclosure with a 4oz solid brass knob. The construction is dual mono starting with the PS. The PS uses potted mini toroids then two stages of 10,000uf Nichicon caps for a total of 40,000uf of filtering. The PS uses discrete ultra fast diodes and like the large filter caps these are individually snubbed. The whole PS is layered in bitumanised heavy Al foil for shielding and resonance control. There are two separate PSs. The output caps are 10 X 10uf polypropylene to make up the 100uf required. There are two banks of these output caps for a total of 20 caps. The output caps are also snubbed.

 

The internal audio wiring is 0.7mm five nines pure silver and power connection via OFC. Frequency -3db points are 10Hz to 135KHz.There are two switchable inputs both RCAs with one RCA is also connected to a 6.5mm phone jack. The output RCAs are also connected to 6.5mm phone jack. This is so the preamp can be used as a preamp and\or a headphone amp. Great sound, absolutely dead silent and excellent dynamics.

 

post #2 of 13
Jeez, talk about overkill, you could win WWIII with that.

It wouldn't be my way to go, I don't really admire overengineering, after all, anyone can throw resources at a project, it's doing the same thing in a couple of cubic inches for a few dollars that I prefer. How much bias current are you burning? It's all contributing to global warming.

Each to his own though, execution looks superb.

w
post #3 of 13
Thread Starter 
Thanks for the nice comments (sort of). I guess that's the beauty of DIY is for the cost of parts only you can go nuts. Yes it is class A but all currents etc are low as this is not a power amp. no huge idles currents. I wanted the PS to be dead quiet and the only way to do that is careful layout and lots of good filtering. I used the ploys on the output because I didn't want to use electros NP or other.

Compared to my tube headphone amp also posted on this site it does not compare but on its own an excellent performer.
post #4 of 13

Thank you for sharing your amp with us.

 

After 20 years of working with ever more under-engineered industrial machinery/electronics, I find your "no holds barred" design/construction approach a refreshing contrast to price driven modern electronics.

 

I build tube amps and often take a similar approach to yours, using industrial rather than consumer designs and components.

 

There are often sonic benefits to this approach that don't show up in standardized design methods.

 

Keep up the good work! 

post #5 of 13
Thread Starter 

FrankCooter: Thanks for the nice comments. Two of the most over engineered power amps (a little off thread here) are my 300B I call "The Silver Dragon" and my 807 amp named "Luciano". The reason why they are so over engineered is they were designed by an electronics engineer in Seattle who works in high frequency electronics and designs and builds valve amps. The 300B (SE) cost my over $3K in parts and boasts 30W Hammond OPTs for a 6W output. That's just the start of it.

 

Thanks once more for the nice comments. Really I never thought the 2N3055 preamp\headphone amp over engineered. More like just right!

post #6 of 13

Except where it's under-engineered...

 

Don't take it all to heart, Frank has even been known to be kind to me.

 

100uF into 33 ohms = 3 dB down @ 48 Hz. 

 

1 dB is reckoned to be audible.

 

3dB down @ 48Hz, ~1db@100Hz, which is not that wonderful for solid state, low E on a guitar is ~82 Hz.

 

I'm guessing you don't know how to make it direct-coupled?

 

w

 

The foil isn't doing anything as far as shielding is concerned. To do anything meaningful a faraday cage has to be a cage, and it's not magnetic material, so the transformer fields pass through it. I'm not sure what kind of resonance it's supposed to control, unless you mean acoustic?

post #7 of 13
Thread Starter 
I actually build this quite some time back but had it out the other day and was really enjoying it and thought I should post the project. This is something I designed myself and design work is not my strongest point. Probably, concept, layout and construction are I'm better at. No I do don't know how to direct couple the load to a single stage, singe transistor, single B+ voltage amp.

I rap everything in the bituminised Al foil (flashing). Yes probably vibration and transformer resonance control at the PS. I line all my enclosures with it to stop ringing. It is extremely effective. Even a small prices will dampen a heavy Al enclosure lid. As it is well well known: if it rotates, oscillates or vibrates then it resonates.
post #8 of 13
Quote:
Originally Posted by mwhouston View Post
No I do don't know how to direct couple the load to a single stage, singe transistor, single B+ voltage amp.
 

 

No, neither do I, but this is why it's better not to cling too assiduously to a given topology.

 

w

post #9 of 13

For the safest way to DC couple the output you need a dual (+/-) supply as opposed to *just* a single supply. There are ways to do it with a single supply, but they get scary. 

 

After that the easiest thing to do is put a cap at the *input* of the circuit, and bias it VERY carefully. If the circuit already has an input cap, so much the better. 

 

I would personally add a simple op amp servo and MAYBE (probably not) an output protection relay. Ooh, also keep the output cap for the preamp. 

 

Could you post a schematic? I am always interested in seeing. 

post #10 of 13

Something like this, perhaps?

 

 

w

post #11 of 13

I'm blinking in confusion here... A pre-amp that attenuates the signal by 10%, instead of amplifying it? Isn't that the opposite of what a pre-amp is meant to do?

 

Other than that, great build. I always had a weak point for clean layouts, though I've always failed at them myself. =X

post #12 of 13
Thread Starter 

It is more of a driver (being emitter follower) than a preamp. Usually you would expect a preamp to have multiple inputs and be able to attenuated the signal and drive into low impedance. With most players putting out over 2V these days a small loss of this voltage should not hamper power amps from obtaining full power. There a some tranni based preamps and light speed style which do not amplifier the signal.

 

The preamp to me is more of a buffer also. Buffers usually have a gain of 1 or unity but are able to drive difficult loads. This driver\buffer can drive into 33ohms, is dead quiet and is good to 135KHz!

post #13 of 13
Quote:
Originally Posted by wakibaki View Post
 

Something like this, perhaps?

 

 

w

 

Yeppp. 

 

 

Quote:
Originally Posted by mwhouston View Post
 

It is more of a driver (being emitter follower) than a preamp. Usually you would expect a preamp to have multiple inputs and be able to attenuated the signal and drive into low impedance. With most players putting out over 2V these days a small loss of this voltage should not hamper power amps from obtaining full power. There a some tranni based preamps and light speed style which do not amplifier the signal.

 

The preamp to me is more of a buffer also. Buffers usually have a gain of 1 or unity but are able to drive difficult loads. This driver\buffer can drive into 33ohms, is dead quiet and is good to 135KHz!

 

I expected there to be some gain from the transistor (common emitter). 

I do like simple buffers though. It should be VERY easy to DC couple the outputs to the headphones. 

 

I dont understand preamps with gain. Well, I do. I guess I should say I dont understand power amps with 0.5v input for max power. :p how are you supposed to get low noise on a 12ft cable with 0.5v (not even) signals? Power amps should have 5-10v inputs for max power. Manly inputs! Save a gain stage in the power amp, put it in the preamp that you already have where it is surrounded by a beautiful power supply. Isolated from the power supply for the power stage. Plus with those high voltage lines you get lower noise pickup... Someday. Someday. 

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