3 Transistor HP Amplifier with low dist

[Julian RO]

Many details are provided on the topic of denoiser. Just read it carefully.

 

[joensd]

An variant with IRF610 would also be interesting.

I am building a simple source follower a la Nelson pass for a compression driver and thought I should add a preamp just in case I want to use the PCB as headphone amp or for a less sensitive tweeter. (Nelson´s simple follower)
I tried with 1x or 2x 2SK117GR but 2xBJT always give me much better distortion values in sim than a FET preamp.

Current plan is to make a compact PCB for the follower and include an optional vertical PCB for the preamp in order to play with different implementations.
Made PCB-mockups with the 2BJT´s in SMD too.

If low distortion incl. H2 is your ultimate goal I´d stick with lineup´s designs though.

 

[joensd]

Just for inspiration. No final PCBs and actually not sure if I will ever get any of these produced.
1. Simple follower with optional preamp card (on perfboard or so)
2. Simple follower with 2xBJT-preamp in SMD on the bottom layer.

 

[TR00]

Hello! Can you post the exact schematics of amp and supply used? I also have build two versions of this amp and own HE400SE. The Denoiser is knauf1919's project? Which transformer and capacitors used in the Denoiser?

Hello carageae@, i have external linear supply 2X25V dc feeding 2X Denoiser, one pcs for channel. I use Prasi`s HPA Fast pcb. I cut one trace that i can use 2 X Denoiser.

 

[Rick PA Stadel]

Hi El Reinoo,

Ur . . um . . your 'LM317 sch.png' has the LED, D8, in reverse polarity.

Cheers

 

[TR00]

You've got sharp eyes Rick PA Stadel👀 Yes there is fault. Denoisier works ok and led is right polarity at gerbers. This is tombo56 schema and gerbers. Thanks to tombo56 btw

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[avtech]

Out of interest, what is the purpose of D7 on the LM317 schematic?

 

[Rick PA Stadel]

To protect Q2's B-E junction at supply power down. Without it, C7 will reverse bias the junction with almost the full output voltage.

Not certain, but that's my hypothesis.

Regards

 

[Julian RO]

Correct.

 

[joensd]

When I think about it, a IRF610 or similar could right drop into the circuit.
Some quick adjustments, not yet optimized. Supply voltage raised to 24V for a quick solution.

 

[joensd]

That´s better for total consumption and performance.

 

[Julian RO]

Hi, joensd

Can you do a simulation with BC556 / 546 instead of 550/560 and then post a diagram with some voltage / current values in the essential parts?
Thanks.

 

[joensd]

Here you go (used "A" types from Philips for the transistors ; there is also B types).
Just consider this is probably still not the best it can be!
For higher impedance headphones bias could be lowered of course.
Watch the power dissipation of the source resistors!
R1&R6 (2x27R) could be 1x56R/2-3W-type for example.
R8 could still be a 0.6W-type but right at the edge with 0.3W of dissipation.

 

[Kuzmenko]

does it have any sense against simple TDA2030 loaded to 150 mA current source (biased toward class-A operation) ??

 

[carageae]

does it have any sense against simple TDA2030 loaded to 150 mA current source (biased toward class-A operation) ??

I regularly listen to a TDA2009, much better than 2030...I made an amplifier with higher negative feedback, specially suited for headphone use.
But let's stick to the original thread...
How does it sound, psycho-acusticaly, compared to BD139 version? Is there some change in the sound signature?

 

[Julian RO]

Try TBA810.

 

[IanA]

I'm thinking of using Prasi's PCB with built in rectifier/regulator.

Would I be correct in thinking a 14V AC input would be optimal?

 

[auriga2001in]

Finally built the 5V version on a perf board. I used a 2SC4793 as the output device just for fun. Initial tests done, and everything is under design specs. Now to install it in the DAC cabinet using a regulated 5V power supply.

 

[auriga2001in]

Fitted a beefy power supply, with 9400uF + 2 RC filters before the regulator. Sounds good, with crystal clear highs and good instrument separation.
Brought down the gain by using 10R + 20R resistors. Plenty loud for my headphones.
Thanks Lineup.

 

[Julian RO]

The latest version of pcb. I'm moving on to another project as good or better.