Thanks for the detailed review. Glad you like it and that the PCA still has a place in your amp stack.
One has 2 transistors and the other has 9 plus an opamp so makes sense it is going to have an edge. But for smooth and simple, the PCA does it well.
Have fun at the Head-Fi meet!
One has 2 transistors and the other has 9 plus an opamp so makes sense it is going to have an edge. But for smooth and simple, the PCA does it well.
Have fun at the Head-Fi meet!
Hello PDB builders,
I'm putting together a parts order and wanted to verify if changing C105/106 to 47pF is an active recommendation for pre-populated boards putchased from the Etsy shop. Thanks!- Dave M.
I'm putting together a parts order and wanted to verify if changing C105/106 to 47pF is an active recommendation for pre-populated boards putchased from the Etsy shop. Thanks!- Dave M.
The pre populated boards will have the correct 47pF caps installed. Unless you ordered one of the early ones (before I discovered that it was an issue).
But if you are assembling from scratch, yes, please change to 47pF NP0/C0G cap for C105/106.
But if you are assembling from scratch, yes, please change to 47pF NP0/C0G cap for C105/106.
Hi X,
Looking to add another product to my cart. Thought I would give the PDB headphone amp a try. Before purchasing, I would like to inquire if the PDB headphone amp can handle more than a +/- 9V power supply ? What would be the max.?
Thanks
MM
Looking to add another product to my cart. Thought I would give the PDB headphone amp a try. Before purchasing, I would like to inquire if the PDB headphone amp can handle more than a +/- 9V power supply ? What would be the max.?
Thanks
MM
The PDB can handle up to +/-15v if you have enough heatsinking or decrease the quiescent bias current. Right now it is about all the heat (1.5W) it can handle at 9v for a mint tin case. I would add some thermal silicone pads to conduct to the lid even.
Thanks X,
I have a few odd heat sinks that I may be able to work with. Looking forward to expanding my smd soldering skills.
I have a few odd heat sinks that I may be able to work with. Looking forward to expanding my smd soldering skills.
Well, things didn't go quite according to plan. Got everything soldered up only to just get nothing. No light nor sound. I suspect one of three things: 1) I didn't get good contact with the radial caps since I wasn't super confident with my sorta-thru-hole solders. I did try to touch those up, so I'm judging this the least likely. 2) I didn't do a good job with the battery harness. I quadruple checked the polarity but I also kinda hacked it together using some 9V battery holders and an existing JST I had. I have the proper crimps coming in soon, so I'll give that a better crack at properly pinning those. 3) I have spare volume knobs/power switches from the Ali link. I forget which one I installed, but I'll give that a crack. Any other suggestions are welcome.
Use a voltmeter to check to see if you have voltage on the rails where the caps are. If you have +/-9v or thereabouts, the LED will light up and there will be sound. Please post closeup photos and we can help debug.
Thanks X. My shipping notification says the JST crimps came in. Provided I finish my chores, I should be able to redo the battery harness properly and try from there. I think I just had a bad connection - I rechecked the pinout for the batteries. I actually might've misplaced my DMM, so hopefully I can find that quickly and get some actual data on the table.
Derp, I ordered the wrong connectors. I thought I would get cute by ordering from Mouser to save on shipping with my other caps I was getting but I should've just used the Amazon links you sent me, X. So, no troubleshooting will take place till probably Friday when I will have a chance to try again with something.
She sings! Turns out that I was doing the battery thing wrong all along. I still don't have the right connector/pins, but I did have a spare JST. I trimmed it and soldered the battery holder wires properly. The light coming on was a great relief.
What surprised me was how warm the unit gets! I had no idea that an Altoid tin could be even hotter than what the PCA could reach. I have some thermal pads on the bottom of the unit which are helping to bleed off heat from when it used to be the PCA (I dremeled out the holes a bit wider since I hadn't done a clean job with the PCA in the first place). When I can find my sheet of thermal material, I'll put some on the lid too (clearance seems pretty tight, so I don't know about heat sinks). Please let me know if I should be worried about the heat too, I guess.
But overall, I'm very pleased! I used it to juice up the USB-C DAC/AMP from my phone with IEMs (Alclair Electro), then I plugged it into my audio interface and did some music and gaming from my computer with my full-size cans (DCA Aeon C RT). It handled both marvelously (though with lots more temperature warmth than I anticipated).
What surprised me was how warm the unit gets! I had no idea that an Altoid tin could be even hotter than what the PCA could reach. I have some thermal pads on the bottom of the unit which are helping to bleed off heat from when it used to be the PCA (I dremeled out the holes a bit wider since I hadn't done a clean job with the PCA in the first place). When I can find my sheet of thermal material, I'll put some on the lid too (clearance seems pretty tight, so I don't know about heat sinks). Please let me know if I should be worried about the heat too, I guess.
But overall, I'm very pleased! I used it to juice up the USB-C DAC/AMP from my phone with IEMs (Alclair Electro), then I plugged it into my audio interface and did some music and gaming from my computer with my full-size cans (DCA Aeon C RT). It handled both marvelously (though with lots more temperature warmth than I anticipated).
If you want, change the output emitter resistors to a larger value to cut the heat. It’s at 2R2 now, maybe change to 4R7 to cut that in half. The high current ensures Class A up to 278mW. You may not need that much Class A power.
Which parts need the most heat dissipation? Q206/7/306/7?
Did you have figures on the power output? I don't recall seeing earlier in the thread. I would be interested in seeing how it goes with higher impedance, lower sensitivity cans. If the bias current is higher, I'm assuming it'll take it and spit it back out. I'm curious to see how my 9V rechageables handle themselves time-wise.
Did you have figures on the power output? I don't recall seeing earlier in the thread. I would be interested in seeing how it goes with higher impedance, lower sensitivity cans. If the bias current is higher, I'm assuming it'll take it and spit it back out. I'm curious to see how my 9V rechageables handle themselves time-wise.
Max dissipation per channel is 2x 9v x 70mA (about) or about 1.2W. So 2.4W for both channel. The bias current varies a little depending on transistor intrinsic properties. Most of the heat is in the SOT223 transistors and some in the large 2R2 resistors. If you change to 4R7, you can expect about 35mA bias current and half the dissipation.
You can measure the bias current by probing the voltage drop across the the 2R2 resistors. Use ohms law I = V/R.
Power dissipation in resistors is V^2/R.
Power dissipation in transistors is VCE x Ibias.
You can measure the bias current by probing the voltage drop across the the 2R2 resistors. Use ohms law I = V/R.
Power dissipation in resistors is V^2/R.
Power dissipation in transistors is VCE x Ibias.
I just confirmed that if C105 and C106 are replaced with 47pF NP0/C0G caps, there is no oscillation and no output snubber is needed.
I tried to repeat your project, I made a mistake somewhere. There is no sound output to the headphones. The buffer LEDs are on. The LED that is in the DC protection circuit is not lit.
If you turn off the headphones and apply a sinusoidal signal of one kilohertz to the input, then a variable voltage appears at the output. In my case, I turned the volume knob to full and a value of 1.6v appears on the multimeter. When connecting a simple wire at the output of the amplifier, the voltage drops twice, when connecting headphones, the voltage disappears altogether.
If you turn off the headphones and apply a sinusoidal signal of one kilohertz to the input, then a variable voltage appears at the output. In my case, I turned the volume knob to full and a value of 1.6v appears on the multimeter. When connecting a simple wire at the output of the amplifier, the voltage drops twice, when connecting headphones, the voltage disappears altogether.
Hi Lexey22,
Neat circuit you made. If your LED401 does not light up, it means your TLP opto is not on. You can check with an ohm meter across the back to back MOSFETs as SSR. Should be close to zero ohms when on. Make sure you have your Source and Gate pins on the SSR MOSFETs correctly wired.
It looks like you have combined the HPA SSR protection circuit by Jhofland with the output of the Diamond Buffer HPA by Jhofland and both circuits are known to work well. In fact, Jhofland has combined them for me in a prototype for a new headphone amp with built in PSU and SSR. The SSR is configured just as you have drawn and it works.
There is something off with your SSR protection circuit. Something is not allowing it to engage in conductive mode.
Is your LED mounted in correct polarity?
Finally, change the feedback caps C105/106 from 470pF to 47pF or else it will oscillate. It might be the oscillation that is causing the SSR protection to kick in?
Cheers,
X
Neat circuit you made. If your LED401 does not light up, it means your TLP opto is not on. You can check with an ohm meter across the back to back MOSFETs as SSR. Should be close to zero ohms when on. Make sure you have your Source and Gate pins on the SSR MOSFETs correctly wired.
It looks like you have combined the HPA SSR protection circuit by Jhofland with the output of the Diamond Buffer HPA by Jhofland and both circuits are known to work well. In fact, Jhofland has combined them for me in a prototype for a new headphone amp with built in PSU and SSR. The SSR is configured just as you have drawn and it works.
There is something off with your SSR protection circuit. Something is not allowing it to engage in conductive mode.
Is your LED mounted in correct polarity?
Finally, change the feedback caps C105/106 from 470pF to 47pF or else it will oscillate. It might be the oscillation that is causing the SSR protection to kick in?
Cheers,
X
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@xrk971 Is that the same unit as in Post #12 on this thread, just modified, or has it been rebuilt with the new circuit you mentioned? Are you using the same PSU setup as on Post #12? In general, I'd be interested in what people think would be a good "plug and play" PSU for this. I realized the rechargeable Tenergy batteries I have probably have some noise from the protection circuits (it happened on my PCA too and I thought it was just because I was bad at SMT soldering). I could buy more batteries and live with it, but being able to use a wall-powered PSU would be neat too.