Excellent!
BTW: If any of you are looking for a high-end headphone amp on par with the HP-2, the TCA HPA-10 may be just the ticket. I have it on sale for $299 while supplies last.
HPA-10 Headphone Amplifier – Tom Christiansen Audio
Lower cost that the parts cost of the HP-2. No supply chain issues. But also not DIY. Tradeoffs, tradeoffs...
Tom
BTW: If any of you are looking for a high-end headphone amp on par with the HP-2, the TCA HPA-10 may be just the ticket. I have it on sale for $299 while supplies last.
HPA-10 Headphone Amplifier – Tom Christiansen Audio
Lower cost that the parts cost of the HP-2. No supply chain issues. But also not DIY. Tradeoffs, tradeoffs...
Tom
I have Neurochrome HP-1, HP-2. Also have a Benchmark AHB2 power amp. Don't use any of them anymore. When I was using the HPAs I liked the sound of HP-1 better than HP-2, even though IIRC the latter measured a bit better.
What I learned was that AP metrics don't completely predict SQ. Nothing new, but I still find it interesting we put so much weight on the 'figure of merit' metrics.
What I learned was that AP metrics don't completely predict SQ. Nothing new, but I still find it interesting we put so much weight on the 'figure of merit' metrics.
Unfortunately for the readers, one's anecdotal experience doesn't mean anything unless they can plug a wire and share a direct experience (not available technology at this time).
The HP-2 provides a bit more power into 32 Ω. At impedances 50 Ω and above I doubt you'll notice much difference and the HPA-10 may actually have the edge there.
The balanced input on the HP-2 is nice. The HP-2 also has lower gain (just shy of 6 dB) vs 10 dB for the HPA-10.
The HPA-10 is in stock and I can ship one tomorrow. If you order by FedEx or UPS you'll have it before Friday (US, Canada) or early the following week (elsewhere).
Last I checked about 1/3 of the parts on the HP-2 BOM were out of stock at Mouser. You can find substitutes pretty easily, but expect to have to spend some time hunting down parts. The OPA1656 was out of stock at Mouser last I checked, but Digikey have some. I have some too, so if you get stuck on those, just toss me an email.
Tom
Hi Tom, I would like to use your HP-2 as a pre-amp + headphone amp. Some questions:
1. I just see the (SE) HP OUT pins in the board. Does the output keep having signal after removing the headphones? What would be a good way of switching HP vs pre-amp out?
2. I want to have 3 or 4 audio sources. If it was just two I would use the XLR connector for one source. I was thinking to also buy your Input Selector board (I don't see a thread for this here in the forums but please correct me if I'm wrong, I will move part of the conversation there if needed). That board seems to be able to allow for Arduino controlling through the Input Select pins + the (what seems to be) ULN2003 relay driver. Is that a good assumption?
3. Both the Input Selector board and the HP-2 have pins for the Volume control. What would be the ideal place, choosing between the two, to connect the pot?
4. I am quoting the "SPI pot" message because eventually I would change the pot with a digital controller. Provided I have the controller, what do I need to take into account for that change?
Thank you
1. I just see the (SE) HP OUT pins in the board. Does the output keep having signal after removing the headphones? What would be a good way of switching HP vs pre-amp out?
2. I want to have 3 or 4 audio sources. If it was just two I would use the XLR connector for one source. I was thinking to also buy your Input Selector board (I don't see a thread for this here in the forums but please correct me if I'm wrong, I will move part of the conversation there if needed). That board seems to be able to allow for Arduino controlling through the Input Select pins + the (what seems to be) ULN2003 relay driver. Is that a good assumption?
3. Both the Input Selector board and the HP-2 have pins for the Volume control. What would be the ideal place, choosing between the two, to connect the pot?
4. I am quoting the "SPI pot" message because eventually I would change the pot with a digital controller. Provided I have the controller, what do I need to take into account for that change?
Thank you
You can certainly use the HP-2 as a preamp. Nothing wrong with that. The HP-2 does not sense when you plug/unplug the headphones, so if you need that functionality you'll have to implement it yourself. That could be as simple as using a switched headphone jack.
I may not have started a thread for the Input Selector. You're more than welcome to start a build thread and send me a link to it. I'll join you there. The Analog Line Level would be a good spot for it. We can also continue the conversation here. You're not the first to turn the HP-2 into a preamp.
I think I would go: Input Selector -> HP-2 (with volume pot). In that case you just bypass the volume control connections on the Input Selector. I would need to think a bit about how to best integrate the two, though. The easy route is to simply use the single-ended input on the HP-2 and connect the Input Selector to that. But it would be nice to use the differential input on the HP-2 in a way that would allow you to have both single-ended and differential inputs controlled by one selector switch. I know you can get there with two Input Selector boards, but doing the same with one would be nice.
The Input Selector uses a 3.3 V compatible version of the ULN2003, so you can control it with any uC that provides 3.3-5.0 V logic level signals.
I haven't looked at digital pots in quite a while, so it's possible that my advice here is outdated. But last I looked the pots were all linear pots. You'll have a hard time making a good audio attenuator with those. I also seem to recall that they were pretty noisy. If you want to go that route you'll need an actual volume control chip, such as the CS3308, MUSES72323, or PGA2311.
Tom
I may not have started a thread for the Input Selector. You're more than welcome to start a build thread and send me a link to it. I'll join you there. The Analog Line Level would be a good spot for it. We can also continue the conversation here. You're not the first to turn the HP-2 into a preamp.
I think I would go: Input Selector -> HP-2 (with volume pot). In that case you just bypass the volume control connections on the Input Selector. I would need to think a bit about how to best integrate the two, though. The easy route is to simply use the single-ended input on the HP-2 and connect the Input Selector to that. But it would be nice to use the differential input on the HP-2 in a way that would allow you to have both single-ended and differential inputs controlled by one selector switch. I know you can get there with two Input Selector boards, but doing the same with one would be nice.
The Input Selector uses a 3.3 V compatible version of the ULN2003, so you can control it with any uC that provides 3.3-5.0 V logic level signals.
I haven't looked at digital pots in quite a while, so it's possible that my advice here is outdated. But last I looked the pots were all linear pots. You'll have a hard time making a good audio attenuator with those. I also seem to recall that they were pretty noisy. If you want to go that route you'll need an actual volume control chip, such as the CS3308, MUSES72323, or PGA2311.
Tom
switched headphone jack seems like a good idea, thx
that's what made more sense to me as well respect the selector.
I don't think I ever need a differential input, tbh. I can always use the differential input in the future, and then change between SE (input selector output) and differential using another switch.
I will use the HP-2 differential output to the modulus-86 though.
Great, this opens lots of possibilities, since I should be able to control the input and the volume from one Arduino, have a display, etc.
I have a WM8816 chip+board ready to be built.
I understand that your suggestion was to place the volume control in the HP-2.
Thank you as always,
Hi Tom,
Just finished putting together one of your HP-2 amplifiers. I plan to use it as a combination headphone amp and pre-amp and am testing the setup before I put it in a case. Works perfect into headphones. However when I use a y-adapter to to plug it into my amp and sub then turn it on it cycles on and off a few times with audible thumps before fully powering up. Once up there are no issues. I am just taking the output from the headphone jack and running it single ended into a Modulus 86 (single ended input pin 1 and 3 together) and sub. If I power it up with the amp off I still get thumps through the sub if I have it in standby mode. Any easy way to solve this? Also is there a way to get a differential output from the HP-2 to take advantage of the Modulus 86 differential input? Thanks.
Just finished putting together one of your HP-2 amplifiers. I plan to use it as a combination headphone amp and pre-amp and am testing the setup before I put it in a case. Works perfect into headphones. However when I use a y-adapter to to plug it into my amp and sub then turn it on it cycles on and off a few times with audible thumps before fully powering up. Once up there are no issues. I am just taking the output from the headphone jack and running it single ended into a Modulus 86 (single ended input pin 1 and 3 together) and sub. If I power it up with the amp off I still get thumps through the sub if I have it in standby mode. Any easy way to solve this? Also is there a way to get a differential output from the HP-2 to take advantage of the Modulus 86 differential input? Thanks.
If the LED/relay blink slow enough that you can hear it you should be able to measure the voltage drop with a DMM. Measure the incoming voltage and the voltage at Q3 drain (middle pin). They should be rock solid when the amp is turned on. If they bounce when you have the sub connected I'd like to know about it.
Tom
Tom
Voltage is rock solid. I fear I must have done something wrong. Behavior seems different now. When I turn it on the led is solid but the relay clicks twice and there is a thump through the speakers or headphones if I have them plugged in. When I first tried it with just headphones I don't remember a thump and only remember the relay clicking once? Also if I don't have anything plugged in I still hear the relay clicking twice.
Did you build it according to the BOM or did you have to make substitutions to the parts values? Changing the output capacitors to, say, 4700 uF from 3300 uF would result in a longer start-up time. Another possibility would be R67 (10 kΩ), C41 (100 uF). R4 (1 MΩ), C3 (100 uF), Q1 (2N7000) would be other possibilities. As could R5, R6 (both 10 kΩ), C4 (100 uF), and Q2 (BC547). Missing R1 and R2 (22 Ω) could do it too.
Another possibility is that the volume control is disconnected. Are you using the Alps RK27 or something else?
I would check the board for solder blobs and cold solder joints. Check for wrong part in wrong place types of things. Also make sure that you're working on just the HP-2 (with volume control plugged in and source connected) to isolate the issue. If that yields nothing I think it's time to ship the board here so I can take a look. Without tools it's hard to know what's going on.
I know I measured startup with the HP-2. I'm not sure if I documented it, but I would not have released the product if it created thumps on startup. Thumps are a common issue with low-end headphone amps and they always create a stir. Just see all the drama around Schiit amps thumping. I think they even had to have a recall on those. Anyway...
It's nearly impossible to avoid all clicks, pops, and thumps, but I generally aim for below 1 mV of disturbance when the relay clicks. That might be audible in IEMs but shouldn't be more than a subtle tick that's probably drowned out by the click from the relay. Even though the HP-2 is not intended as a preamp, a 1 mV pop on the output should not cause any issue if the HP-2 is connected to a power amp that drives a speaker.
Let me know if this gets you anywhere or if you need my shipping address.
Tom
Another possibility is that the volume control is disconnected. Are you using the Alps RK27 or something else?
I would check the board for solder blobs and cold solder joints. Check for wrong part in wrong place types of things. Also make sure that you're working on just the HP-2 (with volume control plugged in and source connected) to isolate the issue. If that yields nothing I think it's time to ship the board here so I can take a look. Without tools it's hard to know what's going on.
I know I measured startup with the HP-2. I'm not sure if I documented it, but I would not have released the product if it created thumps on startup. Thumps are a common issue with low-end headphone amps and they always create a stir. Just see all the drama around Schiit amps thumping. I think they even had to have a recall on those. Anyway...
It's nearly impossible to avoid all clicks, pops, and thumps, but I generally aim for below 1 mV of disturbance when the relay clicks. That might be audible in IEMs but shouldn't be more than a subtle tick that's probably drowned out by the click from the relay. Even though the HP-2 is not intended as a preamp, a 1 mV pop on the output should not cause any issue if the HP-2 is connected to a power amp that drives a speaker.
Let me know if this gets you anywhere or if you need my shipping address.
Tom