Henry, All I can say is this: The A3 circuit was designed to work with a certain type of power supply that interacts with the amplifier circuitry in such a way that would be incorrect to think of the whole as merely an amplifier module, and a power supply module, that plug together but function independently. If you don't try it you will never know if your assumptions about power supply interchangeability and or equivalence are correct. Okay then, you don't want to know, fine. At least you were informed of the issue before you made your choice.
What's really disappointing is I've just built a killer amplifier, maybe my best one yet, and we're still hung up on the HPA-1. Do you want to contribute something to the community? Do you want to see more people building the HPA-1 clone? Here, I have a link for you:
https://www.kicad.org
Get to work, Mark.
-Henry
https://www.kicad.org
Get to work, Mark.
-Henry
As you offered some hints to Stereophile having your amps as their new refference and HPA-1 is a name that's probably having a patent on it, I don't see any legal way for you to change Nelson Pass's HPA-1 with yours.I think you made a serious mistake if you wanted to compete NP this way cause once you're on the market and not in the diy community you can be sued with the name of your choice and believe me...the money you get on your Rolex won't be enough to pay the lawyers for such an issue against NP.:
Attachments
Interesting point. It's hard to separate out the effect of the attenuator and the signal circuit. So far, I have experience with the following types:
1) Elma ladder attenuator with Vishay RN55 metal films
2) Elma ladder attenuator with Beyschlag 1/8W metal films
3) Eizz series attenuator with stock carbon film resistors
4) Eizz series attenuator upgraded with Vishay RN50 metal films
5) Daven series attenuators with Susumu metal film SMD resistors
6) Bourns conductive plastic pots
I would say on the whole that the stock Eizz carbon film attenuator didn't sound good. The Vishay RN resistors are noticeably bright and detailed, but not overbearingly so. The Beyschlags and the SMD resistors seem perfectly balanced to me. And the Bourns pots, surprisingly, are very good also.
I really hate to get into the whole sound-of-passive-components thing because it's so controversial. The difference between the carbon film attenuator and the one with the Vishays seemed pretty pronounced, though. The other differences are subtle enough that I don't think they overshadow the differences between the amp circuits.
You don't...unless you go sell some hpa-1 to Stereophile
I named my first amplifier HPA1. I didn't realize there was already a Pass Labs HPA-1 (and a Neurochrome amplifier of the same name, too). When I started the HPA-1 project, people were getting confused by the difference between the HPA1 and HPA-1. Being a computer programmer, it seemed obvious to me, but it became a problem. So I renamed my amps A1, A2, etc. My amp called A3 is a clone of the Pass Labs HPA-1. The names are only partially interchangeable, because, as Mark is eager to point out, I am using a different power supply than the official clone, which itself has never been verified as a 100% accurate.
The comment about Stereophile was a dig at Mark, who is fond of saying that the HPA-1 is Stereophile's reference headphone amp. For some reason, a good part of Mark's identity seems to revolve around that amplifier. This confuses me. Maybe he can explain his near-religious devotion.
I don't actually know anyone at Stereophile, have no plans to put any of these amplifiers into production, and will never send anything I build for review to the magazine. So, rather like certain prominent US politicians, I have no fear of going to jail, much as I may deserve it.
I hope this clears up any confusion.
Henry, please take it easy. Wouldn't bother with you if I didn't think you have some potential. Try the HPA-1 power supply with A3, A4, whatever. You can learn from trying things instead of avoidance, that's all. Up to you what you want to do.
I was responding to dreamth's comment about the HPA-1 copyright when I made the jail comment, but I get the point.
I want to try to settle this thing about the A3 power supply.
Designing the A3 signal board was a lot of work. All these projects are. I started a new job in February and it was a tough slog (still is). I got the main A3 board done and I wanted to listen to the amp. I had the A1 breadboard already, so it was a no-brainer to use its power supply to run the A3 initially.
After a few weeks, I got my Toroidy transformer. It's huge. I started working on a board for the official power supply. I was having trouble squeezing it down to a reasonable size. I realized I was going to have to build a huge chassis with an awkward shape. I thought about it a lot and couldn't come up with a good solution. Meanwhile, the A3 was sounding pretty good. I decided to take the path of least resistance and box up the A3 with my power supply. Later, I figured I could redesign the A3 with one board per channel to give me more flexibility with the mechanical layout.
I have a couple of issues with the A3. I have reason to suspect the MOSFET output stage is sub-optimal. I wanted to try the HPA-1 front end with my A2 diamond buffer output stage. That was the genesis of the A4 project. It evolved from there. Now I have the A4 and I like it a lot. So it's not clear whether I want to keep developing the HPA-1 or concentrate on this new design.
I don't have any more Super Regulator boards left. I will probably use an HPA-1 style regulator in future projects. Since I use wire-to-board connectors now, I can easily cobble a new supply and run it outboard of the A3 chassis. This is in my queue. You will just have to be patient.
I don't know how to put this delicately, so I will just say it. Whether you intend it or not, whether I am being too sensitive, I find your attitude very condescending. I would take it up privately, but I'd rather keep it in the open. I'm not someone to be "bothered" with, and I'm not an up-and-coming young designer seeking a patron. I'm just me, following my interests. There's a lot of hype and mystique surrounding the HPA-1. You seem to feel you have the authority to dictate the terms of development related to this project. It really rubs me the wrong way, and this explains my pissy fit in February, as well as my comments now. I am well familiar with your opinions. My focus is different.
I'm serious when I say I would gladly contribute to a thread that you own about developing the HPA-1 clone design. But that particular circuit is not my sole objective. You are going to be disappointed if you keep trying to steer me in a particular direction that doesn't align with my own goals. These four amplifier designs (not to mention the two DCG3s I built) are the product of hundreds of hours of hard work. I get to decide how I invest my time and energy. You are welcome to make suggestions, but stop telling me what to do. I do not need to be "informed" of my choices. If you can figure this out, we will get along better.
Hopefully, we're done with this unpleasantness. I will follow up here with updates on existing business, and start a new thread if and when there is an A5 project.
I hooked up the A3 again last night and my impressions are the same as before. The A3 adds warmth and body to the sound at the expense of detail. The A4 is colorful but more revealing. I do not believe in magic. I have to assume the low feedback of the A3 gives it a higher output impedance and a thicker distortion spectrum. I have experienced in the past that reducing feedback widens the soundstage and fattens the sound. The A3 has about 18 dB of feedback, IIRC, enough to introduce some feedback-related artifacts but not enough necessarily to suppress them entirely. SPICE (and Stereophile measurements) show the HPA-1 distortion rises smoothly with output level. Some articles claim this is a psychoacoustic cue that the ear interprets as lifelike. Evidently, it's a matter of fine-tuning to get a pleasing balance.
With low feedback, the circuit is going to be more sensitive to component choices and power supply interactions. I can't characterize it with formulas, but it makes intuitive sense. The sound of the HPA-1 is said to be highly parts-dependent. The A3 uses different parts so it's no surprise if it fails to capture the HPA-1 magic. It could also be a matter of personal taste. I cannot dismiss the possibility that the reputation of the HPA-1 is partly based on hype. I don't have much faith in audio reviewers. The ear is very adaptable. I won't go so far as to impugn anyone's taste, but I will say this: Some people prefer ketchup on their hotdogs, some prefer mustard, and some like them plain.
I noted earlier that the HPA-1 has low feedback because the driver stage is heavily loaded. I confirmed in SPICE that it's easy to tweak the A3 to have the same gain-bandwidth profile as the A4. This is an A3 Bode plot with the two driver load resistors changed from 4.7K to 200K, giving 100K in parallel, like the A4. I doubled the feedback network resistance to bring the loop gain back down to 40 dB and lowered the compensation capacitor accordingly.
The theory is this may make the A3 sound more like the A4. To my ear, that would be an improvement. We will have to see. Assuming a good result, it may be that the same tuning would not sound good in a production HPA-1. Different amps, different tradeoffs.
We can learn something from these experiments even if we are not trying to replicate the HPA-1 exactly. There's no need to avoid deviating from the established path. If this were my design and other people were tweaking it, I'd say, "Good for you. You're on your own, but please let me know what you find." I am incredibly mindful of the infinite possibilities audio design presents.
These projects are my escape from the grim reality of modern life. Do I prattle too much? Maybe. No one forces you to read it.
I will order these parts today and report on the results next week.
I hooked up the A3 again last night and my impressions are the same as before. The A3 adds warmth and body to the sound at the expense of detail. The A4 is colorful but more revealing. I do not believe in magic. I have to assume the low feedback of the A3 gives it a higher output impedance and a thicker distortion spectrum. I have experienced in the past that reducing feedback widens the soundstage and fattens the sound. The A3 has about 18 dB of feedback, IIRC, enough to introduce some feedback-related artifacts but not enough necessarily to suppress them entirely. SPICE (and Stereophile measurements) show the HPA-1 distortion rises smoothly with output level. Some articles claim this is a psychoacoustic cue that the ear interprets as lifelike. Evidently, it's a matter of fine-tuning to get a pleasing balance.
With low feedback, the circuit is going to be more sensitive to component choices and power supply interactions. I can't characterize it with formulas, but it makes intuitive sense. The sound of the HPA-1 is said to be highly parts-dependent. The A3 uses different parts so it's no surprise if it fails to capture the HPA-1 magic. It could also be a matter of personal taste. I cannot dismiss the possibility that the reputation of the HPA-1 is partly based on hype. I don't have much faith in audio reviewers. The ear is very adaptable. I won't go so far as to impugn anyone's taste, but I will say this: Some people prefer ketchup on their hotdogs, some prefer mustard, and some like them plain.
I noted earlier that the HPA-1 has low feedback because the driver stage is heavily loaded. I confirmed in SPICE that it's easy to tweak the A3 to have the same gain-bandwidth profile as the A4. This is an A3 Bode plot with the two driver load resistors changed from 4.7K to 200K, giving 100K in parallel, like the A4. I doubled the feedback network resistance to bring the loop gain back down to 40 dB and lowered the compensation capacitor accordingly.
The theory is this may make the A3 sound more like the A4. To my ear, that would be an improvement. We will have to see. Assuming a good result, it may be that the same tuning would not sound good in a production HPA-1. Different amps, different tradeoffs.
We can learn something from these experiments even if we are not trying to replicate the HPA-1 exactly. There's no need to avoid deviating from the established path. If this were my design and other people were tweaking it, I'd say, "Good for you. You're on your own, but please let me know what you find." I am incredibly mindful of the infinite possibilities audio design presents.
These projects are my escape from the grim reality of modern life. Do I prattle too much? Maybe. No one forces you to read it.
I will order these parts today and report on the results next week.
I have an offer someone can't refuse. These are my A1 boards and a pair of prototype super regulators. With a 25V raw supply, you can build a pretty nice little headphone amplifier. My audiophile friend, Geoff from Salt Lake City, spent a few weeks with the A1 breadboard and loved it. The boards are set up with Miller compensation and the last time I listened to it I thought it sounded pretty much like the A2.
I am willing to give these away for the price of postage. The only ask is you commit to building up a working amplifier. And that you're confident enough with electronics to do a proper job of it. The boards should not end up in a drawer. If you can't get the job done and post listening impressions in a reasonable time (say a month or two), I would like the boards back. Or don't ask for them in the first place. And if you like the amp and want to send me some cash to fund future projects, that's cool too.
Sorry, but I don't feel like dealing with foreign post, so offer is limited to the US.
PM if interested.
Hi, I've been following this thread with interest but have been put off from building any due to difficulty in obtaining some of the components.
In post 540 you mentioned further development of the A4 , esp a change in the regulators which are unobtainable.
I for one would be grateful if you would continue the development. Ashley
In post 540 you mentioned further development of the A4 , esp a change in the regulators which are unobtainable.
I for one would be grateful if you would continue the development. Ashley
Thanks for asking this, Ashley. I really like the sound of the A4 and was thinking this morning about how to simplify it to make it easier to build. My prototype works well enough that I don't think I'll do a second iteration just for me. But I would be willing to design a new board, especially if I had some encouragement from other members.
I'd like to ask the group if there is interest in this project. If, say, five people were seriously inclined to build it, that would be a good motivator. Please let me know; I get tired of talking to myself all the time.
Another thing that would be great would be some community participation in the design. I have my ideas, but would appreciate suggestions.
I will post more about this later, but I have to go to my piano lesson now.
I'd like to ask the group if there is interest in this project. If, say, five people were seriously inclined to build it, that would be a good motivator. Please let me know; I get tired of talking to myself all the time.
Another thing that would be great would be some community participation in the design. I have my ideas, but would appreciate suggestions.
I will post more about this later, but I have to go to my piano lesson now.
Here is my proposal:
1. Ditch the front-end regulators and replace with passive RC filters.
2. Remove the servo. Use an offset trimpot on the input instead.
3. Capacitor-coupled input.
4. On-board regulators similar to Salas' L-Adapter. The Darlington in the Pass regulator is no longer available.
5. Reduce output stage bias. Use board-mounted heatsinks.
6. Switch from BC550/560 to BC549/559 which are still in production.
KSA992F/KSC1845F are still available to order. TTA004B is available. TTC004B is hard to get, but can be had from trusted suppliers on eBay.
As I said, I'm happy to design this board and support the project if people are interested in building it.
1. Ditch the front-end regulators and replace with passive RC filters.
2. Remove the servo. Use an offset trimpot on the input instead.
3. Capacitor-coupled input.
4. On-board regulators similar to Salas' L-Adapter. The Darlington in the Pass regulator is no longer available.
5. Reduce output stage bias. Use board-mounted heatsinks.
6. Switch from BC550/560 to BC549/559 which are still in production.
KSA992F/KSC1845F are still available to order. TTA004B is available. TTC004B is hard to get, but can be had from trusted suppliers on eBay.
As I said, I'm happy to design this board and support the project if people are interested in building it.
These differences are probably well within HP sound differences... How do you choose which one is "right"? For whom? For your HP - for other? For that reference FR that everyone seem to care about? I would think that when you have more than one contender and they all sound "good", it has to be the best measuring unit that should win - no? I mean if one had to just make one of them...
//
I don't have the gear to measure noise and distortion. The perceived differences vary from imperceptible to profound depending on my state of mind. I can only report what I hear. Other people will have different experiences. I'm skeptical myself, so take what I say with a grain of salt. I have a commercial amplifier with state-of-the-art published specs and can't bring myself to listen to it long-term. Why should that be? No idea. We don't listen to distortion analyzers, so measurements are really only useful to verify the amplifier is working properly. It's a mystery. We could debate it, but wouldn't resolve the question. This debate will continue as long as there are hi-fi systems and people to listen to them. Maybe another ten to twenty years, given current trends.