For once I unequivocally agree with an audio review. The musicality is something that's very hard to find.
New Portable Amp - "Pocket Class A" by xrk971 - now available as complete PCB
- Thread starter stellarelephant
- Start date
xrk971
Member of the Trade: XRKAudio
Thanks Gikigill. I am glad you agree 
II have been so busy listening, I'm not even ready to send it back for the modifications I proposed
One of these days, I'll send it.....
One of these days, I'll send it.....
xrk971
Member of the Trade: XRKAudio
I know how that goes. Take your time but I do think you will benefit tremendously if the caps are upgraded to 1000uF Oscons to give you more bass extension.
Its clean, crisp, musical and very soothing to listen to. The background blackness rivals the mighty Beta 22 and that's saying something although it falls short of the body and muscle in the sound overall compared to the Beta 22 but then again, there aren't too many amps that can keep up with a Balanced B22. The NHB tries it's best but it's a little small compared to the Beta 22. Both were compared with the TH900 as it doesn't need a lot of power.
Now imagine a grown up version of the NHB with the Beta22 specs and it would be something.
Xkr971 has a real shot at making a once in a lifetime item here. A grown up NHB could be a worthy successor to the Beta 22.
4 Board balanced with an outboard power supply would be good.
Now imagine a grown up version of the NHB with the Beta22 specs and it would be something.
Xkr971 has a real shot at making a once in a lifetime item here. A grown up NHB could be a worthy successor to the Beta 22.
4 Board balanced with an outboard power supply would be good.
xrk971
Member of the Trade: XRKAudio
Gikigill,
Do you think the big amp would need a single ended to balanced drive converter?
Four SE Class A amp boards each burning 30watts is a full size chassis. Perhaps maybe even 50w dissipation ea board. Depending on what you want to drive. The SE Class A topology sounds glorious but comes at a price of thermal inefficiency. It will be able to do about 1w into 50ohms at reasonable distortion levels. For HE-6, I would go with singleton input stage Class AB quasi-complementary hybrid MOSFET-BJT output stage for delivering up to 10w into 50ohms with maybe 15w dissipation per board.
The Silicon Harmony may just be the ticket qnty 4 to provide balanced drive (ignore puny heatsink it is mounted on for testing purposes - way too small):
The SE Class A four board balanced amp would need a case like this:
Do you think the big amp would need a single ended to balanced drive converter?
Four SE Class A amp boards each burning 30watts is a full size chassis. Perhaps maybe even 50w dissipation ea board. Depending on what you want to drive. The SE Class A topology sounds glorious but comes at a price of thermal inefficiency. It will be able to do about 1w into 50ohms at reasonable distortion levels. For HE-6, I would go with singleton input stage Class AB quasi-complementary hybrid MOSFET-BJT output stage for delivering up to 10w into 50ohms with maybe 15w dissipation per board.
The Silicon Harmony may just be the ticket qnty 4 to provide balanced drive (ignore puny heatsink it is mounted on for testing purposes - way too small):
The SE Class A four board balanced amp would need a case like this:
Last edited:
How about a separate board summing up to both balanced and single ended.
A Pic of the Beta22. Not mine but similar to mine.
A Pic of the Beta22. Not mine but similar to mine.
At the risk of sounding like a philistine, how about low rpm fan running at say 800-1200rpm.
Krell uses them in their monster amps so maybe that might be something that can be used to facilitate heat dissipation. Just a fixed fan running at 800 or so rpm quietly moving air out of the sides.
Krell uses them in their monster amps so maybe that might be something that can be used to facilitate heat dissipation. Just a fixed fan running at 800 or so rpm quietly moving air out of the sides.
xrk971
Member of the Trade: XRKAudio
I use speed reduced fans all the time to keep heatsinks reasonable in size. But for products aimed at high end low noise - some people sneer at such things even though they are very quiet. Simple 100ohm resistor in series with 12v fan really slows it down to silent. There is a risk that fan can malfunction. In which case an auto shutoff due to heat is needed.
I was reading the description of the Beta22 and it says it is fully Class A and capable of 18w into 8ohms or 50w into 8ohms balanced. How can Class A be achieved with single pinner local heatsinks rated for maybe 3w ea? A Class A amp capable of 50w into 8ohms would normally have heatsinks the size of a 5U Dissipante case. Huge in other words.
Maybe its Class A for first 2watts and goes into Class AB after that?
I was reading the description of the Beta22 and it says it is fully Class A and capable of 18w into 8ohms or 50w into 8ohms balanced. How can Class A be achieved with single pinner local heatsinks rated for maybe 3w ea? A Class A amp capable of 50w into 8ohms would normally have heatsinks the size of a 5U Dissipante case. Huge in other words.
Maybe its Class A for first 2watts and goes into Class AB after that?
Last edited:
Its pure Class A, just checked the specs again and outputs 18w at the headphone jack.
xrk971
Member of the Trade: XRKAudio
I understand that is what the spec says but I don't believe it is possible. Because to make 18W Class A means you need to dissipate about 43w of power continuously. There is no way a locally mounted little heatsink on a TO220 MOSFET can dissipate heat like a fin on large case, which is what is supposed to be used to keep temps below 55C. Or the Beta22 runs with temps that are much hotter thereby risking premature failure. How hot do the little heatsinks get? Can you touch them for more than 10seconds?
Here is a 25w Class A amp (F5). Notice size of heat sinks and this is for just 2 MOSFETs per channel.
Compared to this for 18w (or 50w in balanced - which means it needs to dissipate twice as much as above Amp):
In reading the detailed technical description of the Beta22 it says this about the power dissipation:
"
True Class A amps dissipate the same amount of heat no matter what is playing and in fact, the heat dissipated by the heatsinks is *less* when the speakers (or phones) are producing a lot of power. That is basically the definition of Class A. They burn hot no matter what. In addition, quiescent current on Class A amps like the Silicon Harmony or F5 is about 1250mA (not 160mA). Max output current swing can be no more than 2-3x the quiescent current. So if you have cans that need current - a Class A amp with 1.25amps can swing 2.5amps easily.
160mA quiescent current x 60v (both rails) = 0.16amps x 60v = 10w dissipation in heatsinks. With 4 locally mounted heatsinks this is 2.5w ea.
So, I am not saying that Beta22 is not Class A, but probably runs Class A within the 160mA bias range. For 30v rails, that is about 3W max in Class A before switching to Class AB. Note that being a fully symmetric circuit it will reduce all H2 (and even orders) and emphasize H3 and H5 distortion.
If you like H3 and H5, H7, ...
Here is a 25w Class A amp (F5). Notice size of heat sinks and this is for just 2 MOSFETs per channel.
Compared to this for 18w (or 50w in balanced - which means it needs to dissipate twice as much as above Amp):
In reading the detailed technical description of the Beta22 it says this about the power dissipation:
"
- For headphone amp application, I = quiescent current of the output stage, typically 160mA. For speaker amp application, I = output current. To determine this current, we use the following formula (assuming a load impedance of 8Ω):
I = √(Po / 8)
Where Po is the output power of the amplifier. For ±30V rails, this would be 18W, and for ±24V rails, this would be 12W. Note that this gives the continuous current assuming that the amplifier is playing a sine wave at maximum output all the time. When playing real music the average current is a lot less, you can safely use 30% (which corresponds to about -10dB) of the calculated current, as long as the amplifier is only to be used in a home audio application."
True Class A amps dissipate the same amount of heat no matter what is playing and in fact, the heat dissipated by the heatsinks is *less* when the speakers (or phones) are producing a lot of power. That is basically the definition of Class A. They burn hot no matter what. In addition, quiescent current on Class A amps like the Silicon Harmony or F5 is about 1250mA (not 160mA). Max output current swing can be no more than 2-3x the quiescent current. So if you have cans that need current - a Class A amp with 1.25amps can swing 2.5amps easily.
160mA quiescent current x 60v (both rails) = 0.16amps x 60v = 10w dissipation in heatsinks. With 4 locally mounted heatsinks this is 2.5w ea.
So, I am not saying that Beta22 is not Class A, but probably runs Class A within the 160mA bias range. For 30v rails, that is about 3W max in Class A before switching to Class AB. Note that being a fully symmetric circuit it will reduce all H2 (and even orders) and emphasize H3 and H5 distortion.
If you like H3 and H5, H7, ...
Last edited:
xrk971
Member of the Trade: XRKAudio
So ultra-low impedance is not a problem if you have very high sensitivity.
Carmantom
1000+ Head-Fier
This latest bad boy NHB is shipping out to Poland tomorrow. It's got dual 1000uF OSCONs and 10uF Silmics on the output and Silmics on the input. Uber hand tuned and measures 0.02%THD driving 270ohm load at 700mV with almost all of it H2. The huge output caps are so that it can drive the user's favorite 13.8ohm 115dB sensitive Andromeda's. Sim in LTSpice shows THD is only 0.05% at listening level of 106dB. Frequency response is flat to 15Hz (-0.5dB point).
So ultra-low impedance is not a problem if you have very high sensitivity.
Carmantom
1000+ Head-Fier
This is my short review of my new " Pocket Class A Headphone Amplifier / Desktop Amplifier NHB Edition " Made custom by xrk971 Let me tell you I had a great experience with this purchase. This is one of those rare purchases where you get some of the man who built the product as well as this wonderful and magical amp.
Let me start by saying my review is only of my listening enjoyment and how I hear it. I have absolutely no idea of any technical aspects or any parts included with this build. He is welcomed to post any of the specs if he likes.
xrk971 asked for my listening preferences and gear I was using. It is Fiio X5 gen 3 DAP and Audeze LCD 2 headphones. Although many reviewers indicate the Fiio X5 gen 3 to be plenty strong to drive the Audeze LCD 2s, I did not. It seemed to me to be so much more there that wasn't being revealed. One day recently while trolling on Head Fi I came across what looked like a little jewel if 1/2 of what was being said about it was true.
I decided to try it and boy am I glad I did. xrk971
kept me up to speed continuously. He custom built it to my hardware and listening specs and he sure delivered. All in all from time I ordered, he built, shipped and delivered it was only about 5 days.
Short and sweet, these are my impressions. As always I try to remember to listen clean and mastered recordings. In this case I listened to the DSD recording of Christian Mc Brides " Live at Village Vanguard " This would be a sure workout for the bass. I'm a fan of " Steve Hoffman " masterings. I listened to some of his " Dreamboat Annie " Pee Wee Russell and his clarinet. And others.
Please be aware, this amp is very unforgiving in its reproduction of poor music source. This is clear evidence of not trying to color but to convey music as artist intended.
The sound stage was huge and wide. Most folks know LCD2S are well know for bass. The base this amp gave my setup was nothing less than articulate, good transit response, natural and detailed. I am a big believer in " It's not how low it goes. It's how well it goes low " . The speed of Mc Brides fingers up and down his bass is accurate. Who would ever believe this box could deliver so much bass. Next up instrument imaging and placement very distinct in height, width and depth. However vocals more up front in my face than I prefer. This may be unfair since I did not listen to very many recordings yet.
I could not believe the musicality this magical amp would provide me with. Here's how it was for me laying in my recliner listening Lincoln Mayorga and Distinguished Gentlemen on the Sheffield lable. " Limehouse Blues " toes are tapping relentlessly, shoulders rolling in and around and head rhythmically swaying side to side.
I found mids to be airy not congested. The highs are accurate and warm with some sparkle. Not as much sparkle as I prefer.
All in all this is a gem of an amp and great value at that. I have had amps costing much more not deliver nearly as much.
The man, the amp and the music are all delivered in this amp.
Let me start by saying my review is only of my listening enjoyment and how I hear it. I have absolutely no idea of any technical aspects or any parts included with this build. He is welcomed to post any of the specs if he likes.
xrk971 asked for my listening preferences and gear I was using. It is Fiio X5 gen 3 DAP and Audeze LCD 2 headphones. Although many reviewers indicate the Fiio X5 gen 3 to be plenty strong to drive the Audeze LCD 2s, I did not. It seemed to me to be so much more there that wasn't being revealed. One day recently while trolling on Head Fi I came across what looked like a little jewel if 1/2 of what was being said about it was true.
I decided to try it and boy am I glad I did. xrk971
kept me up to speed continuously. He custom built it to my hardware and listening specs and he sure delivered. All in all from time I ordered, he built, shipped and delivered it was only about 5 days.
Short and sweet, these are my impressions. As always I try to remember to listen clean and mastered recordings. In this case I listened to the DSD recording of Christian Mc Brides " Live at Village Vanguard " This would be a sure workout for the bass. I'm a fan of " Steve Hoffman " masterings. I listened to some of his " Dreamboat Annie " Pee Wee Russell and his clarinet. And others.
Please be aware, this amp is very unforgiving in its reproduction of poor music source. This is clear evidence of not trying to color but to convey music as artist intended.
The sound stage was huge and wide. Most folks know LCD2S are well know for bass. The base this amp gave my setup was nothing less than articulate, good transit response, natural and detailed. I am a big believer in " It's not how low it goes. It's how well it goes low " . The speed of Mc Brides fingers up and down his bass is accurate. Who would ever believe this box could deliver so much bass. Next up instrument imaging and placement very distinct in height, width and depth. However vocals more up front in my face than I prefer. This may be unfair since I did not listen to very many recordings yet.
I could not believe the musicality this magical amp would provide me with. Here's how it was for me laying in my recliner listening Lincoln Mayorga and Distinguished Gentlemen on the Sheffield lable. " Limehouse Blues " toes are tapping relentlessly, shoulders rolling in and around and head rhythmically swaying side to side.
I found mids to be airy not congested. The highs are accurate and warm with some sparkle. Not as much sparkle as I prefer.
All in all this is a gem of an amp and great value at that. I have had amps costing much more not deliver nearly as much.
The man, the amp and the music are all delivered in this amp.
Last edited:
Users who are viewing this thread
