A cap multiplier like the Juma/Prasi one being used in some builds here, reduces mains ripple by 50dB. I doubt switching cap brands can have such a profound effect. And the cost of the cap Mx with common and inexpensive parts is about $20. This is not in the direct signal path so maybe use of non-audio grade caps is justified.
If low ripple, low ESR and capacity are all that is important, it’s hard for a single cap (no matter what brand) to beat a cap array. For example, a 20 position array can use very economical bulk (in a bag) 2200uF 35v 105deg C caps that measure 60mOhm ESR. But qnty 20 x 2200uF is 44mF and ESR is now 60mOhm/20=3mOhm. And the cost of the caps is $5 for a bag of 50. These are more helpful in a Class AB amp where dynamic currents swing wildly depending on music content. With SE Class A, we want a steady current and we know what that current is and max is maybe 2x.
Here is an example of a cap array that I sometimes use. I found it unnecessary in this case for the Alpha 20.
If low ripple, low ESR and capacity are all that is important, it’s hard for a single cap (no matter what brand) to beat a cap array. For example, a 20 position array can use very economical bulk (in a bag) 2200uF 35v 105deg C caps that measure 60mOhm ESR. But qnty 20 x 2200uF is 44mF and ESR is now 60mOhm/20=3mOhm. And the cost of the caps is $5 for a bag of 50. These are more helpful in a Class AB amp where dynamic currents swing wildly depending on music content. With SE Class A, we want a steady current and we know what that current is and max is maybe 2x.
Here is an example of a cap array that I sometimes use. I found it unnecessary in this case for the Alpha 20.
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Thank you Hugh and X for your responses! I am also considering the big boy version but something about forced cooling is not appealing. I realize getting bigger heat sinks are also an option as well as the input transformer. I am glad there are options though! Once again, thank you for the wonderful amplifier!
Bao
Bao
You are right.
But they are not exotics. Very expensive yes.
An array is not always possible. For example, when the big capacitors of amplifiers of a certain age are replaced.
It would be interesting to know Pinnocchio's opinion. If the great improvement was due mainly to the multiplier or those very expensive capacitors, in case he had tried before with others.
But they are not exotics. Very expensive yes.
An array is not always possible. For example, when the big capacitors of amplifiers of a certain age are replaced.
It would be interesting to know Pinnocchio's opinion. If the great improvement was due mainly to the multiplier or those very expensive capacitors, in case he had tried before with others.
Maty Tinman,
Thanks for all your comments and discussions. I know that audio caps on direct signal path (like the input coupling and output coupling) do have an impact that is audible. Use of good quality ones here is advised and avoid MLCC caps at all costs as coupling caps. I have been pleasantly surprised on many occasions how good a $0.30 Elna Silmic II 10uF 35v cap sounds as an input cap. It's up there with the best - in my opinion. Bypass with a 1uF film cap and really, 99% of SQ is there.
For PSU, though, isn't it all about ability to control ripple and have low ESR (if in a dynamic Class AB load)? With steady bias current SE Class A, is a boutique rail smoothing cap really necessary?
One of the goals of this amp, and the design philosophy mentioned in Post 1 and also pointed out by hajj is that this amp is meant to make superb sound quality and performance accessible to everyone without resorting to hard to find or expensive components. Using decent components (Elna Silmic caps, Wima film caps, Panasonic power resistors, Vishay MOSFETs), but no-name cheap metal thin film resistors, I was able to achieve a remarkably low 0.0067% THD for 1w into 8ohms for a pure SE Class A amp and an ultra-quiet noise. My experience with other Aleph CCS based amps has been much higher THD levels. Most of the reduction is purely topology (Aksa Lender front end and P-MOS output stage). We are also trying to keep the PSU for this amp accessible so I think major brand quality parts should be fine. The 47mF 35v cap for $11 is a reasonable one to get for the cap Mx. Nothing fancy is needed here really as it is the bridge smoothing cap and needs to provide reasonably low ripple to allow the cap Mx to do its -50dB suppression thingy.
Having said all that, I just spent nearly $29 on Vishay-Dale "brown sausage links" 0.5w 1% metal thin film resistors for this amp to see if things can get even better. That's a lot of money for a handful of resistors (not even in qnty 10 to reduce the price), but I won't be happy until I try for myself and maybe I will be a brown sausage convert.
Thanks for all your comments and discussions. I know that audio caps on direct signal path (like the input coupling and output coupling) do have an impact that is audible. Use of good quality ones here is advised and avoid MLCC caps at all costs as coupling caps. I have been pleasantly surprised on many occasions how good a $0.30 Elna Silmic II 10uF 35v cap sounds as an input cap. It's up there with the best - in my opinion. Bypass with a 1uF film cap and really, 99% of SQ is there.
For PSU, though, isn't it all about ability to control ripple and have low ESR (if in a dynamic Class AB load)? With steady bias current SE Class A, is a boutique rail smoothing cap really necessary?
One of the goals of this amp, and the design philosophy mentioned in Post 1 and also pointed out by hajj is that this amp is meant to make superb sound quality and performance accessible to everyone without resorting to hard to find or expensive components. Using decent components (Elna Silmic caps, Wima film caps, Panasonic power resistors, Vishay MOSFETs), but no-name cheap metal thin film resistors, I was able to achieve a remarkably low 0.0067% THD for 1w into 8ohms for a pure SE Class A amp and an ultra-quiet noise. My experience with other Aleph CCS based amps has been much higher THD levels. Most of the reduction is purely topology (Aksa Lender front end and P-MOS output stage). We are also trying to keep the PSU for this amp accessible so I think major brand quality parts should be fine. The 47mF 35v cap for $11 is a reasonable one to get for the cap Mx. Nothing fancy is needed here really as it is the bridge smoothing cap and needs to provide reasonably low ripple to allow the cap Mx to do its -50dB suppression thingy.
Having said all that, I just spent nearly $29 on Vishay-Dale "brown sausage links" 0.5w 1% metal thin film resistors for this amp to see if things can get even better. That's a lot of money for a handful of resistors (not even in qnty 10 to reduce the price), but I won't be happy until I try for myself and maybe I will be a brown sausage convert.
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That is why it would be interesting to know what Pinnocchio has to say about it.
The only thing I can assure you, with my two class AB amplifiers, is:
* DCB mundorf 47,000uF, 125ºC sounds much better than the DCB EPCOS 15,000uF, 85ºC
* DCB mundorf 47,000uF, 125ºC sounds better than the DCB EPCOS 18,000uF, 105ºC
* DCB mundorf 47,000uF, 125ºC sounds better than DCB EPCOS 15,000uF, 85ºC + DCB EPCOS 18,000uF, 105ºC.
If only two Mundors the price is affordable. The problem is if you need 8 Mundors!
The only thing I can assure you, with my two class AB amplifiers, is:
* DCB mundorf 47,000uF, 125ºC sounds much better than the DCB EPCOS 15,000uF, 85ºC
* DCB mundorf 47,000uF, 125ºC sounds better than the DCB EPCOS 18,000uF, 105ºC
* DCB mundorf 47,000uF, 125ºC sounds better than DCB EPCOS 15,000uF, 85ºC + DCB EPCOS 18,000uF, 105ºC.
If only two Mundors the price is affordable. The problem is if you need 8 Mundors!
Minutes before I wrote in my Audiocircle thread:
Holton DC Blocker One – Holton Precision Audio
[url]https://www.stereo.net.au/forums/uploads/monthly_2017_12/5a307561b8878_DCBlockerOne-6.thumb.jpg.dd67e6575b43c1b78c98af4bb1fe0ab9.jpg[/url]
AUS $490 = EUR 311 = USD 384.5
It has a [B]RF/EMI inlet[/B]. Only one output. Without varistor. Well, two meters.
The price is audiophile!
[B]Four generic? cheap capacitors: 47,000uF, 85 ºC, 16V[/B]
[IMG] [URL]http://maty.galeon.com/WP-imagenes/hum/Holton-Audio-DC-Blocker-47000uF-85C-16Vx4.jpg[/URL]
Holton DC Blocker One – Holton Precision Audio
[url]https://www.stereo.net.au/forums/uploads/monthly_2017_12/5a307561b8878_DCBlockerOne-6.thumb.jpg.dd67e6575b43c1b78c98af4bb1fe0ab9.jpg[/url]
AUS $490 = EUR 311 = USD 384.5
It has a [B]RF/EMI inlet[/B]. Only one output. Without varistor. Well, two meters.
The price is audiophile!
[B]Four generic? cheap capacitors: 47,000uF, 85 ºC, 16V[/B]
[IMG] [URL]http://maty.galeon.com/WP-imagenes/hum/Holton-Audio-DC-Blocker-47000uF-85C-16Vx4.jpg[/URL]
Yes, we had a discussion about this early on in the thread where 6L6 pointed out that it is the same as the signal that goes to the other side of the LTP and hence a film bypass cap was suggested for this spot as well. Although Panasonic FC/FM are very good. FG is excellent as well and Nichicon KA series.
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There is some case prototyping to do, but lacked motivation today. Instead I was just sitting with a cup of coffee and thinking about casing. Image is too dark, but I was wondering that I might add some kinda "shield" for heatsink, theres some space between shield and sink for ventilation. This was just a cardboard version and some exploration with power indicator light blue leds were the only one at hand. This is probably why Im so slow builder..
Sorry about constant off-topic, I'll stop it now
blue leds were the only one at hand. This is probably why Im so slow builder..Sorry about constant off-topic, I'll stop it now
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That’s a nice blue glow effect Juntuin. Very stealth understated high tech. I am listening to my ALPHA20 at present with a Cayin N3 as source. Interestingly, the Cayin being a portable has the most advanced DAC of all my hardware. Ak4990EN and a TI OPA1622 output stage which lets the N3 drive the ALPHA20 to clipping, if desired. The sound is very addictive. I have work to do by find myself lingering in front of my ScanSpeak 10F/8424 & RS225-8 FAST speakers for a lot longer than I would have liked to. Norah Jones sounds sublime on it.
Looks like a nice DAP, interesting set of features for the price! The DAC chip is a AK4490EN. I know one of the reviewer says 4990 but it is a typo. The AK4490 is probably one of my favorite DAC chip when well implemented.
Do
Hi Pinocchio,
My bad, it’s AK4490EN as you say. I got it based on recommendations by two people on HeadFi that I trust. Also, the Headfonics review is pretty good too. A lot of features for the price and pretty much beats all my other DACs. One really big point is that it is battery powered - and that lets you get away from mains hum and ground loops at the source.
How close are you to starting the build on the Alpha 20?
My bad, it’s AK4490EN as you say. I got it based on recommendations by two people on HeadFi that I trust. Also, the Headfonics review is pretty good too. A lot of features for the price and pretty much beats all my other DACs. One really big point is that it is battery powered - and that lets you get away from mains hum and ground loops at the source.
How close are you to starting the build on the Alpha 20?
I'm currently (as I'm writing this) reviewing the BoM, looking what I already have in stock and what need to be bought. There's not many components on this amp so it should be inexpensive to build. I might need a set of the cap MX since the only cap MX I have is the older PMI which I never assembled and don't feel like assembling it since it is now unsupported.
Do
Do