as posted here ACA with Linear PSU
i did a LPS for my friend. now i did another update - i need 2 Volts more for power and want to try the LT4320 active rectifier.
the cost are about 20Euro and i got 2,2 Volts more with a bias of both channel about 4A i got 23,7Volts--Yes... that is fine.
we compared the sound with the SMPS LRS150-24V with 2xPOZ89 Filter and the winner as the LPS. the dynamic is increased and the "class A" sound is much better then the actual SMPS. now we get less "fog" = darker.
LT4320 is done without snubber at the sec. winding because i haven´t done quasimodo.
next step will be an update of the Apple G3 for compare.
apple G3
have fun
chris
i did a LPS for my friend. now i did another update - i need 2 Volts more for power and want to try the LT4320 active rectifier.
the cost are about 20Euro and i got 2,2 Volts more with a bias of both channel about 4A i got 23,7Volts--Yes... that is fine.
we compared the sound with the SMPS LRS150-24V with 2xPOZ89 Filter and the winner as the LPS. the dynamic is increased and the "class A" sound is much better then the actual SMPS. now we get less "fog" = darker.
LT4320 is done without snubber at the sec. winding because i haven´t done quasimodo.
next step will be an update of the Apple G3 for compare.
apple G3
have fun
chris
Attachments
I finally retired and had time to assemble to ACA kit I bought in 2018. It worked beautifully the first couple of times I used it, but now when I turn in on there a a soft thumb coming out of both speakers every second or so. I purchased a different power supply from a recommendation in the forum (which I now can't find) but it made no difference. The fact is work correctly the first couple of times before this started has me stumped. Any ideas?
Why do you need R3? which looks as though it will introduce noise from the 24V rail direct to the input. Dropping R4 a little would allow more base current to cater for 'average' gain small signal NPN's.
You can also add a bjt output stage... but then its not an ACA in the true sense of the word
You can also add a bjt output stage... but then its not an ACA in the true sense of the word
Why? What does it do.
Here is a standard ACA with a high gain small signal transistor at the input. Try it with what you have. A 2N3819 JFET also seems to work well.
There were some discussions about ACA in one of our local audio groups. I wanted to build this but 2SK170 and ZTX450 were unavailable in my place ( almost unobtainable except for importing which incurred a huge cost). So I requested a friend Mr. Joshi Liadel to make some alterations to use locally available components like BC series transistors. And this is the schematic of mods made by him.
I tried this but the gain was less so used a simple gain circuit and it sounded very good. Not sure how dose it compares to the original with jfet input stage, It may sound entirely different, I will attach a pdf of the layout I used for this so someone can try and compare it.
Mr Joshi is not a member of this forum he can be contacted through Facebook for any clarification
Ok Mooly. Now I remember that I have some k170 that I bought on Aliexpress more than 5 years ago, but I never used them because they cost me very little thinking that they are fake. And surprise!!! The DS resistor is between 49 and 52 ohms out of the 10 I have. Is it possible that they are such good copies or clones?
The ACA has a special sound. Part of that sound is having a small JFet at the input.
The JFet does not need to be a Toshiba K170. The J112 or J113 would be acceptable substitutes. It is important that the part can supply enough current to bias the lower output Mosfet properly. That means being able to provide about four volts across a 1k resistor.
If two JFets can be matched closely, it would be possible to use two in parallel to achieve both higher current and transconductance.
The JFet does not need to be a Toshiba K170. The J112 or J113 would be acceptable substitutes. It is important that the part can supply enough current to bias the lower output Mosfet properly. That means being able to provide about four volts across a 1k resistor.
If two JFets can be matched closely, it would be possible to use two in parallel to achieve both higher current and transconductance.
I didn't have time to finish the ACA this weekend. In fact, I have a stereo ACA already working with original 2sk170s that a guy gave me, but I want to test this other ACA that I'm going to build with several type of transistors for Q4. I don't remember the basic parameters exactly, but I used two J231 to replace a 2sk109 in an amplifier and it worked perfectly. I know that the 2sk109 contains well-matched 2x2sk170s. In theory it should work. Okay. I'm going to check that's all I have here. bjt, j231, bf245, bf256, k117, k30, k246 and the k170 from aliexpress which are more than likely fake. Gentlemens, thank you for everything and I will keep you informed. Strength and health!