Lumba Ogir said:
It is, after all, a well received and respected design. And I only use gate stoppers when they needed. ZD1 greatly improves the power supply rejection on the CCS for the input differential pair. C14 and C15 are part of the frequency compensation arrangement and I would not recommend to take these out. Q7 gives this simple circuit over 120 dB OL gain at low frequencies and closed loop distortion below 1 kHz measure under 0,0005% . For the gain of the power amp = 57 it is not a bad performance. And it does sound good
. Alex
I simulated the A3i and got excellent performance.
Many of these have been produced commercially here in the UK, a lot of them still working, with the only fault being poor PCB layout (not Alex's fault!)
I've now had the chance to repair one... the usual fault, the owner is very happy with it and is really happy I managed to repair it.
Alex, I have a 35-0-35 500VA transformer eating a hole in my desk... I am wondering would this design take much work in up-rating it for 48V supplies? I'm thinking 2x pair of MJL4281/4302 or Fairchild's 2SA1943/2SC5200 copies, along with a triple EF stage.
Many of these have been produced commercially here in the UK, a lot of them still working, with the only fault being poor PCB layout (not Alex's fault!)
I've now had the chance to repair one... the usual fault, the owner is very happy with it and is really happy I managed to repair it.
Alex, I have a 35-0-35 500VA transformer eating a hole in my desk... I am wondering would this design take much work in up-rating it for 48V supplies? I'm thinking 2x pair of MJL4281/4302 or Fairchild's 2SA1943/2SC5200 copies, along with a triple EF stage.
jaycee said:
It is my fault
, as I did the PCB's layout for that amp as well. As I've noted earlier, the PCB was not supposed to work with that much supply voltage and was designed for a proper glass-filled material. Using cheaper material and raising the power supply voltage created local overheating in few places. Electrically, the PCB layout is actually quite good as it produces very low induced distortion and makes good sounding amplifier. jaycee said:
Yes, that should be possible. One thing to watch out for is the dissipation on the output pair of VAS (Q8 and Q10) as the current there is quite high (~10mA). I am using now MJE243/253 in these positions for a modified version of A3i. Triple on the output can reduce the distortion further but probably is not really required for 48V supplies, just using 2 output devices in parallel should be enough. If you are going to use triples than you'll need some additional current limiting circuit to protect the output devices. Pre-outputs (Q11 & Q12) best to be mounted on the same heatsink as the output devices as, obviously, Q9 too.
Alex
Whoops! but ok... well they weren't made to your original specification. I'm also quite sure you didn't specify some of the junk parts they used... cheap capacitors for example. I'm sure they made you bite your tongue more than once!!
I was looking at going to town with this and using quite a few improved devices, mostly Fairchild stuff as they have some excellent parts:
KSC1845/KSA992 for small signal use
KSC3503/KSA1381 for the VAS
KSC2690/KSA1220 for predrivers.. or possibly just the above.
For the outputs, well I have some MJL4281/4302 and MJE15032/15033.. but I was also looking at Fairchild's FJP5200/FJP1943 for drivers, and their 2SA1943/2SC5200 clones (also called FJL4215/FJL4315) for outputs.
Most of what Cambridge makes now seems to be ultra budget stuff. I think only their top amplifier is a discrete design (by Doug Self), and most of the others are all based around the LM3886 chip!
I was looking at going to town with this and using quite a few improved devices, mostly Fairchild stuff as they have some excellent parts:
KSC1845/KSA992 for small signal use
KSC3503/KSA1381 for the VAS
KSC2690/KSA1220 for predrivers.. or possibly just the above.
For the outputs, well I have some MJL4281/4302 and MJE15032/15033.. but I was also looking at Fairchild's FJP5200/FJP1943 for drivers, and their 2SA1943/2SC5200 clones (also called FJL4215/FJL4315) for outputs.
Most of what Cambridge makes now seems to be ultra budget stuff. I think only their top amplifier is a discrete design (by Doug Self), and most of the others are all based around the LM3886 chip!
Well, the recent Cambridge Audio stuff is sold to people who want hifi on a budget. Really, it's for people who want something better than the common microsystems you get nowadays, but aren't prepared to blow £500-£600 on each seperate. Even the LM3886 based amps blow away pretty much any microsystem.
So, can you tell me if it would make sense to put in larger mains caps instead of the 6800 my F which are currently build in ? Especialy if you want to draw a lot of current with 4 Ohms Speakers.
Also, they are just ratet 35 V and the supply voltage is not mutch lower. (i already changed the rectifier diodes as you suggested)
And at what level of current does the current protection come on ? Does it hard switches of the amp for a few secounds ?
Sorry for all the questions and the bad english, have a nice day, falk
Also, they are just ratet 35 V and the supply voltage is not mutch lower. (i already changed the rectifier diodes as you suggested)
And at what level of current does the current protection come on ? Does it hard switches of the amp for a few secounds ?
Sorry for all the questions and the bad english, have a nice day, falk
Lumba Ogir said:
Are you going to provide any constructive suggestions, or just continue with these boorish one-liners?
You mentioned earlier that you would remove Q7, without any elaboration as to why. When Alex explained why it, and other parts you had questioned, were in the circuit, you had nothing to say.
If you have some useful, specific, recommendations on improving this circuit, I, for one, would be interested in hearing them. So far, though, your feedback looks to me to be unhelpful complaints that also seem to be unfounded.
My .02,
Paul
Because we have a good topic here - the original designer of a pretty good amplifier who's willing to share a lot of the design history and his own recommendations (both theoretical and tested) for improving it.
I think I could learn a lot, both about general amplifier design, and about this specific amp, if you guys were to have an actual discussion about your ideas for improvements.
I think I could learn a lot, both about general amplifier design, and about this specific amp, if you guys were to have an actual discussion about your ideas for improvements.
at-2600 said:
Hi Falk,
A3i power supply was made originally with 10000uF 50V caps and that is what should be there. Short circuit protection should trip if you drive 2 Ohm or lower hard enough. It re-sets the relay and will trip continuously every few seconds if the short or the signal is not removed. It is not recommended to leave it like that as the relay contacts will deteriorate quickly.
Alex
Good stuff, I was planning to put 2x15000uF 80V that I have spare here
Alex, what did you think of the transistor selection I posted a few posts back? Fairchild have a nice selection, mostly Japanese second source stuff, but good parts nontheless. I particularly like the KSA1381/KSC3503 parts.
Alex, what did you think of the transistor selection I posted a few posts back? Fairchild have a nice selection, mostly Japanese second source stuff, but good parts nontheless. I particularly like the KSA1381/KSC3503 parts.
Paul,
unfortunately, I don`t think this is the right place for theoretical discussions. Let me just say that I would omit Q7 because, in my view, it does more damage than good and an excessive open-loop gain is undesirable. Cob is harmful enough already, external extension is not a good practice.
unfortunately, I don`t think this is the right place for theoretical discussions. Let me just say that I would omit Q7 because, in my view, it does more damage than good and an excessive open-loop gain is undesirable. Cob is harmful enough already, external extension is not a good practice.
Hi, i have an A3i, Its my brothers so Im not to familiar with the cambridge audio, i have a problem where the unit is totaly dead, so i have been told, it popped when swiched on and has been dead ever since,
I have resoldered tones of poor solder connection on the power amp Pcb and have found R112 is cremated and split in two. Also C211 (100uf 50V bipolar) look like it may have leaked. Is their any thing else i should be looking for and also does anyone know the value of R112 as i have no circuit diagrame to work from.
Also where is the best place to get spares from, we tend to use RS, CPC, SEME or CHS, or can any one here supply parts.
Any help would be great.
Kindest Regards
Sam
I have resoldered tones of poor solder connection on the power amp Pcb and have found R112 is cremated and split in two. Also C211 (100uf 50V bipolar) look like it may have leaked. Is their any thing else i should be looking for and also does anyone know the value of R112 as i have no circuit diagrame to work from.
Also where is the best place to get spares from, we tend to use RS, CPC, SEME or CHS, or can any one here supply parts.
Any help would be great.
Kindest Regards
Sam
Samgti6 said:Hi, i have an A3i, Its my brothers so Im not to familiar with the cambridge audio, i have a problem where the unit is totaly dead, so i have been told, it popped when swiched on and has been dead ever since,
I have resoldered tones of poor solder connection on the power amp Pcb and have found R112 is cremated and split in two. Also C211 (100uf 50V bipolar) look like it may have leaked. Is their any thing else i should be looking for and also does anyone know the value of R112 as i have no circuit diagrame to work from.
Also where is the best place to get spares from, we tend to use RS, CPC, SEME or CHS, or can any one here supply parts.
Any help would be great.
Kindest Regards
Sam
Hi Sam,
please get in touch by email through my website (it is in my profile) and I will try help you out.
Cheers
Alex
By A3i I carried out the repair service some years ago for the German distributor at this time. (I did this one also by the cambridge audio models "CD4", "Trac I", "CD6" "Discmagic" "A1" and "Atac3").
At this time I don't know about p-spice simulation of amplifier circuits and therefore I had no experience. Now I have "Circuitmaker" and can investigate and verify many reasons for blown output devices.
I recall your special topologie by voltage amplifier of A3i. If I remove the ZVP3306, I see a normal folded cascode. Your topology I have never see by other brands. In the next time I will investigate by simulation the advantages of this topology.
Unfortunately, the workmanship of the A3i was not particularly good and the Sanken power devices (MT-200 outline) were most counterfeit devices as describt about
http://sound.westhost.com/fake/counterfeit-p2.htm#sank1
Nevertheless it sounded very good, but after a short time there are errors occurred through local overheating predrivers and consequently broken solder joints. The cross current through this stage cause not present heatsinks are too large). I replace still the BC 639 and BC 640 trough BD139/140 with heat sinks. For the ZVP3306 I use a special heat sink. Additional I choise 4 times larger resistor devices (arround 3 W).
Are you also the developer of the SRPP phono RIAA head amp module for the A1 and Atac3 ?
This is one the best MM phono modul, that I have ever heard. Together with a Mark Levinson JC-1 (MC head Amp) it sounded better for me as the Linn phono preamp " Linto".
At this time I don't know about p-spice simulation of amplifier circuits and therefore I had no experience. Now I have "Circuitmaker" and can investigate and verify many reasons for blown output devices.
I recall your special topologie by voltage amplifier of A3i. If I remove the ZVP3306, I see a normal folded cascode. Your topology I have never see by other brands. In the next time I will investigate by simulation the advantages of this topology.
Unfortunately, the workmanship of the A3i was not particularly good and the Sanken power devices (MT-200 outline) were most counterfeit devices as describt about
http://sound.westhost.com/fake/counterfeit-p2.htm#sank1
Nevertheless it sounded very good, but after a short time there are errors occurred through local overheating predrivers and consequently broken solder joints. The cross current through this stage cause not present heatsinks are too large). I replace still the BC 639 and BC 640 trough BD139/140 with heat sinks. For the ZVP3306 I use a special heat sink. Additional I choise 4 times larger resistor devices (arround 3 W).
Are you also the developer of the SRPP phono RIAA head amp module for the A1 and Atac3 ?
This is one the best MM phono modul, that I have ever heard. Together with a Mark Levinson JC-1 (MC head Amp) it sounded better for me as the Linn phono preamp " Linto".