No.
You are both not reading what I told you.
Set up a Push Pull ClassA amplifier with an output bias of 1A. The ClassA output limit is ~ 2Apk.
Measure the supply voltage at the amplifier at quiescent condition.
Now attach a load and draw sinewave power from the output. The supply voltage does not change until the output current exceeds that 2A ClassA limit.
All that changes is the ripple on the supply rails.
You are both not reading what I told you.
Set up a Push Pull ClassA amplifier with an output bias of 1A. The ClassA output limit is ~ 2Apk.
Measure the supply voltage at the amplifier at quiescent condition.
Now attach a load and draw sinewave power from the output. The supply voltage does not change until the output current exceeds that 2A ClassA limit.
All that changes is the ripple on the supply rails.
Hi everyone,
DISASTER Finished both channels and started to check out, I am using Jan's boards. Set bias to 1.5 amps on each channel and set offset to 0v,all set up easily. With amplifier still powered up I connected a pre-amp (Quad 44 ) and CD player.Re-checked offset and all OK. Again with the amplifier still powered I connected my normal listening speakers (Spendor BC1's).
Both channels sounded super, there was no hum and all was well until I turned the amplifier off at the wall socket at which point both bass drivers nearly popped out the cabinets. Being really stupid I switched back on from the socket and again the bass drivers shot forward with a terrible thump.
One of my beloved BC1's bass driver cone is now out of centre, I'm really angry with myself for not using a set off cheap speakers first.
What have I done wrong, is there normally a thump when powering on or off?
The only thing I can think off is that the input ground was only connected to ground via the phono lead going to the pre-amp ( although this connection was not broken at any time.
Since this has happened I tried without speakers connected and the offset is at 0v, but when the power is turned off the offset goes to about 12volts.
Any suggestions (except telling me how stupid I am ) will be gratefully accepted.
Thanks
Alan
DISASTER Finished both channels and started to check out, I am using Jan's boards. Set bias to 1.5 amps on each channel and set offset to 0v,all set up easily. With amplifier still powered up I connected a pre-amp (Quad 44 ) and CD player.Re-checked offset and all OK. Again with the amplifier still powered I connected my normal listening speakers (Spendor BC1's).
Both channels sounded super, there was no hum and all was well until I turned the amplifier off at the wall socket at which point both bass drivers nearly popped out the cabinets. Being really stupid I switched back on from the socket and again the bass drivers shot forward with a terrible thump.
One of my beloved BC1's bass driver cone is now out of centre, I'm really angry with myself for not using a set off cheap speakers first.
What have I done wrong, is there normally a thump when powering on or off?
The only thing I can think off is that the input ground was only connected to ground via the phono lead going to the pre-amp ( although this connection was not broken at any time.
Since this has happened I tried without speakers connected and the offset is at 0v, but when the power is turned off the offset goes to about 12volts.
Any suggestions (except telling me how stupid I am ) will be gratefully accepted.
Thanks
Alan
You have learnt a lesson the hard way unfortunately.
Many amps thump at power on and off, this one obviously more than is acceptable.
I have not followed the thread and 8000+posts it's to big to refer back through.
A KSA50 (AKSA !!! no no no
)
How does your KSA 50 differ from a production one ? Is it missing relays as Andrew suspects ? Do you have massively oversized reservoir caps that hold a lot of energy ? Could the amp be "latching" or swinging to one rail as the rail voltage falls due to some difference in circuit detail ?
Many amps thump at power on and off, this one obviously more than is acceptable.
I have not followed the thread and 8000+posts it's to big to refer back through.
A KSA50 (AKSA !!! no no no
) How does your KSA 50 differ from a production one ? Is it missing relays as Andrew suspects ? Do you have massively oversized reservoir caps that hold a lot of energy ? Could the amp be "latching" or swinging to one rail as the rail voltage falls due to some difference in circuit detail ?
Hello
Sorry to hear that.
When you test any amplifier never connect a good speaker for test!
Some amplifier after you turn it of the power the power transistor will open and let 10V or so out to the speaker coil. Even if when is on full power you don't get any offset.
Sometimes enough to destroy your driver.
I have a NAIM clone it does the same. I also burnt a driver about 15 years a go.
Also thermal runaway and so many things can go wrong.
Better just hook up a cheap speaker or just a driver if you don't have but never a expensive speaker.
Greetings Gabor
Sorry to hear that.
When you test any amplifier never connect a good speaker for test!
Some amplifier after you turn it of the power the power transistor will open and let 10V or so out to the speaker coil. Even if when is on full power you don't get any offset.
Sometimes enough to destroy your driver.
I have a NAIM clone it does the same. I also burnt a driver about 15 years a go.
Also thermal runaway and so many things can go wrong.
Better just hook up a cheap speaker or just a driver if you don't have but never a expensive speaker.
Greetings Gabor
If constant then yes. 12 volts across a 4 ohm driver, 3 amps/36 watts. I can solder with half that power.
If the voltage were due to "just" reservoir caps discharging and didn't go over 12 (and a DVM is no good to check that) then it is possible the large cone excursion could push a coil outside its limits. What happens after that depends on the physical construction of the speaker and whether the cone passes a point of no return.
Hi all, thanks for the swift replies.
ANDREW T. I am using jan Du ponts PCB's and circuit shown in post 63,there is no relay shown and I am not using one, I don't know if original KSA50 had any protection.
MOOLY, A WAYNE, PINKMOUSE. the power supply for each channel is 2x 18volt secondaries 2 bridge rectifiers 2 47000uf 2 1ohm 2 47000uF in CRC for each rail. I wanted to run with approx 24v rails instead of the 37v to give me a KSA25.I do not require lots of output power and certainly did not want to dissapate too much heat.
Because of the lower voltage Jan;s circuit was modified thus:
R108 and R109 were reduced from 1.6K to 1.3K
R110 and R 111 were reduced from 9.1K to 4.7K
ZD101 and ZD102 were reduced from 27v to 13v zeners.
These mods were to retain the correct current through the LTP
The other thing was that the current limiting circuit for the output was ommitted.
C102 and C103 are 1000uF as per drawing.
No other alterations were carried out on the PCB.
As I said, when the amp was playing it sounded sweet from both channels.
Both channels set up easily and were stable.
I can,t help but think I have done something daft but don't know what.
Thanks
Alan
ANDREW T. I am using jan Du ponts PCB's and circuit shown in post 63,there is no relay shown and I am not using one, I don't know if original KSA50 had any protection.
MOOLY, A WAYNE, PINKMOUSE. the power supply for each channel is 2x 18volt secondaries 2 bridge rectifiers 2 47000uf 2 1ohm 2 47000uF in CRC for each rail. I wanted to run with approx 24v rails instead of the 37v to give me a KSA25.I do not require lots of output power and certainly did not want to dissapate too much heat.
Because of the lower voltage Jan;s circuit was modified thus:
R108 and R109 were reduced from 1.6K to 1.3K
R110 and R 111 were reduced from 9.1K to 4.7K
ZD101 and ZD102 were reduced from 27v to 13v zeners.
These mods were to retain the correct current through the LTP
The other thing was that the current limiting circuit for the output was ommitted.
C102 and C103 are 1000uF as per drawing.
No other alterations were carried out on the PCB.
As I said, when the amp was playing it sounded sweet from both channels.
Both channels set up easily and were stable.
I can,t help but think I have done something daft but don't know what.
Thanks
Alan
Hey all,
Off-Topic, but has anyone considered "X'ing" a KSA-50 Clone?
I have been thinking of this lately and I have the component parts / PCB / tranny / heatsinks for such an animal...but I believe its a little more involved than what I think I need to do -
What I think I need to do: (go easy on me please):
Balanced input and neg signal / ground to one KSA-50, and the pos signal / ground to the other amp (looks to be a simple bridged config). Speaker outs not referenced to ground.
Thought I would throw this out to see if anyone would further consider this? Bad Idea?
Off-Topic, but has anyone considered "X'ing" a KSA-50 Clone?
I have been thinking of this lately and I have the component parts / PCB / tranny / heatsinks for such an animal...but I believe its a little more involved than what I think I need to do -
What I think I need to do: (go easy on me please):
Balanced input and neg signal / ground to one KSA-50, and the pos signal / ground to the other amp (looks to be a simple bridged config). Speaker outs not referenced to ground.
Thought I would throw this out to see if anyone would further consider this? Bad Idea?
I have a question about the use of the 2SA968/2SC2238 pair for Q5 (or Q105) and Q7 (or Q106). Also replaced by MPSA42/92 and MJE15033/32 in later KSA50 clone designs.
Both transistors are biased at appx. 0.5mA. This wil achieve very low loading of the differential input stage. But with this low collector current the transition frequency (Ft) drops to about 10 MHz, while the current gain linearity is not at its best. The actual dissipation is only 25mW, these transistors are rated for 20 Watts.
I could imagine that its high internal capacitance could act as a lag compensation or the 3.3k resistor value simply is not correct. So what is the secret behind the use of the 2SA968/2SC2238 here?
Both transistors are biased at appx. 0.5mA. This wil achieve very low loading of the differential input stage. But with this low collector current the transition frequency (Ft) drops to about 10 MHz, while the current gain linearity is not at its best. The actual dissipation is only 25mW, these transistors are rated for 20 Watts.
I could imagine that its high internal capacitance could act as a lag compensation or the 3.3k resistor value simply is not correct. So what is the secret behind the use of the 2SA968/2SC2238 here?
Hi all, sorry for the long delay in getting back. Problem was very simple ( like me ) I had somehow omitted to ground the input ground on the PCB's, did this and amplifiers set up and worked fine.
I think I have become obsessed with this amplifier, it was passivly cooled and I felt that the other components within the chassis were running too warm, transformers, filter caps etc. So i have decided to now re-build using fan cooling with a completely different layout.Progress will be quite slow as not much spare time, but if anyone is interested I will post some pics during the build.
Off to the doctors now to see if there are any pills for Krell paranoya.
Alan.
I think I have become obsessed with this amplifier, it was passivly cooled and I felt that the other components within the chassis were running too warm, transformers, filter caps etc. So i have decided to now re-build using fan cooling with a completely different layout.Progress will be quite slow as not much spare time, but if anyone is interested I will post some pics during the build.
Off to the doctors now to see if there are any pills for Krell paranoya.
Alan.
Hiya!!
Does anybody still have unfurnished pinkMouse KSA-50 clone boards for sale? I'd VERY much like to buy a couple
I think i have some, will check tomorrow.
Loek