I'm sorry , i just see a 'broken' jpg symbol. is there a secret to viewing images here ?
also. i don't know how to locate the driver transistors. I've looked at the pcb parts list and schematic but ignorance alas means I'm none the wiser !
You need a readable diagram in from of you.
Here is the same image saved as a .png file. See if that works. Lets link it as well.
http://www.diyaudio.com/forums/attachment.php?attachmentid=650531&stc=1&d=1512931486
Attachments
*goes upstairs to turn on pc that is possibly of interest to local museum*jpg's should open with any browser. It should be visible as a small image and enlarge when clicked. It can be enlarged again by clicking the box that appears in the lower left corner.
If you are on a phone then I don't know details but I'm guessing it should work.
I don't do mobiles
aha ! it works now . Thank you so much I'll check them all tomorrow evening. that's very kind of you , much appreciated !
You're right unfortunately, for the cyrus one issue 07 they no longer fitted a bias adjustment. I wonder if i could add that back as I'm guessing the circuit board didn't change much. If not I think you were suggesting a work-around using preset components?
right, so, the outputs are all npn. But the drivers are one npn and one pnp ? I looked at each of the pairs you suggested. They seem to have different specs in regards to hFE , is it important to pick a device with the right hFE or is the gain decided by the circuit and all i need are drivers with sufficient headroom to cope ?
Don't for get the bulb limiter if you miss adjust the bais as you can blow the output devices very quickly with out it.
Two ways to set bais..1 current, where you place the meter in current mode and place the probes in the + rail with the fuse removed or the 2 one is read the millivolts across the .22 ohm resistors.
Now say your reading is 15mv with bulb limiter pluged in and your need to reset it once you remove the limiter as it will be higher!
Good luck there
Two ways to set bais..1 current, where you place the meter in current mode and place the probes in the + rail with the fuse removed or the 2 one is read the millivolts across the .22 ohm resistors.
Now say your reading is 15mv with bulb limiter pluged in and your need to reset it once you remove the limiter as it will be higher!
Good luck there
cheers. at this stage I'm enlisting the help of a neighbour who recently built a pass f5t and I'm certain i saw lighbulbs and multiple meters and biasing going on.
thanks for your continued help. In return I'll do everything possible to educate myself to minimise the questions . cheers!
Very easy to do, essentially snipping one resistor out and tagging the preset in its place.
The overall gain of the circuit is determined by the feedback network, the individual gains of the transistors having no practical effect once the feedback loop is closed. That's one of the beauties of feedback, it means the circuit is reproducible with a wide variety of different semiconductor parameters.
Hi, the service manual seems to suggest that the bias can be adjusted to reduce the voltage (measured at R107A & R108A) by increasing the value of R81 to 180R or if the voltage is too low, by connecting a 220R cross R81. Does that sound plausible ?
The bias current is calculated from the volt drop across either of the 0.22 ohm resistors (always with no speaker attached).
The bias adjustment is done by what is called a vbe multiplier and altering the conduction of the transistor. The network of R81 and R83 would be replaced by a preset giving total control.
The numbers in the manual are so poor (blurred) that its difficult to quote which transistor it is. I think its Q39.
The trouble with fixed resistors are that you have no fine control and in fact very few amplifiers use fixed.
Here is the Cyrus redrawn and put into a simulation (it all works correctly) but I'm not 100% sure I've got all the reference numbers correct.
The bias adjustment is done by what is called a vbe multiplier and altering the conduction of the transistor. The network of R81 and R83 would be replaced by a preset giving total control.
The numbers in the manual are so poor (blurred) that its difficult to quote which transistor it is. I think its Q39.
The trouble with fixed resistors are that you have no fine control and in fact very few amplifiers use fixed.
Here is the Cyrus redrawn and put into a simulation (it all works correctly) but I'm not 100% sure I've got all the reference numbers correct.
Attachments
Thanks and yes, very handy. I couldn't do that on a mobile.
I was trying to find something on vbe multipliers and expected a zillion hits, but no......
Class AB amplifiers
Rubber diode - Wikipedia
And I have never come across the term 'rubber diode' before. How weird is that.
and yes, very handy. I couldn't do that on a mobile. I was trying to find something on vbe multipliers and expected a zillion hits, but no......
Class AB amplifiers
Rubber diode - Wikipedia
And I have never come across the term 'rubber diode' before. How weird is that.
I'll be very careful with autocorrect when i google it. hoping to get time to test those resistors tonight after work (I'm tempted to replace them all tbh, though disturbing the tracks on the board unnecessarily might be unwise)Thanks
I was trying to find something on vbe multipliers and expected a zillion hits, but no......
Class AB amplifiers
Rubber diode - Wikipedia
And I have never come across the term 'rubber diode' before. How weird is that.