Unfortunately I am not very familiar with circuit diagrams. The layout of my PCB looks a little different than in your graphic ZEN. Where would I have to connect this resistor on my PCB for measurement? Do you have any idea where I can find this bias pot(s)? Do I have to remove the complete left side of the PCB to get to pot(s)? Do any of you know the problem with the different temperature between the left and right side of the monoblock (note from Mr Pass)?
Thank you for your efforts so far. The documentation is very informative.
Thank you for your efforts so far. The documentation is very informative.
@ADH
Have a look at post #123 picture no. 5.
This should be similar to your amp.
I don't know where the pot is located, but the fact that there is a temperature-difference between both sides on this amp, doesn't really make sense, unless one side has been disassembled and poorly reassembled, or some of the output-critters in one side are toast.
Personally I would measure the voltage across all the output-resistors, starting with the 'cold' side.
Have a look at post #123 picture no. 5.
This should be similar to your amp.
I don't know where the pot is located, but the fact that there is a temperature-difference between both sides on this amp, doesn't really make sense, unless one side has been disassembled and poorly reassembled, or some of the output-critters in one side are toast.
Personally I would measure the voltage across all the output-resistors, starting with the 'cold' side.
Actually on page 9 it’s apogee wrote there is a way to convert this amp into a 3.9
I didn’t quite got the how part.
Frontend is identical to the S/300, S/500, SA/1, SA/2, SA/3 and S/1000.
Powersupply, Railvoltage, biassettings and number of output devices differ.
There were three different incarnations of that frontend:
First series,
Series II (on the Stylished logo)
and optical bias, left under designated as such.
https://www.diyaudio.com/forums/attachment.php?attachmentid=957569&stc=1&d=1622901345
https://www.diyaudio.com/forums/attachment.php?attachmentid=957568&stc=1&d=1622901345
https://www.diyaudio.com/forums/attachment.php?attachmentid=957570&stc=1&d=1622901345
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I know this is going back a bit but I just acquired a Thershold Ta 300 and came across this post that has about the only information I can find on the internet regarding the amp. I am intrigued by the option of turning this into a class A amp. Do you recall or still have the information regarding the mods necessary? I tried a private message but I'm new to the forum and haven't put up enough posts yet to allow private messaging. Thanks
Hello guys, There are several questions here on this thread, because each model series has a different set of details.
Yes, you can convert some products to a lower voltage and obtain class A operation if the that model has the lower voltage tap. The Ta 300, for example, does indeed share a common transformer with a Forte 4 and those taps will provide the lower voltage. I believe they are green. Measure to verify.
Bias is measured across an emitter resistor on Series 1 and 2 products, but early E-line needs to have a .01 ohm placed in series with the positive rail as in the document posted. Later E-line products and T series (T200, T400 and T800) also have the .01 ohm mounted on the power supply PCB for convenience. Now the T800 is another story. It has a total of 8 adjustments. There are 4 amps. Each amp has a bias and a DC offset. DC offset can only be measure relative to chassis ground as the output is fully bridged.
Yes, you can convert some products to a lower voltage and obtain class A operation if the that model has the lower voltage tap. The Ta 300, for example, does indeed share a common transformer with a Forte 4 and those taps will provide the lower voltage. I believe they are green. Measure to verify.
Bias is measured across an emitter resistor on Series 1 and 2 products, but early E-line needs to have a .01 ohm placed in series with the positive rail as in the document posted. Later E-line products and T series (T200, T400 and T800) also have the .01 ohm mounted on the power supply PCB for convenience. Now the T800 is another story. It has a total of 8 adjustments. There are 4 amps. Each amp has a bias and a DC offset. DC offset can only be measure relative to chassis ground as the output is fully bridged.