Cathode biased PR trem depth ?

[floyd]

Can I reduce the value of the  1Meg resistor , ( in red ) to increase the trem depth in this circuit ?

[sluckey]

Can I reduce the value of the  1Meg resistor , ( in red ) to increase the trem depth in this circuit ?

No. Read this thread...

http://www.el34world.com/Forum/index.php?topic=15087.0

[floyd]

Sluckey.. I have the LED already, but I thought that the 1Meg may also affect the depth, ( I want a lot of depth. ).

[HotBluePlates]

No. Those 1MΩ resistors change the trem speed, in concert with the coupling caps.

[sluckey]

Reds and yellows seem to work the best. But if the LED does not give you enough depth, I'm not sure the answer lies inside the PR chassis. My Boss TR2 is plenty deep (for me).  

[tubeswell]

Bias-vary trem in the PR works by changing the bias of the output tubes, by cyclically decreasing the tube current towards cutoff at each peak trem swing. Having the output stage as fixed-bias in the stock PR is an advantage, because you can 'dial-down' the tube current of the 6V6s to get the trem to work more intensely.

However, if you have built a cathode-biased output stage in your PR, then the 'auto-bias' behaviour of the cathode bias resistor will counteract the effect of the trem bias-vary voltage swing, and you need an even bigger swing and/or more current being driven from the trem output in order to 'fight' and overcome the auto-bias characteristic of your cathode-biased output stage.

One way of adding more voltage swing in the LFO is to increase the gain of the LFO (hence the LED bias recommendation). You could also increase the LFO HT voltage if that was an option.

Or you could add a buffer stage (i.e. using a surplus triode from somewhere to make a cathode-follower or a high voltage MOSFET like an IRF820 source-follower) to the LFO to increase the current supply from the trem oscillator.

[plexi50]

What schematic version of the PR are you using? My AA1164 PR tremelo is wonderful and plenty deep

[floyd]

What schematic version of the PR are you using? My AA1164 PR tremelo is wonderful and plenty deep

           I have a stock PR clone at the moment , BUT I'd like to cathode bias it instead of fixed. So.. I need a different trem circuit... I thought I'd use the circuit seen below , with the addition of a red LED.

[sluckey]

I have a stock PR clone at the moment , BUT I'd like to cathode bias it instead of fixed. So.. I need a different trem circuit...

It's unclear to me what you really have. I thought you had already converted the PR to cathode bias. And I thought you already had replaced the cathode cap and resistor on V4 pin 3 with a LED. And the trem was still too weak for your taste.

But now you say "I have a stock PR clone at the moment , BUT I'd like to cathode bias it instead of fixed." Please clear up my confusion. What do you currently have and what mods have you actually done?

[tubeswell]

I have a stock PR clone at the moment , BUT I'd like to cathode bias it instead of fixed. So.. I need a different trem circuit...

It's unclear to me what you really have. I thought you had already converted the PR to cathode bias. And I thought you already had replaced the cathode cap and resistor on V4 pin 3 with a LED. And the trem was still too weak for your taste.

But now you say "I have a stock PR clone at the moment , BUT I'd like to cathode bias it instead of fixed." Please clear up my confusion. What do you currently have and what mods have you actually done?

Ditto

[floyd]

What schematic version of the PR are you using? My AA1164 PR tremelo is wonderful and plenty deep

           I have a stock PR clone at the moment , BUT I'd like to cathode bias it instead of fixed. So.. I need a different trem circuit... I thought I'd use the circuit seen below , with the addition of a red LED.

I think my statement is pretty clear.. I have a totally stock PR , except for the LED in the trem circuit. Today though , I'll be changing over to cathode bias .

[sluckey]

I think my statement is pretty clear.. I have a totally stock PR , except for the LED in the trem circuit. Today though , I'll be changing over to cathode bias .

Sometimes I'm just dense. Is the trem intense enough as the amp is now?

You shouldn't have to do anything to the trem circuit to change over to cathode bias. The trem 'may' not be quite as intense as it is in a fixed bias PR, but you'll know soon enough if it is sufficient for you.

BTW, that red 1meg resistor in your original pic does not connect to ground in a stock PR as shown in that pic. It connects to V4-3.

[floyd]

OK... I cathode biased the PR , using the Vox trem. I used the red LED instead of cap/resistor , AND added  a 1N4007 diode on the intensity pot. I'm very pleased with the trem.

[floyd]

I think my statement is pretty clear.. I have a totally stock PR , except for the LED in the trem circuit. Today though , I'll be changing over to cathode bias .

Sometimes I'm just dense. Is the trem intense enough as the amp is now?

You shouldn't have to do anything to the trem circuit to change over to cathode bias. The trem 'may' not be quite as intense as it is in a fixed bias PR, but you'll know soon enough if it is sufficient for you.

BTW, that red 1meg resistor in your original pic does not connect to ground in a stock PR as shown in that pic. It connects to V4-3.

Yeah , that red 1meg is part of a layout change inserted into the original Fender layout, showing the Vox trem.