Clipping the input of the H9Optical wrote:Is it clipping the input of the H9? Or the H9 clipping the fx return?
Line level valve fx loops
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Re: Line level valve fx loops
Re: Line level valve fx loops
Ok.. replacing the tube with a 12AU7 wont work assuming the circuit is a standard cathode follower send stage. It might work if for some reason it's a rare plate send stage with NFB (highly unlikely).
What you would have to do is change the attenuation circuit at the send point. I dont know what the circuit is as I cant see a schematic anywhere, but you can try putting a 1.5k resistor across the send output. A very easy way to do this is connect a 1.5k resistor across the jack that plugs into the fx send, that will add more output attenuation, if it works great, if it doesnt it wont hurt anything. I think Bruce Egnater had a hand in designing these amps so that might do the trick if the fx send is his design
What you would have to do is change the attenuation circuit at the send point. I dont know what the circuit is as I cant see a schematic anywhere, but you can try putting a 1.5k resistor across the send output. A very easy way to do this is connect a 1.5k resistor across the jack that plugs into the fx send, that will add more output attenuation, if it works great, if it doesnt it wont hurt anything. I think Bruce Egnater had a hand in designing these amps so that might do the trick if the fx send is his design
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Re: Line level valve fx loops
That's in line with what i've come to understand about valve buffers, the mu valve isn't a factor in this particular function right?Ok.. replacing the tube with a 12AU7 wont work assuming the circuit is a standard cathode follower send stage. It might work if for some reason it's a rare plate send stage with NFB (highly unlikely).
What you would have to do is change the attenuation circuit at the send point. I dont know what the circuit is as I cant see a schematic anywhere, but you can try putting a 1.5k resistor across the send output. A very easy way to do this is connect a 1.5k resistor across the jack that plugs into the fx send, that will add more output attenuation, if it works great, if it doesnt it wont hurt anything. I think Bruce Egnater had a hand in designing these amps so that might do the trick if the fx send is his design
When you say across the send output, you mean across the hot and earth tabs of the jack?
Re: Line level valve fx loops
yes the fx send stage is not configured to produce gain, so the tube mu is not a factor.
Just found the schematic and the resistor across the output wont work very well. You'll need to get inside it and change R55 and R57. If you reckon you can do that i'll tell you what to do.
Just found the schematic and the resistor across the output wont work very well. You'll need to get inside it and change R55 and R57. If you reckon you can do that i'll tell you what to do.
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Re: Line level valve fx loops
You will need boost the gain in the return circuit too unless you don’t mind your amp losing volume.
Tube amp and guitar tones straight from 1958… amazing how believable the sounds were back then, even without the modellers...
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Re: Line level valve fx loops
I have a similar problem with my RM100 and its line level loop. The quick and easy solution is to turn down the volumes on the individual pre-amp modules and turn up the master. That of course only works if you've still got enough volume after all that. I've got the ebtech level shifter thing, and that sort of works, it still had issues with some gear though. I'd love to DIY up a send level at some point, maybe when I do the dual channel mod.
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Re: Line level valve fx loops
Iv'e taken the amp out of the head shell. I can access R55 & R57 but they are on the main board. It will be a massive PITA to undo all the jacks and plugs and carefully remove the PCB.Optical wrote:yes the fx send stage is not configured to produce gain, so the tube mu is not a factor.
Just found the schematic and the resistor across the output wont work very well. You'll need to get inside it and change R55 and R57. If you reckon you can do that i'll tell you what to do.
Can i go parallel across the existing resistors to change the values?
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Re: Line level valve fx loops
That's no worries, plenty loud enough and the H9 can boost the outputsizzlingbadger wrote:You will need boost the gain in the return circuit too unless you don’t mind your amp losing volume.
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Re: Line level valve fx loops
I reckon the modules sound naff until they are past 12'o clock though. Thanks for the heads up about the line shifter.moliere wrote:I have a similar problem with my RM100 and its line level loop. The quick and easy solution is to turn down the volumes on the individual pre-amp modules and turn up the master. That of course only works if you've still got enough volume after all that. I've got the ebtech level shifter thing, and that sort of works, it still had issues with some gear though. I'd love to DIY up a send level at some point, maybe when I do the dual channel mod.
Mmm not a lot space on either side for send/return level knobs. I don't know the practicalities of mounting them in the jacks if they are board mounted.
Re: Line level valve fx loops
Mattallica wrote:Iv'e taken the amp out of the head shell. I can access R55 & R57 but they are on the main board. It will be a massive PITA to undo all the jacks and plugs and carefully remove the PCB.Optical wrote:yes the fx send stage is not configured to produce gain, so the tube mu is not a factor.
Just found the schematic and the resistor across the output wont work very well. You'll need to get inside it and change R55 and R57. If you reckon you can do that i'll tell you what to do.
Can i go parallel across the existing resistors to change the values?
Just a note - the FX return stage is pretty much at max gain already, so boosting it further wouldnt be possible.
Can you post a photo of the board? You might be able to work from the top
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Re: Line level valve fx loops
Optical wrote:It's a bit tight but doable:Mattallica wrote:Iv'e taken the amp out of the head shell. I can access R55 & R57 but they are on the main board. It will be a massive PITA to undo all the jacks and plugs and carefully remove the PCB.Optical wrote:yes the fx send stage is not configured to produce gain, so the tube mu is not a factor.
Just found the schematic and the resistor across the output wont work very well. You'll need to get inside it and change R55 and R57. If you reckon you can do that i'll tell you what to do.
Can i go parallel across the existing resistors to change the values?
Just a note - the FX return stage is pretty much at max gain already, so boosting it further wouldnt be possible.
Can you post a photo of the board? You might be able to work from the top
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Re: Line level valve fx loops
R55 is bottom right and R57 is tucked in behind the big capMattallica wrote:Optical wrote:Mattallica wrote:
Iv'e taken the amp out of the head shell. I can access R55 & R57 but they are on the main board. It will be a massive PITA to undo all the jacks and plugs and carefully remove the PCB.
Can i go parallel across the existing resistors to change the values?
Just a note - the FX return stage is pretty much at max gain already, so boosting it further wouldnt be possible.
Can you post a photo of the board? You might be able to work from the top
Re: Line level valve fx loops
I've just had a thought after looking at the circuit more - you are probably distorting the fx loop return stage (and maybe the send stage too) when you have the channel masters high. If that's the case, I dont think that lowering the send signal is going to fix your problem because you wont keep the tone of the channel masters above 12, because essentially the fx loop mod is going to do the same thing as turning the channel masters down.
I might be wrong and the extra gain from the channel masters being high actually causes the fx send stage to clip/add gain. In which case lowering the send level might keep some of the gain, but definitely not all of it because the fx return wont clip then.
You might just need to turn the channel master down so the H9 input doesnt clip, then turn the H9 output up to as loud as it can go to try and get the fx return stage to clip again. Have you tried that?
If that's not enough gain then it might still be worth modding the fx loop to keep the send stage clipping, but you wont be able to do anything about the return stage which wont clip. Although you could mod that for more gain too. But you are then going to start altering the compression and feel of the amp overall...
I might be wrong and the extra gain from the channel masters being high actually causes the fx send stage to clip/add gain. In which case lowering the send level might keep some of the gain, but definitely not all of it because the fx return wont clip then.
You might just need to turn the channel master down so the H9 input doesnt clip, then turn the H9 output up to as loud as it can go to try and get the fx return stage to clip again. Have you tried that?
If that's not enough gain then it might still be worth modding the fx loop to keep the send stage clipping, but you wont be able to do anything about the return stage which wont clip. Although you could mod that for more gain too. But you are then going to start altering the compression and feel of the amp overall...
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Re: Line level valve fx loops
I see what you're saying. I haven't tried bringing down the channel masters with the H9 yet. Worth a shot for sure. Back in she goes then!Optical wrote:I've just had a thought after looking at the circuit more - you are probably distorting the fx loop return stage (and maybe the send stage too) when you have the channel masters high. If that's the case, I dont think that lowering the send signal is going to fix your problem because you wont keep the tone of the channel masters above 12, because essentially the fx loop mod is going to do the same thing as turning the channel masters down.
I might be wrong and the extra gain from the channel masters being high actually causes the fx send stage to clip/add gain. In which case lowering the send level might keep some of the gain, but definitely not all of it because the fx return wont clip then.
You might just need to turn the channel master down so the H9 input doesnt clip, then turn the H9 output up to as loud as it can go to try and get the fx return stage to clip again. Have you tried that?
If that's not enough gain then it might still be worth modding the fx loop to keep the send stage clipping, but you wont be able to do anything about the return stage which wont clip. Although you could mod that for more gain too. But you are then going to start altering the compression and feel of the amp overall...