Yes that's what it's supposed to do but apparently "line level" was defined quite differently in the 70s. It's not even mic level with the Lpad engaged.
In theory, removing it raises the impedance significantly but I have found no issues so far. And besides, I really don't care for the high end anyhow in my situation. I soldered together a simple 9V stereo buffer on a veroboard (with dual 7809 voltage regulators mounted directly to the chassis backwall) and tried to use the JC's internal +15V rail but it caused some horrible distortion so I disconnected it.
In theory, removing it raises the impedance significantly but I have found no issues so far. And besides, I really don't care for the high end anyhow in my situation. I soldered together a simple 9V stereo buffer on a veroboard (with dual 7809 voltage regulators mounted directly to the chassis backwall) and tried to use the JC's internal +15V rail but it caused some horrible distortion so I disconnected it.
...On a side note: Do you think a noise gate would help reduce the inherent chorus noise or is this simply part of the deal with an old amp like this?
Also, how likely is it that the two giant caps in the power supply need to be replaced (all other electrolytics have been done by a friend of mine)?
Lastly, do you think a larger transformer could increase headroom for electric bass or would it inevetibly alter the tonal characteristics of the amp?
Also, how likely is it that the two giant caps in the power supply need to be replaced (all other electrolytics have been done by a friend of mine)?
Lastly, do you think a larger transformer could increase headroom for electric bass or would it inevetibly alter the tonal characteristics of the amp?
...These caps are still the original ones.
Nevermind the transformer/headroom question. I remembered that I still have a Crest CA6 in the basement.
You would need two DIs for stereo..
The delicious JC120 analog stereo chorus is largely due to the sound (and spacing) of the speakers, which also tend to roll off the inherent chorus and amp noise heard through a line out. A noise gate kills the entire signal below threshold, attack may be missed, note tails are abruptly cut off.
Stereo bass guitar is a bit unusual, but the usual practice would be bass guitar into the DI, thru output of the DI into the amp, mic the speakers, pan speaker mics left and right, blend and EQ between the three inputs for the mains and monitors. The low end from the DI through the main speakers would usually be plenty on stage, and the amp can be just used for the instrument sound- you won't need to carry the low end through the JC120.
47 year old caps are getting old, but if you are not hearing hum harmonics (multiples of 50/60 Hz) the large caps in the power supply are probably OK.
I have a quad channel passive rack DI from Palmer.
Since I mostly play through headphones I can confirm that the chorus sounds even better in that configuration because you can adjust stereo width (50% seems to sound the best to my ears). I also put custom dual gang speed/depth knobs and did the CE1 chorus depth mod, so I can finetune the effect in both parameters.
I usually have the speed all the way down and depth at 12-2 o'clock. So very subtle without the big bass loss due to phase cancellation. In stereo it gives an amazing surround effect.
Alternatively I could go into the dry channel with a Y cable for an extra (unmodulated) bass foundation.
The noise dampening of the speakers is certainly missing but I guess this would only really matter for recording because in a live situation the signal will ultimately end up at a speaker somewhere.
Why would I need three channels? And also I don't quite understand the reason for micing the (high-pass filtered) speakers when I can just send the unfiltered lineout directly to the PA.
Just checked and damn, with the chorus engaged there is a significant hum around a flat G#/D#.
Since I mostly play through headphones I can confirm that the chorus sounds even better in that configuration because you can adjust stereo width (50% seems to sound the best to my ears). I also put custom dual gang speed/depth knobs and did the CE1 chorus depth mod, so I can finetune the effect in both parameters.
I usually have the speed all the way down and depth at 12-2 o'clock. So very subtle without the big bass loss due to phase cancellation. In stereo it gives an amazing surround effect.
Alternatively I could go into the dry channel with a Y cable for an extra (unmodulated) bass foundation.
The noise dampening of the speakers is certainly missing but I guess this would only really matter for recording because in a live situation the signal will ultimately end up at a speaker somewhere.
Why would I need three channels? And also I don't quite understand the reason for micing the (high-pass filtered) speakers when I can just send the unfiltered lineout directly to the PA.
Just checked and damn, with the chorus engaged there is a significant hum around a flat G#/D#.
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The reason for micing the speakers is their transfer function- their hi-pass/low-pass, FX, distortion and EQ imparts the stage sound that a musician normally hears. If you prefer the line out/headphone sound with it's hiss and hum noise not reproduced by the speakers, micing them doesn't make sense.
Got ya but I think this applies more to guitar, where even the best lineout usually still sounds sterile and cold.
...So I still don't get which rating will tell me if the capacitor will be able to handle the power.
Going by voltage would mean a tiny <1€ cap is sufficient.
Going by voltage would mean a tiny <1€ cap is sufficient.
This is the primary function of the capacitor. Inductors too, ideally don't consume power so in theory they don't get hot.
On a secondary level they have parasitic resistance, ie it's not an intentional part of them but a practical one. As a result, inductors can get hot but it is not related to the power being routed through them, but their parasitics. Similarly, capacitors also have a ripple current rating.
On a secondary level they have parasitic resistance, ie it's not an intentional part of them but a practical one. As a result, inductors can get hot but it is not related to the power being routed through them, but their parasitics. Similarly, capacitors also have a ripple current rating.
And which ranges should I go for in terms of these two parameters?
Strange, though because all the parts I find on specialized audio/speaker building websites are extremely huge (and expensive).
Strange, though because all the parts I find on specialized audio/speaker building websites are extremely huge (and expensive).
At that price and size, the capacitor is probably polarized, only designed for use with direct current. You need non-polar capacitors for crossover use, the audio signal is AC- a polarized cap may blow up at < 15% of it's voltage rating when AC voltage is applied.
Electrolytic caps are cheaper than film capacitors, but generally don't last as long.
Ok and for the inductors there isn't anything special apart from voltage rating that I need to look for?
Not much- there is a trade off between series resistance reducing damping factor, ferrite core reducing series resistance but increasing distortion, low resistance air core requiring a load of thick copper wire costing a lot of money.
Considering the amount of distortion in the amp, probably not worth worrying about as long as the coil can handle the power without burning the insulation.
Considering the amount of distortion in the amp, probably not worth worrying about as long as the coil can handle the power without burning the insulation.