JCA50 SLO Mod - Need some information please
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frankencat
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JCA50 SLO Mod - Need some information please
Can anybody explain what this mod does and what the difference is vs stock? Thanks -Frank
Last edited by frankencat on Mon Apr 14, 2014 12:40 pm, edited 1 time in total.
Re: JCA50 SLO Mod - Need some infomraiton please
the only correct answer is: it depends.
in the most basic form, there are a few component values that need to be changed. the jet city amps are the same circuit as the soldano hot rod+, which is very similar to the SLO.
beyond that, it's just a matter of how many parts you want to change...you could swap all the coupling and ceramic caps for orange drops and silver mica like the ones use in an SLO. one could go as far as to change transformers to something that's closer to the deyoung pieces use in the SLO.
i'd say you can get about 80% there with the most simple component value mod, though.
in the most basic form, there are a few component values that need to be changed. the jet city amps are the same circuit as the soldano hot rod+, which is very similar to the SLO.
beyond that, it's just a matter of how many parts you want to change...you could swap all the coupling and ceramic caps for orange drops and silver mica like the ones use in an SLO. one could go as far as to change transformers to something that's closer to the deyoung pieces use in the SLO.
i'd say you can get about 80% there with the most simple component value mod, though.
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frankencat
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Re: JCA50 SLO Mod - Need some infomraiton please
I'm not really interested in creating a SLO clone. I want to change the OD channel a little bit and it would be helpful to know what the individual component changes do.
Thanks.
Thanks.
Re: JCA50 SLO Mod - Need some infomraiton please
i can give some basic guidelines:
larger anode resistors create a larger voltage swing (on plate driven gain stages), resulting in more gain. bypassing them with small capacitors dumps high frequencies...the smaller the cap, the smaller the band of high frequencies that are filtered away.
lower value cathode resistors can have a similar effect. a large value cathode resistor, ~4K-39K+, will cause the stage to go into cutoff for some portion of one half of the signal which creates what we perceive as a high gain tone by clipping, or squaring off, that portion of the wave. adding a cathode bypass capacitor will increase the gain of the stage, and also act as a bass shelving filter. the larger the value of that cap, the lower the bass frequency range of that stage.
coupling capacitors can be used to control low frequency transmission from one stage to the next. a pretty standard value is .22uF. smaller than that will attenuate more low end, larger will allow more to pass to the next stage.
interstage attenuation (resistors between coupling capacitors and the next gain stage) will reduce signal and attenuate high frequencies. bypassing them with a small capacitor will prevent the high frequency loss. these resistors are typically used to prevent blocking distortion.
grid leak resistors are connected to ground and the input of a gain stage. a low value will shunt some signal to ground. in general, a value of 1M will shunt little or no signal to ground. gain and volume pots commonly function as grid leak resistors as well as pots, so an easy way to change gain is to change the value of the gain pot. always use audio taper pots for gain and volume.
B+ voltage, while typically not something that one can easily change, is also a fundamental part of how a stage operates. higher B+ tends to cause more linear operation of a stage, with increased headroom. this is not always desired.
ultimately, the best way to figure out what each part does is to change it and see how it sounds. we can talk about theory, do math, etc. and it still won't translate into how it makes the amp sound and feel.
larger anode resistors create a larger voltage swing (on plate driven gain stages), resulting in more gain. bypassing them with small capacitors dumps high frequencies...the smaller the cap, the smaller the band of high frequencies that are filtered away.
lower value cathode resistors can have a similar effect. a large value cathode resistor, ~4K-39K+, will cause the stage to go into cutoff for some portion of one half of the signal which creates what we perceive as a high gain tone by clipping, or squaring off, that portion of the wave. adding a cathode bypass capacitor will increase the gain of the stage, and also act as a bass shelving filter. the larger the value of that cap, the lower the bass frequency range of that stage.
coupling capacitors can be used to control low frequency transmission from one stage to the next. a pretty standard value is .22uF. smaller than that will attenuate more low end, larger will allow more to pass to the next stage.
interstage attenuation (resistors between coupling capacitors and the next gain stage) will reduce signal and attenuate high frequencies. bypassing them with a small capacitor will prevent the high frequency loss. these resistors are typically used to prevent blocking distortion.
grid leak resistors are connected to ground and the input of a gain stage. a low value will shunt some signal to ground. in general, a value of 1M will shunt little or no signal to ground. gain and volume pots commonly function as grid leak resistors as well as pots, so an easy way to change gain is to change the value of the gain pot. always use audio taper pots for gain and volume.
B+ voltage, while typically not something that one can easily change, is also a fundamental part of how a stage operates. higher B+ tends to cause more linear operation of a stage, with increased headroom. this is not always desired.
ultimately, the best way to figure out what each part does is to change it and see how it sounds. we can talk about theory, do math, etc. and it still won't translate into how it makes the amp sound and feel.
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frankencat
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- Joined: Sat Apr 12, 2014 6:11 am
Re: JCA50 SLO Mod - Need some infomraiton please
Thanks for the reply. One of the things I am interested in is bringing the high end content of the two channels closer together. I like the basic tone of each channel but if I set the Crunch channel the way I like it the OD channel is too dark and vice versa so I would like to either cut some highs in the Crunch channel or increase highs in the OD channel. Either way works for me but preference for the latter. I also would not mind losing a little gain on the OD channel as a tradeoff for more clarity. That is why I started looking into the SLO mod but I am still not 100% sure what it brings to the OD side. So I am really interested in changing one channel and not the other.
On a general note. I am not after metal tones, I am more into Classic and Hard Rock tones. I have had many Soldano Hot Rod's and I am familiar with the way they sound and operate and this is pretty darn close to an HR50+ although the mids are a little murky/splatty but not terrible. I am sure some modding could get it to where I would like it. Thanks -Frank
On a general note. I am not after metal tones, I am more into Classic and Hard Rock tones. I have had many Soldano Hot Rod's and I am familiar with the way they sound and operate and this is pretty darn close to an HR50+ although the mids are a little murky/splatty but not terrible. I am sure some modding could get it to where I would like it. Thanks -Frank
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frankencat
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- Posts: 8
- Joined: Sat Apr 12, 2014 6:11 am
Re: JCA50 SLO Mod - Need some information please
BTW, what the heck is infomraiton? Lol. 