JCA OWNERS!!! (RE)JOIN THE JET CITY LOUNGE!!!

[Jase01]

I would almost reverse the positions of V1 and V5. I have always used the TungSol in V1 and the LPS in V5. To my ears, Long-plate tubes work best in the phase inverter. For some reason, they seem to stay more 'open' and less compressed than using short-plate tubes in the PI.

Nice easy mod! But still not enough. Is there something else to try?

[Jay]

Ok, just cranked this baby up at Matt's house through a Bogner 4x12. WOW. Biggest difference I notice is gain usability. OD gain dropped down to 2 is still a healthy amount of gain. Overall a lot more clarity and openness. Very crisp and quick pick attack. The "sweet spot" that you usually find at 5 on these amps appears much sooner with the mod. OD volume at 3 is well saturated. More than happy with this. Pots do make a difference at gig volume. Much brighter now, even through the V30 Bogner cab. Love it, love it, love it.

glad to hear it man! Can't wait to get my build underway.

[Jay]

I would almost reverse the positions of V1 and V5. I have always used the TungSol in V1 and the LPS in V5. To my ears, Long-plate tubes work best in the phase inverter. For some reason, they seem to stay more 'open' and less compressed than using short-plate tubes in the PI.

Nice easy mod! But still not enough. Is there something else to try?

Still just for the Crunch channel?

[Jase01]

Yeah.Would I be better off using a boost? I didn't want to have to resort to pedals tho.

[Jay]

Try changing R4 to 4.7k and/or change R5 to 470k and add a 470p cap in parallel to R5.

[Jase01]

Cheers. I'll order some more parts ASAP!

[Jay]

Cheers. I'll order some more parts ASAP!

While you are at it, could you do me a favor and measure the resistances of R52, R53, R11 and R8? Trying to build an accurate clone.

[Jase01]

Cheers. I'll order some more parts ASAP!

While you are at it, could you do me a favor and measure the resistances of R52, R53, R11 and R8? Trying to build an accurate clone.

Sure no probs.
When I swap the R4 resistor do i still leave the 1uf cap in parallel? Cause I've already drilled a hole for the switch! haha

[Jase01]

R8=15k, R11=15k, R52=21k, R53=211k. I think anyway. Here's some pics that might help too..

[Jay]

Cheers. I'll order some more parts ASAP!

While you are at it, could you do me a favor and measure the resistances of R52, R53, R11 and R8? Trying to build an accurate clone.

Sure no probs.
When I swap the R4 resistor do i still leave the 1uf cap in parallel? Cause I've already drilled a hole for the switch! haha

Nice! Thanks for the pics. That helps immensely.

Yes, Leave the 1uF cap in there.

[Jay]

Ok, here once again:

In my opinion, there is no need to change a lot of the things in a 22H.

What I would do (and have done ^^):

- C2 to 4,7nF (instead of the stock 22nF - that will bring you much more clarity and less mud and fizz)
- R26 to 39k (instead of the stock 47k - that makes the amp a little brighter sounding, slope is like in Orange or Diezel, for modern Marshall use 33k)
- R42 to 56k or 68k (instead of the stock 47k - that will push the amp towards modern mesa rectifier direction, will give a little bit more punch)
- C21 to 68nF (instead of the stock 100nF - that will reduce the fizz at presence a little bit)
- Depth Mod (I prefer a 6,8nF over the recommended 4,7nF, because this will boost lower frequencies, the 22H has enough low mids)

optional:

- change all caps up to 1nF to good high voltage ceramics
- change all coupling caps and bass and middle cap to Sozos (I like them better in this amp than Orange Drops 225 or 715 Series, for Metal use Cornell Dubilier DME)
- change all cathode bypass caps (the 1uF ones) to Röderstein or mix Röderstein with Solen Fast for more bite and clarity

- swap out R9 (this will brings more clarity and reduce the woolyness in sound)
- use C10 (stock is 1nF) in series with a 220k, 470k or 680k - the higher the resistor value, the less difference will be. With only 220k the amp would sound much brighter and has more edge in sound. If this is too much, raise C20 (stock is 270pF) to 330pF
- reduce C8 to 0,68uF (less gain, clearer sound)


I don't like all these SLO Conversations or "Predator Mod" at all. They all give this amp even more gain and "boomyness". In my opinion, these are the problems. This amp has too much gain, to much mud and fizz. All my suggestions will bring more clarity, less gain, less fizz. If you don't like this, then don't do these changes!

Do one thing after another - not all at the same time. So you will see (and hear) which mod makes which difference in sound.

And take care about the high voltage. If you have no idea about, how this works, then please let do that an amp tech.

this sounds like what I'm shooting for
Is there any way I could get some part no. I've been looking & it get confusing to a rookie

Do you want something that is budget conscious, or just go all out? What kind of music do you play mostly? I know the tone of capacitors is very subjective, if people can even hear the difference. Also, would you rather get all the parts from one supplier?

[Jase01]

Cheers. I'll order some more parts ASAP!

While you are at it, could you do me a favor and measure the resistances of R52, R53, R11 and R8? Trying to build an accurate clone.

Sure no probs.
When I swap the R4 resistor do i still leave the 1uf cap in parallel? Cause I've already drilled a hole for the switch! haha

Nice! Thanks for the pics. That helps immensely.

Yes, Leave the 1uF cap in there.

Thanks, I've just changed back to passive pickups and kinda miss a bit of the gain.
I like the sound of the crunch channel, just need some extra bite. I'll try your suggestions as soon as I can.
Let me know if you need more pics or anything.

[Tortuga]

Ok, just cranked this baby up at Matt's house through a Bogner 4x12. WOW. Biggest difference I notice is gain usability. OD gain dropped down to 2 is still a healthy amount of gain. Overall a lot more clarity and openness. Very crisp and quick pick attack. The "sweet spot" that you usually find at 5 on these amps appears much sooner with the mod. OD volume at 3 is well saturated. More than happy with this. Pots do make a difference at gig volume. Much brighter now, even through the V30 Bogner cab. Love it, love it, love it.

Sahl - just so I have this clear, you're saying that the SLO mod makes more gain at lower settings? I'm wanting to know because I'd be after less gain - I barely run the preamp gain above 4 (usually closer to 3) on the OD channel as it is.

[Jase01]

Grimespace, just wondering, do you use your Bad Monkey and 250 as boosts with your JCA?

[Hipster Salad]

Ok, just cranked this baby up at Matt's house through a Bogner 4x12. WOW. Biggest difference I notice is gain usability. OD gain dropped down to 2 is still a healthy amount of gain. Overall a lot more clarity and openness. Very crisp and quick pick attack. The "sweet spot" that you usually find at 5 on these amps appears much sooner with the mod. OD volume at 3 is well saturated. More than happy with this. Pots do make a difference at gig volume. Much brighter now, even through the V30 Bogner cab. Love it, love it, love it.

Sahl - just so I have this clear, you're saying that the SLO mod makes more gain at lower settings? I'm wanting to know because I'd be after less gain - I barely run the preamp gain above 4 (usually closer to 3) on the OD channel as it is.

*Assuming I performed the SLO mod correctly and with the correct parts*, yes - that is exactly what my experience is. I normally had the OD gain at 6 when it was stock, and after the mod, was comfortable with it at 5, but I could turn it down to 3 or even 2 and was still enough to have a healthy palm mute. Also, with the OD gain dimed it did not fizz, flub out, or overly compress like it would on a stock JCA100H. I don't think it made the amp have any more gain, it just has more gain at lower settings and more usable throughout the sweep. I didn't mess with the Normal channel at all so I can't comment on if that changed or not. Again, this is assuming the mod was done correctly.

Honestly, when mine was stock, I found the OD gain at 3 to have identical characteristics to the Normal gain maxed.

[Kevin Brush]

I'd very much like to see the labels on the transformers, inside wiring for the 50/100 switch, channel LED, and depth knob, and some shots of the PCB and back panel wiring as well.

Hi Grime, I took some pics of the HDM this morning. The transformers and choke look to be the same as the JCA100H. The first pic of the guts is the half power switch and the depth mod pot. The half power switch has a black and red wire that go into the board at J13 and another set at J14. I took a picture of J13, J14 is under a cluster of wired to the left of it. Let me know if you would like any other pics.

[Hipster Salad]

I'm interested to see what value of components are on that Depth control on the HDM . . .

I see the NFB location is on the other side of the board

Interesting that the board says JET CITY 100H PLUS

Thanks for the pics!!

[kissmyace]

Ok, here once again:

In my opinion, there is no need to change a lot of the things in a 22H.

What I would do (and have done ^^):

- C2 to 4,7nF (instead of the stock 22nF - that will bring you much more clarity and less mud and fizz)
- R26 to 39k (instead of the stock 47k - that makes the amp a little brighter sounding, slope is like in Orange or Diezel, for modern Marshall use 33k)
- R42 to 56k or 68k (instead of the stock 47k - that will push the amp towards modern mesa rectifier direction, will give a little bit more punch)
- C21 to 68nF (instead of the stock 100nF - that will reduce the fizz at presence a little bit)
- Depth Mod (I prefer a 6,8nF over the recommended 4,7nF, because this will boost lower frequencies, the 22H has enough low mids)

optional:

- change all caps up to 1nF to good high voltage ceramics
- change all coupling caps and bass and middle cap to Sozos (I like them better in this amp than Orange Drops 225 or 715 Series, for Metal use Cornell Dubilier DME)
- change all cathode bypass caps (the 1uF ones) to Röderstein or mix Röderstein with Solen Fast for more bite and clarity

- swap out R9 (this will brings more clarity and reduce the woolyness in sound)
- use C10 (stock is 1nF) in series with a 220k, 470k or 680k - the higher the resistor value, the less difference will be. With only 220k the amp would sound much brighter and has more edge in sound. If this is too much, raise C20 (stock is 270pF) to 330pF
- reduce C8 to 0,68uF (less gain, clearer sound)


I don't like all these SLO Conversations or "Predator Mod" at all. They all give this amp even more gain and "boomyness". In my opinion, these are the problems. This amp has too much gain, to much mud and fizz. All my suggestions will bring more clarity, less gain, less fizz. If you don't like this, then don't do these changes!

Do one thing after another - not all at the same time. So you will see (and hear) which mod makes which difference in sound.

And take care about the high voltage. If you have no idea about, how this works, then please let do that an amp tech.

this sounds like what I'm shooting for
Is there any way I could get some part no. I've been looking & it get confusing to a rookie

Do you want something that is budget conscious, or just go all out? What kind of music do you play mostly? I know the tone of capacitors is very subjective, if people can even hear the difference. Also, would you rather get all the parts from one supplier?

I play in a more classic rock type band. One supplier would be good, and always budget conscious !!! lol

thanks !!!

[Kevin Brush]

I'm interested to see what value of components are on that Depth control on the HDM . . .

I see the NFB location is on the other side of the board

Interesting that the board says JET CITY 100H PLUS

Thanks for the pics!!

Hi Sahl, you are welcome! I am looking at the schematic and the capacitor value is .0047uF, pot is 1M, a .1uF cap going to ground, and a 39k resistor going to the 4 Ohm speaker jack if I am looking at it correctly. I am rather new to all of this. Here is a link to the schematic:

http://starin.info/Product%20Info/Jet%20City/Manuals/JCA100HDM%20-%20Schematic.pdf

[Jay]

Ok, here once again:

In my opinion, there is no need to change a lot of the things in a 22H.

What I would do (and have done ^^):

- C2 to 4,7nF (instead of the stock 22nF - that will bring you much more clarity and less mud and fizz)
- R26 to 39k (instead of the stock 47k - that makes the amp a little brighter sounding, slope is like in Orange or Diezel, for modern Marshall use 33k)
- R42 to 56k or 68k (instead of the stock 47k - that will push the amp towards modern mesa rectifier direction, will give a little bit more punch)
- C21 to 68nF (instead of the stock 100nF - that will reduce the fizz at presence a little bit)
- Depth Mod (I prefer a 6,8nF over the recommended 4,7nF, because this will boost lower frequencies, the 22H has enough low mids)

optional:

- change all caps up to 1nF to good high voltage ceramics
- change all coupling caps and bass and middle cap to Sozos (I like them better in this amp than Orange Drops 225 or 715 Series, for Metal use Cornell Dubilier DME)
- change all cathode bypass caps (the 1uF ones) to Röderstein or mix Röderstein with Solen Fast for more bite and clarity

- swap out R9 (this will brings more clarity and reduce the woolyness in sound)
- use C10 (stock is 1nF) in series with a 220k, 470k or 680k - the higher the resistor value, the less difference will be. With only 220k the amp would sound much brighter and has more edge in sound. If this is too much, raise C20 (stock is 270pF) to 330pF
- reduce C8 to 0,68uF (less gain, clearer sound)


I don't like all these SLO Conversations or "Predator Mod" at all. They all give this amp even more gain and "boomyness". In my opinion, these are the problems. This amp has too much gain, to much mud and fizz. All my suggestions will bring more clarity, less gain, less fizz. If you don't like this, then don't do these changes!

Do one thing after another - not all at the same time. So you will see (and hear) which mod makes which difference in sound.

And take care about the high voltage. If you have no idea about, how this works, then please let do that an amp tech.

this sounds like what I'm shooting for
Is there any way I could get some part no. I've been looking & it get confusing to a rookie

Do you want something that is budget conscious, or just go all out? What kind of music do you play mostly? I know the tone of capacitors is very subjective, if people can even hear the difference. Also, would you rather get all the parts from one supplier?

I play in a more classic rock type band. One supplier would be good, and always budget conscious !!! lol

thanks !!!

Alrighty. Let me see what I can come up with.

[jhall]

Too bad that my JCA 20 RC112 Sounds like warm wet doodoo. I tried to like for ever and through a ton of speakers and with different tubes. But alas even with the Bitmo mods it is a dog. I'm wondering if it's that I'm a moms basement kind of guy and can't grasp that an amp mixed into a proper recording
may actually NOT be the best bedroom sound. I wish I could like this amp but it eludes me and my feeble dialing in ability.

[Tortuga]

Grimespace, just wondering, do you use your Bad Monkey and 250 as boosts with your JCA?

No - I have them on a pedalboard with some other effects for my Church rig, being played through my Fender Pro Reverb. They're really great in that configuration. Only thing my JCA needs is a 'clean' pedal to reduce the amount of gain that the thing has

I've tried the pedals out with the amp on different settings, and the only place I found them to be of much use was when I switch on the clean mod, but it's nowhere near as good as my Fender. I'm still determined to put in a boost switch on the amp (MV limiter, or whatever you want to call it - see my discussions earlier in this thread) at some point, but it's just to jump / reduce overall volume - not affect the gain, which as I say is way to dam much as it is. And, that's me with my SG hammering out various things from rock, hard rock, early metal, 80's thrash, and everything I've got in between with the OD gain running between just under 3 to 4 on the dial. I don't know how the world got such a need for higher gain, but they can have everything from 5 to max on my amp if they need it

*Assuming I performed the SLO mod correctly and with the correct parts*, yes - that is exactly what my experience is. I normally had the OD gain at 6 when it was stock, and after the mod, was comfortable with it at 5, but I could turn it down to 3 or even 2 and was still enough to have a healthy palm mute. Also, with the OD gain dimed it did not fizz, flub out, or overly compress like it would on a stock JCA100H. I don't think it made the amp have any more gain, it just has more gain at lower settings and more usable throughout the sweep. I didn't mess with the Normal channel at all so I can't comment on if that changed or not. Again, this is assuming the mod was done correctly.

Honestly, when mine was stock, I found the OD gain at 3 to have identical characteristics to the Normal gain maxed.

Hmmmm... as much as I want to tame gain, this still piques my interest. I have noticed that the amp does tend to turn into a big, unusable, muddy mess when I get up to the upper-end of what I'll dial for gain - I wonder if it'd be worth all that work to do the mod and see how it'd do for me...

Hi Grime, I took some pics of the HDM this morning. The transformers and choke look to be the same as the JCA100H. The first pic of the guts is the half power switch and the depth mod pot. The half power switch has a black and red wire that go into the board at J13 and another set at J14. I took a picture of J13, J14 is under a cluster of wired to the left of it. Let me know if you would like any other pics.

Holy moley - this totally made my day!!! Thanks so much, Kevin! Do you mind if I take your pics and put them into a separate 100HDM documentation thread like we've done for some the other models and I'll index it at the beginning of this thread?

I haven't had a chance to look at the pics much (yet), but might come back to ask for a few more. Thanks again!

I play in a more classic rock type band. One supplier would be good, and always budget conscious !!! lol

thanks !!!

Alrighty. Let me see what I can come up with.

+1 on the classic rock thing! We need mods to help shore up the lower-gain usefulness of this amp!!! And no, I don't want to just relegate myself to using the normal channel for regular playing - that's reserved for cleaner stuff - need moderate gain capabilities throughout the entire sweep of the OD gain dial.

Jay - how's the quest for a 50 head going? We need to get a donation hat going 'round? I'm starting to put together a small personal fund for some transformers later this year...

Too bad that my JCA 20 RC112 Sounds like warm wet doodoo. I tried to like for ever and through a ton of speakers and with different tubes. But alas even with the Bitmo mods it is a dog. I'm wondering if it's that I'm a moms basement kind of guy and can't grasp that an amp mixed into a proper recording
may actually NOT be the best bedroom sound. I wish I could like this amp but it eludes me and my feeble dialing in ability.

Welcome! Never heard too much positive about the bitmo mods. Actually, I haven't heard much about them in ages - is that company still out there making this mod? Have you checked out any of Edge11's mods for the 20 platform? (see the index on page one of this thread). Can you give us some indication (examples would be helpful) of what you're really wanting to achieve?

[Kevin Brush]

Holy moley - this totally made my day!!! Thanks so much, Kevin! Do you mind if I take your pics and put them into a separate 100HDM documentation thread like we've done for some the other models and I'll index it at the beginning of this thread?

You are welcome. Feel free to do whatever you want with the pics. Let me know if you would like any other pictures.

[Jay]

[+1 on the classic rock thing! We need mods to help shore up the lower-gain usefulness of this amp!!! And no, I don't want to just relegate myself to using the normal channel for regular playing - that's reserved for cleaner stuff - need moderate gain capabilities throughout the entire sweep of the OD gain dial.

Jay - how's the quest for a 50 head going? We need to get a donation hat going 'round? I'm starting to put together a small personal fund for some transformers later this year...

Donation hat sounds great! lol Quest is going slower than I'd like, but it's coming. I'm starting to put together a 22H clone from some old SLO parts I have, so I'm still on board for JCA goodness!

As far as classic rock type sounds, Warren Haynes uses an SLO in Gov't Mule. He has a good classic tone, but I don't know what channel he uses mostly. He has a switch on his which has been called the Warren Haynes mod lol (go figure) that reduces the brightness/gain on the OD channel. To do that, put C21 on a switch for the 50/100 or on the 22, it's C6. I'll see what other things can be done to bring the gain down a bit, too.

Also, you might try changing R36 from 1M to 470k and/or R32 from 2M2 to 1M and C30 to a 4n7.

[käsebrot]