Guitar Gear Forum

Is this still relevant for biasing a Jca22h? https://youtu.be/V4T83PgEIhc

I measured from ground to the end of the red wire and it was 376. But, when trying to measure mA between the red wire and either the blue or brown wire, I'm not getting a reading.

It should be. It's the same power amp design. I'm not sure if they changed the wiring color code though. Shoot Doug an email.

Does anyone know where to get the metal grill faceplates?

Used to be able to get them direct from JCA, but I'm guessing that avenue is closed for now. I made my own using expanded metal from Home Depot and created a frame for it that I could attach with velcro so I didn't have to break out the screwdriver whenever I wanted access to the tubes.

Asking again. Does the depth mod use a 1uF or 0.1uF cap? In this thread it says 0.1uF, but this post says 1uf. https://toboy-diy.blogspot.com/2013/10/ ... h-mod.html

.0047uf and a 1M pot.

Gainzilla wrote:.0047uf and a 1M pot.

Thanks Bryce. I'm seeing something about using an additional cap to reduce noise?

The 1uF cap there is to block any DC that might make its way onto the pot and make it scratchy when turning it. 0.1uF/100n should be fine though.

I changed mine to a .0068uF cap and 1M pot. That is a slightly lower frequency to bring the deep chugs. That is the value the 5150 heads use.

Revisiting the schematic and the picture of the mod posted, you most likely want the 100n cap on the other side of the pot, i.e., going to the NFB connection on the board, not from the wire from the speaker jack/OT secondary. This is to block the DC from the tail of the PI. This is much the same as why the presence control on old Marshalls is scratchy, as the old configuration would have DC on the pot. Most amps now use a DC blocked presence configuration but that comes as the expense of useful range on the control.

You might want to play around with the value of the depth cap too. Bellow is a graph of the tuning to give you an idea of how to change the range.
Increasing the cap value moves the boost corner frequency lower. Going too far will make the amp thin by cutting too much low mid to give a tits n ass tone with nothing in the middle
It's pretty easy and quick to tack a few caps in parallel to get the ball park right. Remember, capacitance adds in parallel 3n3//3n3 = 6n6.



Finally, for the same corner frequency, a greater resistance and lower capacitance will sound bassier. e.g., 4n7//1M and 47n//100k have the same corner frequency, but the impedance presented to the PI will be different. This is why you never really see larger caps and smaller pots, well that and smaller caps are cheaper

I installed the Epic Tone Cap'n Crunch mod in my JCA22H tonight. It sounds killer! Gives 2 different voicings on the crunch channel via a toggle switch. Plexi type and 800 type. I can't say enough about Bryce at Epic Tone. He's been super cool and extremely helpful! Answering all of my annoying email questions.

I installed Bryce's Silver Hammer mod on my JCA22H tonight. So now with the Cap'n Crunch on the crunch channel and the Silver Hammer on the OD channel, this amp is a Marshall voiced beast! Thanks again to Bryce from Epic Tone for these amazing mods. With all of the parts and instructions provided, it couldn't have been any easier to perform.

I'm installing the depth mod and the negative feedback mod in my JCA22H, and I have a few questions.

Should I go from R42 to the Negative feedback pot, to the depth pot, then to the FB location on the PCB? Or should I go from R42 to the depth pot first, then the negative feedback pot, then to the FB location on the PCB?

ledvedder wrote:

Gainzilla wrote:.0047uf and a 1M pot.

Thanks Bryce. I'm seeing something about using an additional cap to reduce noise?

I wouldnt bother trying to reduce the DC on the pot. Its not like you are moving the pot mid song.

I know its the sum of all parts, but use your ears and don't take the .0047 cap as gospel. I find its too much and smears the sound a bit. I use a .0033 ceramic cap. Ceramic is very important tonally here. Of course the depth circuit is important part of getting a big sound, so experiment here. You can add resistors here to really focus the frequencies.

Also, after this pandemic clear, I know we dont live that far away.


Another big also, I use NOS Russian 6P14P power tubes (I bought 3 quads from someone in Moldovia for like $35 a quad. They all tested within 2mA of each other). To me they sound a LOT better than JJ or Chinese EL84's. I even prefer them over some of the old NOS versions as well. With the power section mods I did to my JCA20, I'm still on my first pair of power tubes going on many years....crazy to think I started tinkering with my JCA20 almost 10 years ago.

psychodave wrote:

ledvedder wrote:

Gainzilla wrote:.0047uf and a 1M pot.

Thanks Bryce. I'm seeing something about using an additional cap to reduce noise?

I wouldnt bother trying to reduce the DC on the pot. Its not like you are moving the pot mid song.

I know its the sum of all parts, but use your ears and don't take the .0047 cap as gospel. I find its too much and smears the sound a bit. I use a .0033 ceramic cap. Ceramic is very important tonally here. Of course the depth circuit is important part of getting a big sound, so experiment here. You can add resistors here to really focus the frequencies.

Also, after this pandemic clear, I know we dont live that far away.


Another big also, I use NOS Russian 6P14P power tubes (I bought 3 quads from someone in Moldovia for like $35 a quad. They all tested within 2mA of each other). To me they sound a LOT better than JJ or Chinese EL84's. I even prefer them over some of the old NOS versions as well. With the power section mods I did to my JCA20, I'm still on my first pair of power tubes going on many years....crazy to think I started tinkering with my JCA20 almost 10 years ago.

Yeah, I'm thinking about trying a lower value cap for the depth mod. The 47 seems a bit too much. After a quarter of the way on the pot, it gets too mushy.

Yeah man, we do live pretty close to each other!

I have a pair of 6P14P tubes on the way from ebay!

Did you see my question above about the NFB and depth mods?

I finished up the Epic Tones mods on my JCA22H this weekend.

Depth mod - I like this one, but it's really only useful up to about 9 o'clock on the knob. After that, it gets boomy and mushy. I may try replacing the 0.0047 cap with a 0.0033 cap.

Negative feedback knob - Again, this is only useful to about 9 o'clock on the knob. After that, it gets to high end and raspy, but does get louder.

Front panel channel switch - No description needed here.

High cut knob - This is very subtle, but I can hear some smoothing out of the high end frequencies when adjusting the knob.

Saturation switch - I'm not a big fan of this. It drops the volume, which I'd expect. But it's a pretty significant drop. It also adds more saturation and gain than I'd ever use, and increases the bass a bit too much. I'm considering changing some of these components, but have to learn more about which ones to adjust.

Presence mod - This adds a switch to go from the stock presence value to a different value. The new value makes the knob much more useful in its sweep. It doesn't introduce that sudden high end spike at about 8 on the stock value.

Overall, I'm extremely happy with these mods. My favorites being the main mods (Cap'n Crunch and Silver Hammer), which revoiced both channels. Cap'n Crunch gave the crunch channel 2 modes (plexi-ish and jcm800-ish), and the Silver Hammer turned the overdrive channel into and 80s hair metal machine.

Again, thanks to Bryce at Epic Tones for all of his help and recommendations. Super nice guy!

ledvedder wrote:I finished up the Epic Tones mods on my JCA22H this weekend.

Depth mod - I like this one, but it's really only useful up to about 9 o'clock on the knob. After that, it gets boomy and mushy. I may try replacing the 0.0047 cap with a 0.0033 cap.

Negative feedback knob - Again, this is only useful to about 9 o'clock on the knob. After that, it gets to high end and raspy, but does get louder.

Front panel channel switch - No description needed here.

High cut knob - This is very subtle, but I can hear some smoothing out of the high end frequencies when adjusting the knob.

Saturation switch - I'm not a big fan of this. It drops the volume, which I'd expect. But it's a pretty significant drop. It also adds more saturation and gain than I'd ever use, and increases the bass a bit too much. I'm considering changing some of these components, but have to learn more about which ones to adjust.

Presence mod - This adds a switch to go from the stock presence value to a different value. The new value makes the knob much more useful in its sweep. It doesn't introduce that sudden high end spike at about 8 on the stock value.

Overall, I'm extremely happy with these mods. My favorites being the main mods (Cap'n Crunch and Silver Hammer), which revoiced both channels. Cap'n Crunch gave the crunch channel 2 modes (plexi-ish and jcm800-ish), and the Silver Hammer turned the overdrive channel into and 80s hair metal machine.

Again, thanks to Bryce at Epic Tones for all of his help and recommendations. Super nice guy!

I hate to say it, but lots of the final sound is the sum of all of the parts.

Just guessing by what you are tellign us... here are some thoughts.

Depth... try .0022uf ceramic cap. Clearly .0047 is way too much.

NFB... not sure what values you are using? You could likely change to a lower resistor which will make the pot more useful. Again, I dont know the mods you are using and how the pot is setup.

High Cut. Not sure about this mod either. There are several versions... some for the preamp, so in the power section (I think Vox has one in the power section that lots of people like when using EL84's).

Sat switch. Again, it could be the location used. If its like Friedman amps, it will be dark and mushy, which is why lots of people dont like using the sat switch. On my amps clip, I go down to 5 volt zeners and my amp stays tight and full. Note that the diodes "clip" the signal and you will get a normal volume drop. When modding my amp this is all taken into consideration since you can now turn up the amps which will work the power section differently and change the sound. Remember the amp is using EL84's which sound great being pushed, but could over saturate the sound making it a bit mushy.

Presence... sounds like a simple switch changing resistors. Of course this will likely change how the NFB reacts as well.

Can somebody help me out here? I'm trying to bias my 22H. B+ to ground is reading 356V. This would mean around 23mA for bias. Well, when reading from B+ to both the brown and green wires, it's reading 0.4mA. If I turn the bias adjustment wheel, it goes from 0.0 to 0.7. Something is wrong here.

Is the tube good? Is the amp off standby? I responded on RT as well.

psychodave wrote:Is the tube good? Is the amp off standby? I responded on RT as well.

Yep, the tubes are good, and it's off standby.

What does everyone use to label any new switches or knobs that you've added from mods?

ledvedder wrote:What does everyone use to label any new switches or knobs that you've added from mods?

You can get letter decals at your local arts and crafts store like Michael's etc... Or just buy label sheets that can be printed on. Or use a silver marker pen on a black chassis.

ledvedder wrote:Can somebody help me out here? I'm trying to bias my 22H. B+ to ground is reading 356V. This would mean around 23mA for bias. Well, when reading from B+ to both the brown and green wires, it's reading 0.4mA. If I turn the bias adjustment wheel, it goes from 0.0 to 0.7. Something is wrong here.

Just an update. I got a new multimeter and the tubes are testing correctly now. Each are at 23.6 and 21.4 mA.

Hi all JCA owners! I started off at HC reading and rereading the Edge11 posts. (That guy knows his stuff!). I've also read this thread twice and thought it was far past time to post. I know I'm very late to the JCA game. I purchased mine on a stupid deal on GC right before they were phased out. Love this thing but have some questions regarding the mods.

1 - The depth mod. Am I understanding this mod will only be connected to one of the speaker outs? Seems more usable if it applied to all of the speaker outs. Please correct me if I'm wrong.
2 - I've read several different methods of taming the 5150 type "fizz" and would like to know the most effective method to tame this a bit.

There are several different mods I plan to do but they're well laid out due to you guys really explaining them well.

All in all this is a fantastic board and would like to thank all of the great contributions of the members.

ibzguy wrote:Hi all JCA owners! I started off at HC reading and rereading the Edge11 posts. (That guy knows his stuff!). I've also read this thread twice and thought it was far past time to post. I know I'm very late to the JCA game. I purchased mine on a stupid deal on GC right before they were phased out. Love this thing but have some questions regarding the mods.

1 - The depth mod. Am I understanding this mod will only be connected to one of the speaker outs? Seems more usable if it applied to all of the speaker outs. Please correct me if I'm wrong.
2 - I've read several different methods of taming the 5150 type "fizz" and would like to know the most effective method to tame this a bit.

There are several different mods I plan to do but they're well laid out due to you guys really explaining them well.

All in all this is a fantastic board and would like to thank all of the great contributions of the members.

Welcome! I'd recommend talking to Bryce (he's Gainzilla here). He knows his stuff, and has helped me out a ton with mods to my JCA22. He also offers a bunch of pre-packaged mods with great instructions.