Amps

[Borderline11]

Regarding an amplifier reference book for beginers.... I purchased "The Guitar Amp Handbook" by Dave Hunter. It seems to be exactly what I need to understand the schematics and what changes affect tone.

[Borderline11]

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Borderline11 wrote:

BTW, how do the 1st 3 pre-amp tubes affect the JCA22h? Are they just gain stages that sequentially add gain or do they get used for the different channels? Correct me if I'm wrong, I believe V4 is the effects loop and V5 is the phase inverter. I figure V1 and V2 are gain stages, but I'm not sure about V3.

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I've been reading "The Guitar  Amp Handbook".  The schematics are starting to make sense and I thought I would answer my own question! Ha! The preamp tubes in the JCA22h seem to follow the same signal path as the JCA50H.

V1 - Primary Gain stage for both Crunch/Overdrive channels

V2 - 2nd Gain stage for Overdrive channel  (activated by footswitch)

V3 - Tone Stack (signal from both channels go through v3 and arrive at shared tone controls)

V4 - Effects loop

V5 - Phase inverter (hands off the signal to the power tubes)

[GRIMESPACE]

So, Edge - time to move this thread to another board? There's great stuff here in this thread - would hate to see it lost to this hideous mess of a forum 'upgrade'

The Open Jam looks like a good board. What'cha think?

[Borderline11]

Hey Grimespace, ... I thought the conversion has already happened? The gear/guitar/amp forum still shows as a forum in the menus.

Also, I appreciate all your posts! It built my confidence to see you go through the mods.

[Edge11]

I'm going to take my time deciding what forum I want to go to.
I'll keep supporting this thread regardless.
Also if you sent me a pm question before the new harmony central, it got deleated, sorry, feel free to pm me again.

[Borderline11]

Ok, I've been looking at the mods on page 1 of this thread. The examples are from the JCA50 schematic and I have a JCA22. I would like to do some of the gain mods, but the JCA22 does not have the capacitor at C28, it only has a single resistor (R5 on the JCA22, which coresponds to R42 on the JCA50) before the crunch channel volume. I'm assuming that I simply ignore the C28 changes on the JCA50 and just make changes to R5 on the JCA22.

For example, the "Simple Crunch Channel" on my JCA22 would only be replacing R5 with a 470k resistor.

BTW - I would love to see some "gut" pictures of your mods... particularly the SLO Clean/Crunch switch. I understand that we need to follow the schematics. My purpose for the pictures is to see how you arranged the wires, pots and what your solder jobs look like. I'm new at this... any pictures would be helpful.

[Edge11]

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Borderline11 wrote:

Ok, I've been looking at the mods on page 1 of this thread. The examples are from the JCA50 schematic and I have a JCA22. I would like to do some of the gain mods, but the JCA22 does not have the capacitor at C28, it only has a single resistor (R5 on the JCA22, which coresponds to R42 on the JCA50) before the crunch channel volume. I'm assuming that I simply ignore the C28 changes on the JCA50 and just make changes to R5 on the JCA22.

For example, the "Simple Crunch Channel" on my JCA22 would only be replacing R5 with a 470k resistor.

BTW - I would love to see some "gut" pictures of your mods... particularly the SLO Clean/Crunch switch. I understand that we need to follow the schematics. My purpose for the pictures is to see how you arranged the wires, pots and what your solder jobs look like. I'm new at this... any pictures would be helpful.

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I really don't think I will have the time to post gut shots any time soon in the forseable future.

[diapsalmata]

Picked up a JCA22H about a month ago, played through the stock tubes for about 24 hours or so, i couldn't help but feel that it sounded too bright and harsh. Swapped out all of the tubes for JJ's, matching set in the power amp and new 12ax7's for V1 to V5. Still feel like the amp sounds a little fizzy and bright.

Can anyone reccomend some tubes that'll give me more bottom end? Do they have a depth mod for the 22H? For the cost of this amp, i'll gladly mod the crap out of it.

[Edge11]

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diapsalmata wrote:

Picked up a JCA22H about a month ago, played through the stock tubes for about 24 hours or so, i couldn't help but feel that it sounded too bright and harsh. Swapped out all of the tubes for JJ's, matching set in the power amp and new 12ax7's for V1 to V5. Still feel like the amp sounds a little fizzy and bright.

Can anyone reccomend some tubes that'll give me more bottom end? Do they have a depth mod for the 22H? For the cost of this amp, i'll gladly mod the crap out of it.

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jjs tamed mine, and yes you can do the depth on a 22h.

[diapsalmata]

Can i get a depth mod explained in "plain english". I'm mechanically enclined, i've repaired and modified pedals, guitars, no problem with most kinds of wiring or soldering. Don't really know where to start on a depth mod.

What do i need to do the mod, and how do i do it?

[Borderline11]

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diapsalmata wrote:

Can i get a depth mod explained in "plain english". I'm mechanically enclined, i've repaired and modified pedals, guitars, no problem with most kinds of wiring or soldering. Don't really know where to start on a depth mod.

What do i need to do the mod, and how do i do it?

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Sure! The depth mod is designed to tighten up the bottom by adding a tone contol on the negitive feedback circuit.

The negitive feedback wire (in the JCA22H comming from the output board, it's blue and marked FB) feeds a little of the power from the speaker out terminal and gives power back to the phase inverter (preamp tube V5). I think what it does is provide a signal boost?  The pot and cap for the mod basically work as a tone control.

All the mods are on page one of this post. There is a picture of the depth mod components on that page. Most (not all) people are installing the pot on the rear. I'm about to do the mod on my JCA22H. I'll let you know how it goes and take a picture.

[Borderline11]

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Edge11 wrote:

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diapsalmata wrote:

Picked up a JCA22H about a month ago, played through the stock tubes for about 24 hours or so, i couldn't help but feel that it sounded too bright and harsh. Swapped out all of the tubes for JJ's, matching set in the power amp and new 12ax7's for V1 to V5. Still feel like the amp sounds a little fizzy and bright.

Can anyone reccomend some tubes that'll give me more bottom end? Do they have a depth mod for the 22H? For the cost of this amp, i'll gladly mod the crap out of it.

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jjs tamed mine, and yes you can do the depth on a 22h.

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JJs firmed mine up too, that seems to be the standard for tube replacement.

However, I also tried the Solvtec 12AX7LPS tubes in position 1 and 2  and heard a dramatic all around improvement over the JJs. They kept the same bottom end as the JJs, but gave better definition and tone all around. They made a big difference to the clean sound as well. I tried the EH 12AX7s, but they did not respond as well for me. I'm using an Ibanez s420 with DiMarzio Joe (neck), and Mo' Joe (bridge).

[Borderline11]

I made an amp holder to use during mods. This way, I don't have to worry about the tubes or it being unbalanced while I'm working on it.

Built out of 2x8, with pieces of 3/4 plywood nailed to the sides. The gray carpet is a 4x4 sample piece from Home Deopt. I cut it with scissors and glued it to the plywood. The 2x8 is longer than the JCA22 because I may own full size heads at some point. If I'm working on a larger amp, I can just unscrew and reposition the right side. Total cost 6$ (I already had the ply scraps and wood glue).

The metal tray is a magnetic tray. It's great for keeping screws from getting lost!

[Edge11]

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Borderline11 wrote:

I made an amp holder to use during mods. This way, I don't have to worry about the tubes or it being unbalanced while I'm working on it.

Built out of 2x8, with pieces of 3/4 plywood nailed to the sides. The gray carpet is a 4x4 sample piece from Home Deopt. I cut it with scissors and glued it to the plywood. The 2x8 is longer than the JCA22 because I may own full size heads at some point. If I'm working on a larger amp, I can just unscrew and reposition the right side. Total cost 6$ (I already had the ply scraps and wood glue).

The metal tray is a magnetic tray. It's great for keeping screws from getting lost!

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Thats a pretty sweet set up!

[diapsalmata]

Any pics would be great! Even a small walkthrough.
I'm not the greatest at interpreting wiring diagrams, lol.

[sahlomonic]

Agreed. If I/we could get a walkthrough for a front mounted depth mod, that would be great!

[Edge11]

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sahlomonic wrote:
Agreed. If I/we could get a walkthrough for a front mounted depth mod, that would be great!

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Do backmounted, less of a long cable run. It's litteraly just this guy. I believe in you. you can litterally just cut the nfb cable in 2 and plug this into the middle.

[Borderline11]

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diapsalmata wrote:
Any pics would be great! Even a small walkthrough.
I'm not the greatest at interpreting wiring diagrams, lol.

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I was right there with you a couple of weeks ago. Since then, I bought "Guitar Amplifier Handbook" by Dave Hunter (http://www.amazon.com/Guitar-Amplifier-Handbook-Understanding-Amplifiers/dp/087930863X/ref=sr_1_1?s=...) . It has greatly helped me to understand the amp stages and schematics. You can also do an internet seach on wiring diagrams to find description of the symbols.

I'll be taking some pictures as I do the mods, but Edge is right to encourage us to learn it.

[Borderline11]

Could someone recomend free software for making an amp schematic? I received the JCA22H service manual from Jet City and would like to add the specific values to the components so it will look like the JCA50 on post 1.

Thanks!

[Edge11]

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Borderline11 wrote:

Could someone recomend free software for making an amp schematic? I received the JCA22H service manual from Jet City and would like to add the specific values to the components so it will look like the JCA50 on post 1.

Thanks!

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Don't really knwo any since i work in photoshop or illustrator.
If all else fails use a pen!