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That's an interesting set up, and a good solution to the problem of projection a JazzKat might have in a big room.
Do you think that JazzKat amps offer any special challenges to an average amp tech because of their construction or availability of replacement parts?
I still remember some techs refused to work on Polytone amps years ago, due to their comparatively unusual construction back then.
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10-05-2018 03:35 PM
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Mine has never needed service. There’s an earlier post in this thread from someone who managed to diagnose and replace a bad capacitor, so it must not be that difficult to work on their circuit boards. I’ve never been able to find a schematic, but I’ve peeked inside the cabinet. I have enough electronics knowledge to figure out where each of the functions in my block diagram are located and component values seem to be marked on the circuit board. I’d think any decent tech could deal with them. Replacing resistors and capacitors shouldn’t be too difficult. Replacing pots and input connectors would be tricky since they appear to be soldered to the board. The pots seem to be good quality though — mine has never gone scratchy.
Originally Posted by sgcim
There’s a Phatkat on ebay right now, where they added a tube to the preamp with a 12 inch speaker. It would be interesting to do the stereo thing with that and a regular Jazzkat.
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Here are some photos of the Jazzkat guts. First the back panel.
Ignore that white zip cord — I added that so I could connect an outboard tweeter. The power supply is at the bottom and includes a toroidal transformer helps keep the hum and weight down. The output stage of the power amp is center left, using the back panel as a heat sink. (Touch that spot after a gig and you can tell it’s working!) The effects loop and the line out circuits are center right. The hole on top is for the speaker port, not for cooling.
Here’s the control panel looking from the back side. The top of the photo is the top of the amp. I count nine plies of wood!
The top board has the preamp for channel 1 and the master volume. The lower board has the preamp for channel 2 and the digital reverb (which I suspect is the daughter board soldered to the main board). With better photos you could easily read the component values and trace the circuits.Last edited by KirkP; 10-05-2018 at 11:01 PM.
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Yes this is a zombie thread, but since I started it I thought I’d bring it back to life. Here’s a JazzKat group photo I had an opportunity to take yesterday.
The tweed I bought new in 2006.
The BluesKat was an ebay find I grabbed as a backup and to have the option to connect in stereo. Despite the name, the electronics are the same as the other two amps.
The black JazzKat was another ebay find I recently bought for a friend.
They all have different speakers, so I’ve lined them up to compare the tone. One has an Eminence Beta-8A one has a discontinued Celestion TN0820 and the other a discontinued Eminence with a whizzer cone. They sound quite different from another when EQ is set flat. The TN0820 is much lower in volume. But if I carefully tweak the EQ I can bring them fairly close to each other. When my friend stops by to pick his amp up I’ll ask him to play all three blindfolded and see if I can adjust the EQ such that he can’t distinguish between them.Last edited by KirkP; 11-22-2019 at 09:02 PM.
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I was going through my desk this afternoon (
) and came across the papers for my JazzKat, bought new from Legato Guitars on October 4, 2006. I paid $725 for the amp, and $25 S&H.
What a bargain!
And thanks to Greentone's post #23, above, I can now retire my quest for a Polytone. Woo-hoo! 
Last edited by citizenk74; 11-22-2019 at 08:44 PM. Reason: Additional thought (hey I don't have that many, I need to jot 'em down before they escape!
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As I’m tweaking the EQ to try to make one speaker sound more like another, it seems like the most critical knob is the mid control. A bit of bass and treble adjustment is required too, but a very small adjustment to the mid control can dramatically change the voicing, almost like swapping speakers.
For the 13 years I’ve had the amp I’ve pretty much focused on the treble and bass controls, usually leaving the mids flat. In the future when adjusting EQ on that amp I’m going to start with the mids.
I think JazzKat has Baxandall-type tone controls where the mid position is flattest, as in a hi-fi amp, PA , acoustic guitar amp, or Polytone. Fender tone controls are a much different design, so I approach them differently.
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I found one for about 200€, forgotten in a store. What a useful little piece of kit. I am using both channels, one as an acoustic amp, the other with a Jr. Barnyard in front for electric sound. I still have lots to learn about it, but I’m happy it’s home with me.
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I used both channels on mine, as well. Ch 1 for guitar; Ch 2 for a mic for rooms where PA was un-available or impractical. Originally Posted by radiofm74
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Channel 2 is voiced much differently than channel 1. I’ve never been able to get a tone I like from channel 2 whether with electric guitar, acoustic guitar (with active pickup) or microphone. I’ve used channel 2 for announcements or rehearsing with a vocalist, but I’d avoid doing a whole gig with it. I’ve tried to EQ it to a pleasing neutral tone and I just can’t get there.
For acoustic guitar with an active pickup or mic, I prefer the tone of channel 1, but I use an external tweeter (the discontinued Hendrickson Tweety) to extend the highs.
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I have an original, with side handle only. Reverb was making springy noises and had an 'amptech' try to fix it. But now there is still some reverb, but the sound comes and goes as I play so i'm going to try again. Anyone have a schematic for the original jazzkats?
David
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I’ve tried searching for schematics, but I think they held them closely, and they are now defunct. I’ve opened mine up and figured out more or less where the different functions were. If the reverb circuit is creating problems it would probably be easy for a tech to bypass it, but it think it would tricky to diagnose and fix. If my reverb fails I’ll just use a pedal. Originally Posted by jazzdog
You might try some diagnostics for clues though. Does the reverb have the same problem in both channels? It it the same for all reverb settings? Are there any problems when you switch it off (center position)? Does the amp have any other problems that might be related?
My two original Jazzkats are still going strong, and I helped a friend snipe one one on ebay. The only reverb issue is that thump that it makes right after powering up, but if you cut the volume when powering up you don’t hear it.
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I have a Tomkat that seems to have developed the hum issue. It’s definitely related to the effects because the volume of the hum gets louder when I turn the effects volume up. It still is never completely Gone when the effects volume is at 0. The hum is present on both channels and starts usually after the amp is on for a few minutes.
Anyone have any advice for removing the effects completely from the amp or repairing it? I’m ok with eliminating the effects circuit as I don’t use it.
thanks
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hope you get an answer to the hum issue.I been offered a Twin Kat for 400.00 being i sing and play any one have thoughts on that model?
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Kinda funny that John P was the endorser, but I've seen him three times and never with a JK. I'm not dissing the amp, just thought that was odd.
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Because of the current small gigs (solo)i am trying to find what everybody wants i guess best sound for the money.lol audiences may not b aware but subconsciously if the sound is pleasing even over clinging mugs glasses and chit chat.I may get called back to play or they see where im at and showup.Thats my fantasy
Bose maybe out unless do end up selling my lp
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I did not resolve this issue. Ended up getting a Boss Katana mk2 100w. With some tweaking of the tone studio software I can get some really pleasing jazz tones. Originally Posted by EarlBrother
The Jazzkat amp seems pretty much un-repairable.
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I've used TomKat for many years until... It become unpredictable. I had hum issue years back when JazzKat company was able to send me replacement for effect loop. It was (is) cheap chinese(?) box which deliveres several of effects. I never used anything except small reverb. But then this second box also broke - in a manner that you can play and at some random point (when it "worms up") it starts making very loud noises. Sth which is ofc not acceptable live... so my TomKat is "backup" to play at home from time to time.
As this is for sure effect circut should be possible to eliminate this out of the amp - I would also pay for this if someone will find a method
This is very nice amp, preamp tube, light...
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I have an early tweed with a whizzer cone. Anyone know if switching out the speaker with a beta 8a would make a noticable improvement?
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I’m 2-1/2 years later answering this, but I replaced the whizzer with a Beta 8A and like the tone better. As I recall I found it warmer and cleaner. Whizzers compromise fidelity to extend the trebles. The ceramic magnet adds two or three pounds though. If you’ve already made the change I wonder how you like it. Originally Posted by TheGrandWazoo
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I did switch to the Beta 8a. Solved the problem but added a lot of weight. Sounded better too. I eventually just got a Bud 6 soon after though.
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Purchased mine around 2008 from Bill Fender at Legato Guitars. He recommended setting everything flat for a traditional jazz tone. I’ve been very happy with mine and still have it.
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I wish I’d noticed this post earlier. Years ago I opened up my Jazzkat to look at the layout of the circuit board. As I recall the effect chip was on a separate small circuit board. I don’t think it would be difficult for a person familiar with electronics to find the output and input of that board to bypass it. I wonder if that would be necessary though. Seems like turning the effects level all the way down would eliminate the noise. Of course, then you’d need an outboard effect pedal, which could either be put ahead of the amp or in the effects loop. That’s what I plan to do if mind fails, but fortunately it’s been reliable. Originally Posted by asedas
I've used TomKat for many years until... It become unpredictable. I had hum issue years back when JazzKat company was able to send me replacement for effect loop. It was (is) cheap chinese(?) box which deliveres several of effects. I never used anything except small reverb. But then this second box also broke - in a manner that you can play and at some random point (when it "worms up") it starts making very loud noises. Sth which is ofc not acceptable live... so my TomKat is "backup" to play at home from time to time.
As this is for sure effect circut should be possible to eliminate this out of the amp - I would also pay for this if someone will find a method This is very nice amp, preamp tube, light...Last edited by KirkP; 09-20-2024 at 04:07 PM.
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I had pretty much the same symptoms befall my own TomKat model. Took it to my very reliable local tech guy a few months ago, and he couldn't repair it. Originally Posted by jmccanna
He did point out, however, that the rest of the amp worked just fine and to simply stay off the effects section. Oh, well... There's always the effects loop.
My tech guy enjoys the challenge of fixing stuff and is quite willing to put in the time if he feels he's getting somewhere. I'm going to send your suggestion to him and see how he feels about a second visit to his bench. Thanks!
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I had the jazzkat 8 for a longest time and ended up selling it to get a Fender Super Champ XD. I played through a fender princeton for the first time but was too broke to afford one and the XD was the closest thing. I didn’t like the ports and closed back design of the jazzkat when I realized that the sound projection was very directional. From that day one, I used amps with open back cabinets during the rest of my career.
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