Boss Katana Amp - Inside View

Started by Elantric, October 28, 2016, 01:56:02 AM

Previous topic - Next topic

0 Members and 2 Guests are viewing this topic.

dazco

Quote from: KeldAmpworks on June 01, 2018, 08:23:29 AM
The power scaling isn't power scaling in the traditional sense. It's a stepped master volume. I scoped the input connection to the power chip and the level going into the power amp changes proportionally as you change the power scaling switch.


Post from 6 months ago and i just saw this. But i have been saying this from day one....the power switch is NOT power scaling or attenuation of the power amp etc. It's nothing more than signal attenuation, same as a master volume but instead of a pot it's a stepped 3 position switch. So it's like having a second master who's only real function is to give the master a less sensitive taper when you aren't playing real loud. Well, maybe one other function....a marketing ply for boss to make customers feel it's got some sort of power attenuator. I think it's very obvious from the fact the tone doesn't change at all from one setting to the next if you change the setting then adjust the master to the same volume level. Anyone who hears a difference in tone is IMO living in placebo city. And if u have ever used a power attenuator you'd know. The effect is not subtle. If anyone made a attenuator to use with a tube amp and the tonal difference was like this one, they'd be out of business faster than Malmsteen on crack.

admin

#26


Ryan attempts to repair the katana 50 that he fried, will he be successful? NO SPOILERS! GIVE ME THOSE CLICKS!

Vguitar forum post about this part. https://www.vguitarforums.com/smf/index.php?topic=19475.msg181632#msg181632

Amazon link to the soldering iron, because why not?

FX-888D KIT version with CHP170 cutter

https://www.amazon.com/gp/product/B00AWUFVY8/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=B00AWUFVY8&linkCode=as2&tag=sixtycyclehum-20&linkId=93fe403d7c0fa730ef13bef980408b95


Elantric

#27
QuoteDenzil D'Cruz
3 hours ago
Ryan, the best way to replace a multi-pin chip like this is to cut the legs off the chip from the component side of the PCB ensuring you leave enough of the pin in the circuit board that you can grasp it with a pair of tweezers whilst heating the solder pad from beneath. You should be able to easily remove each leg remanent this way then use you solder sucker to clean up the hole, you might need some solder wick which is resin impregnated copper braid which will give you nice, clean PCB holes ready to accept the new chip.
Also, do not be tempted to remount the heatsink with only one screw - Boss have fitted two for good reasons, also get some heatsink compound to smear between the chip / heatsink interface to aid heat transfer.   Good luck!

Some comments  -
without prior experience with Lead FREE Solder, This is NOT a repair normal folks pursue - without prior experience ( spend a few hours learning to desolder / solder with high temp lead free solder on an old discarded PCB Board  before attempting this type "dead power amp " Katana repair)
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1281311/
1) Consumer electronics built since 2006 employ Lead Free Solder which requires special high temp soldering tools and skills  -  _ when replacing a dead  TDA7293 Power amp IC - it works best to use side cutters and cut ALL the pins directly under the IC chip housing  - then remove each pin separately from the PCB board  - one at a time  using a lot of flux and special dilute  lead free solder ( to get things  flowing ) and use a higher temperature soldering iron with an appropriate tinned soldering tip.
https://forum.allaboutcircuits.com/threads/desoldering-lead-free-solder.109784/
https://pdfs.semanticscholar.org/268a/b371b20b9bf08edddd1392172f3dbedd60fd.pdf

At his point I would join VGuitarforums  - and I will try to connect you to Boss US Service



DIY Repair Tools area
https://www.vguitarforums.com/smf/index.php?board=21.0







bowtomecha

Quote from: dazco on December 28, 2018, 10:32:39 PM
Post from 6 months ago and i just saw this. But i have been saying this from day one....the power switch is NOT power scaling or attenuation of the power amp etc. It's nothing more than signal attenuation, same as a master volume but instead of a pot it's a stepped 3 position switch. So it's like having a second master who's only real function is to give the master a less sensitive taper when you aren't playing real loud. Well, maybe one other function....a marketing ply for boss to make customers feel it's got some sort of power attenuator. I think it's very obvious from the fact the tone doesn't change at all from one setting to the next if you change the setting then adjust the master to the same volume level. Anyone who hears a difference in tone is IMO living in placebo city. And if u have ever used a power attenuator you'd know. The effect is not subtle. If anyone made a attenuator to use with a tube amp and the tonal difference was like this one, they'd be out of business faster than Malmsteen on crack.

I'm thinking it's a simple job to limit the 100 setting on the kat100 to 50 in this case, probably by using a resistor right? I could always turn things down on the master but I like the idea of not having the huge jump in volume if the wattage knob isn't turned from 25 to 100. I almost never need the 100 setting on.

Vintenar

I don't suggest running this amp near or below 4 ohm's it will get ruined. I know because I accidentally ruined the transformer by plugging it into the 4-ohm input on the Plug n Play jack. If you update the transformer it might possible do the 4 ohm's but that is hard to say.

vtgearhead

Quote from: Vintenar on October 14, 2019, 05:33:09 PM
I don't suggest running this amp near or below 4 ohm's it will get ruined. I know because I accidentally ruined the transformer by plugging it into the 4-ohm input on the Plug n Play jack. If you update the transformer it might possible do the 4 ohm's but that is hard to say.

Transformer is the least of it.  The power amplifier IC is not able to source enough current and will destroy itself in a hurry trying to do so.

admin

Quote from: vtgearhead on October 15, 2019, 06:38:19 AM
Transformer is the least of it.  The power amplifier IC is not able to source enough current and will destroy itself in a hurry trying to do so.

Agreed

Review the Power Amp employed on all Katanas

Katana Class AB power Amp ic
Used in all Katana's

http://www.st.com/en/audio-ics/tda7293.html

https://www.ebay.com/i/162779349462

Vintenar

Quote from: admin on December 28, 2018, 12:45:31 PM


I fried mine twice once not putting the jack all the way into the speaker, and the second time I put into the 4 ohm input on the cabinet on accident which killed the transformer. Fixed it two times at Marshall's music in Lansing, Mi, and was going to sell it afterward because I couldn't get anything that sounded remotely close to my Hughes and Kettner Coreblade, and Switchblade but I'm glad now that no one bought it, because I finally got a really close approximate sound to my H&K amps. It only took me 28 backups in the Katana software lol.