Katana 4 ohm mod

Started by alancarl, April 13, 2021, 07:45:41 AM

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alancarl

Hi Everybody,
     Does anybody have any ideas of a MKI Katana 100 head power amp mod (module replacement)that would allow for running the amp at a 4 ohm load?
I am wanting to take my amp head to gigs that have say a back line twin that I would just patch into the speakers which are generally two 8 ohm 12" speakers in parallel which create a 4 ohm load and most likely smoke from the stock Katana head:-0
Any ideas would be greatly appreciated!
Thanks
Al

philjynx

#1
Something like that in series with the speaker?Caveat, this isn't a recommendation, it's a question waiting for an answer!
So it wouldn't be a mod to your Katana, it would be somewhere in your speaker line (wasting half your power too I imagine).

gumtown

The 4 ohm resistor in series with the speaker will work, but 50 watts of your 100 watt output will dissappear in heat.
Free "GR-55 FloorBoard" editor software from https://sourceforge.net/projects/grfloorboard/

alancarl

Thanks Phil and Colin for sharing your thoughts.
I don't need the full 100 watts but I probably would find that with 50 watts I needed to go 'one better' like up to 11 so oh well:-)
With the mammoth heat sinked resistor I would actually not want to introduce that much non-inductive series DC resistance in the speaker circuit as it would change things sonically no doubt. ???

Now I did read the data sheet of the ST TDA7293
https://www.st.com/resource/en/datasheet/tda7293.pdf
and I noticed that the factory spec states that the high current opamp can operate at 8 or 4 Ohms.
I strongly suggest for everybody to DON'T TRY THIS AT HOME!!!
Roland has been using this opamp for years and they must have a reason for sticking to 8-ohms as the minimum load impedance.
My plan is to investigate the Katana power amp module and setup a testing rig to monitor currents and temperatures when placed under a greater load.
Hopefully this won't result in smoke:-0
Any thoughts or ideas would still be great.
Thanks Steve and everybody for maintaining this terrific information resource for the tweak head community of guitar players etc worldwide!
-AL

admin

#4
I believe Boss states 8 ohm minimum because they did not provide the power supply and heat sink requirements (which raises cost) to operate at 4 ohms

Review that data sheet
https://www.st.com/resource/en/datasheet/tda7293.pdf
But when things blow on Katana , 90% of time it's not the
ST TDA7293 Power Anp IC, it's the power supply

And pay attention to the basics

Never allow either speaker lead wire to touch each other or any part of chassis ground

= instant dead kit.

admin

#5
If you own a Katana 100 or 50 and find it too loud for your needs

Swap stock speaker for a 16 ohm speaker

Cuts wattage , amp runs at half power all the time.

If you must use Load Resisters , get the noninductive type from Parts Express

https://www.parts-express.com/4-Ohm-100W-Non-Inductive-Dummy-Load-Resistor-019-015


alancarl

Thanks Steve,
      what I want to do is to take my Katana 100 head to a gig and plug it in to the Fender Twin's speakers which stock would be 2 8 ohm speakers in parallel resulting in 4 ohms ...less to carry for sure but I don't want to fry the Katana 100 power amp!
-Al

admin

#7
Quote from: alancarl on April 15, 2021, 10:16:04 AM
Thanks Steve,
      what I want to do is to take my Katana 100 head to a gig and plug it in to the Fender Twin's speakers which stock would be 2 8 ohm speakers in parallel resulting in 4 ohms ...less to carry for sure but I don't want to fry the Katana 100 power amp!
-Al

I would bring my own speaker cable with fast-on  clips and tie into one 8 ohm 12" speaker on Fender Twin-just avoid playing loud through one 12" speaker in a Fender Twin

philjynx

Quote from: admin on April 15, 2021, 10:31:11 AM
I would bring my own speaker cable with fast-on  clips and tie into one 8 ohm 12" speaker on Fender Twin-just avoid playing loud through one 12" speaker in a Fender Twin
You'd still need to disconnect one of the speakers or they'd still be in parallel wouldn't they?

admin

#9
Quote from: philjynx on April 15, 2021, 10:33:56 AM
You'd still need to disconnect one of the speakers or they'd still be in parallel wouldn't they?

Absolutely must connect to only one speaker

Bring pliers to temporarily remove the stock Fender speaker wires from one speaker

And remember to restore original connections when you leave the stage

But might advise to find a small 12"speaker cab for katana head

Myself I have swapped katana MK2 head chassis into an older katana 100 cab as blown dead Katana 100 amps are often located cheap *local craigslist)


alancarl

Sure but I want to run the Katana 100 at 4 ohms... if I won't destroy it...
its a quicker connect to pull the speaker plug out of the twin and plug it into the Katana.
It's a club gig fwiw:-)
I got this idea from my friend Steve Kahn as he used to use a Pearce G2R head and he carried around a few 1/4" speaker cables,  adapters, and couplers to be able to plug into the speakers from most any backline combo.
Thanks guys!
Al

admin

#11
Small world,, I was friends with Steve Kahn - often visited Valley Arts 1980-86.
His dad was lyricist  Sammy Cahn

Read All prior posts

If you must use Load Resisters , get the noninductive type from Parts Express

https://www.parts-express.com/4-Ohm-100W-Non-Inductive-Dummy-Load-Resistor-019-015



Make custom cable with 1/4" male plug for Katana Head speaker out , then use 4 ohm load resistor above in series with positive speaker lead

Terminate with 1/4"  female inline jack -

Allows swift connection to Fender Twin Speaker lead which is pre-wired to two 8 ohm speakers (4ohms)

Above yields a 8 ohm Speaker load for Katana Head-but 1/2 power delivered to Fender Twin speakers , other half dissipated as heat in the load resistor.

And be sure to employ a twisted pair strategy-the Katana Head power Amp will oscillate if the speaker wires are random and placed with too much distance between opposing polarity wires

alancarl

Thanks Steve,
        i did not thnk of the twisting speaker wires:-)
I understand what you so thoroughly described:-) will work but I am curious what will happen if the Katana sees a 4 ohm speaker load. which BTW was my original question(I think)
The Single IC power amp spec states that its will handle 4 ohms albeit w 10% THD.
I guess I could give and do the sensible safe method but the mad scientist in me is itching to know!
Thanks everybody!
Yes Steve Kahn is a great guitarist and kind human being!
-Al

admin

#13
Quote from: alancarl on April 15, 2021, 11:39:25 AM
Thanks Steve,
        i did not thnk of the twisting speaker wires:-)
I understand what you so thoroughly described:-) will work but I am curious what will happen if the Katana sees a 4 ohm speaker load. which BTW was my original question(I think)
The Single IC power amp spec states that its will handle 4 ohms albeit w 10% THD.
I guess I could give and do the sensible safe method but the mad scientist in me is itching to know!
Thanks everybody!
Yes Steve Kahn is a great guitarist and kind human being!
-Al

Katana on 4 ohm load should work for 20 minutes-really depends on volume too

But the Katana Power supply will fail if subjected to extended high decibel use with 4 ohm load.
And might be a battle locating a Boss Service Center for timely repair

alancarl

Sage advice my friend!
I suspect that it would be a glorious 20 minutes though as the devices that have blown up on me always sounded their best in an unrepeatable way right before they went up in smoke!
I will try the 4 ohm non-inductive load when they are back in stock and see how that works out.
Thanks everybody!
-Al