Kustom Quad Jr. 100HD - Impedance Question

[kinglerch]

I can't find a schematic for this head. The manual says the impedance is 4 Ohms, but there are two outputs (unlabeled). I am building a cab so I can choose the impedance. If the output on the head is really 4 Ohms on *each* output, and I attach each one to an 8 Ohm speaker, then the power capability will be reduced. Another option is to wire the cab in parallel to get a single 4 Ohm input and attach to *one* of the two head outputs.

 

I really wish there was a schematic so I can tell which way would be preferable. There are 100DFX schematics floating around, but I am not 100% sure they are the same with respect to the output impedance and jacks.

 

Can anyone help?

[DeepEnd]

From the manual:

Speaker Outputs - These jacks are used to deliver the amplified signal to the speakers. Total minimum load is 4 ohms.

https://www.manualslib.com/manual/454897/Kustom-Quad-100-Head.html?page=4#manual

The jacks are wired in parallel so you can get by with two 8 Ohm cabs or two 16 Ohm cabs but not two 4 Ohm cabs.

[WRGKMC]

The key words are 4 ohm minimum. Like most SS amps you can run them higher then the minimum and not do any damage.

2X8 ohm cabs will give you 4 ohms for maximum power as Deep end mentions.

 

Power is divided between the speakers if they are similar ohms. A 4X4 ohm speakers wired in series parallel for example will have 25W applied to each speaker for a total of 100W. Normally you'd want speakers that have a total wattage that's higher then the heads RMS Rating. The head is 100W so you want to use 35~50W speakers so you have 50~100% above the heads maximum power rating total. You can go higher but you wont gain anything by doing so. If anything, high wattage speakers may have a lower sensitivity and consume additional power just to get them moving.

 

 

 

You can run 8 ohms or 16 ohms total but the head might not put out a full 100W. SS heads typically put out lower total wattages as the load impedance is increased. Some can drop as much as 50% running at 16 instead of 4 ohms so you want to target 4 ohms if you can.

 

Main thing is don't run the head below 4 ohms. Again as Deep end says, each jack is wired in parallel. If you plug two 8 ohm cabs into those jacks you wind up with 4 ohms total.

 

 

[DeepEnd]

I don't know if you're still there since all we have is the one post from four days ago. In any event, I wouldn't worry too much about reducing power output. I won't get into Tube Watts vs. SS Watts but you're talking about a 100 Watt (at 4 Ohms, I believe it's rated 65 Watts into 8 Ohms but I could be wrong) SS head and that should be enough for any reasonable need. If it's not, you need to talk to the rest of the band (especially the drummer) about playing too loud.