James Freeman
Rock Star
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- 3,191
I thought I should start a thread about my modifications to the Fractal X-Load LB-2.
The goal was to fix the resonance frequency and Q by changing the resonance inductor and caps.
The stock X-Load has two 330uF in series which sums to 160uF in UK mode and the switch adds the other two 330uF in parallel for a total of 330uF in US mode, the inductor is about 18mH.
The values above form two center frequencies of 95Hz in UK mode and 65Hz in US mode, neither offers the "correct" 110Hz - 120Hz resonance for a typical Marshall 4x12.
Stock gut shot and response:
I bought a few 220uF and 100uF 100V bi-polar capacitors and a big 9mH inductor from Aliexpress for a total of 60$ to bring the X-Load more in spec with Suhr and a 4x12 cab.
Desoldered the stock inductor and caps out.
Soldered in the new caps.
The upper position is permanently wired (UK) and the bottom cap is switched in in parallel (US), so either 220uF or 330uF.
The fun part was to unwind the inductor form 9mH until the resonant circuit measured exactly 115Hz in REW impedance measurement tool.
9mH + 220uF gave me around 107Hz, unwinding the inductor raises the resonance frequency.
Unwind 10-15 turns, strip the tip, touch the black wire, measure, repeat until exactly 115Hz.
All done.
I also unsoldered one end of the 20RJ resistor closer to 220uF cap to disable the resonance limiting which measures more like a cab, Suher RL doesn't have limiting either.
Impedance measurement in REW with the final result, 116Hz for UK mode and 96Hz for US mode, both are useful now.
I'm happy with the results.
Yes, I have cranked the Plexi and JCM800 into it, no fireworks or magic smoke so far, the inductor does not make more noise than the stock potted one, it's tight.
Measured amp response.
The goal was to fix the resonance frequency and Q by changing the resonance inductor and caps.
The stock X-Load has two 330uF in series which sums to 160uF in UK mode and the switch adds the other two 330uF in parallel for a total of 330uF in US mode, the inductor is about 18mH.
The values above form two center frequencies of 95Hz in UK mode and 65Hz in US mode, neither offers the "correct" 110Hz - 120Hz resonance for a typical Marshall 4x12.
Stock gut shot and response:
I bought a few 220uF and 100uF 100V bi-polar capacitors and a big 9mH inductor from Aliexpress for a total of 60$ to bring the X-Load more in spec with Suhr and a 4x12 cab.
Desoldered the stock inductor and caps out.
Soldered in the new caps.
The upper position is permanently wired (UK) and the bottom cap is switched in in parallel (US), so either 220uF or 330uF.
The fun part was to unwind the inductor form 9mH until the resonant circuit measured exactly 115Hz in REW impedance measurement tool.
9mH + 220uF gave me around 107Hz, unwinding the inductor raises the resonance frequency.
Unwind 10-15 turns, strip the tip, touch the black wire, measure, repeat until exactly 115Hz.
All done.
I also unsoldered one end of the 20RJ resistor closer to 220uF cap to disable the resonance limiting which measures more like a cab, Suher RL doesn't have limiting either.
Impedance measurement in REW with the final result, 116Hz for UK mode and 96Hz for US mode, both are useful now.
I'm happy with the results.
Yes, I have cranked the Plexi and JCM800 into it, no fireworks or magic smoke so far, the inductor does not make more noise than the stock potted one, it's tight.
Measured amp response.
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