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Post subject: Rumble 150 internal Review: ICE is Nice
Posted: Thu Mar 10, 2016 11:01 am
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So I finally had a Rumble amp come across my bench and I got a chance to see what is really going on inside these amps. I don't have a schematic, but many of the features are obvious.
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Its important to keep the fan blades clean and dust out of the unit. Don't touch the tops of the capacitors unless you want a big surprise.
The power module is a standard ICE module. These are a spinoff of The Danish stereo maker Bang & Olufson.
These modules are an engineers wet dream. They combine a power supply and amplifier into a small package. They are used in home subwoofers and other guitar amps. The kits are available for stereophiles on Ebay.
This particular one is from 2010 and is the ICEPower50ASX@. I had occasion to replace one of these a while back and received an updated module. There was a modification to it where the previous module had a visibly burnt resistor. You can see this circled in red in the photo. This change may help date how current your module is.
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This module tracks the audio signal and only turns up the power supply when it needs more voltage. This allows the use of output transistors without needing heatsinks. Most of the transistors operate in a switch mode and produce very little heat. They are shown on this backside photo as the 4 pea-sized black squares in the red circle
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Their specs and sonic signature are well covered in other literature in the web. The 2 notable things that I see on the scope is the 1 Volt high frequency wave at zero volume. While this is typical for a digital amp, it's disconcerting to myself as a tech as to how a speaker handles this.
The other feature is no latency in the digital output. There is even less phase shift than many analog amps.

The preamp is constructed on a solid fiberglass double sided board. This makes for reliable solder joints over the long term.
The traces are plated in gold. This significantly reduces the resistance of traces and improves high frequency response.
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The preamp sports an LM13700 chip that is commonly used for compressors and this Rumble sports a limiter that has a faster slew rate than most compressor chips.

There are a couple LEDs in the preamp that expose a real distortion circuit built into the preamp.
It produces waveshapes unlike most other pedal effects and must be played in the pocket to maintain waveshape. It could be interesting for a signature guitar distortion..
One notable design flaw is the swedged input jacks. They loosen up and rotate in the chassis without tightening. The ground connection always is a bit loose and probably won't take much abuse before it works itself loose. I'm not sure of the best cure there yet; epoxy or solder. We'll see how it works out.
Overall, the amp is a modern quality product that earns the Fender name, IMHO.


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Post subject: Re: Rumble 150 internal Review: ICE is Nice
Posted: Thu Mar 10, 2016 6:42 pm
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Location: On the loo, regretting that gas station burrito.
That's interesting. I'm curious, is there a way to replace that ICE power module to have a more powerful version, like the Rumble 350 had? If so, would it even worth that do so? I don't own this amp (I have the 350,) it;s just general curiosity.

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Post subject: Re: Rumble 150 internal Review: ICE is Nice
Posted: Thu Mar 10, 2016 7:48 pm
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It might work, but the preamps probably have different features and pinouts.
You would also have to get a new speaker to handle more power. I'm not sure it would be worth it.


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Post subject: Re: Rumble 150 internal Review: ICE is Nice
Posted: Fri Mar 11, 2016 1:20 pm
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I figured as much. It's probably one of those things where you could just buy a used Rumble 350 cheaper than modding a 150, but that would be interesting to have the 350 specs in a 15" speaker configuration.

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Post subject: Re: Rumble 150 internal Review: ICE is Nice
Posted: Sun Mar 13, 2016 9:11 am
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You can get the schematics right here at the Fender Support knowledge base.

http://support.fender.com/schematics/bass_amplifiers/Rumble_150_2010_schematic_Rev-B.pdf


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Post subject: Re: Rumble 150 internal Review: ICE is Nice
Posted: Mon Mar 14, 2016 8:19 pm
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Thanks Linin. It gets even more interesting with the puzzle solved.
The Gain control has the distortion LEDs wired across it, so you can figure on distortion any time the blend control is off clean limit and the Gain is up..
That’s a nice Stereo effects loop, but it is mixed to mono one stage later.
The dual LM13700 is used as a clipping detector with a four stage smoothing circuit and the second half makes up the compressor stage. It only limits the power stage, not Line Out
Tone controls are EQ style notch filters centered at 60, 400, 1200, 5000Hz.
This is unlike most guitar tone controls with a Treble sweep control. It may make it difficult to find your sweet spot.
Right after the R8 volume control is a classic tone stack circuit. The controls normally found are replaced with fixed resistors for a pre-determined tone. It looks ripe for tweaking the values for different tone balance. Just keep the overall resistance to ground the same. Fine tuning the caps can focus your tone where you want it.
The ICE module is a 2 channel amp running in bridge mode. Both speaker wires are hot. Do not connect the black wire to ground.
Do not attempt to connect external speakers.
Its the best way to blow this module.
Last I checked, thet were $150 for a new one. They are not field repairable, period.


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Post subject: Re: Rumble 150 internal Review: ICE is Nice
Posted: Tue Mar 15, 2016 5:28 am
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WOW Tim! Thanks for this entire thread. Especially your insight contained in your last post. Very enlightening.


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Post subject: Re: Rumble 150 internal Review: ICE is Nice
Posted: Tue Mar 15, 2016 8:43 am
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On further consideration, the Effects loop is a mono send and a stereo return. The mixing circuit is not mono as I first thought.
It is a pseudo-stereo differential amp
This creates a difference signal that attempts to preserve both effects channels in a mono format.
If you won't ever use it, the Loop and the monofier circuit can be bypassed by clipping a couple jumper wires and cross-connecting.
At P9 or PW9, there are 10 jumper wires or a 10 pin connector, depending on if its a head or combo.
Cut W4 and W8.
Connect the preamp side of W4 to the amp side of W8
There may be a difference in gain, but the effects of the monofier circuit will be eliminated. I'm not sure what the difference will be, but if you try it, let us know.

The long signal chain in this amp means that better chips can reduce noise in a meaningful way. Upgrading the Preamp ICs has many other benefits.
The TL072 ICs are harder to get out with the double sided board. Desoldering usually damages the board before you can pull the chip out.
So for a crowded board like these ones, I like to cut off the pins with an Xacto knife or a Dremel with a cutoff wheel, remove the chip and pull each pin individually.
Replace with a socket and a TLE2074 or other high quality IC.


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Post subject: Re: Rumble 150 internal Review: ICE is Nice
Posted: Tue Mar 15, 2016 2:10 pm
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I posted a link to this thread on the TalkBass Fender Rumble Club, because we love this sort of thing.
https://www.talkbass.com/threads/fender-rumble-club.1118826/page-508

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