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Discussion Starter #1
I bought the Rockford Fosgate PBR300X4 2 weeks ago and received it on Monday. I am hooking it up on my 2008 Victory Vision motorcycle stock radio this weekend to new speakers since the stock speakers are awful.

The stock radio does not have low-level outputs. No problem because I can use the high-level inputs for the PBR300X4 that connect to the stock radios' speaker lines.

My question is....if I use the high-level inputs (by cutting off the low-level inputs from the supplied cable as stated in the manual) and connect them to the stock radio speaker cables (after disconnecting the stock speakers) and connect the output of the amp to the new speakers, Do I need to use load resistors on the stock speaker lines?

I am worried that I could hurt the stock amp by not providing it a proper load since it will not be driving speakers anymore just the input of the PBR300X4 .

Thanks,
 

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I'm not sure I get the SN "RadioTeacher" and this question, but I'll do my best...

The stock radio speaker outputs will go to the high level inputs on the amp.. think no further beyond this, besides the specifics of what you have to do to do this...

The new speakers hook to the outputs of the amp... think no further beyond this than what you need to do...

Simple...

Load resistors?

You could consider a LOC or Line Output Converter to convert speaker level outputs to LINE level (RCA) if you liked ...

Not sure about this load resistor thing you got goin on...
 

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Discussion Starter #3 (Edited)
Thanks for the reply.

About the Radioteacher screenname....I have taught Amateur Radio classes for more than ten years and mentor to both new and old. This is an old screen name and email address for me. I admit is does look odd on this forum.

One of the nice features about this RF amp (PBR300X4) is that it can connect to both low and high level inputs without a line convertor. Since space is a premium on a motorcycle that is one less connection and device to fail.

I will be using the stock radio on the motorcycle that will be disconnected from its speakers (4 ohm). The high-level input of the PBR300X4 will be the only thing putting a load on the output of the stock radio. Should I add some 4 ohm resistors to the stock radio's speaker lines to provide a proper load for the radio's amp?

I am concerned about blowing my stock radio output transistors.

I think I read that the high-level input cable has an impedance of 20,000 ohms. I would think I would need to load the stock speaker lines better then that to protect the stock radios amp.
 

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I understand the question and am interested in the answer but do not know how to figure it out either.

Subscribed.
 

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Napoleon of DIYMA
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no, you don't need to

the voltage output will always be the same whatever the ohm load, only the current draw will change.

So the stock amp will simply produce it's voltage and the IC chip will be lot cooler since the current draw will minimal due to the high resistance of the amp input (the load).
 

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OP-Yes Basshead has it, it works the other way around from what you are thinking. Remember the load is what controls the current from an amplifier. The higher the ohm load the less current will flow, but the same voltage will be there. This is good for an amplifier then it just loafs along. Too low a load (low ohms under its ratings) will cause excess current to flow easily, and can exceed the current ratings of the electronic parts involved namely the output transistors and/or power supply for the amplifier.

Actually the input impedance of the amplifier should be so high that your 4 ohm resistors would have virtually no effect, because it is already running against a huge load.

Sometimes the high power inputs on an amplifier do not work that well, sometimes they are fine. A lot of people use a LOC because they work nicer or tackle noise issues and usually are adjustable. They are small should not be an issue if you end up using one, but try the amp alone first.
 

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Discussion Starter #8
no, you don't need to

the voltage output will always be the same whatever the ohm load, only the current draw will change.

So the stock amp will simply produce it's voltage and the IC chip will be lot cooler since the current draw will minimal due to the high resistance of the amp input (the load).
Thanks! That makes sense to me.

This is taking a bit longer then I stated above. I mounted the amp in the saddle bag but I have not hooked it up.

Here is what slowed me down. I kept seeing in my mind the sixteen wire splices under the radio and sixteen more splices near the amp. That would look terrible. Besides, I started getting an uneasy feeling about cutting into the bikes wiring harness.

So, now I am designing and building a wiring harness with the correct connectors that interfaces with the radio and the amp without cutting into motorcycles wiring harness. This audio harness will not have any splices and be wrapped like the original equipment.

I have ordered almost all of the parts and just need to find some more pins for the TE Superseal connectors. It was a challenge but I did identify the audio connectors that Rockford Fosgate uses on the PBR300X4.

This biggest issue is that Tyco Electronics only makes the female Superseal connectors for cable mounting. The male Superseal connectors are only for PC board mounting. I came up with a way to take a female Superseal cable mount connector and epoxy it to the back of a modified male Superseal connector to make a cable mounted male connector.

Anything worth doing is worth doing right.
 

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Discussion Starter #9
OP-Yes Basshead has it, it works the other way around from what you are thinking. Remember the load is what controls the current from an amplifier. The higher the ohm load the less current will flow, but the same voltage will be there. This is good for an amplifier then it just loafs along. Too low a load (low ohms under its ratings) will cause excess current to flow easily, and can exceed the current ratings of the electronic parts involved namely the output transistors and/or power supply for the amplifier.

Actually the input impedance of the amplifier should be so high that your 4 ohm resistors would have virtually no effect, because it is already running against a huge load.
Thanks

Sometimes the high power inputs on an amplifier do not work that well, sometimes they are fine. A lot of people use a LOC because they work nicer or tackle noise issues and usually are adjustable. They are small should not be an issue if you end up using one, but try the amp alone first.
This amp is adjustable on input from 150 mV to 11V with an input impeadance of 20,000 Ohm. I figured that this is as good as most LOC's.

Thanks again,
 

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I have a MTX jackhammer and it came with a RCA plug set with normal wires hanging out. It says to wire the HU direct and it will sense what type of input the RCA is getting high or low. There is no separate high input.
 
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