Radial ProRMP modification

[Wolfeman]

Depends on the impedance of your interface that is feeding the box.

IMO, I'd want that transformer being fed with a proper low-z impedance.

Will it make a difference at that value? Probably not noticeable. But it would bug the hell outta me knowing it's there for no reason

 

[Trevoire520]

Just ripped that 3rd resistor out of my RMP. Will do another test in a day or two to see what difference it's made.

 

[deLuther]

Today completely removed all resistors, did not notice significant changes
Run test 1 kHz sine (with -1 dbFS=+19 dbu), multimeter measurements was 5.2 V before unit and 5.0 V at output with trim pot at maximum.

 

[006]

So you took out all three instead of taking out the one and jumping two?

 

[deLuther]

I decided that if I`m remove 620 Ohm resistor then I can remove other two and properly solder two replacement conductors

 

[006]

Ah cool. Are these conductors/jumpers the actual name of the pieces? Or are they just short snips of copper or...? I'm going to go by RadioShack in the next couple of days and see if I can pick some up to do this to mine.

 

[deLuther]

Short snips
This time I`m used short snips from resistor leads, to fit in PCB holes.

 

[deLuther]

Final version:

But now I`m thinking that maybe better to use twisted pair of wires and solder closer to transformer inputs?

 

[DigitalMetal]

Im glad this thread popped up, i made my own reamp box using the Jensen schematic but a sowter transformer of a similar spec a year or so ago,
I always wondered about the output level/impedance,
Obviously what we are trying to do is replicate a guitar with our boxes, so i went round all my guitars testing the impedance value of the jack outputs to see what it was i should be setting the level knob on my box up as,
I got some massively different results and i can only put this down to some being active EMG's and some being passives,
As a comparison would any of you guys care to take a multimeter and test the impedance and perhaps voltage if measurable at the output of your boxes so we can compare?

Sorry if this is a bit of a hijack of the thread but i thought it was a good place to discuss this.

Thanks !

 

[deLuther]

Multimeter will give only DC resistance which, for example, for Jensen JT-11P-1 is 1.45 and 1.55 kOhm for primary and secondary windigs, while rated output impedance is 2.34 kOhm and input impedance is 13 kOhm.
http://www.jensen-transformers.com/datashts/11p1.pdf
Transformer in ProRMP has lesser DC resistance, primary resistance is around 800 Ohm.

As for voltage drop I post measurements earlier (for modified unit):
http://www.ultimatemetal.com/forum/equipment/568415-radial-prormp-modification.html#post9638060

 

[DigitalMetal]

ok thanks, so do you have any suggestions as to how to best match the output of the reamp box to a guitars output, not just doing it by ear?

 

[deLuther]

I`m just running some test signal (sine, DI etc.) through ProRMP into Hi-Z of my preamp and set levels on reamper (I`m not using maximum output position, so there is some volume reduction) and preamp so loopback signal shows me the same level. Such setting on clean amp channel gives illusion to my ears of same volume as direct
At least, if reamper has close to unity gain, recorded signal (without additional amplification) should be the same after reamper if input and output levels of interface are the same.

 

[deLuther]

It seems that removing 620 Ohm resistor can improve low end response of ProRMP.
Tested ProRMP into Hi-Z of my mic pre with RightMark Audio Analyzer 6 (because I`m have results from previuos modification, say V1):

Longer cable from reamper to Hi-Z (and amp) can improve top end response.
Long cable is like 3m and other measurements was performed with short (20 cm) cable.
But it seems that different ProRMP can have different frequency response, one guy, that made V1 modification, measured response with his ProRMP and same preamp as mine and his results had more top and bottom rolloff.

 

[Trevoire520]

Just tested my RMP after ripping the third resistor out and now with the level at maximum my reamped signal is 1.7db louder than the original (before removing the third resistor it was 1.1db quieter)

 

[AudioGeekZine]

So is this more like a guitar signal with the mod?

 

[006]

Wow so you actually don't have to turn it all the way up to match... I'm gonna do this tonight, just take out the 3rd resistor and see how that sounds. So, Trevoire, you just left the other two alone?

 

[Wolfeman]

You'll still want to bypass the resistors on the signal lines if you remove the shunt resistor

 

[deLuther]

So is this more like a guitar signal with the mod?

Yes. But device without resistors has almost unity gain, so interface output still must have sufficient output (+4 dbu reference).
Maybe there is some differences between different ProRMPs.

Trevoire520, how do you performed your test?

 

[Trevoire520]

Wow so you actually don't have to turn it all the way up to match... I'm gonna do this tonight, just take out the 3rd resistor and see how that sounds. So, Trevoire, you just left the other two alone?

Nah I bypassed them with a couple of bits of wire.

Yes. But device without resistors has almost unity gain, so interface output still must have sufficient output (+4 dbu reference).
Maybe there is some differences between different ProRMPs.

Trevoire520, how do you performed your test?

I just plugged my guitar into my interface and recorded a riff. Then sent it through the reamp box and back into the interface (kept the gain on the pre at the same level) and measured the difference in level.

 

[deLuther]

Such way I`m also have boosted signal (also around 2 db) with trim pot at maximum, vertical position gives close to unity gain.