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Reamping guitar with the gracedesign m101?
Old 26th January 2013
  #1
Here for the gear
 
🎧 10 years
Reamping guitar with the gracedesign m101?

I was doing some research on reamping... And I recently discovered the issue of impedance...

I recently purchased a gracedesign m101 (awesome preamp btw!) and I noticed that it has a hi z input and an unbalanced out for guitar amps. The hi Z can be used with balanced or
Unbalanced. (I would be sending a balanced, prerecorded guitar signal to it. Sent from a tascam us1641 interface.)

If you look in the manual for the m101 it shows the impedance level of all the outputs and inputs on page 9.
http://www.gracedesign.com/support/m101_manual_RevA.pdf


It might also be worth mentioning that when using the high Z input, the gain range levels change with the lowest being -10 instead of 0. This could be useful because I also heard that the volume level from the interface could be an issue when dealing with reamping.

Anyways, i figured i would ask before trying because i don't wanna blow all my friends $1000+ amplifiers. So.... bring on the knowledge? Lol
Thank you


-Aaron


Edit: ok so I made my main points but I am also curious if anyone can answer this: for recording a guitar signal with intentions to reamp it, I bought a passive radial JDI box. But, when I was on their site it seemed like the j48 (the powered version of the JDI) was better for electric guitar. Would the grace design be better to use than the JDI for this part of the process as well? Answer this one for bonus points.
Old 26th January 2013
  #2
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Lotus 7's Avatar
Since the M-101 is a ultra-clean mic pre, there is really no reason to include one in the signal path for re-amping. You should be able to just connect the Tascam 1641 line out to the guitar input, although you may need a -10 or -20 dB pad with some guitar amps. The grace won't add or subtract anything from the guitar character and will just act as a buffer between The Tascam output and the guitar amp input, although it can provide up to 10 dB of attenuation.

The Tascam output impedance is very low and will, easily drive the high input impedance of either a guitar amp or the Grace High-Z input so impedance is not an issue using either configuration.

If you still want to include the M-101 in the signal path, you shouldn't have any problem driving the M-101 from a Tascam line output. The Tascam maximum output (at clipping) when set to +4 is no more than +20 dBu. The M-101 can tolerate that if the output gain is at "0" (full CCW) and the input switch is on step 1 (-10 gain), step 2 (-5 gain or step 3(unity gain) when using the balanced input, High-Z front panel input. Don't set the M-101 higher than step-3. As long as you keep the Tascam at reasonable levels, the M-101 will handle it.

You may have possible input overload at the guitar amp depending on the amp model. Most guitar amp "instrument" inputs operate at a normal signal level of between 200 mV (-12 dBu) and usually no more than 1 volt (+2dBu). They can overload at levels as low as 3 volts (+11dBu). The Grace M-101 can put out as much as +25 dBu which will overdrive the input stage on most guitar amps. If the guitar amp has a input pad switch, use it (set it to "pad"), if it has a hi/low output pick-up switch, set it for "high-output". Keep the M-101 gain on the low side (-10 or -5 dB) and keep the guitar amp input gain low. the M-101 should be operating at a level that never causes the signal light to change from green to red since that represents an output level of +16 dBu. You aren't risking any amp damage, but you are risking input stage clipping if you're not very careful.

It's actually "safer" to connect the Tascam to a guitar amp input since it's max output is +20 dBu vs, the +25 dBu output of the Grace.

I have (4) M-101s ahead of an Apogee Ensemble and love them as clean, low-noise mic pres, but have never connected anything to the High-Z inputs.

Not familiar with the Radial JDI, so no bonus points.
Old 26th January 2013
  #3
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🎧 10 years
thanks for the reply!
I think the main reason I thought to use the m101 was the conversion from balanced to unbalanced, because guitar amps are unbalanced. I don't know if plugging an unbalanced cable in the balanced line outs of the tascam would cause noise or something. And then the other thing was the -10db reduction which I thought would act kind of like a pad? It just seemed to me like it would be a better option based on what I was reading about reamping. But I could be wrong.

Basically, I was looking at the manual to a reamp device and kind of realized there is a reason that they make devices made specifically for reamping. But then I looked at my preamp and felt that using the hi Z input (automatically detects if balanced or unbalanced, so it'd work with the balanced line from the tascam) and the unbalanced output looked like it might provide a sufficient alternative to spending an additional 200 bucks :P

On another note... One of the amps I want to try has a 0db input and a -15db input. I think I'll start with that one using the -15
Old 26th January 2013
  #4
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🎧 10 years
Ok, I took another look at things and it appears that the part I'm missing is the conversion from low impedance to high impedance! But I think I can do this with the gear I have. Just for the heck of it, here is a link to an explanation of how to use the radial JDI backwards to reamp. Just find page 14:

http://www.radialeng.com/pdfs/manual-duplex-mk4.pdf

So I just need to use my preamp to convert it to xlr out and use a female to female cable I think.
Old 26th January 2013 | Show parent
  #5
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Lotus 7's Avatar
Quote:
Originally Posted by tehkeytar ➑️
thanks for the reply!
I think the main reason I thought to use the m101 was the conversion from balanced to unbalanced, because guitar amps are unbalanced. I don't know if plugging an unbalanced cable in the balanced line outs of the tascam would cause noise or something. And then the other thing was the -10db reduction which I thought would act kind of like a pad? It just seemed to me like it would be a better option based on what I was reading about reamping. But I could be wrong.

Basically, I was looking at the manual to a reamp device and kind of realized there is a reason that they make devices made specifically for reamping. But then I looked at my preamp and felt that using the hi Z input (automatically detects if balanced or unbalanced, so it'd work with the balanced line from the tascam) and the unbalanced output looked like it might provide a sufficient alternative to spending an additional 200 bucks :P
You can use the M-101 to provide the balanced output to unbalanced input conversion, but you can also wire an unbalanced cable to do the same. An unbalanced cable always has the potential to pick up more induced noise or to create ground loops, but the TS output of the M-101 is unbalanced anyway and the guitar amp input is unbalanced, so there is no advantage at all in terms of potential noise pick up using the M-101 in the signal path when the TS output is used.

The unbalanced guitar amp input will always be unbalanced.

Quote:
Originally Posted by tehkeytar ➑️
On another note... One of the amps I want to try has a 0db input and a -15db input. I think I'll start with that one using the -15
I think you may have a mis-understanding of how inputs are probably marked. The "-15dB" input is probably for lower output pick-ups and has 15 dB more gain - it's the high gain input. The "0dB" input is for "hotter" pickups and it's the low gain input. Of course the inputs may be marked as you've assumed and the "-15 dB" jack may actually mean 15 dB more attenuation. Either way you want to use the input with the lowest gain. For re-amping, the problem is you have too much signal coming from the interface and need to pad it down. Even the "0dB" input has too much gain for the line output.

The Tascam output is at a nominal +4 dBu with a peak capability of +20 dBu. You could run the output at a reduced signal level but that would compromise your signal to noise ratio. A much better solution would be to just insert a 20 dB fixed attenuator in the line between the Tascam and the guitar amp.

Again, matching the input impedance is not an issue, any low impedance output can drive the very high impedance guitar amp TS input.

A re-amp box like the Radial RMP is just an isolation transformer and attenuator which "floats" the output to eliminate ground loops and the hum/buzz that can be created with some guitar amp inputs.
The M-101 TS input is single-ended and won't provide the ground loop isolation of a real transformer-coupled re-amp box.

You are correct to assume that going into the M-101's balanced XLR inputs will provide isolation. The problem there is that the input gain is way too high for the Tascam's output. If you use the M-101 XLR input you will need a 30 dB pad at a minimum, and you still have the issue of the M-101's outputs being about 10 dB too high for your guitar amp's input even using the "0dB" input setting.

If I were trying to do this I'd TRY connecting the Tascam output to the M-101 TS (High-Z) input with an unbalanced cable (a simple TS to TS cable). Which is what you first proposed.

I'd set the M-101 for minimum gain and connect it's single ended TS output to the guitar amps "0dB" input with another unbalance TS to TS cable. I'd run the Tascam at normal levels and use the M-101 for the 10 dB gain reduction it provides at minimum gain.

If you're lucky, you won't have any ground loops causing hum issues with the guitar amp input and the 10 dB gain drop through the Grace will be enough. That's the "no cost" option.

If that connection results in NO hum, but still too much gain using a low input gain setting on the guitar amp, then I'd get a 20 dB passive attenuator and insert it in the line between the M-101 output and the guitar amp input. If you can solder, it's even possible to build the attenuator yourself with a couple of resistors placed inside of a TS plug. Using good quality resistors will pad the signal down (at the guitar input) with no noise issues.

IF you get hum with the M-101 set-up, then it's necessary to isolate the guitar amp input and break the ground loop. the best and easiest way to do that is really just to get an isolation transformer like a Radial RMP and go into the guitar amp that way.

If you have a couple of TS cables it won't hut to try the first set-up. Just remember to start with all the gain controls at minimum.

I know there are a lot of "Ifs" above, but it's easy to try and may actually work with no issues.
Old 27th January 2013
  #6
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🎧 10 years
Ohhh ok! So an unbalanced cable should work just fine I think I get that part now.
I attached a picture of the diagram from left to right of the JDI. If I use this backwards for reamping (making the diagram from right to left) would the -15 db pad still work? It also has a ground lift so I will try that if I run in to any ground loop issues using the method you suggested.

I was also curious if I could run the gracedesign backwards, but I don't think I feel comfortable trying that lol. I'd rather experiment with a $200 DI box than a $750 preamp... Plus the JDI's manual suggested using it backwards.

Hopefully I can try this all out soon!
Attached Thumbnails
Reamping guitar with the gracedesign m101?-imageuploadedbygearslutz1359263718.918770.jpg  
Old 27th January 2013 | Show parent
  #7
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Lotus 7's Avatar
Quote:
Originally Posted by tehkeytar ➑️
Ohhh ok! So an unbalanced cable should work just fine I think I get that part now.
I attached a picture of the diagram from left to right of the JDI. If I use this backwards for reamping (making the diagram from right to left) would the -15 db still work? It also has a ground lift so I will try that if I run in to any ground loop issues using the method you suggested.

I was also curious if I could run the gracedesign backwards, but I don't think I feel comfortable trying that lol. I'd rather experiment with a $200 DI box than a $750 preamp... Plus the JDI's manual suggested using it backwards.

Hopefully I can try this all out soon!
The M-101 strictly works in one direction - inputs to outputs, don't even think of applying a signal source to a Grace M-101 output.

The JDI is really designed to work as a plain direct box: to connect a guitar (or a guitar amp output) to a mic input. It includes a "speaker" filter which is intended to attenuate and filter the signal when the JDI input comes from a high-level speaker output. It's really not intended to work as a re-amp interface.

However, it does have a 15 dB pad (30 dB if you press the "speaker switch") and there's no harm in trying it. The JDI has a balanced XLR output so to connect it to a guitar amp input you'd need a XLR (F) to TS cable or an adapter. It does have a nice Jensen transformer to isolate the output (the guitar amp input) so should eliminate any potential ground loops.

The JDI is rated for up to +21 dBu input levels so since your Tascam interface max output is +20 dBu is safe to connect to the Tascam without risk of damage.

Having said that, there is no risk of damage to the Grace mic pre by running a Tascam line out to the Grace High-Z input. As long as the Tascam is running at normal levels. the Grace M-101 [High-Z] input is isolated by 1-meg series resistors so the worst thing that will happen is the input will clip if you accidentally overdrive it. As long as you keep the input gain switch on step 1, 2, or 3 and the output gain at minimum (full CCW) you shouldn't run into any problems with the M-101.

Since you have the JDI and the Grace, you can always run the Tascam into the JDI, then run the JDI XLR out into the M-101 mic input (as the JDI is designed to be used) and then run the unbalanced M-101 TS out into the guitar amp. You should have plenty of gain range possibilities by using the 15 dB pad in the JDI and the wide gain range control of the M-101. You still have to be careful to keep the M-101 output to a reasonable level to avoid overloading the guitar amp's input.

You have a lot of possibilities that can work, and each will potentially give you slightly different sound modification (although adding the Grace won't change things very much since it's so "transparent"). The main sound "character" of the re-amp process will still come from the pass through the guitar amp in all cases.

It's time to try some of the possibilities and to decide if the re-amp effect is really what you want. Have Fun!
Attached Thumbnails
Reamping guitar with the gracedesign m101?-jdi-passive-direct-box.jpg  
Old 27th January 2013
  #8
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🎧 10 years
The purpose of a reamp box is:

To take a low impedance line level source (an interface or mixer output)
And convert it to (lower) instrument level high impedance.

Sending interface or mixer outputs into a preamp will be an impedance mismatch and change the tone as well as overdrive the input of the preamp or instrument amp.

Hence the reason reamp boxes are used/needed.

Hi z inputs on preamps, interfaces, and guitar/bass amps are designed for the tiny signals (millivolts) produced by guitar pickups.

Not Understanding:
1. Mic level/impedance
2. Instrument level/impedance
3. Line level/impedance
4. Balanced vs unbalanced

Is what gets most into trouble and prob the root of 50% of the questions in forums regarding "how do I connect unit x to unit y.
Old 28th January 2013
  #9
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Lotus 7's Avatar
That's exactly what has been discussed on this thread. The OP is trying to create a re-amp set-up without purchasing a real re-amp box. He's trying to use the components he already has. The solutions suggested will work, but with limitations that have been mentioned. Of course a real re-amp box would be simpler and easier to use, but there''s no harm in trying the several possible configurations that have been offered as alternatives as long as the limitations are understood.

The high-Z input of a Grace M-101 is not the same as most guitar amp instruments inputs, It's padded and can tolerate a significant signal level as long as the gain is kept low. The output can easily overdrive a guitar amp input if levels are not keep low, which is which the use of an in-line attenuator was mentioned if needed.

In fact, sometimes the unorthodox solution yields the most interesting results.
Old 28th January 2013
  #10
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You already have a line level from an Interface that's too hot and the wrong impedance for a guitar amp. Then you're gonna run it thru a pre amp that still is too hot and the wrong impedance for a guitar amp as well.

You might as well just plug the interface output to the guitar amp input with a standard guitar cable, and turn down the interface output fairly low and call it good. It's still an impedance mismatch with or without the 101 in between. If you like the tonal change due to the impedance mismatch then you're all set.
Old 28th January 2013 | Show parent
  #11
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Quote:
Originally Posted by Manfrensengensen ➑️
...You might as well just plug the interface output to the guitar amp input with a standard guitar cable, and turn down the interface output fairly low and call it good. It's still an impedance mismatch with or without the 101 in between. If you like the tonal change due to the impedance mismatch then you're all set.
Correct, that was one of the possibilities discussed (see the very first sentence of Post No. 2). The only reason to include the Grace M-101 in the path is that at its lowest gain setting it provides a transparent 10dB gain drop. The M-101 becomes in effect a very expensive 10 dB pad and reduces the likelihood of input stage overload by 10 dB. Since the OP has the M-101, it's a no-cost option.

There is no argument that using a real re-amp device is a better way to go, but that option was not what the OP wanted to try.

Driving a high-Z input like the M-101's from a low Z line output will not change the sound due to the impedance "mis match". The signal at the input will be exactly the signal being presented at the output of the interface. Obviously loading a high-Z output impedance like the output of a guitar pick-up by connecting it to a low-Z mic input is an impedance mis match (that's why transformer-based direct boxes are used in that application), but going from a 150 ohm line output impedance to a 1 meg input is no different then going into a typical 10k ohm or 20k ohm line input, except the source is loaded even less. Ever since matched 600:600 ohm line impedances achieved via transformer coupling stopped being generally used, the way most audio is transferred is via low source impedances being connected with minimum loading to high input impedances. It's done that way to eliminate the possibility of an input changing the character of a signal.

Connecting the Tascam line out to the 1-meg input of the M-101 or the 1 meg input of the guitar amp is like looking at the output waveform with a 1-meg scope probe. It won't change the signal, and won't change the sound coming from the interface. It obviously won't be the same effect as if the guitar amp was being driven by a high-Z pick-up. If the OP wants to include the effect of a simulated guitar pick-up in the re-amping path (which is redundant since the original signal was presumably recorded with a guitar pick-up in the first place), he can simply add a 500k or 1 meg series resistor in the line feeding the guitar amp. That's a 20 cent (0.15 Euro) option. That will give the HF roll-off caused by the input capacitance of the guitar amp being driven from a high source impedance.

The major disadvantage of using the direct line connection or the routing through the M-101 is that there is no ground-break as there could be with a transformer-coupled re-amp box with a ground-lift switch. That may or may not be an issue depending on the guitar amp and was discussed in post No. 5.

What was proposed here are a few of the possibilities open to the OP to try with the hardware he has. We're talking about re-amping here. It's a process of adding controlled distortion by running a signal through a guitar amp a second time. It's not a discussion of providing a pure "straight wire with gain" signal path for handling a pristine recording of a violin done with a Schoeps MK 2 and a H3V feeding a Prism ADC.
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