Eq in fx loop

NelsonP

....works perfectly on my marshall dsl20 as a boost, with a volume and mid bump.

Try the same trick on my mesa .50 caliber and it farts out. It's almost as though the power tubes can't handle the increased gain. Is that right? Could using an eq in this way on the mesa damage it?

MARVlN

What levels are the respective FX loops? There might not be the headroom in your EQ pedal to handle a line level loop, so it might be causing distortion in your EQ pedal, rather than the Mesa.

Nerine

Placement of fx loop in the amp most likely. The extra volume could be smashing the phase inverter causing the extra distortion. 

Try an under-boost. 

Set the EQ for rhythm sounds and turn it off for leads etc. 

NelsonP

MARVlN said:

What levels are the respective FX loops? There might not be the headroom in your EQ pedal to handle a line level loop, so it might be causing distortion in your EQ pedal, rather than the Mesa.

Good question. The internet suggests it might be line level.

I have some other pedals in the loop though, walrus julia, tc bucket brigade delay, stryom flint, and they are fine.

NelsonP

EFFECTS SEND & RETURN

 These jacks provide a low-noise patch loop within the 50's preamp for connecting external accessories. Compatibility is quite good with most line-level or rack-mount devices, although some will require you to trim down their input attenuators to prevent overload. (Pedal-type effects are designed to handle the low-level signals emanating directly from your guitar; therefore this type of device should be connected “in front” of the amplifier, rather than in the Effects Loop.)

Some manufacturers offer rack-mount multi-effects units for guitar which include compression, distortion, overdrive, etc. Although a good-quality compressor can be used effectively in your Boogie's Effects Loop, we do not recommend the use of multi-effect "guitar processors" in the Loop, as their inputs are often too sensitive and their added gain stages will tend to contribute some noise. If you wish to use this type of device with your Boogie, it should be patched in between the guitar's output and the amplifier's input.

Danny1969

I would think the pedal is distorting. Most simple EQ pedals are biased at half 9V so can swing around 4V peak each way and then it will clip. It doesn't have the headroom for the higher voltage coming in from the line level of the send socket which 775mV as a ref. 

Try lowering all the faders then see what you have .... you can always invert it's use ...as in bypassed is the boost 

MARVlN

NelsonP said:

MARVlN said:

What levels are the respective FX loops? There might not be the headroom in your EQ pedal to handle a line level loop, so it might be causing distortion in your EQ pedal, rather than the Mesa.

Good question. The internet suggests it might be line level.

I have some other pedals in the loop though, walrus julia, tc bucket brigade delay, stryom flint, and they are fine.

It's not hard and fast that pedals won't handle line level - like @Danny1969 says, the design of the pedal in question will affect its ability to take line level signals.

The Strymon for example will take line level (it is apparently adjustable).

Also some of the other pedals might be distorting slightly, but depending on their design, they might do so in a pleasing way (where you may either not notice, or prefer) or in a harsh, unpleasant way. Much like pedals flipping phase, it's a circuit by circuit thing...

To test, you could try sticking a passive volume pedal between the FX send and your EQ pedal and reduce the volume going to the EQ pedal (compensate by increasing the gain from the EQ) to see whether the EQ is the problem or the amp return (as @Nerine mentions).

ICBM

Old Mesa loops are notoriously shit - not properly buffered, at a high signal level, with passive mixing that doesn't go to fully wet and allows some of the output signal to leak back to the input...

I would guess either what Danny said and the pedal is distorting, or possibly that if there's enough gain, it's feeding back on itself via the amp - if so be careful, in rare cases this can damage the amp by making it self-oscillate, although usually only with overdrive/distortion pedals. (Not common at all, but I've seen it on a couple of older Mesas - I forget which models.)

Does the problem still occur when the EQ is used *just* as an EQ and not to boost level?

NelsonP

So I've tried a few things:

Other pedals in the loop - If they are distorting I can't hear it. Order is amp send > Julia v2 > TC bucket brigade delay > Strymon Flint > Source audio EQ > amp return.

I have 2 different eq pedals, a Boss ge7 and a source audio eq (digital). They both work fine as *just* an eq, so long as I don't try to boost the level on the pedal.

Boosting the level above unity results in different behaviours:
- The Boss eq farts out or passes no signal at all
- The source audio eq emits a weird and slightly creepy wailing noise. This goes away if I engage one of the other pedals in the loop (which are ahead of it in the signal chain).

So it looks like the eq pedals just can't boost the level any higher than it is already?

I heard that the mxr 6 band eq can cope with line level. Maybe I need one of those? 

NelsonP

I found this post on TGP....

GE-7 if you want to be able to boost/cut the level. Be aware that it can be hissy - some of the newer designs (Danelectro Fish&Chips, Mooer Graphic G etc) may be quieter, just by virtue of using more modern components. This is mostly an issue when using the pedal in front of an amp, so if you're going to use it as a master eq for a powered wedge, it may not be a problem. What might be, though, is the headroom. The GE-7 is meant for use with guitar signals, so if the signal to the wedge is true +4dB line level, it probably won't fare so well.

The MXR 6-band works if you're mainly going to make tone adjustments (you can boost/cut all the sliders, but it won't be a flat response boost - there will be notches in between the sliders' frequencies). Also, the silver MXR (M109S) is true bypass, while the older black one (M109) is "hardwire". This is really only relevant if you're going to turn it off at times, and plug the guitar directly into it (if there's a buffer before it, the bypass becomes largely irrelevant). The M109S can handle line levels as well

Danny1969

Some opamps can be damaged if the input swings more than the supply rail (the supply rail of a non charge pump /  DC to DC boosted pedal is half the 9V battery / pedal power so it's feasible you could damage something with a high enough line level signal. 

When you boost a frequency or the main gain of an EQ it needs more voltage, if the supply rail can't provide the higher voltage than it will either clip and  / or cut out  because the opamp is reverse biased internally and no longer acting as a linear device. 

You could lower the level before it hits the EQ pedal by using a pot or 2 resistors as a potential divider. 

ICBM

NelsonP said:

Boosting the level above unity results in different behaviours:
- The Boss eq farts out or passes no signal at all

As Danny says, don't do that - it sounds like the ICs in the pedal might be 'latching up', which can blow them.

NelsonP said:

- The source audio eq emits a weird and slightly creepy wailing noise. This goes away if I engage one of the other pedals in the loop (which are ahead of it in the signal chain).

This sounds like it might be self-oscillating via the amp when there isn't a buffer in front of it - this is even worse, as it could possibly damage the amp.

NelsonP

OK, good advice, thanks folks. I'm still looking for an EQ pedal that could do what I need. I've bought a 2nd hand mxr 6 band that I'll try out (one of the older, black ones).

I've also sent a query to mesa boogie. Let's see what they say.

NelsonP

This is Mesa's advice....

"The FX loop on the 50 Cal is a series loop, and will usualy perform at instrument level, unless you crank the gain and master, the amp will get to line level.  However, those are not really realistic settings.  It will be totally fine to run those pedals in the loop.  With that said, boosts can be run there, but it will depend on how much you are boosting the signal, not only on the boost, but how much the EQ'd sound is boosting the signal as well.  The loop is really designed for time based FX.  EQ's and boosts will work, but you really have to listen to the amp and how much boosted signal it can handle.  From the symptoms, it sounds like the phase inverter tube, or the power section is being over driven.  
There may not be a way around the issue, but I would find the point at which the signal is being driven and then back that off a little to see if you can find a mid point to use.  "

Nerine

Have you tried the under boost method as I mentioned earlier? 

Set the EQ when on to be the quieter sound and turn off the EQ when it comes to volume boost, effectively just raising the amp back to “unity” gain. 

NelsonP

Nerine said:

Have you tried the under boost method as I mentioned earlier? 

Set the EQ when on to be the quieter sound and turn off the EQ when it comes to volume boost, effectively just raising the amp back to “unity” gain. 

Yes, it could work, but for some reason I don't like it. More of a conceptual thing and pretty ridiculous as it may work.

I'm hoping that a mid boost without too much overall gain could do the trick.

Nerine

NelsonP said:

Nerine said:

Have you tried the under boost method as I mentioned earlier? 

Set the EQ when on to be the quieter sound and turn off the EQ when it comes to volume boost, effectively just raising the amp back to “unity” gain. 

Yes, it could work, but for some reason I don't like it. More of a conceptual thing and pretty ridiculous as it may work.

I'm hoping that a mid boost without too much overall gain could do the trick.

As someone that runs a volume boost in the fx loop of every single amp I’ve owned, and has enjoyed a healthy 3-6dB of boost for solos pretty much all the time, I’m pretty certain a bump in the mids is gonna do very little other than make
your sound mid-heavy and honky. You’re not making up a 6dB boost in volume by adding some mids without making your sound pretty iffy IMO. 

NelsonP

So the mxr 6 band works perfectly, does exactly what I need. A little mid boost actually helps with cut through as long as it's not overdone. Same as kicking in a tubescreamer.

So weird that the Boss and Source audio eq's don't work with the mesa. Both are fine on my Marshall.

Net result is, I'm happy, I still don't fully understand why they didn't work and will shortly have an EQ pedal up for sale.

ICBM

Poorly-implemented FX loops are remarkably common - possibly ‘normal’ - even on amps you would think were designed by people who should know what they’re doing.

viz

I didn’t like the idea of using boost pedals in the negative way suggested by Nerine and Danny, until I saw Steve Vai using his Little Aligator volume pedal, which is purely an attenuator; it goes from silent to normal. Not normal to louder. I bought one, and when I went from heel to toe, my brain’s thinking of it unlocking the wonderful roar of my untethered, unconstrained amp’s power valves. Awesome. Nothing artificial, nothing added, just pure unleashed, untaimed amp glory. Think of that and suddenly using your pedal in this way makes sense. Try it!

ICBM

viz said:

I didn’t like the idea of using boost pedals in the negative way suggested by Nerine and Danny, until I saw Steve Vai using his Little Aligator volume pedal, which is purely an attenuator; it goes from silent to normal. Not normal to louder. I bought one, and when I went from heel to toe, my brain’s thinking of it unlocking the wonderful roar of my untethered, unconstrained amp’s power valves. Awesome. Nothing artificial, nothing added, just pure unleashed, untaimed amp glory. Think of that and suddenly using your pedal in this way makes sense. Try it!

It’s easy to think that pushing something harder always sounds better - most guitarists seem to default to that option - but actually, it often doesn’t. Pulling back a bit so you have more room to go louder/more without saturating the living daylights out of everything often works better in my experience.