help with feedback

I've recently started playing with an electric Americana group. The singer really likes the sound of the mandolin along with the lead electric guitar. So I got a LR Baggs Radius pickup; at the first gig I had really bad feedback, and low gain.

I then got a LR Baggs Para-acoustic DI to hopefully address that. I did all the adjustments they recommend for setting gain and notching frequencies for feedback.

I tried it at home in two amps, my Fender Hot Rod Deluxe and my Boss Katana 50. I was hoping to use the Fender as sometimes I may need to switch to electric guitar, but the feedback was unmanageable. I got it under control with the Katana on its acoustic setting, but it's a quieter amp, and I like the Fender better (the Katana is for practices as it's lighter). Some gigs will have a PA, but others will be outside so I worry about holding up against the full band.

Is this just natural-hot tube amps will feedback and I need an amp designed for acoustic instruments, even with a preamp? Should I get a better acoustic amp? Or is there something else I can do?

Quote:

---

Originally Posted by Pehenne

Is this just natural-hot tube amps will feedback and I need an amp designed for acoustic instruments, even with a preamp? Should I get a better acoustic amp? Or is there something else I can do?

---

My 2 cents:
A tube amp will compress the sound. This is great for electric guitars. But any compression will increase feedback when used with a microphone.

Tube amps only limit (technically not compression) when clipping, overdriven.

In my experience, electric-loud bands will require a bridge pickup for useful signal above feedback. Drew Emmitt of Leftover Salmon uses one on his Nugget, ditto Don Stiernberg. The sound is less "acoustic", but can be plenty musical with the right EQ.

I played a gig with a loud band, and the guitar player switched to his inexpensive mandolin with basic Fishman bridge. Plugged it straight into his Deluxe Reverb, no preamp, sounded fine and plenty loud,

Most tube amps have an input impedance of 100K so it will work without a preamp. It's not the 1M you want to see, but it makes the factor of 10 in electronics. The Fishman has a 10M, which is ten times higher than the 1M that is the best, the tube amp 10 times lower. The bridge pickup, as recommended, will work better for feedback. Not sure what kind of mandolin you are playing, but a strap around the body to keep it from resonating will help, if you don't want to spend more $$$. Put close behind the bridge.

Thanks. I had read that some other solid state like my Katana for that reason

On the undrstanding that it’s impossible to diagnose your problem from the other side of the Atlantic ..............

A piezo pickup needs an input impedance of at least 1 Meg.ohm (a million ohms) and an amp with a flat frequency response (i.e. one which responds equally at all useable frequencies.

Your average guitar amp - intended for electric guitars - will have an input impedance less than this and, consequently, the amount of gain available will be limited. Electric guitars rely to a greater or lesser extent on the amp for their tonal character (imagine two guitarists arguing about which is their favourite amp!) and this character is derived from the vagueries in the way any particular amp responds to a range of frequencies. As a result, as you turn up the gain some of the more prominent frequencies will feed back before others - which more or less describes the problem you’re having. Yes, you might be able to notch out frequencies but you’ll likely run out of notches to curb an amp with a response curve like the sea on a choppy day.

The simple solution is to use an acoustic amp which should have the correct input impedance and where everything starts off flat in the first place. You can then use the tone controls to dial in the sound you want or make up for any inadequacies in the instrument or pickup.

I’m not familiar with the Katania but “acoustic” amps would include any number of specifically built ones, keyboard amps, PA systems and, as you appear to have one, a Padi into a powered speaker.

It's a slight digression, but as I noted above, piezos straight into a tube amp are not inherently a problem. In the 70s we plugged our Barcus-Berry or Fishman pickups into our Twin Reverb amps. It was not a gain problem, as the piezos were a hotter signal than my Les Paul Deluxe. And tube amps are not inherently a lumpy frequency curve--that is the speakers.

I have one legacy-type chorus pedal that loses a bit of signal with the output of my Headway under-saddle pickup (built in EQ). The others are fine. The only issue I have with a raw piezo output is it always needs EQ of some kind to sound natural.

For playing with a really loud electric band, I use a relatively cheap Fender Robert Schmidt mandolin, which has a piezo pickup in the bridge. It needs a lot of eq help to sound reasonable, but it doesn't feed back even at high volumes.

Feedback also depends greatly on where you are standing relative to amp or the monitor, that's something you have to experiment with and get used to in loud bands. I've had a number of gigs where I had to stand in a very specific spot to avoid feedback from a really resonant acoustic guitar or an acoustically better mandolin than the Fender.

Quote:

---

Originally Posted by Tom Wright

It's a slight digression, but as I noted above, piezos straight into a tube amp are not inherently a problem. In the 70s we plugged our Barcus-Berry or Fishman pickups into our Twin Reverb amps. It was not a gain problem, as the piezos were a hotter signal than my Les Paul Deluxe. And tube amps are not inherently a lumpy frequency curve--that is the speakers.

I have one legacy-type chorus pedal that loses a bit of signal with the output of my Headway under-saddle pickup (built in EQ). The others are fine. The only issue I have with a raw piezo output is it always needs EQ of some kind to sound natural.

---

I too started with a Barcus Berry back in the 70s although I never had a twin reverb! You could plug them into an ordinary guitar amp (acoustic amps had yet to be invented) but they lacked gain and bottom end. This was entirely down to the amp input being too low impedance. Barcus Berry did produce a, so called, “preamp” which solved the problem and I managed to borrow one from a local shop in order to try it. What I really wanted to do was to see what was inside it and I took it to a friend who lived a short way away and built sound systems for military simulators for a living.

We were both surprised at how little the box contained and the conclusion was that it was something called a FET buffer - basically a device to widen the impedance of the amplifier input. I took it back and didn’t buy it.

The BB has been inside a Martin guitar since the 70s and plugged into a modern 1Meg + input preamp, it sounds better than it ever did. Little has actually changed with piezo pickups since the invention of the telephone.

If you are still using the Radius with the Para-DI it should be ok, impedance-wise, if you take the unbalanced (1/4") output to an amp, but it would be better if you could run a balanced (XLR) signal to the PA, and only use the on-stage amp at a level for monitoring, IMO. I would not be using a guitar amp for that.

And, you do need to roll the bass off a fair amount on everything along the way because, let's face it, there's no bass in a mandolin so anything below 200kHz picked up and amplified is going to be a problem.

Before we get too much into kit, how's your stage hygiene? By which I mean sound levels on stage. If it's loud and you're all competing with each other to be heard then you're on a hiding to nothing trying to compete with an acoustic instrument. Sorry, but you just are. Ideally sound levels on stage should be "normal listening volume" - much easier said than done - but if you can get there or somewhere near it it will largely fix your feedback issues. Ideally you would be using a PA with your amps at low volume just for monitoring purposes, or else you will need the amps out in front of you with the sound going away from you (but then you can't hear what you're doing).

Quote:

---

Originally Posted by Tavy

Before we get too much into kit, how's your stage hygiene? By which I mean sound levels on stage. If it's loud and you're all competing with each other to be heard then you're on a hiding to nothing trying to compete with an acoustic instrument. Sorry, but you just are. Ideally sound levels on stage should be "normal listening volume" - much easier said than done - but if you can get there or somewhere near it it will largely fix your feedback issues. Ideally you would be using a PA with your amps at low volume just for monitoring purposes, or else you will need the amps out in front of you with the sound going away from you (but then you can't hear what you're doing).

---

Agree. It’s going to be tough sledding with so much stage volume. I had trouble with that pickup even in a benign church environment. I made a rubber sound hole plug for my A which helped and the sound person would spend a lot of time finding the feedback threshold beforehand. It was workable but got better after I had a Reso-coil pickup installed. We have in-ear monitors at church now and that has taken away all of my feedback anxiety.

Best of luck