Multi Amp Rigs

I've had a lot of messages asking about the amps Kirk Fletcher was using on his recent UK shows. On both shows he had two amps running with a Radial Hotshot passive A/B/Both box. This allowed us to connect to both amps without any ground loop induced noise. When using this box it is crucial to make sure the guitar is buffered or there will be a very noticeable (read unusable) loss of top end on the 'B' output when it is isolated. Kirk has a Boss DD pedal on his board which fulfilled this requirement. Any Boss pedal will buffer the signal even in bypass.

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At both shows Kirk used his 633 ‘KF30’ tweed combo which is based on a mid 50’s Fender Pro Amp. The original used a 15” speaker, Kirk’s uses a 12” Celestion Alnico Gold and I squeezed the amp complete with oversized transformers into an off-the-shelf Tweed Deluxe chassis. The feature set is two inputs, Bright and Normal, each with it’s own Volume control, then Treble, Bass & Presence. I also added a solid state/tube rectifier switch which drops the output power from around 35 watts to 28 watts and adds more compression to the tone. Kirk was using the solid state setting and the Normal input on the amp.

At the Borderline show the second amp was a Drive King 50 Head feeding a 2x12 open backed cabinet loaded with one Celestion Alnico Gold and one Celestion G12-75H Creamback wired in series. The Drive King was set to use the clean channel with the Headroom set to position 3 - so around 25 watts. On stage there was an equal mix of both amps.

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At the Bristol Jazz & Blues Festival show we used the same rig but experimented using a Classic 45 head with the 2x12 cab. Alas during soundcheck Kirk was asked by the sound engineer to reduce his stage volume so we ended up using just the combo.

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When using two or more amp/cabs it’s important to make sure the amps are working together and in phase. The Radial box has a phase reversal switch but it’s also important to get the speakers aligned in the same plane, particularly if they are place close together. Try and line up the cabinets as if the speakers were all on one baffle. To establish the correct position of the phase switch position yourself in front of both cabs and play a muted note on the low E string using the neck pickup with the tone control turned down and listen to how much low end thump there is. Then flick the Phase switch and listen again. the setting that produces the most bass is the most in phase.

Jazz & Blues

With the craze for stomp boxes ever growing the overdrive pedal has never been more popular and there are literally hundreds if not thousands of variants to choose from.  I figured a new design of amp could be beneficial for lovers of pedals.

You may have experienced this - you get your amp set up for a great clean sound then you hit the drive pedal and the tone is too fuzzy or has too much mid so you want to adjust the amp again and bang goes your amazing clean tone.  

The 'Jazz & Blues' is a 45 watt single channel amp with remote voicing that can switched when you select your drive pedal.

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The Jazz & Blues also has an FX loop located right at the front end of the amp right after the first valve stage, which is configured as a unity gain buffer. Your pedals get the right signal level and your guitar sees the amp directly regardless of how many FX you have switched in. There's no loss of tone and you can even put drive pedals in the loop. And your guitars' volume and tone work consistently without being affected by the first pedal in the chain.

Pickups

This past week I had two conversations with guitarists about pickups. Both players believed that the "ohms" was a measure of how the pickup would sound. One also believed that 'hotter' was better. Given some of the marketing techniques employed by pickup manufactures I guess this an easy assumption to make. Pickups are seldom described as 'full', 'muffled', 'thin' or 'boxy' even though these descriptions might be more representative than say 'hot', 'warm', 'vintage' or 'mellow'. 

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In the 70s when I first 'discovered' replacement pickups, the only models my local music shop stocked was the Dimarzio Dual Sound Super Distortion. I ended up with three of them installed in my Strat copy along with a switch to coil tap all of them at once! 

Since then the replacement pickup market has ballooned so you can now choose from infinitesimal numbers of designs and over the years I've tried more than my fair share of them. And what I've found is that I've gone for lower and lower output pickups because I can hear more of the tone of the guitar.  When shopping for pickups there's always the temptation to go for the "vintage spec but over wound for more balls" because you feel you're getting a better product; more for your money.  Certainly high output pickups are great for very overdriven tones because of the way they drive the amp but I have found that the lower output ones make better guitar sound. 

So why is this? Electronically speaking a pickup is a second order low pass filter.  This means it has a resonant peak just below ( in frequency ) the cutoff frequency of the filter. This is mostly what defines the tone of the pickup. Above the resonant peak the output of the pickup rapidly falls away to nothing. High output pickups have a lower resonant frequency than low output pickups, so they reproduce much less of the harmonic spectrum of the guitar. Lower output pickups have an extended frequency response and reproduce more of the higher order harmonics.

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At this point it's worth mentioning the effect of load impedance on the tone of the guitar. The load is basically the resistance of the volume pot(s) in parallel with the input impedance of the first thing connected to the guitar. The lower (in ohms) the load on the pickups the smaller the size of the resonant peak. The higher the load resistance the greater the size of the peak. The device at the end of the guitar lead also works with the capacitance of the lead to gentily roll off some of the higher frequencies.  It's worth recognising all these factors and their effect before deciding your pickups sound below par. It may also explain why your tone varies when you use different leads and pedals. One way to ensure a consistent tone is to always use the same lead and if you're using a pedal board make the first pedal a buffered one.

 

Fix It Before It Breaks

You arrive at your gig and set up your gear. That funny noise your amp was making stopped when you wiggled the speaker jack at the midweek rehearsal so it must have been a temporary fault that has now fixed itself. So all is well.  Not!  The first song into the second set your amp makes an almighty noise then cuts out leaving a whiff of electrical burning.........

Last Saturday morning I got a call from a bass player I know - ".... my amp was playing up last night and I'm going on tour next week - can you take a look it?.....". He reported that the amplifier had been losing volume and then at one point produced no output, but the DI was still working so it looked like the fault was in the power amp stage. The amp in question was an Eden. I'd worked on one of these before and knew that they had lots of inter-PCB connectors, a possible source of intermittent problems, but I didn't have any schematics so serious diagnosis of component failure would be difficult.  I agreed to take a look to see if it was something fixable.  

The amp was in a flight case. As I started to undo the screws to remove it I noticed that the rack ears on the amp were both loose. When I actually removed the amp I felt something heavy move around inside! I also noticed quite a few screws missing from base of the chassis. It wasn't looking good. 

Usually I would power up an amp to test for the reported fault before opening it up, but in this case I was concerned that the insides were in bad shape so the first thing I did was to take off the lid. 

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It didn't take too long to establish that a loose transformer had trapped a cable against the edge of a circuit board and managed to break through the insulation. The wires in question were connected to a thermal cutout switch so there was a possibility this had caused the amp to cut out. 

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It could have been much worse.  A few more trips on the road and the transformer could have damaged the circuit board. Or the insulation on the transformer could have worn away creating untold damage. It would have been new amp time.

While I had the amplifier open I decided to give it a once over cleaning all the connectors, checking for poor or cracked solder joints and touching them up, 

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Unused FX Loops (this amp has 3!) are sometimes a source of intermittent problems . It is quite common for the normalising contacts on the jack sockets to corrode and interrupt the signal flow, sometimes causing the signal to cut out completely and on other occasions causing distortion when the poor contact acts as a diode.  This is all easily fixed with a squirt of contact cleaner followed by a few insertions with a jack plug.   Better still - leave a jack patch lead permanently connected in your unused FX loops.

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Lastly I took a look at the transformer mounting. The lock nut had not actually loosened but over time the chassis had deformed slightly and the rubber gasket had compressed allowing the transformer to move around.  I re-tightened the nut and bolt securing the large transformer. 

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With the damaged cable repaired and the missing screws replaced, tightened and secured with locking compound, the amp is fit for use and ready for another stint on the road. 

If you're serious about your music, your band and your audience get your gear periodically checked.  If you feel anything loose or hear any strange noises it's definitely going to get worse until it breaks.  Something as simple as a loose screw can mess up a gig and cause hundreds of pounds in repairs.  For just a few quid an periodic check can prevent this and give you piece of mind.

 

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