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.

IMG_4163.JPG

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'. 

image.jpg

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.

image.jpg

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. 

image.jpg

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. 

image.jpg

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, 

image.jpg

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.

image.jpg
image.jpg

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. 

image.jpg

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.

 

FX loops pros and cons

Many modern amplifiers have effects loops principally to allow time delay effects to be applied after the amplifier's distortion producing circuitry. But effects loops are very rarely found on old vintage style amplifiers. This series of articles looks in depth at how effects loops came about, their limitations, how they can affect your tone and how you need to set up your gear to use them to their best.

Read More

Tone & Technology

TONE - is a difficult thing to describe.  It comes in many forms and means so many different things to each person.  It can mean one thing to a player and another to the listener.   To the player tone is everything they experience as the process of playing and hearing forms a feedback loop, and a big part of that experience is the amplifier.

Read More

The Kirk Fletcher Approach

I first saw Kirk Fletcher a year ago at a gig in Oxford and was immediately struck by the way he created such a wide range of tones using just his guitar's volume and tone controls and the amp.  I've seen a few other guitarists play in the same way and they all have several things in common - they use no pedals, always have a great tone that cuts through the mix and they can all make the guitar sing using just the amplifier.

Read More

Cascaded Gain Stage Amplifier Design

A few of my friends and customers have amplifiers that are based on the Dumble Overdrive Special, made by Ceriatone and Bludotone.  In contrast to my current designs they are very much 'clean and lead' with very little breakup from the power valves.  I took the opportunity to spend some time with them to try and discover what the fascination and mystique of these revered designs was all about. 

Read More