Builder Profile

BUILDER PROFILE – Andrews Amplification started in Roswell, GA as an offshoot of Andrews Amp Lab. Back in 2005 Jeff Andrews built the first Andrews Amp for his personal use. The idea was to use knowledge gained from years of servicing, modifying and playing thousands of amps to come up with a solid amp that could fill the role of previously owned amp. That amp was a 1971 Marshall Super Lead head. The new amp was to reside in a smaller, lighter package that could achieve the tone without so much volume. He started with a vintage Trayner YGM3 chassis and cabinet. It was gutted other than the power transformer and tube sockets. The prototype that was built produced about 25 watts and the circuit was similar to a “plexi” but the voicing of the 2 channels was combined and refined. With a few more refinements, transformer upgrades, a master volume control and other features, it eventually became the model A-22.

The A-22 was officially launched on 2006 and was later joined by the A-45 which was later replaced by the A-50.

After discussions with friends and customers at the summer NAMM show in 2011, development began on the new channel switching models, the Para-Dyne 20 and Para Dyne 50. The designs took many months and hundreds of hours to complete. The result is a versatile tone machine that will not disappoint the most demanding player. More recently, the Spectraverb 22 and award winning Spectraverb 40 were developed which added lush spring reverb to the lineup.  In late 2015, the Spectraverb 16 joined the lineup.

The design philosophy for all the Andrews Amps has consistently been to build the highest quality amps with the best tone. Andrews Amps does not cut corners by using off the shelf cabinets, chassis or boards. These and other components are custom designed and built for Jeff’s critical designs and all the amps are hand-wired on the premises.

Solid State and Tube-Type Effects Loops Compaired

I’ve come to realize that there is a lot of confusion and misinformation floating around regarding effects loops. First, what is an effects loop? Generally speaking, an effects loop (aka FX loop) is a set of connections on an amp that allows the user to connect effect units such as reverb, delay, vibrato, chorus etc. after the preamp and before the power amp.

There have been countless on-line discussions and articles written on how and when to use an FX loop, what kind of effects should be connected to them and so on. The purpose of this article is to explore the different types of loops and the advantages and disadvantages of each type.

The most basic loop is achieved simply by disconnecting the internal connection between the preamp and power amp and installing jacks on the amp so that effect units can be connected to the signals. This type of loop is still being used in many amps today because of the ease and low cost to install it. However, it often provides very disappointing results for a couple of reasons. #1 A typical power amp needs around 7 volts RMS to drive the power amp (phase inverter) to full power. That means your effects units need to be able to provide that much signal to drive the amp since the effect’s output now provides the signal to drive the amp. Most effects run on 9 volts DC. The most amount of signal generally available for a 9VDC source is around 3 volts RMS. #2 – The impedance of the internal circuits and the effects are usually not well matched. That means there will be additional looses when long cables are used. This is clearly the worst type of effects loop.

A better type of loop is one that is buffered. Buffering means the loop circuit can correct for mismatched impedances and not create incorrect loads on the circuits of the amp or the effects. In addition to buffering, signal cutting and boosting can be added. That means that the loop can reduce the level of the signal coming from the preamp down to a proper level so the the effect unit is not overloaded and then boost the low signal coming from the effect back up to the proper level for the power amp if necessary. The best loops have a switch or variable control to accomodate both low level (stomp boxes) and high level (rack mount) effects.

There are two main types of buffered loops that can be used in tube amps. They are tube driven loops and solid state loops. Let’s look at the advantages and disadvantages of each type.

Tube Driven Loops
Advantages
1) Maintains a pure tube signal path for all signals in the the amp? Remember however that when a loop is used, you will be connecting effects that are solid state devices so you really won’t have a pure tube signal at all. Most effects that would be connected to your loop have many solid state gain and buffer stages your signal will pass through. Therefore, there is no real benefit to having a tube buffer over a solid state one.

Disadvantages
1) Will cause more noise such as hiss and hum.
2) Will alter the tone somewhat.
3) Will take up space necessitating a larger camp chassis
4) Higher cost

Solid State Loops
Advantages
1) Lower noise
2) Less distortion
3) Can be made extremely “transparent”
4) Smaller footprint
5) Lower cost

Disadvantages
1) No longer a pure tube signal path? See above. A switch can be added to allow the loop to be completely disconnected from the circuit when not needed. That switch also allows an easy A/B comparison of the affect the loop circuit has on the tone and noise of the amp. Truthfully, there is no disadvantage.

I highly recommend buffered solid state effects loops with a level switch and a bypass switch for any application.

Jeff Andrews

Latest News from Andrews Amps

Steel String Singer

Check out this video of a special build we did.  Clone of a Steel String Singer serial # 002. This build requires a lot of speciality parts and is extremely labor intensive. Cost is $5600.