Fuchs Clean Machine Part 2
Before I continue with part 2 of what will be a multi part in depth long term review I would like to repeat a few things that I said in part 1.
I will be going into this amp in depth over many days or perhaps weeks. I will also be posting the thoughts of others who will be using the amplifier over time.
This particular amplifier is available for loan for live gigs, studio work or if you just want to check it out. I can be reached via my normal email address but you can also find me on www.musicplayer.com in the guitar area which is Guitar Player Magazine in the ongoing thread "Feel free to ask Myles" or on the Dr. Z Amp forum in the "Ask the experts" area at http://drzamplifiers.proboards41.com/index.cgi?board=xperts&action=display&thread=11242
On the subject of loan of the head:
If you are in Southern California in the areas of Hollywood, Burbank, North Hollywood, the West Valley such as Calabasas, Universal City, music clubs in these areas above or places such as Third Encore I will be happy to deliver the amplifier head to you upon prior arrangement.
A bit more about how I review amps. I do not test an amp for a few days. It typically goes on for months or even a year. A key part of the review process of any amp is the thoughts of others and travel. It is beneficial to have others use the amp and provide feedback. It is also best if the amp can spend a bit of time on the road. I cannot count how many amps may work on stage just to fail on the truck being moved from one city to another.
Moving along .
The Clean Machine is available in head and combo choices. There are three wattage choices; 75, 100 and 150 watts.
The tube compliment is as follows:
3 X 12AX7 preamp tubes,
1-6FQ7 power amp driver tube or a 12AT7 tube
2 X 6550 power tubes (75 Watt)
4 X 6L6 tubes (100 Watt version)
4 X 6550 (150 Watt version)
Id like to take a moment to make an observation in regard to what Fuchs calls the amp driver tube. Some folks call this the phase inverter. One tube that is used in some amps is called a 6FQ7. There is nothing bizarre or unique about this tube. It is easily replaced if required and they are available at low cost. From folks like Antique Electric Supply they can be bought for less than $15 in NOS versions and even the most pricy RCA clear tops are $28.80. The current tube in most amps is a 12AT7.
In the past I have written a number of articles and some of these pieces were also reprinted in The Tube Amp Book by Groove Tubes where I spent six and a half years as their tech support and tube guy for QA and tube development. In many amps what you hear is the phase inverter giving up the ghost and not being effective in driving the output stage of the amp. A 6FQ7 has about four times the wattage output than a typical 12AX7 and that is IF the 12AX7 meets spec. Most 12AX7 tube them do not meet spec. 85% or more of them do not. The plate current of a 12AX7 at spec is 1.2mA. Most show 0.7mA to 0.9mA. The 6FQ7 has a plate current of 9mA. The 12AT7 is very similar to the 6FQ7. It has a plate current output of 10mA and has about a 2 ½ watt output. Either tube can easily drive an output section of an amplifier and last a very long time doing duty in this critical position. As a comparison, a 12AU7 has a power output of 2 ¾ watts and 11.8mA of plate current and is the tube used for the driver tube in an Ampeg SVT. When it comes to driving an output section of an amp accurately and not having the design interaction of the phase inverter or driver tube breaking down as a factor in tone the Fuchs design from my personal point of view is the way to go when it comes to building an amp designed for the intended application of this particular amp.
Some of the other nice aspects of this amp are things such as single-point star grounding. The transformers are audiophile grade which means wide bandwidth. Just the ticket on an amp designed for clean tones. High speed diodes are used in the power supply of the amp and these DC supplies (which reduce hum) are both regulated and buffered.
DC power supplies for both filaments and high voltage sources are some of the key elements which allow the amp to have such a low noise floor even at the highest settings. To repeat myself this is a very quiet amp.
The chassis work is first rate and even items like the panels are attached with stout pem-nuts. I do not have any worries about this amp handling the stresses of road travel and previous experience with Fuchs construction has proven this point over tens of thousands of miles on the road. As a slight digression the tour bus for Trace Adkins is a 2003 I believe and has over 450,000 miles on it or maybe a bit more.
Briefly on some of the controls I will go into this more deeply in future parts of the review:
The high control pulls for mid boost. The mid control pulls to adjust the mid boost frequency. The low control pulls to adjust the shift point between the low and mid controls. Additionally, a bright switch, an enhanced deep switch circuit, and two distinct EQ settings for the channels tone stack, give this amp one of the widest tone ranges available in four simple knobs.
The all-tube 12AX7 effects loop features a low impedance cathode follower output, which can feed most any tube or solid state effect device. Its send level is adjustable from pedal to rack level. The loop can also be bypassed via footswitch. The return sensitivity can be adjusted to accept both pedal or line level return signals, and provides a high 250-K input impedance.
The effects loop also provides the mixing for the wet and dry reverb signals in the amp. Both the send and return are active at all times, whether you patch through the loop or not. This allows the loop to be used as a line out, as well as a spare input to the power amp.
The reverb implements what Andy describes as a servo-loop push-pull drive stage and a low noise Op-Amp return stage. There is an input level, dwell and tone control, as well as an output level and tone control. As I have said before, the reverb is about as good as it gets and works over a very wide range with an extremely low noise floor.
From the Fuchs manual: We use a high current Hexfet regulator for both the screen voltage as well as to provide a regulated B+ to the driver tubes. This assures the amp stays together throughout its entire power output range. A 12AX7 predriver/phase inverter is followed by a DC coupled 6FQ7 cathode follower, which directly drives the power tube grids.
Designed more like an SVT style bass amp than a guitar amp, this results in a power amp thats tight, articulate and well-defined. The output stage is followed by a custom wound output transformer with 4, 8, and 16 ohm outputs. A separate bias control for each output stage half, and an AC balance control adjust the amp to audiophile levels of low distortion and linearity.
Features:
¾ solid wood cabinet with durable tolex covering.
Anodized aluminum chassis with long-lasting anodized aluminum labeling on brushed aluminum control panel. Crème or black knobs are available. Heavy duty Cliff brand jacks. Solid metal shaft Alpha potentiometers. Ultra-long-life LED pilot lamp and heavy duty AC power, standby switches. Power stage features AC balance control, and separate bias controls for each power tube pair.
- end of info from the Fuchs manual
In part 3 I will be putting some of what Andy Fuchs sent to me directly on the amp which goes into greater detail.
This will end part 2 of this review and look into the Clean Machine. Part 3 is in the works and will be available in the next few days.
Before I continue with part 2 of what will be a multi part in depth long term review I would like to repeat a few things that I said in part 1.
I will be going into this amp in depth over many days or perhaps weeks. I will also be posting the thoughts of others who will be using the amplifier over time.
This particular amplifier is available for loan for live gigs, studio work or if you just want to check it out. I can be reached via my normal email address but you can also find me on www.musicplayer.com in the guitar area which is Guitar Player Magazine in the ongoing thread "Feel free to ask Myles" or on the Dr. Z Amp forum in the "Ask the experts" area at http://drzamplifiers.proboards41.com/index.cgi?board=xperts&action=display&thread=11242
On the subject of loan of the head:
If you are in Southern California in the areas of Hollywood, Burbank, North Hollywood, the West Valley such as Calabasas, Universal City, music clubs in these areas above or places such as Third Encore I will be happy to deliver the amplifier head to you upon prior arrangement.
A bit more about how I review amps. I do not test an amp for a few days. It typically goes on for months or even a year. A key part of the review process of any amp is the thoughts of others and travel. It is beneficial to have others use the amp and provide feedback. It is also best if the amp can spend a bit of time on the road. I cannot count how many amps may work on stage just to fail on the truck being moved from one city to another.
Moving along .
The Clean Machine is available in head and combo choices. There are three wattage choices; 75, 100 and 150 watts.
The tube compliment is as follows:
3 X 12AX7 preamp tubes,
1-6FQ7 power amp driver tube or a 12AT7 tube
2 X 6550 power tubes (75 Watt)
4 X 6L6 tubes (100 Watt version)
4 X 6550 (150 Watt version)
Id like to take a moment to make an observation in regard to what Fuchs calls the amp driver tube. Some folks call this the phase inverter. One tube that is used in some amps is called a 6FQ7. There is nothing bizarre or unique about this tube. It is easily replaced if required and they are available at low cost. From folks like Antique Electric Supply they can be bought for less than $15 in NOS versions and even the most pricy RCA clear tops are $28.80. The current tube in most amps is a 12AT7.
In the past I have written a number of articles and some of these pieces were also reprinted in The Tube Amp Book by Groove Tubes where I spent six and a half years as their tech support and tube guy for QA and tube development. In many amps what you hear is the phase inverter giving up the ghost and not being effective in driving the output stage of the amp. A 6FQ7 has about four times the wattage output than a typical 12AX7 and that is IF the 12AX7 meets spec. Most 12AX7 tube them do not meet spec. 85% or more of them do not. The plate current of a 12AX7 at spec is 1.2mA. Most show 0.7mA to 0.9mA. The 6FQ7 has a plate current of 9mA. The 12AT7 is very similar to the 6FQ7. It has a plate current output of 10mA and has about a 2 ½ watt output. Either tube can easily drive an output section of an amplifier and last a very long time doing duty in this critical position. As a comparison, a 12AU7 has a power output of 2 ¾ watts and 11.8mA of plate current and is the tube used for the driver tube in an Ampeg SVT. When it comes to driving an output section of an amp accurately and not having the design interaction of the phase inverter or driver tube breaking down as a factor in tone the Fuchs design from my personal point of view is the way to go when it comes to building an amp designed for the intended application of this particular amp.
Some of the other nice aspects of this amp are things such as single-point star grounding. The transformers are audiophile grade which means wide bandwidth. Just the ticket on an amp designed for clean tones. High speed diodes are used in the power supply of the amp and these DC supplies (which reduce hum) are both regulated and buffered.
DC power supplies for both filaments and high voltage sources are some of the key elements which allow the amp to have such a low noise floor even at the highest settings. To repeat myself this is a very quiet amp.
The chassis work is first rate and even items like the panels are attached with stout pem-nuts. I do not have any worries about this amp handling the stresses of road travel and previous experience with Fuchs construction has proven this point over tens of thousands of miles on the road. As a slight digression the tour bus for Trace Adkins is a 2003 I believe and has over 450,000 miles on it or maybe a bit more.
Briefly on some of the controls I will go into this more deeply in future parts of the review:
The high control pulls for mid boost. The mid control pulls to adjust the mid boost frequency. The low control pulls to adjust the shift point between the low and mid controls. Additionally, a bright switch, an enhanced deep switch circuit, and two distinct EQ settings for the channels tone stack, give this amp one of the widest tone ranges available in four simple knobs.
The all-tube 12AX7 effects loop features a low impedance cathode follower output, which can feed most any tube or solid state effect device. Its send level is adjustable from pedal to rack level. The loop can also be bypassed via footswitch. The return sensitivity can be adjusted to accept both pedal or line level return signals, and provides a high 250-K input impedance.
The effects loop also provides the mixing for the wet and dry reverb signals in the amp. Both the send and return are active at all times, whether you patch through the loop or not. This allows the loop to be used as a line out, as well as a spare input to the power amp.
The reverb implements what Andy describes as a servo-loop push-pull drive stage and a low noise Op-Amp return stage. There is an input level, dwell and tone control, as well as an output level and tone control. As I have said before, the reverb is about as good as it gets and works over a very wide range with an extremely low noise floor.
From the Fuchs manual: We use a high current Hexfet regulator for both the screen voltage as well as to provide a regulated B+ to the driver tubes. This assures the amp stays together throughout its entire power output range. A 12AX7 predriver/phase inverter is followed by a DC coupled 6FQ7 cathode follower, which directly drives the power tube grids.
Designed more like an SVT style bass amp than a guitar amp, this results in a power amp thats tight, articulate and well-defined. The output stage is followed by a custom wound output transformer with 4, 8, and 16 ohm outputs. A separate bias control for each output stage half, and an AC balance control adjust the amp to audiophile levels of low distortion and linearity.
Features:
¾ solid wood cabinet with durable tolex covering.
Anodized aluminum chassis with long-lasting anodized aluminum labeling on brushed aluminum control panel. Crème or black knobs are available. Heavy duty Cliff brand jacks. Solid metal shaft Alpha potentiometers. Ultra-long-life LED pilot lamp and heavy duty AC power, standby switches. Power stage features AC balance control, and separate bias controls for each power tube pair.
- end of info from the Fuchs manual
In part 3 I will be putting some of what Andy Fuchs sent to me directly on the amp which goes into greater detail.
This will end part 2 of this review and look into the Clean Machine. Part 3 is in the works and will be available in the next few days.
