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Fuchs - an amp review - part 2

myles111

Member
Messages
2,954
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)

I’d 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 channel’s 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 that’s’ 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.



 

TaronKeim

Member
Messages
2,937
Great to hear more about this amp, I've wanted one since their release but there just isn't enough information out there. Plus I also play a 7-string, and what a lot of people consider "tight enough bass response" just isn't enough to handle a Low B/Low A.

_TJK*
 

myles111

Member
Messages
2,954
Great to hear more about this amp, I've wanted one since their release but there just isn't enough information out there. Plus I also play a 7-string, and what a lot of people consider "tight enough bass response" just isn't enough to handle a Low B/Low A.

_TJK*
You probably should try to check the amp out. It has terrific focused bass. The transformers and power section are very high grade and very wide bandwidth which may be just the ticket for dropped tunings as well. There are also a few pedal steel guys that I'd like to look at the amp as well.

A bit if insight on the amp that was sent to me by Andy Fuchs that talks a bit about your concern ...

The power amp stage is a 12AX7 in a traditional Schmidt style diff-amp configuration, which feeds a 12AT7 cathode follower. The cathode follower driver tube runs from a -200V supply on it’s cathodes, which drives the power tube grids directly. This is similar to an SVT bass amp or the Dumble Steel String Singer circuit. The positive supply to the driver tube is a regulated power supply, which also drives the power tube screens. The power tube screens run about 100 volts lower than the plates, for greater dynamic range and higher power tube reliability. Each half of the output stage has it’s own bias control, so matched pairs per half are used.
 

TaronKeim

Member
Messages
2,937
You probably should try to check the amp out. It has terrific focused bass. The transformers and power section are very high grade and very wide bandwidth which may be just the ticket for dropped tunings as well. There are also a few pedal steel guys that I'd like to look at the amp as well.

A bit if insight on the amp that was sent to me by Andy Fuchs that talks a bit about your concern ...

The power amp stage is a 12AX7 in a traditional Schmidt style diff-amp configuration, which feeds a 12AT7 cathode follower. The cathode follower driver tube runs from a -200V supply on it’s cathodes, which drives the power tube grids directly. This is similar to an SVT bass amp or the Dumble Steel String Singer circuit. The positive supply to the driver tube is a regulated power supply, which also drives the power tube screens. The power tube screens run about 100 volts lower than the plates, for greater dynamic range and higher power tube reliability. Each half of the output stage has it’s own bias control, so matched pairs per half are used.
Very cool to hear... are you going to try an array of cabinets with it? I have to go with closed back no matter what, I've had the best success with front loaded... though they can be a little sterile.

I'm thinking a 4x10 ported cab might be my best bet... or a very deep front loaded cab that is completely sealed in the back. I'll have to talk to Andy about cab suggestions.

Thanks for your input Myles, I look forward to hearing more of your review!

_TJK*
 

remocity

Silver Supporting Member
Messages
2,260
I have a Clean Machine 75 and use it with the Glaswerks 112th ported/Theile cabs he sells with Celestion Heritage G12-65's.
Like it better than the Emmi R,W,B's for what I do.
I also use it with an open back Glaswerks 212 cab with G1265's as well.
Sounds great either way.
 

myles111

Member
Messages
2,954
Very cool to hear... are you going to try an array of cabinets with it? I have to go with closed back no matter what, I've had the best success with front loaded... though they can be a little sterile.

I'm thinking a 4x10 ported cab might be my best bet... or a very deep front loaded cab that is completely sealed in the back. I'll have to talk to Andy about cab suggestions.

Thanks for your input Myles, I look forward to hearing more of your review!

_TJK*
I will be trying many cabs with the amp. Folks that borrow the amp will be using their own cabs as when I loan out the amp I generally will not supply cabs.

One cab I want to try is a cab of mine that currently resides with Carl Verheyen ( www.carlverheyen.com ) which is a Rivera ported 4x10 cab with 280 watt capacity.



The K&K ported 1x12 in the below photo is another one I want to try. I have a few of these and one has an older 100 watt Celestion speaker in it. I have these cabs set up so I can change the speaker within the cab in a matter of moments so it is a good testbed cab.



Since this amp does not have the need to be driven to high wattage levels and sounds terrific at even the lowest levels I can also use speakers such as a Vox Blue without too much concern by keeping the levels lower.

The amp is currenty being used with a Metropoulis 4x12 Marshall type cab with Heritage M's from Celestion inside. A short video can be seen at http://www.youtube.com/watch?v=iEhcmVor9ns and ignore the background music as it was coming from another area in the shop.
 

TaronKeim

Member
Messages
2,937
Very excited to hear how it works out with that Rivera 4x10... as a side note: that looks like a lot of stuff in a small chasis, definately digging that - very compact and tidy.

_TJK*
 

myles111

Member
Messages
2,954
Very excited to hear how it works out with that Rivera 4x10... as a side note: that looks like a lot of stuff in a small chasis, definately digging that - very compact and tidy.

_TJK*

It will be a few weeks before I can hook it up to the Rivera cab. My cab is at Carl Verheyen's house and he is on tour in Europe for a bit longer.
 

strat-rock

Member
Messages
272
Awesome review series so far, thanks! I've been interested in this amp since Andy told me about it just before he released it. If it had been available I might have picked one up. Alas I ended up with a Heritage Patriot head (effects loop and no reverb) and I'm pretty darn happy with it. I'd really like to hear the CM though, or maybe not since I bet I'd want to buy it!
 

myles111

Member
Messages
2,954
Awesome review series so far, thanks! I've been interested in this amp since Andy told me about it just before he released it. If it had been available I might have picked one up. Alas I ended up with a Heritage Patriot head (effects loop and no reverb) and I'm pretty darn happy with it. I'd really like to hear the CM though, or maybe not since I bet I'd want to buy it!

If you are down in L.A. You are more than welcome to try the head out or borrow it if you have some sort of gig down here.
 

myles111

Member
Messages
2,954
Excellent review.
But how could it possibly sound good if it's not PTP.LOL:mob

I cannot comment on that other than posting another question ....

How does an FA-18 fly so where when it is filled with PCBs and surface mount technology ... pull 9 Gs and land on a carrier flight deck in a controlled crash?

Maybe there are good and bad PTP and PCB amps? I bet that is possibly the case?
 

RNRBabyHead

Member
Messages
55
I cannot comment on that other than posting another question ....

How does an FA-18 fly so where when it is filled with PCBs and surface mount technology ... pull 9 Gs and land on a carrier flight deck in a controlled crash?

Maybe there are good and bad PTP and PCB amps? I bet that is possibly the case?

Just a joke in reference to the nimrods that actually think that PTP is superior even though a PCB can sound identical.

But, on another note, I just met all the guys from the USAF that fly the Thunderbirds today and got their autographs with my son. They were amazingly nice guys, and have no problem flying multi million dollar PCB planes.....LOL
 




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