Champion 600 Speaker Upgrade Comparison

I installed four different speakers in my Champion 600 and ran some frequency response sweeps for the sake of comparison.*

What I saw in the graphs pretty much confirmed what I heard in each of them.

First the stock speaker compared to a Jensen Mod:






Just as my ear was telling me - the Jensen is a touch more efficient and a touch smoother but they really didn't sound all that different. I found the difference to be hardly worth the upgrade cost.

Here is the Weber alnico with a late breakup cone compared to the stock Champion 600 speaker:






Notice that the Weber late breakup alnico is a good bit more efficient than the stock speaker up to about 3K, where it drops off dramatically. This probably accounts for some people experiencing the Weber as dark sounding. What isn't evident from the graph is that in addition to the increased bass response the Weber is more able to handle the bass so it doesn't fart out the way the stock speaker does.

The next graph is interesting. It compares the Weber late break up ribbed cone to the Weber early break up smooth cone:






They're pretty similar in the bass but in the upper mids and treble they're very different. So in addition to the breakup characteristics they have quite different upper range response. Personally I prefer the smooth cone sound - it sounds a bit more vintage to my ear. The ribbed cone sounds tighter and more modern. They both sound great though and are both worth the upgrade.

Here is the smooth cone Weber compared to the stock speaker:






It look much more like the original in the treble response. Kind of like the stock speaker with increased bass and mids (and better bass handling).


Here's plots for all four speakers on the same graph - just for ease of comparison:






Incidentally, I found that the stock grill cloth really does flap around at higher volumes making some nasty farting and flapping along with the low notes. I cut mine out when I cut down the baffleboard for the Weber speaker installation and am looking for something to replace it with.




* These graphs are for the sake of comparison between the speakers. Since they aren't anechoic chamber tests the graphs include the room effects so don't pay to much attention to each tiny peak and dip. They don't show isolated speaker response but work fine to illustrate how the speakers differ from each other under the same room conditions.

Fender AB764 Vibro Champ Output Transformer Measurement

Here's a chart showing the measurements I took on the output transformer in a Fender AB764 Vibro Champ that was in for repair. The measurement procedure is the same as in the Champion 600 output transformer post.

Look at the boxed impedance ratio 2,343 : 1
That's the impedance ratio at 1,000 Hz (or 1KHz).

It indicates a 2,343 ohm plate load with a 1 ohm speaker load. But obviously the speaker load isn't 1 ohm. For the Vibro Champ it's meant to be about 4 ohms.

To figure out what the transformer ratio is with a 4 ohm speaker load, just multiply both sides of the ratio by 4.

( 2,343 times 4 ) : ( 1 times 4)

is

9,370 : 4


9,370 is about 9.5K. That's a bit lower than the 11K I measured on the Champion 600 I modded back in December. The plate voltage in the Champion 600 is higher as well (366 volts as apposed to the 342 volts in the Vibrochamp). The AB764 serves as a template for the Champion 600. I'd assume the higher impedance ratio in the Champion 600 was made to compensate for that higher voltage.

That's not a capacitor that's just two wires twisted together. Right?

Here's a picture of the inside of a Fender AB764 Vibrochamp that was in for repairs:



An new JJ 6V6 got it running again but even with it's Weber alnico speaker it didn't sound all that good. I replaced the tone stack and coupling caps and that helped. But the interesting part of this repair was a more elusive capacitor problem.

Many later Fender amps have capacitors in the output section that were put in to suppress parasitic oscillations. I like to remove these if possible to brighten the amp up a bit.

In this particular one there were actually two ceramic caps (one dark brown and one tan) connected in parallel from pin 5 to pin 8 on the 6V6 power tube. The arrow indicates them in the picture and I've highlighted the cap in red on the schematic to the right.




The trick about removing these caps is that they were originally installed to fix a problem. So sometimes when you remove them the problem rears it's head again.

That was the case in this one. When I removed the parasitic oscillation cap the amp got a bit dirtier and actually sounded darker not brighter.

You'll notice the picture of the Vibrochamp circuit that there are two wires twisted together sort of like these two I've twisted together here:

One of these two wires carries the B+ voltage to the preamp stages from the power supply and the other connects the output of preamp to the input of the 6V6 power tube.

They're going in the same general direction. So why not twist them together? Nice and neat, isn't it?

Well let's hook the two wires I've twisted together up to the capacitance meter. Here are the leads of the meter connected to two ends of the wire:



And here's what the capacitance meter reads with the probes connected to the ends of the wires:



That's almost 30pF that would be connecting the preamp B+ to the 6V6 input at high frequencies! Doesn't sound like a great idea does it?

The fact is that capacitors exist in all sorts of places where we don't intend them to be. And this can cause problems, especially at high frequencies. Capacitance is, after all, just an electrical characteristic of physical materials. The components we call capacitors are just things that are carefully manufactured to optimize and control the capacitance of those physical materials. There are plenty of capacitors that we buy and install into our amps. But there are plenty of others that happen through accidents of layout and lead dress.

Suspecting unwanted capacitance in the twisted pair of wires in this Vibrochamp I unhooked them, straightend them and hooked them up again.




Above you can see them reconnected. The amp sounded more open, a bit less gritty. And as I'd hoped I was also able to remove the parasitic suppressor cap to brighten it up a touch.

Trippy Reverb Trick for Two Channel Fender Amps

This is a trick to get a deep and spacey reverb sound out of most 2 channel Fender Amps.

Here's the set up with the "Normal" channel jumpered to the "Vibrato" channel:

Generally people DON'T jumper channels on their Fender amps because
the two channels are phase reversed*. This means the two channels cancel each other out.
So instead of getting more volume from the second channel
when you turn it up, you get less.

This trick takes advantage of that cancellation to get rid of a lot
of the straight guitar sound leaving mostly reverb.

----Video Quality Disclaimer----

The video makes it sound like the amp has loads of buzz.

It doesn't actually - it's the foolish AGC
circuit on the camera.

Soldier through and you'll get the basic idea though.

--------

This video shows the basic setup:





The sound on the video will give you the "how to" but doesn't capture the depth of the reverb, so I suggest you try it yourself to hear what it sounds like in person. It's much more dramatic.

You can also toy with the tone control settings to get more variations from the reverb sound.
It can get pretty wacky with some tweaking (and it can get loud quick so be careful).



* Technically they are "reversed polarity" or "180 degrees out of phase".
Though incorrect "phase reversed" or "out of phase" are the more colloquial usage
and they're the ones you're more likely to hear in music circles.

Are these two resistors different?

One of the first steps you'll read in any set of tube amp troubleshooting instructions is "visual inspection". It just means looking over the components for any obvious signs of stress. Here I've stuck two 100K resistors in a piece of foam for the sake of comparison.






Looking at the two 100K resistors pictured an astute observer might notice the slightly darker midsection of the upper resistor. It's fairly subtle here and even more so when it's still in the circuit, not positioned right next to a normal looking one.


These resistors are plate resistors taken from a Fender '65 Twin Reissue that came in with a broken Normal channel. The resistor that shows slight signs of overheating was completely open. It was passing no current at all, effectively shutting off the tube. It might as well have not have even been in the circuit. I replaced it to get the channel working again.


So why did I take out both resistors? Well the second one is actually completely open as well, it just doesn't happen to show any visible signs of fatigue.


That's the trick with visual inspection. It's a very good first step. But troubleshooting effectively means knowing how to use your meter to see for you. Parts can fail in many ways that you never have any hope of catching with your eyes.

Fender Champion 600 hum reduction mod

The Champion 600 I've been working on came back in with a request for the cathode referenced heater mod to reduce the hum. For a single ended amp this particular one is actually pretty quiet already. It certainly hums less than any of the vintage Champs I've seen. I don't mind a little bit of hum myself but the owner is new to tube amps so he's a bit more sensitive to it than I am. The mod is a real simple one though so I thought I'd take a crack at it and see if it did anything.



R15 and R16 are the resistors that reference the heater filaments to ground. A old trick for single ended amps is to move the end of these resistors to the cathode of the output tube.

Since I've moved the cathode bypass cap as part of another mod, I had a convenient place to connect the resistors. If the cap is still there the resistors could be connected to the top of R10 instead (indicated by the red circle).



Here's a measurement taken off the output with a 4 ohm dummy load connected:



You'll notice that there's almost no reduction in the fundamental or even any of the lower harmonics. It's not until about 2K Hz that we start to see a reduction in the hum. As I mentioned earlier, this amp was pretty quiet to begin with. Curiously the owner actually perceived it as humming slightly more with the mod installed so I'm going to put it back to stock when it comes back in to get a Weber Alnico speaker put in.

Fender Champion 600 Preamp Bias Part 3

In Part 2a we plotted the maximum current for the first 12AX7 gain stage in a Champion 600. That point was connected to the maximum voltage point to find what's called the load line for the stage.


This is the place to come to terms with a essential concept. Every point on the graph of plate curves represents a possible combination of plate voltage and plate current for a 12AX7. Let's choose a few for the sake of illustration. Let's pick Point A at 1.1 milliamps of plate current and 140 volts at the plate. Here's that point graphed onto the 12AX7 plate curves:



Now we'll pick another one we'll call Point B at 0.4 millamps of plate current and 230 volts at the plate. Here's that point graphed onto the 12AX7 plate curves:


Now we'll a third, Point C, at 1.1 milliamps of plate current and 230 volts at the plate. Here's that point graphed onto the 12AX7 plate curves:

Here's the fundamental concept. The load line we've drawn crosses all the possible combinations of voltage and current that can occur in our circuit given the 100K plate load we've chosen - so any dot which plots a combination of current and voltage must lie on this line for it to be a possible occurance in the circuit. We've plotted three different points but only Point C lies on the load line. When the circuit is drawing 1.1 mA of plate current the plate voltage must be the 230 volts indicated by point C NOT the 140 volts indicated by Point A. And with 230 Volts on the plate the circuit must draw 1.1 mA as indicated by Point C, NOT the .4 mA indicated by Point B.

The load line indicates that Point A and Point B do not exist for the circuit given our chosen 100K plate load. Points A and B can still exist as long as we adjust either the current or the voltage so that they lie on the load line:

This all may seen somewhat abstract, but it's essential to understanding the biasing of the preamp stage. It should all become clearer as we begin to discuss bias in the next few posts.

Fender Champion 600 Preamp Bias Part 2b

In Preamp Bias Part 2a we derived this load line for the first 12AX7 gain stage:





To find the maximum current we imagined that the full preamp B+ voltage was across the plate resistor. This post is an addendum to for those interested in why that is a reasonable way to estimate the maximum current. First we should look as the path of the current from the B+ power supply to ground:





From the 340VDC power supply the current flows through the plate resistor, on through the tube itself and then through the cathode resistor to ground.* So here's what he circuit "looks like" for DC current flow:





So there are three separate resistances to the flow of current. All three are in series so the total resistance will be all three of those resistance added together. Using Ohm's law again:






The total current flowing in the circuit will be 340 volts divided by the the total of those three resistances.

From both Ohm's law and from intuition we know that more resistance will mean more opposition to current flow. Hence less resistance will mean more current flow.

So to find the maximum current flow we want to be thinking of the condition under which the circuit has the least possible resistance.

This means that we have to make all three of those resistances as small as possible. The plate resistor (Rp) is a fixed value of 100,000 ohms - nothing we can do about that.

The cathode has a fixed resistor too (Rk) - 1500 ohms. It's value is not going to change either.

The internal plate resistance (ra) is the resistance the tube itself contributes to the circuit. This value varies very widely - practically from zero to infinity. This change in resistance is actually key to it's functioning as an amplifier.

We want to be calculating the point at which the total resistance is smallest. Since that will occur when the tube's internal resistance is smallest we'll use the smallest possible internal resistance in our calculation. That makes things easy. That's effectively zero.

So that leaves us with the following:




That means the total resistance is just the sum of the plate resistor value and the cathode resistor value.

But in Part A I said all we used to calculating the maximum current is the plate resistor value. Now we're using the cathode resistor too. Why the change?

There's no change really. The cathode resistor is very small compared to the plate resistor - only 1.5% of the value so we can ignore it for the calculation. If you're designing a stage from scratch you won't pick the cathode value until after you've drawn the load line so it's easiest to be in the habit of ignoring it for the common stages you'll find in most guitar amps.



* Capacitors block DC. Since we're looking at the DC current flow, no current will be flowing through any of the capacitors.

Fender Champion 600 Preamp Bias Part 2a

The the last post we found one of two points we need to draw the load line for first 12AX7 gain stage in a Champion 600. We'll use the load line to find the bias point and later reset that bias point for the 12DW7 mod.

The first point was found by simply plotting the B+ voltage on the X axis of the 12AX7 plate curves:





Now we need to find the maximum plate current. To do this we use Ohm's Law to calculate how much current will flow with the full B+ voltage dropped across the plate resistor.





We know the B+ is 340 volts and the plate resistor is 100,000 ohms.

340 divided by 100,000 is .0034 amps or 3.4 milliamps

Now we plot 3.4 mA onto the Y axis and connect that dot to the one we made on the X axis:






The line connecting these two points is what's called a "load line" and it's what we use to determine the bias point for the tube. I'll cover the bias point in an upcoming post.

Fedner Champion 600 12DW7 / ECC832 Mod Part 1 - Update

I'm focusing here on the 12DW7 / ECC832 partly out of curiosity and partly because it's half the work to rebias for the new tube. What is a 12DW7? Technical details can be found in the 12DW7 mod part 2.

The goal of the mod is to get a good bedroom level clean sound with a more useful range in the volume control. You can lower the gain and get more headroom by substituting a 12AT7,12AY7 or 12AU7 for the 12AX7. It won't be biased properly, but you may like the sound anyway and you're not going to hurt anything.

You can also plug a 12DW7/ECC832 in place of a 12AX7. A 12DW7 / ECC832 is one half 12AX7 and one half 12AU7. If you like the sound, try this mod to bias the lower mu half of the tube correctly.

THE UBIQUITOUS DISCLAIMER: AKAVALVE ASSUMES NO RESPONSIBILITY FOR THE SAFETY OF ANYONE IMPLEMENTING THESE INSTRUCTIONS. IF YOU ARE NOT FAMILIAR WITH SAFE PRACTICE IN HIGH VOLTAGE CIRCUITS, DO NOT ATTEMPT THIS YOURSELF.

All it takes is a 12K resistor jumpered in parallel with the stock 100K plate resistor R8 and a 1K resistor in parallel with the 1.5K cathode resistor R2. They're the two dark brown 3 watt IRC resistors shown in the middle of the picture.




The effect of putting 2 resistors in parallel is to reduce the overall resistance:



So the stock plate resistor in parallel with the additional 12K one gives a combined value of 10.7K for the plate. This greatly increases the current through the tube, which is what we need for a 12AU7.

With the current increased we need to change the bias of the stage to suit a 12AU7. With the stock resistor it will be running quite cold. The added 1K resistor in parallel with the stock 1.5K one yields a total resistance of 600 ohms.

If you're interested, the working through of the parallel resistance formula is covered in more depth in the Fat Boost Resistor Value post.


Here's a close up of the plate resistor. This jumpering method makes it very easy to remove the mod if you decide to go back to stock.




You can see below that the joint on the left hand of the plate resistor is not perfect - the solder hasn't flowed onto the lead of the original as completely as one would like. This is just for a listening test though so I didn't bother touching it up.


With this mod in place the amp is much cleaner and much quieter. It's important to note that you should NOT plug a 12AX7 back into the socket with the mod in place. A 12AX7 triode can't handle the amount of current that a 12AU7 triode can, so half of your 12AX7 will be toasted by the rebiased stage.

Fender Champion 600 Input Voicing Mod "Kit"

Instead of selling "kits" for the Champion 600 mods on this site, I'm putting together a series of posts with direct links to sources for the parts involved.

Below is a chart of capacitor values and -3dB points for the Champion 600 low input revoice mod.

This mod will work in a great number of amps with high and low inputs including the 5E1, 5F1 Champs and a host of other Fender Amps. You can find the the measured frequency response for a .012 uF cap in Part 2 of the mod post.


Clicking on any of the capacitor values in the chart should take you directly to a suitable part for the mod on the Mouser Electronics website. You can order directly from there.

If you have any questions about the parts links here, feel free to drop me an email.

Fender Champion 600 akavalve Mods

Since the blog format is a bit awkward to navigate through, I thought I'd make up a table of contents for my Fender Champion 600 Mod posts. First are the essential safety posts and then the mods listed in order of difficulty with the easiest ones first.

Discharging the filter caps:

Part 1
Part 2



Tube Upgrade:

New preamp and power tubes


Input Voicing Mod

Part 1

Part 2
Frequency Response Measurement

Input Mod "Kit"
Cap values for different frequency response and
Mouser Electronics Parts Links.


Presence Plus Mod:

The Presence Plus Mod
The Presence Plus "Mod Kit"


Cathode Bypass Mod

Part 1
This one includes a couple charts for bypass cap values
and their frequency response for both
the stock circuit and the Frondelli mod.

Part 2
This is the installation of the mod.
It uses large cap values
but smaller ones detailed in Part 1
could easily be substituted.

Part 3
This shows the measured frequency response
with the four different settings of the
cathode bypass lift described in part 2.


Tone Stack and Fat Boost Mods

Tone Stack Test

Installation Details and Frequency Response Graph

Explanation of the Fat Boost Mod resistor values

Tone Stack Bypass Cap Values (same as 5E1 Champ)


The 12DW7 / ECC832 mod

Part 1

Part 2


Miscellaneous:

Animated GIF of the disassembly

A look inside the chassis

Stock Speaker response measurement

Comparison of the Champ 5E1 and 5F1 schematics

Stock Output Transformer Measurement


I'm pretty sure that's all of them.
I'll add new ones to this list as I post them.

Fender Champion 600 Presence Plus Mod Kit

I've had a number of requests to provide kits for the mods described here. The components are generally quite simple - it's finding the sources and actual part numbers that may give people some trouble.

So instead of bagging up components, figuring out how to price them and sending them out, I'm going to try to provide links to Mouser for the exact parts needed for each of the mods.

This post is for the Presence Plus Mod.

If you're not making it switchable, the only part you need is the 16uF capacitor. Here's the link to the part on Mouser's website.

This is a lot easier for me than trying to make up "mod kits" and mailing them out. And it's cheaper for anyone interested in doing the mods too since you won't be paying for my time in the price of the kit. Let me know if it works well for you.

Fender Champion 600 - Discharging the Filter Caps Pt 2

Here's a more detailed look at discharging the filter caps in a Fender Chapion 600.

First I'll get this out of the way:

THE UBIQUITOUS DISCLAIMER: AKAVALVE ASSUMES NO RESPONSIBILITY FOR THE SAFETY OF ANYONE IMPLEMENTING THESE INSTRUCTIONS. IF YOU ARE NOT FAMILIAR WITH SAFE PRACTICE IN HIGH VOLTAGE CIRCUITS, DO NOT ATTEMPT THIS YOURSELF.


With the amp turned off connect the black lead of the multimeter to ground at the speaker jack. This will be the bare wire connected to the sleeve connection on the jack. You can use any ground connection really, but this on is very easy to get a clip onto. Connect the red lead to the top of R11. Set the meter to read DC Volts. Now flip the amp on.


You'll see the voltage on the meter rise quickly to around 420 volts. If you don't see any voltage reading then you've connected things incorrectly or you meter is not set properly. Don't proceed until you've figured out why you have no reading, and be very careful when when moving the probes as there is now very high voltage in the circuit.

When you have the meter connected properly and are getting a 400+ VDC reading shut off and unplug the amp.



When you shut the amp off you will see the voltage dropping slowly on the meter. You are now ready to connect the clip end of the discharge probe to ground. I find the easiest method is to clip it to the sleeve of the input jack.



Mote that the voltage is still dropping slowly even though the probe hasn't been fully connected. This is because the capacitor is bleeding it's charge though the circuit and through the meter itself. This is exactly what we want the discharge probe to do - but faster.

Now touch the other end of the discharge probe to a source of B+ voltage. Here I'm about to make contact with the red lead of the output transformer primary:



Now you will see the voltage drop quite rapidly. This picture covers the change in just a few seconds (click on it for a close up):



Finally all the voltage will be drained out and you're ready to work on you amp.



Note: Turning the amp on is not really not part of the discharging process. The reason I include it is because it insures that you are getting a good voltage reading and that you can watch that reading drop. That way when your meter shows no voltage you know it's because there is no voltage left in the caps not because the meter isn't connected properly.

Second note: If your speaker is still connected to the amp during this procedure you will notice that the voltage drops fairly quickly. This is because the connected speaker is doing the job of the discharge probe. This is actually a perfectly reasonable way to avoid the discharge probe all together. Discharging with the probe is an excellent habit to get into though because not all amps bleed off their caps voltage so quickly on their own. If you decide to forgo the probe, make sure you are absolutely confident in your voltage measurements in order to stay safe.

Fender Champion 600 - Discharging the Filter Caps Pt 1

Here's the procedure for discharging the filter caps in a Fender Champion 600.



The video is pretty small so I'll put up another post with pictures so the detail is a bit clearer.

I'll cover the construction of the probe in a later post.

THE UBIQUITOUS DISCLAIMER: AKAVALVE ASSUMES NO RESPONSIBILITY FOR THE SAFETY OF ANYONE IMPLEMENTING THESE INSTRUCTIONS. IF YOU ARE NOT FAMILIAR WITH SAFE PRACTICE IN HIGH VOLTAGE CIRCUITS, DO NOT ATTEMPT THIS YOURSELF.

Fender Champion 600 Cathode Bypass Mod Pt 3

Here's the response curve for the switched cathode bypass caps in part 2 of this post. The first graph is for the stock tone stack:



From top to bottom the curves show:

6V6, 1st stage (12AU7) and 2nd stage (12AX7) engaged (stock).
6V6 and 1st stage (12AU7) engaged.
6V6 bypass cap engaged.
All bypass caps disconnected.



The curves in the next graph follow the same pattern but this time the Tone Stack Bypass is engaged. There is a great deal more gain with the tone stack bypassed. If you click to enlarge the graphs and look at the right hand scale you'll see that the peak response in the modified amp is about 10dB higher than in the stock one.



This amp has the 12DW7 mod installed so the 1st stage has less gain and correspondingly less increase in gain with the cap engaged. In a stock amp the jump from the aqua curve to the green curve would be increased to about the same as the jump between the green curve and the dark purple curve on top.

Fender Champion 600 cathode bypass mod Pt 2

When I wrote part 1 of this post I'd been planning to lower the cathode bypass capacitor values in order to clean up the up the bass response. What I ended up doing was removing the cathode bypass capacitors all together in order to get a bit of compression for a fuller low volume clean tone. The effect is a more roundness and a good deal less volume - very nice for a bedroom level clean sound. This meant I needed to find some other ways to control the low end (see the Input Voicing and Presence Plus mods).


For this mod I put in a three pole four position rotary switch that adds the cathode bypass caps in one by one. With the rotary switch the gain of the amp goes up with each setting until it reaches the stock (fully bypassed) position:




This could easily have been three separate switches, but I thought the single control made the operation a bit clearer and didn't clutter up the chassis as much. Since I'm limiting bass response in a couple other ways I ended up keeping the caps at their stock values. The first and second stages could easily have values from part 1 substituted if you have a need for greater bass reduction.

Here is:

THE UBIQUITOUS DISCLAIMER: AKAVALVE ASSUMES NO RESPONSIBILITY FOR THE SAFETY OF ANYONE IMPLEMENTING THESE INSTRUCTIONS. IF YOU ARE NOT FAMILIAR WITH SAFE PRACTICE IN HIGH VOLTAGE CIRCUITS, DO NOT ATTEMPT THIS YOURSELF.

And here's the internal view of the switch with the ground wires in place:





This is how the ground wires hook up:




The wire with the black arrow connects to the lower side of the C4 space on the pc board.

The wire with the blue arrow connects to the lower side of the C10 space on the pc board.

The wire with the red arrow connects to the lower side of the C3 space on the pc board.

Here is the rest of the switch wiring. Notice that the leads for the large blue cap (which serves as C4) jump three pins on the switch.


The stage 2 wire jumper two pins. This wire attaches to the shrinkwrapped end of C10 (indicated by the red arrow).



The wire connecting stage 1 to the switch connects to only one pin. It connects to the shrinkwrapped end of C3 (again, indicated by the red arrow).






If you've removed these caps and are reinstalling them, make sure you observe the proper polarity when you put them back in. The indented end of the cap lines up with the indent in the white outline on the pc board.

For convenience of installation, I replaced the original C4 with a axial lead cap of the same value. It's the large blue cap in the photo below. The negative side of the cap connects to the switch and the positive side is connected to the high side of the pc board connection for C4. The negative lead of the cap holds it pretty well in place but there's a dab of silicone underneath just for good measure.



This switch functions kind of like a staged clean master volume. If you're interested in getting distortion out of your preamp circuit, this mod could be rearranged to serve as a sort of dirty master volume instead. If you're interested let me know and I'll post the details.