3 Channel Dual Settings

[afu]

Ok. I have the schematic front of me. Some observations and additions/corrections to my previous thoughts.

The relay that connects Channel 2's modes is wired opposite of Channel 3. This would place Modern out of the NFB Presence circuit on both. Modern for both channels are connected and cause relay 7 to open when either is activated.

The EQ of Channel 1 Pushed and Channel 3 in Raw and Vintage have a resistor in parallel with the cap to the treble control. This makes me think it introduces the inductance necessary for an active EQ. Modern in Channel 3 and Channel 1 Clean bypass these resistors. I don't see anything that makes the tone controls active in Channel 2. Please correct me if I overlooked it.

Also, I'm wondering if relay 7 sends NFB to CH3 Modern to make it an active control and also change the overall tone of the circuit? NFB fed to a tone control of a highly distorted channel adds stability and cancels out noise, much like adding it to a PI.

The Raw Channels are connected to each other as well. It looks like the default settings for switching on Channels 2 and 3 at the Presence is Vintage or Modern. When a person switches to Raw, it technically stays in Vintage and causes an additional switch to throw down between V1 and the Gain control which provides additional filtering. This accounts for the difference in feel and distortion between Raw and Vintage.

I'm not an EE (obviously). I studied amp design and building as a serious hobby some years ago and I like messing with stuff (guitars and effects are more my thing). My cognitive skills have since been compromised a little by a disabling illness, so I get turned around sometimes. Having the schematic in front of me and presenting ideas seems like a better way to go about it.

 

[Shemham]

Ok. I have the schematic front of me. Some observations and additions/corrections to my previous thoughts.

The relay that connects Channel 2's modes is wired opposite of Channel 3. This would place Modern out of the NFB Presence circuit on both. Modern for both channels are connected and cause relay 7 to open when either is activated.

The EQ of Channel 1 Pushed and Channel 3 in Raw and Vintage have a resistor in parallel with the cap to the treble control. This makes me think it introduces the inductance necessary for an active EQ. Modern in Channel 3 and Channel 1 Clean bypass these resistors. I don't see anything that makes the tone controls active in Channel 2. Please correct me if I overlooked it.

Also, I'm wondering if relay 7 sends NFB to CH3 Modern to make it an active control and also change the overall tone of the circuit? NFB fed to a tone control of a highly distorted channel adds stability and cancels out noise, much like adding it to a PI.

Very perceptive and interesting theory. But I'd still assume that the resistor in Channel 3 is simply used to block the signal from passing to the 180pf cap when in Vintage mode. When Modern mode is engaged on Channel 3 the relay adds the cap in parallel to the circuit the 500pf cap to form total capacitance of 680pf for the treble filter. The 10M ohm resistor is simply bypassed then. I make assumption based on the fact that the 2 channel Recto had 680pf treble cap on the Red channel. The page 11 shows that the NFB will be bypassed by RY7b when in modern mode which makes sense.

Interestingly the lack of 180pf cap in Channel 2 in Modern mode takes it much closer to Orange Modern of the 2 ch Recto (500pf treble cap, 22k presence pot + no NFB).

I think Channel 1 Pushed thing you mentioned is simply a tone shaping circuit that is bypassed by the RY5a to remove one of the restrictions used to tailor Clean mode.

 

[ryjan]

Yoo too guyz is mutch smarterr then mee.

Haha. Again guys, thanks for taking the time to post all of that. It's very informative.

 

[afu]

Very perceptive and interesting theory. But I'd still assume that the resistor in Channel 3 is simply used to block the signal from passing to the 180pf cap when in Vintage mode. When Modern mode is engaged on Channel 3 the relay adds the cap in parallel to the circuit the 500pf cap to form total capacitance of 680pf for the treble filter. The 10M ohm resistor is simply bypassed then. I make assumption based on the fact that the 2 channel Recto had 680pf treble cap on the Red channel. The page 11 shows that the NFB will be bypassed by RY7b when in modern mode which makes sense.

Interestingly the lack of 180pf cap in Channel 2 in Modern mode takes it much closer to Orange Modern of the 2 ch Recto (500pf treble cap, 22k presence pot + no NFB).

I think Channel 1 Pushed thing you mentioned is simply a tone shaping circuit that is bypassed by the RY5a to remove one of the restrictions used to tailor Clean mode.

Being such a high value, the 10M resistors probably are for blocking. Running in parallel with the treble cap, I'd still think it would cause some inductance.

 

[afu]

So, after the detour through design aspects, I sat down and decided to compare some sounds between channels and modes to see how it impacts the controls. I decided to turn the gain all the way up on Raw CH2 and approximately match the sound on Modern CH3. I tried to make Vintage Channel 2 approximate the result on CH3, but that became a PIA. In the end, to try and approximate the differences between CH3 Modern and CH2 Vintage, I set up CH3 the way I like it and did my best to make CH2 sound like it. Here's what I came up with:

Epiphone G-310 w/EMG JH pickups
Triple-X Cab

Raw CH2/Modern CH3

P- full on/8.5
V- 11/9.5
G- Full on/2
B- 10/12.5
M- 10.5/9.5
T- 2/1

Vintage CH2/Modern CH3

P- 2/10.5
V- >11/9.5
G- >1/12
B- 1/12
M- 7/10
T- 4/1

They aren't exact. You can't dial in/out all the peculiarities of each one.

 

[afu]

I was interrupted earlier and I wanted to make a couple of points.

Here comes the heresy: I don't like the Presence control in CH2 Vintage for playing heavy music. The frequencies it accents above noon make the tone nasally. The bass response also feels looser than CH3 Modern. What I do like is the subtlety of the Middle and Treble. For less distorted music, it's cool as hell.

I love CH2 Raw. The taper and range of the Gain have more usefulness to my playing than Vintage, the Presence isn't honky, and the tone shaping is easier for me to dial in than in Vintage. I only wish the Presence control had more range to it. It's like nothing.... and then the last 1/8th of a turn makes a difference.

To me, nothing but Modern sounds quite right in Channel 3. I love Modern. It's the reason I love the amp (my love for Raw came soon after). It's a very bright channel, but rolling off the Presence takes care of that. The full-yet-tighter bass response and the low-mid cut make playing very easy and fun.

My new thoughts are this: Why make 2 channels that have the same modes, but change the presence pot value so it makes two of the modes sound weird in CH3? Why have 7 relays to get marginally different gain structures, when the overlap is so great? Why put Modern in Channel 2 without the extra capacitance to shift the tone out of muddy waters?

Don't get me wrong, I love my amp. I just think that it's versatility is more limited than Mesa lets on. I think taking a Roadster and changing the modes a bit would make a good 3 Channel Rectifier. Clean/Fat, Brit/Raw, Vintage/Modern (for simplicity, it could be Clean, Raw, Modern). Voice the channels so you wouldn't want or need to get the same sound in another channel. Put an option for a mid boost on the solo control, so one channel doesn't need to be set up for a solo sound. Have a simple active serial FX loop and get rid of the TRS switching. Use the available space for midi switching.

Now I'm WAAAAAAY off topic.......

 

[Jorn218]

ARG I hate the auto log out....... Just got done hitting enter after writing a very long response only to find out it logged me out

 

[afu]

Shemham, I have a question/thought and I'm wondering if you can help?

After V1, the coupling cap and voltage divider are in parallel with that switchable filter, which are in series with pot, but parallel with the cap from lug 1 to 2. Regardless of mode, it seems the capacitance would add all the way along, even while doing their specific tasks. That would explain some of the sizzle on a recto....

The 2M2 resistors form a voltage divider and the one in series with the pot is blocking signal to it. The 82p cap is only allowing a limited frequency of highs to pass the blocking resistor. It seems that the .02 coupling cap would add to this and lower the shelf of the filter. Then would the caps add to the .001 at the hot/wiper connection?

Going into Raw would decrease the 2M2 to about 1M-ish and the new cap value is high enough for the pf cap not to really matter any longer. The new voltage divider is allowing a little more signal, the blocking is lowered (a little more signal), and the capacitance is higher (less filtering). Then the caps add to the hot/wiper cap which is now made a larger value and decreases the treble response of the gain pot?

Does this sound right? Modern and Vintage pass mostly highs after V1 and the gain pot is set to keep the highs for plenty of it's travel, resulting in retaining some of the treble at lower gain settings. Raw is set to allow a somewhat lower frequency to pass and lower gain settings will have a warmer treble response as it loses the highs.

 

[Shemham]

Actually the bright-boost circuit works the otherway around. The 2M2/82pf circuit is used alone when engaged to Raw mode. When Vintage/Modern is in use, the 680k/2200pf circuit is added in parallel with the the 2M2/82pf circuit. The total combined resistance with the Vintage/Modern setting is about 520k ohms. 2200pf cap allows way more highs(and mids I assume) to bypass the resistor noticeably brightening up the tone.

I don't know how the circuit interacts together with the bright cap on the gain pot. I'm sure many of the amp builders/modders in the board would be more qualified to explain it than me.

Check this website for good read: http://www.ampbooks.com/home/classic-circuits/soldano-slo-preamp-1/

It's actually goes through Soldano SLO circuit step-by-step, but it's very applicable to Rectos because it's essentially a SLO clone (at least the very first revisions). It might help answering some of your questions.

 

[afu]

Thank you for the answer and the link.

 

[Jorn218]

@Alu, I want to thank you for suggestin I play with ch2 vintage. I am truly digging this tone. It sounds fantastic recorded through a camcorder live as well. Using phone to post now, ill edit this and include link to video when I get home from work. I have also switched to using the tube rectofication for fun. Loving how chords bloom using the vintage channel. I dont get the same bloom in modern.

These are the settings I am running right now.
Ch2 vintage, tube, bold
Pr: 1230
Vol: 1200
Gain: 130
Ba: 1130
Mi: 200
Tr: 1100

Floor effects are wah > boss compressor (all knbs at unity, always on) >boss ns2 > delay for leads > amp.

Not been able look at schematics due to work/gig schedule pas two weeks.

Question is it safe to run channel vol on ch1 past 130 if gain not all the way up on clean mode? Use it for intro on one song and output volume a little too drastic/dramatic and would like a little more subtle volume jump when I kick into dirty channel.

 

[afu]

I've run my clean volume high and gain really low. I have since rolled the volume up to about 2 and gain to about 10 or 11. It partially depends on my guitar. My guitars pickups range from .5 to 4 V max.