Sonaro Tone & Volume Characteristcs

[PBman]

I have a Sunn Sonaro. Looks like it's based on the same chassis as a 200s & Sorado. The amp has 2 6550's for tubes. Volume on this amp doesn't really get going until around 6-8 on the dial. While increasing treble , the low end bass density seems to be cut. I was wondering if these were characteristics to this amp

[skullywv]

The boost switches definately work in this manner, the bass boost appears to be a treble cut.
My Sonaro seems to work just like yours except for the volume, 5 is very loud on mine. You might want to test your capacitors.

[EdBass]

I have a Sunn Sonaro. Looks like it's based on the same chassis as a 200s & Sorado. The amp has 2 6550's for tubes. Volume on this amp doesn't really get going until around 6-8 on the dial. While increasing treble , the low end bass density seems to be cut. I was wondering if these were characteristics to this amp

I've got original schematics for both of them from '67, virtually identical tone stacks, but showing EL34's in the Sonaro with a good bit lower PT voltages.
I'm not an engineer, but I don't see (or hear for that matter) any opposite cut on the treble or bass pots. You may have something funky going on. Also the boost switches appear on paper and in person to do just that , BOOST. When I switch on the Bass boost with any of my Sunns, light fixtures and windows start rattling. The Bass boost is actually too bottom heavy for indoor use on my 2000S's.
I still have your email address from our JBL K145 episode last summer, Rich. I'll scan in the Sonaro schematic and send it to you.

[skullywv]

At what volume setting does your Sonaro begin to clip?

In 1969 the EL34's were replaced with 6550's, pins 1 & 8 are connected on my power tubes with resistors. I have not been able to find a Sonaro schematic showing 6550's.

Another very odd thing about mine is in the preamp circut the 250mf 15v capacitor was never installed (or that's the way it looks). This caused clipping to begin at 3 (volume). The date inside the chassis is 1-27-69 (that was a Monday...go figure). I got a cap in there now but I still start clipping at about 5 (volume). I think maybe it's time to start testing caps and resistors 1 at a time. The tone however is great at lower volumes.

[EdBass]

Sunn amps, as with all the other handwired amps I've experienced, seem to have slightly different personalities as far as tone and breakup characteristics, and it doesn't seem to be purely components. I think it's the whole overall balance of the "sum of it's parts" effect.
Among my old Sunns I have a '66 100S and a '66 200S that are both refurbished as close to stock specs as possible; all new caps, any resistors/pots that had drifted replaced, same mfg/age tube compliment, transformers as close to identical as practically possible, etc., and the 100S is louder AND cleaner than the 200S. (of course, just the opposite of what I was shooting for!). I've switched tubes, even transformers, but there it is.. the guitar amp is a better bass amp than the bass amp. I have another '67 200S that has only had the filter caps replaced, and with the original Sunn branded KT88's it's still stronger at high volumes than either of the '66's. The the '67 starts to slightly distort at about 5.5 but doesn't get dirtier-just louder, until it gets to about 8, and then it's "Live at Leeds". The '66 100S stays clean until almost 8, and the '66 200S starts to break up at 6.5.
I have a copy of a letter from Robert P. Selby Jr. to all Sunn dealers announcing (and rationalizing) the switch to domestic 6550’s from British KT88’s dated 3/3/69, so I would imagine that your 1/27/69 date would have had to be an early 6550 equipped amp. I have a Sunn schematic binder that had been kept updated with the most current schematics for all amps from 11/67 through 5/69, and I also can't find a Sonaro schematic showing anything other than EL34's. But, the only real difference I can see on the schematics from the KT88/6550 amps is the power transformer voltages.
None of my old Sunns cut opposing frequencies in the tone stack, pots or boost switches. If yours does, it may need a trip to a amp hospital in your area. 

[JoeArthur]

In a tone stack circuit, the treble control functions as a mixer or blender control between the treble path (i.e. signal with bass cut) and the bass path (i.e. signal with treble cut). 

Due to this "mixing" action, when the treble is boosted there is a slight loss in bass.  This is one of the reasons a 250K pot is normally used for the treble control - because even at max treble settings, the bass reduction is so slight that most people don't even notice it.

However, if the size of the treble control is increased - say to something like 1 meg, then the reduction of bass at max treble settings is difficult not to notice.  The "mixing" or balancing action of the treble control is much more apparent and the control does feel like it is adjusting between bass and treble.

If you have the chance, go out and play through a Vox AC-30.  Both controls in this amp's tone stack are 1 meg values.  As you turn the treble up, bass is reduced - or as you turn the treble down, bass is boosted. 

[EdBass]

In a tone stack circuit, the treble control functions as a mixer or blender control between the treble path (i.e. signal with bass cut) and the bass path (i.e. signal with treble cut). 

Due to this "mixing" action, when the treble is boosted there is a slight loss in bass.  This is one of the reasons a 250K pot is normally used for the treble control - because even at max treble settings, the bass reduction is so slight that most people don't even notice it.

However, if the size of the treble control is increased - say to something like 1 meg, then the reduction of bass at max treble settings is difficult not to notice.  The "mixing" or balancing action of the treble control is much more apparent and the control does feel like it is adjusting between bass and treble.

If you have the chance, go out and play through a Vox AC-30.  Both controls in this amp's tone stack are 1 meg values.  As you turn the treble up, bass is reduced - or as you turn the treble down, bass is boosted. 

As I posted earlier, I am not an engineer. And I would certainly never try to bolster my ego vicariously by giving equipment repair/design instruction through an on line persona. I get enough pleasure from hacking on my own gear! I also learned long ago to learn whenever and wherever I can, so bear with me and walk me through this tone stack thing.
Am I wrong JoeArthur, or are you are describing is what is sometimes referred to as tone stack contour? As you roll the treble up, the response curve peak moves up the frequency scale in a rolling swell, rolling off lower frequencies as it increases higher ones, and vice versa for a bass control, right? And this swell gets shorter (in frequency span, not peak to valley), peakier, and generally more exaggerated as the value of the controlling pot is increased? Don't all passive tone stacks operate in this fashion, with various degrees of response severity, with the James tonestack being probably the most linear standardized design, and the Vox being one of the more dramatic production designs?

I may have misunderstood the intention, but the way I understand this thread is, the posters have Sunns that have tone pots/boost switches that operate as something of a "cut" control, boosting treble by defeating bass response and vice versa, rather than the design intention of a moderate conventional tone stack.
If I do understand the thread correctly, I'll go out on a limb and suggest that sumthin aint right. And as always, suggest using a real (ie;fiscally liable for your old amps) engineer in lieu of one of us "on line" experts.

[PBman]

My lastest update-

After reading skullywv's comment about the 250 mf cap I took a look at the board. I noticed that it not there at all. From my past updating of my 2000s , it seems that that preamp circuit is all to common for these Sunn amps.
I bought a 250 and a 330 (recommendation from soundmasterg, member). Not only did it fix both issues and sounds much stronger. With out the cap is very subdued. Maybe some players may like that .
So the volume now gets going and is even in escalation from 2 on up and maxes at around 7-8 depending what I do with the bass controll and low switch. The treble control is better too. Thanks for all your help!!! The passion for these amps will never die.