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[eddiemac]

I recently purchased a Sunn Sorado to use with a 1-15 cab in smaller rooms.  I had fond memories of the Sonic amp I owned in the late 60's and later sold.  One thing I noticed back then was the unusually large amount of cone excursion, back and forth movement of the speaker, the Sunn's exhibited, more so than that of other manufacturers.  Those JBL's seemed to be almost jumping out of their baskets.  I was thinking newer, more modern speakers and cab designs would handle this better, especially the ones with large Xmax.  But I find the situation is still a limiting factor.  What is it about the Sunn amps that causes this?  My amp tech says he thinks certain frequencies may have been emphasized in the preamp design to compensate for the weaker bass response of the speakers of the day. 

[Soundmasterg]

I would guess that it probably would do that with any tube amp. Tube amps don't have as high of a damping factor (ability to control the load) as solid state amps so the speaker isn't controlled as well. Maybe with the Sunns it might be because they are UL (ultralinear) as opposed to most other tube amps, but I am not sure about that one. All of the Sunn amps were based on Dyncao hi-fi amps, which had full range frequency response, and in the case of a Sunn 2000S, they will amplify cleanly down to 10Hz at least with the Dynaco transformer models. Your speaker cabinet can't reproduce frequencies that low, but it may just be that the Sunns have more energy down low and make the cone move a lot.

What is the problem though? The original amps and cabinets worked fine together even with the excessive excursion and I would bet modern cabinets would also work fine. Just play it and enjoy the sound and feel.

Greg

[bigobassman]

I've had speaker guys tell me that movement is actually a positive.  I don't know one way or the other, but I've had lots of speakers exhibit that movement with great sound and longevity.

[eddiemac]

I'm using a 1-15 cab as I did with my Sonic (back when sound levels were more humane).  I think if I was using 2-15's, things would be better.  I know the JBL D140 has about 1/4" Xmax, if that.  It always looked like it was moving more than a half inch on the deep notes, and now my 15 sometimes bottoms out on the low notes when hit hard.  A Fender Showman has better damping abilty.  I played a gig tonight and started out with the Sorado into a Fearful 15/6, which has an Eminence 3015LF with massive excursion ability.  After two songs, I switched back to my Gallien Krueger.  It just sounded better.  But then, 350 watts compared to 60 tube watts is not a fair comparison.  I will plan on using the Sorado on quieter gigs in smaller rooms, which is why I got it in the first place.  By the way, Soundmasterg, I am in your debt.  Your postings about cap replacement, in our modern age, has been my guide to reconditioning my amp.  Thanks!

[EdBass]

Your D140 is probably at least 40 yrs old, it may be that it's just tired. The suspensions on a driver wear down and loosen. Reconing is a fact of life in the speaker world, just routine maintenance. Until recently I worked for a touring production company that ran stadium sized L-acoustic K series rigs, when they came off the road there were stacked pallets of drivers that needed to be reconed. Some had blown in use, but the majority of them were worn by hours in service and were getting "soft" so were reconed as preventative maintenance.

Modern drivers will take a bunch of power, but generally sacrifice tone and sensitivity. In the SR world accuracy and SPL are the keys to success, and nowadays watts are dirt cheap; so heavy surrounds, spiders, double voice coils/spiders, etc., are commonplace. You can beat the snot out of them and they will take it, but they need huge power to get to to acceptable SPL's.
In the era of the D140, a 100 watt amp was considered a MONSTER. Drivers needed to get all the SPL they could from the low powered amps of the day; diametrically opposed to "You can beat the snot out of them and they will take it, but they need huge power to get to to acceptable SPL's".

But we are talking about something else also. The D, K and E series JBL's were excellent Musical Instrument speakers. Originally the D's were AP drivers, and once they became popular for MI amplification (around the time of the "F" designation on the model), the "lettered" JBL's became MI drivers, and the SR drivers adopted a numbered identification system. MI drivers sound good when used in that application; the idea that the rig as well as the instrument make up the "instrument". Guitar players "get it", but some bass player don't. Which is fine, whatever floats one boat, it's music not rocket science.
I prefer my bass rig to be "musical", and like the majority of guitar players and many pro bass players my rig is an integral part of my tone. I currently gig with a '68 Sunn 200s into a Sonic I-40 cab loaded with a K140. I put it on a X stand at head level with a Heil PR40 stuck in front of it, and use a JBL PRX812W as a floor monitor in front of me. Much easier to transport than my big rigs, sounds absolutely phenomenal, plenty of stage volume. Let the PA do the "heavy lifting". 

Fearful cabs are far closer to a small SR cab than a MI cab, Eminence makes a real nice driver, lotta bang for the buck, but is amateur/semi pro grade as far as SR drivers go. The old "get what you pay for" scenario. a 3015LF is <$200, a 2226 is >$500.

The Fearful is an amateur, free ware designed two way SR cab. no reason it wouldn't sound nice, basic WinISD on a driver that Eminence provides amateur design assistance with, crossed over "by the book" with a 6" mid driver. Through another forum it developed a following of unenlightened "internet experts" for a minute, but was never taken seriously in the pro world.
Honestly, if you were looking for a pure unaltered bass guitar to ear sound, just run direct and use a professional monitor, there are myriad pro designed options available. There are powered 15" 2 way speakers/monitors starting at a few hundred bucks that you can plug straight into, that will absolutely destroy the GK/Fearful if you are looking for full range accuracy and need a free standing rig for your purposes. Heck, you can get a 1500 watt PRX815W for $900 that you can plug straight in to, even control it with an ios or windows device via bluetooth that will carry a FOH many times what that GK/Fearful rig is capable of. 

The bottom line is to play what sounds good to you. The only way you are going to even get close to the SPL of your GK rig with the Sorado is to put a bunch of efficient drivers with it, maybe 2 X 215 cabs, or mic it and run through the PA. But never in a million years will that transistor amp through a homemade PA speaker cop the tone of the Sorado rig; provided of course that your D140 is healthy.

[eddiemac]

I don't actually have a D140F anymore.  I didn't make that clear.  I was speaking about back in the day, and I know what you mean about getting "soft."  Mine did that  -  I even sent it back to JBL under warranty.  Naturally, they sent it back unchanged, but I did get a very nice letter asking me what I was talking about.
I appreciate your insights and wealth of experience, Ed.  I play blues in small clubs, quite often without PA support.  Your rig sounds really cool.  I just need one or two setups that can be stand-alone units, like we all used to play through (I'm 66).  The Fearfuls are useful for very large venues and outdoor events, and my Fearful 12/6 with 12 Sub gets rave reviews from audience and other musicians.  I think it sounds pretty darn good.  But the Sorado is apparently not the amp for it.
I have a K140, but it's been reconed.  So far, the Sorado has worked best with an EV 15B in an EV design box, but I plan to experiment with other cabs on the JBL.

[eddiemac]

Update: I bought an fDeck HPF Series 3, which is a variable frequency high pass filter, adjustable from 35 to 140 Hz.  It effectively tames the low frequency cone excursion that bothered me when using my Sunn Sorado into a 1-15" cab.  The amp will see more use now.

[Soundmasterg]

  By the way, Soundmasterg, I am in your debt.  Your postings about cap replacement, in our modern age, has been my guide to reconditioning my amp.  Thanks!

You're welcome, glad to help!

Greg

[Isaac]

Sounds as though you have the problem solved, Eddie. What I think was happening, touched on by both G and Ed, was that the high fidelity, full range amp was putting out frequencies that were lower than the tuning frequency of the speaker cabinet. When that happens, the driver is no longer loaded acoustically. That is, there is no "air spring" to prevent the driver from flopping about, and can lead to the driver exceeding its excursion limits and even damaging the driver. Using a high pass filter, as you are doing, will prevent that. As G mentioned, tube amps have lower damping factors, and a high damping factor will also help by electrically suppressing excessive excursion.

A lot of amps, even old Sunn tube amps, limit frequency response. IIRC, the 200S rolls off the low end at 80Hz, 40Hz with the LOW BOOST engaged (so it's not really a low boost, just extending the low end by an octave). I don't see a lot of cone excursion when using the 200S. On the other hand, I don't think that the Sceptre line (and my Sentura, etc.) are rolled off anywhere near that high. There's a -6dB shelf in the response on the low end (I don't remember the frequency), but the low end roll off occurs much lower, which is one reason those amps make such nice bass amps. And with my Sentura II, I do see much higher cone excursion.

[eddiemac]

A good sum up, Isaac.  If the roll-off is indeed different in the Sentura and the 200S, can that be seen in the schematics?  I would think so, at least to someone with electrical expertise.  Anyone care to confirm?

[Isaac]

I can see it in the schematics, but you might want confirmation from someone else.

[eddiemac]

O.K., your confirmation is good enough for me.  I wonder if the 200S had the higher roll-off from its inception or if it was modified as time went on.  Did the roll-off have something to do with the speakers used with each specific amp pairing?  Did JBL request modifications due to increased warranty work?  Just wondering  -  ad infinitum . . .

[eddiemac]

Can someone please tell me which specific electrical components are responsible for the roll-off (high-pass filter) in the Sunn Sorado?  I would like to check to see if they are in-spec.  Here's the Sorado schematic (click on the schematic and it will expand):

www.prowessamplifiers.com/schematics/sunn/Sorado.html

[Isaac]

Any time there is a capacitor in series with the signal, it will function as a high pass filter. Also, the cathode bypass capacitor functions as a shelf filter, increasing the gain above the resonant frequency with the cathode resistor. In this case, the cathode bypass resistor is plenty large enough at 250μF that there is virtually no roll off above 40 Hz. The biggest bass blocker, I think, is going to be the .002μF cap that couples the anode of the first stage to the grid of the second. The .0075μF cap connected to the LO BOOST switch is there to let more bass through.

IIRC, on the 200S, the high pass is at 80Hz without the switch engaged, 40 Hz with. I would expect the Sorado to be similar.