spectrum II sound

[TO)))M]

Hi!

my '68/'69 spectrum II is now repaired. new caps, new power tubes and everything checked. costly, but it's a dude who knows what to do. me not
it goes int o a '68 2x15 cabinet (200s?) with jbl k130 speakers.

now i've got a question about the sound.
first, it's extremely "high" and sharp. need to turn down highs to 1-2. i guess it's either in the design, or the speakers support such high frequencies.
suggested was to remove the 16ohm feedback (don't know about that at all ). the polarity switch could be used to switch it on/off.

the main things is about "cleaniness". it's not that clean at all, turning up to 4-5, it's pretty loud, but starts to distort/crunch rather early.
is this the normal behaviour of the amp? i'm not about playing at 10, but i'd expect it to stay clean enough in middle setting. and i'm getting trouble with pedals because the distortion adds up.

pre-amp tube is original and in working condition. i've got a new spare one, though. if it's a matter of the tube.

any thoughts about it?
greets!

[loudthud]

Disconnecting the feedback will make it distort earlier. Is the impedance matched to your speaker cabinet?

[Soundmasterg]

Sunn amps were based off of hi-fi amps, and use the same transformers and similar circuits. As a result, they have a very wide bandwidth, meaning that they amplify lots of lows and lots of highs. The circuit with it's design and higher voltages, and the tubes used are the main culprits.  The amp already has negative feedback, and the UL circuit in the power amp is a form of negative feedback too, so the amp as designed has a lot of negative feedback. One of the downfalls to negative feedback is that the transistion from clean to overdriven to distorted happens suddenly. There is no way to get rid of that effect without reducing or eliminating some negative feedback. Unfortunately, removing negative feedback will make the amp distort earlier and the sound will be more raw. It sounds like you want more headroom, so this isn't the ticket by itself, though it could be part of an overall solution.

The high voltages throughout the amp make it feel hard and less touch responsive, and the only adjustment possibility here is to change dropping resistor values to lower the voltages going to the preamp. The fact that the amp breaks up as it does is a result of the design. If you increase the dropping resistor value feeding the preamp, then that lowers the voltages of the stages that supplies, which makes those stages have less gain. You can get it to break up more around 6-7 instead of 4-5 by doing this, but there is some tweaking involved to get it to sound right. In my old 200S, I changed the 15k resistor to a 22k and it was enough to back off on the gain and high end a little. YMMV on that score.

The speakers you are using are great speakers and are in demand still, but with the aluminum dust cover, they do have a sharp and high frequency emphasis. You may try other speakers to see if it gets you closer to where you want to be, however with just about any other speaker, the amp will break up even earlier in the volume and and will likely be quieter also.

Personally I don't like Sunn amps or 6550/KT88 tubes for guitar. I have always felt, at least for my own sound preferences that the sound of them is harsh with lots of lows, lots of highs, and not much mids. The tones that are there aren't as musical as some amps. Again, that is my personal opinion and YMMV.

Greg

[Isaac]

Whereas I have found that the Sceptre and its clones *with the midboost switch* sound very good for guitar, especially with a hot input, so that the distortion begins in the preamp stages.

[EdBass]

I'm Alpha testing a "dirty mod" for Reeves currently, and have been for some time.
Reeves' C225 is too clean for some apparently, and to attempt to capture some more of the SVT/Orange AD200, etc. buyers, Reeves is exploring ways to offer a factory optional mod that will put a little "hair" on their bass amps.

Phase one involved  removing the negative feedback adjustably via a pot on the back. This had more of a volume boost effect than a distortion effect, no increase in audible distortion until you really open the amp up, and the amp is appreciably louder with feedback removed; which makes sense when you consider how negative feedback actually operates.

Phase two was simply adding a gang pot to the feedback attenuator pot to keep the output level at consistant levels as the negative feedback was removed by simultaneously reducing gain.
Again, you can't really hear a difference in "dirt" until you have the amp pretty much wide open.

The amp is currently at Reeves having an additional, switchable gain stage added. I should have it back soon, hopefully that will do the trick.

[Soundmasterg]

Whereas I have found that the Sceptre and its clones *with the midboost switch* sound very good for guitar, especially with a hot input, so that the distortion begins in the preamp stages.

Which just goes to show you that everyone hears differently.

When I play guitar, I prefer amps based on the Western Electric circuit like Fenders, Marshalls, Voxes etc., but each to his own. For bass, I love the Sunn amps, especially the 2000S.

Greg

[Isaac]

Yup. We hear differently, we play differently, we use different instruments, and we want different results. For one thing, you can actually play, whereas I merely flail about.

I've never played through a 2000S, but I love my 200S. I also like playing bass through my Sentura II (one of the Sceptre amps) and my Model T.

[Soundmasterg]

Yup. We hear differently, we play differently, we use different instruments, and we want different results. For one thing, you can actually play, whereas I merely flail about.

I've never played through a 2000S, but I love my 200S. I also like playing bass through my Sentura II (one of the Sceptre amps) and my Model T.

Thanks for the props Isaac. I try, but there are lots of cats out there that are better than me.

Whenever I get my 2000S rebuilt, you're welcome to come try it out! I've got the head and the bottom with D140's in it. I sold my 200S because there wasn't any need to duplicate sounds and I figure the 2000S can get me where I want to go. I should have time to get the 2000S all rebuilt later this summer...late august or sept probably.

Greg

[Isaac]

Let me know. I'd like to give it a try.

I wonder, would Conrad be interested in doing a frequency response measurement on the 2000S cabinet for comparison with the 200S? I, at least, would find that interesting.

[EdBass]

Let me know. I'd like to give it a try.

I wonder, would Conrad be interested in doing a frequency response measurement on the 2000S cabinet for comparison with the 200S? I, at least, would find that interesting.

They sound pretty similar to my ears, except the 2000S sounds a little bigger and deeper and the 200S has a little tighter bottom.
But, I've never put an RTA to them. Maybe my ears are hearing what my eyes tell me I should be hearing.
This fall I'm supposed to be doing simple indoor 1 meter and 10 meter sweeps of some SR cabs I'm looking at buying after this year's festival season.
If I'm feeling froggy I might bring a 200S and 2000S cab along and get some numbers.

[D.M.N.]

I'm Alpha testing a "dirty mod" for Reeves currently, and have been for some time.
Reeves' C225 is too clean for some apparently, and to attempt to capture some more of the SVT/Orange AD200, etc. buyers, Reeves is exploring ways to offer a factory optional mod that will put a little "hair" on their bass amps.

Phase one involved  removing the negative feedback adjustably via a pot on the back. This had more of a volume boost effect than a distortion effect, no increase in audible distortion until you really open the amp up, and the amp is appreciably louder with feedback removed; which makes sense when you consider how negative feedback actually operates.

Phase two was simply adding a gang pot to the feedback attenuator pot to keep the output level at consistant levels as the negative feedback was removed by simultaneously reducing gain.
Again, you can't really hear a difference in "dirt" until you have the amp pretty much wide open.

The amp is currently at Reeves having an additional, switchable gain stage added. I should have it back soon, hopefully that will do the trick.

That makes me chuckle. If you're looking for a hairy amp, the Reeves is not what comes to mind. I think people that think they're too clean might be missing the point. However, that' pretty cool that they're looking into a dirt mod to them, make them a bit more "versatile".

Wonder what those folks think of the C400. Haha.

[Isaac]

Conrad measured my 200S cabinet a few years ago. I bought it from the first or second owner, and it's quite clean. Looks almost new, original D140 drivers and all. It was essentially flat from 50Hz to 2KHz. I have modeled the 2000S cabinet (using K140's), and can't find a tuning for a cabinet that size with those drivers that comes out as flat. That's not necessarily bad, of course. The larger cabinet could have a deeper response, or a small bump in the low end to give it a more solid bottom. But that's why I'd like to see a frequency response measurement!

[EdBass]

I'm Alpha testing a "dirty mod" for Reeves currently, and have been for some time.
Reeves' C225 is too clean for some apparently, and to attempt to capture some more of the SVT/Orange AD200, etc. buyers, Reeves is exploring ways to offer a factory optional mod that will put a little "hair" on their bass amps.

Phase one involved  removing the negative feedback adjustably via a pot on the back. This had more of a volume boost effect than a distortion effect, no increase in audible distortion until you really open the amp up, and the amp is appreciably louder with feedback removed; which makes sense when you consider how negative feedback actually operates.

Phase two was simply adding a gang pot to the feedback attenuator pot to keep the output level at consistant levels as the negative feedback was removed by simultaneously reducing gain.
Again, you can't really hear a difference in "dirt" until you have the amp pretty much wide open.

The amp is currently at Reeves having an additional, switchable gain stage added. I should have it back soon, hopefully that will do the trick.

That makes me chuckle. If you're looking for a hairy amp, the Reeves is not what comes to mind. I think people that think they're too clean might be missing the point. However, that' pretty cool that they're looking into a dirt mod to them, make them a bit more "versatile".

Wonder what those folks think of the C400. Haha.

The Reeves bass amps will never be nasty like some of the others. Like our Sunns, Reeves are designed to stay clean and fight distortion pretty hard. The exercise was trying to get controlable dirt at reasonable levels; a mod that would also work on the C400.

Which reminds me, I need to call and see what's going on with my C225... Dirty or clean, I have some outside gigs coming up and this;



Is much easier to schlep around than this is!

[EdBass]

Conrad measured my 200S cabinet a few years ago. I bought it from the first or second owner, and it's quite clean. Looks almost new, original D140 drivers and all. It was essentially flat from 50Hz to 2KHz. I have modeled the 2000S cabinet (using K140's), and can't find a tuning for a cabinet that size with those drivers that comes out as flat. That's not necessarily bad, of course. The larger cabinet could have a deeper response, or a small bump in the low end to give it a more solid bottom. But that's why I'd like to see a frequency response measurement!

Did Conrad mention how flat in dBs; +/- 3dB, +/- 6dB, etc.? Even the venerable JBL themselves will use +/- 10 dB when rating SR and MI enclosures; the 4625B, E140 loaded bass cab is factory rated 40hz-2.5khz.
Some would refer to that as "flat", but in actuality it's -10dB, which is more flat than +/- 10dB (a 20dB margin) but not "flat" by most FOH engineer's definition.

I am in no way suggesting that Mr. Sundholm is/was "fudging", but specs are easy to manipulate, and it's not like the manufacturers are "cheating"; the specs may be accurate but the interpretation is generally skewed.

For example, everyone talks about how powerful (loud) Sunns are compared with other amps rated at the "same" output power. That's not so; in reality a watt is a watt, period.
The Sunn ratings are the same as the "donor" Dynacos they were derived from. The 2 X KT88/6550 60 watt Mk III was rated 20hz -20khz, less than 1dB tolerance at less than 1% THD.
That's probably about "3" on the average 60 watt Sunn's volume control...

Most current manufacturers rate output in the amps "power band", around 1khz, and Lord knows at what THD. Bass Gear Magazine has the most comprehensive and unbiased testing I'm aware of, and using 5% THD they regularly "mythbuster" manufacturer claims of output power.
Last year they tested the  TC Electronic RH450 "450 watt" bass amp and using their measuring practices got about half that much; Ampeg, Genz Benz, and others have also been outed for "creative" output ratings.
I don't know (I've offered my amps to BGM as test mules) what a tube rectified 200S would test at, but I'm guessing around 100 watts at 5% THD with a narrower (realistic) frequency range.

All that said, I also would be curious to see what the "specs" are on the 200S/2000S cabs with AlNiCo JBL's, but how they sound is actually the important thing to me!