200s low-end a bit muddy

[hop]

I own a circa '67 200s.  When I crank the volume past 4 or 5 the lows lose their tightness/clean vibe.  I am using a Sunn 215s cab loaded with 2 JBL K140's (great cab  - I also use it with a '98 Sunn 300T for medium/larger venues).  

Tubes in the 200s are new (JJ's  KT-88's).  The sound also gradually turns overdriven as the volume exceeds 5.  Actually pretty amazing sounding if you use that sound at all.  Sounds nice with my '77 Tele.  Problem is that I would prefer to get a nice clean bottom at higher volumes.  Is this amp capable of that?  If not, then I will just use it for smaller venue/gigs - at a volume of 2-4 the amp SINGS clean fat tube sound - and its still pretty loud for most places I play.  I was just wondering the history/skinny on these amps.  Any thoughts?

[Greg Z]

Where do you have your bias set?
Also using a lower gain pre-amp tube might help. 5751 or 12au7
The jj's are not exactly known for big bottom end,a 6500c svetlana or
Nos GE 6550a might be better suited for what your looking for.
Also changing you rectifier to solid state and beefing up the power supply might help tighten things up.

[hop]

not sure where the bias is set.  I had a local luthier/amp tech guru give it the once-over.  He seems to think that the amp sounds as it should - telling me that 65 watts is not going to get you too far in the clean/loudness dept. for a low-end bass amp.  I wonder if he's right or just bailing on me (if he's not too familiar with the make/model).  

Thanks for the tube advice.  Regarding the rectifier to solid state - I have heard others mention the same - and yet another guy says its a bad idea to do it because the amp was not made to do this, and it detracts from the amps value.  Hell, I just want it to sound as best as possible.

[Geoff]

I don't necessarily think your amp guy is bailing on you re: 65W output power -- by today's standards, it's not a lot of power -- certainly nowhere near the clean headroom of your 300T.  This doesn't mean that it isn't a good or useful amp -- it just won't be the cleanest when you turn it up.  Most gig-sized SS bass amp offerings today boast 200-350W power.  For some people, even that isn't enough power.  You're right that the 200S and similar make nice guitar amps, though!  

My Sonaro (pretty much a 200S) came modified with a SS rectifier and what I can only describe as added "stiffening caps" in the power supply.  When these caps blew and I restored the amp to the stock configuration, the clean output was very noticeably reduced and the amp got dirtier quicker.  As Greg Z suggested, updating the power supply and/or adding SS recfifier could help.  5751 is what I use in the preamp too!

Unless your 200S is in museum-type condition or you are concerned about keeping it in factory shape, I wouldn't worry about doing small mods.  A good tech (or you) can reverse the mods if they're unsatisfactory and no damage done.

Good luck!

[RichBriere]

Hop.......are you using THE Sunn 2x15 that came with the 200S........or the one that came with the 300T?  The 200S doesn't really enjoy going past 4. If you have the bottom boost switch on......it likes it even less. During the late 60's, they were KING!. Why? What else was there that could compete? The 200S is still my fave.........but it can't really deliver massive volume levels. Also, what are the ohm ratings on your JBL's?  

Bass-ically Yours,
RB

[Hop]

I picked up the 200s with a 215M "magna" cabinet - right side ported using 2 JBL 15" K-140's - reads "4 ohms" on the rear label.  I use this cab with the 200s when I can keep the volume under 4-5 (smaller gigs), and also use the cab with my Sunn 300T head for larger venues.  I agree with you in that the tone of the 200s head is top notch - especially at the lower volumes.  I also keep the low boost switch off.  My 300T kicks buttl for that bass tone/umph that kicks you in the chest - so you FEEL the sound, not just hear it.  Here is a guess - I didn't think that this cab was the original cab for the 200s.  My 200s is circa '67 (diagonal grill cloth - a bit muted) where as the cab looks to be early 70's (silver sparkle rectangle grill cloth) - you would probably know better than I.  At first I was not certain if the 215M cab could handle the 300T - but folks on this site said the 2 JBL's can handle it.  I don't usually go past 5 on th 300T channel 1 volume.  What do you think? In response to your other posting - I also have an Ampeg B-15 which is nice for recording but can get a bit boomy and lost when using for gigging.  I play a Fender P-bass 1978 and 1962 (the reissue which is still quite nice).  I own a '77 Telecaster U.S.A. blackface '66 Princeton Reverb and newer Custom Vibrolux Reverb amp.  Come to think of it I am not sure how I snuck all this stuff into my house without my wife figuring things out over the years.  Oh well some things are better left unsaid.

[RichBriere]

Hop.......your wife is, obviously, a very good woman and deserves to be treated well.    If I were you I'd see that she gets a Sunn T-shirt or a Sunn bathrobe and matching slippers for Christmas.

By the way......that Vibrolux........a nifty little amp, eh?

Bass-ically Yours,
RB

[Rocketboy]

Cool.  You can always add a SS rectifier with 4 diodes that can be removed if you want to go back to vacuum tube rectification.  See the Kendrick Amplification website and give Gerald Weber a call.  He will tell you everything you need to know about the conversion.  The best part is, the tube socket can just stay there with no mod.  Just remove the tube.  Easy to put back if you like.

I put Svet KT88's in my 200S.  When I bought it (the 200S) it had Chinese 6550's that were awful.  The 200S schematic shows a nominal bias voltage for the finals of -55VDC.  If you go to a SS rectifier, or use other than the original output tubes, this voltage will not work well.  What I did was adjust the bias trim pot, with the assistance of a DVM, such that in a totally darkened room the plates stopped glowing red, and then added negative bias until the sound was right for me.  Very unscientific, but also very effective.  My bias voltage, with SS rectifier and Svet KT88"s, ended up being around -63.4VDC.  It's very HiFi.

One of the many cool things about the 200S (and other Dynaco-based Sunn amps), is their simplicity and ruggedness.  The power transformer and the output transformer in these amps have no problem handling the 50% or so power increase obtained with a SS rectifier.  The front end has enough headroom to accomodate most any preamp/compressor (i.e.: A.R.T TubePac or similar).

Rich's suggestion regarding a 2X10 is a good one.  Especially if you are going through any kind of sound reinforcement, there's no point making your amp work harder than it has to on the stage.  Pay attention to the impedence match between your output transformer and your speaker system.

300T ROCKS!!!  Good luck.  Ric

[Rocketboy]

Cool.  You can always add a SS rectifier with 4 diodes that can be removed if you want to go back to vacuum tube rectification.  See the Kendrick Amplification website and give Gerald Weber a call.  He will tell you everything you need to know about the conversion.  The best part is, the tube socket can just stay there with no mod.  Just remove the tube.  Easy to put back if you like.

I put Svet KT88's in my 200S.  When I bought it (the 200S) it had Chinese 6550's that were awful.  The 200S schematic shows a nominal bias voltage for the finals of -55VDC.  If you go to a SS rectifier, or use other than the original output tubes, this voltage will not work well.  What I did was adjust the bias trim pot, with the assistance of a DVM, such that in a totally darkened room the plates stopped glowing red, and then added negative bias until the sound was right for me.  Very unscientific, but also very effective.  My bias voltage, with SS rectifier and Svet KT88"s, ended up being around -63.4VDC.  It's very HiFi.

One of the many cool things about the 200S (and other Dynaco-based Sunn amps), is their simplicity and ruggedness.  The power transformer and the output transformer in these amps have no problem handling the 50% or so power increase obtained with a SS rectifier.  The front end has enough headroom to accomodate most any preamp/compressor (i.e.: A.R.T TubePac or similar).

Rich's suggestion regarding a 2X10 is a good one.  Especially if you are going through any kind of sound reinforcement, there's no point making your amp work harder than it has to on the stage.  Pay attention to the impedence match between your output transformer and your speaker system.

300T ROCKS!!!  Good luck.  Ric

[mastercaster]

As far as SS rectification, you could always buy a very inexpensive SS plug in to replace the rectifier tube, Hoffman Amps carries them.  As usual, anytime you go solid state, expect a rise in voltage, the Sunns are very tolerant but you will be pushing some filter caps.     'Stiffening caps' I would imagine are just larger filter caps since you don't have to worry about killing your rectifier tube anymore and it will 'stiffen' or tighten the sound up some.  The 200S is what it is and I think you've figured that out, within it's intended realm it is an incredible tone machine..You've retubed but how are your caps?  You'd be surprised how long it's been since a 25-30 year old amp has been limping along on the original electrolytics.

[gbarchus]

I have used 200S cabinets for over 30 years and consider them to be one of the best. But, when they were designed, amplifiers only had 120 watts. A JBL D-140 was rated at 60 watts RMS in the 60s. So, usually, there was no problem. Today, trying to pump 300+ watts into a 200S cabinet can cause problems. the port is NOT tuned using Theile/Small parameters and, so, the speakers are not protected at the lowest notes on a bass (42 Hz). With a lot of power applied to the cabinet the speakers will move too much, which can be sensed as a "muddy" sound.

Gale