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Op Amp upgrade

#21
A graph of SWR's built in voicing in post #12 of this thread.

http://www.talkbass.com/forum/f15/swr-aural-enhancer-bypass-643201/

When you see how far off it is from "even", I'd start compensating for it with the sweeps. Then worry about other stuff. I was constantly boosting lowmids with my SM400S and never figured out why I had to do that to make it sound good....until I read that.

Post #19 is an "easier to see" comparison.
 
#22
will33 said:
A graph of SWR's built in voicing in post #12 of this thread.

http://www.talkbass.com/forum/f15/swr-aural-enhancer-bypass-643201/

When you see how far off it is from "even", I'd start compensating for it with the sweeps. Then worry about other stuff. I was constantly boosting lowmids with my SM400S and never figured out why I had to do that to make it sound good....until I read that.

Post #19 is an "easier to see" comparison.
Click to expand...

So does that mod just eliminate the built in "color" while keeping all tone knobs functional?
 
#24
carvinbassplyr said:
So does that mod just eliminate the built in "color" while keeping all tone knobs functional?
Click to expand...


Yes. Just gives you an "even" starting point instead of having to correct for the built in voicing, which if you'll notice, sucks away the "meat and potatoes" range of the bass. The SWR doesn't have some of of the low slung "50-60hz" hpf's some amps have but it's "voicing" gives you lows that some cabs can't make use of, then takes out lowmids and has a lot of harmonics. Don't get me wrong, I liked mine but you have to know (or hear) how to make it do what you want it to do.

It's one of those "sounds great soloed, sounds weak or muddy in a mix" kind of things, unless you mix around it. That voicing is why I used to think, as did many others that SWR's were low powered or didn't live up to their ratings as say a Peavey or a GK does.
 
#26
BogeyBass said:
Sorry guys the SWR has nothing close to a passive "tonestack"
blah blah blah.
Click to expand...

I'm going off-topic here. Sorry 'bout that. Ignore if you don't care about the technicals...

Not that it really matters, but what makes this not a passive tone stack? It's not a classic "Fender" (or Marshall) tone stack, but I never said it was a "Fender tone stack". It is nothing more than a series of RC filters "stacked" on each other in such a way as to manipulate the signal that passes through it in a unique way. It is ingenious how it works in adjustment - and somewhat intuitive if you understand RC networks - but it is at it's core a passive tone control.

**************
EDIT #2: It *IS* a Fender tone stack - with a few extra components. The basic core is absolutely "Fender Tone Stack". The AE pot does several things; first, it acts as a variable attenuator to effectively boost/cut the total signal into the AE tone stack. The low end of the control is about 1/4 the voltage coming out of the gain stage, the high end of the control is about 1/3rd the voltage. Thus, the overall level is increased. Second, the AE control also changes the resistance corresponding to the "mid" control of the classic Fender tone stack. As you sweep across, the bass/treble components are fixed, but the mid drops as the overall level increases, which gives the effect of increased bass/treble, scooped mids. As with the Fender tone stack, everything is interactive, so as the mids are changes, the bass/treble are also changed a little bit. Definitely ingenious!

No, I did not simulate it - I put that 'spensive eddicashun to use.
**************

As for the bass/treble controls - I'd agree that the treble is similar to any passive tone control, but the use of the gyrator in the bass control is in no way passive, [DEL]nor is the bass control shelving. Perhaps they changed something in the SM900, but every other SWR amp designed by Steve Rabe had a band-pass bass control with the same topology as each semi-parametric mid-band with the exception of a fixed frequency control. [/DEL]

**************
EDIT #1: my bad... The Bass control on the SM400 schematic, and I assume SM900, is shelving with an active 2-nd order LPF. The Bass 350 has a band-pass bass control.
**************

Now, if you have (OTHER...) additional info to what is on the schematics regarding the circuit design and analysis, I'd gladly recant my statements; I'm always up for learning more.
 
#27
I somewhat disagree about how op amps can impact tone. In my experience, they can and do make a difference in sound, though sometimes those differences are subtle. However, I would agree that there are overall design differences between the Avalon and SWR preamps that come down to much more than just op amps. So, I'm doubtful that such changes would bring your SWR up to Avalon sound quality.

I've replaced all of the JRC072D op amps in my Eden WT-500 and it has made a significant improvement in the sound. Other modifications were made as well, like removing or replacing capacitors in the signal path. OPA827s were used for the input and EQ, with OPA211s in the preamp's output stage. The increased current demand of the high performance parts necessitated modifying the zener-regulated power supply.
 
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#28
BassmanPaul said:
And that's why it sounds better than most top of the line bass heads!
Click to expand...
You do get what you pay for so if you tack on a George massenberg labs compressor:
GML 8900 | Sweetwater.com
and dont use the rather cheap onboard compressor in the avalon unit the transparency is improved considerably.
In fact the Avalon is not considered that transparent by
studio engineers anymore its an old school character piece in the these days of straight wire with gain waffle.
Millennia STT-1 Review
But if you want a new pre amp to stick in the rack to stuff up the swr's return socket, I want the fabulous color this thing is.
Link Removed
Reassuringly expensive I feel Sir!.:eek:
But thats nothing in pre amps I have an old pre amp in the studio its got one gain knob an input an output and a mains switch.
It aint got an eq or compressor the only silicon in it might be some sand.
And one in only slightly better visual condition than mine sold for $7000 at Pro Audio Heaven in LA a few weeks ago.:eek::eek::eek:
Now all I need to get Is the matching compressor to go with it:
Invalid Link Removed
Those are like Fairchilds, the only way to get one? is pry it from the cold dead hands of the original owner.
Then all I need is an EQ?.:hmm:
 
#29
Munjibunga said:
It seems to me that you don't like the sound of the SWR 900. The best solution is to sell it and buy something that sounds good to your ear. It also seems that you are oblivious to the techno-geeks here who have repeatedly told you that swapping op-amps will not accomplish your goal.
Click to expand...

I'm not oblivious by any means...when I realized op amps weren't gonna cut it and I saw that mod I immediately changed tactics. Ur right I don't care for the "natural" tone of the SWR, but I like the way they set it up. I liked the tone of my eden better but I didn't like that the frequency sweep knobs didn't have detents on them only the boost/cut knobs did...and edens have/had a realy sharp roll off after around 5khz which made it hard to get a nice clean slap tone. So now if I don't completely like Eden or SWR that doesn't leave much in the way of choices. I think I'd rather take a slightly "flawed" design and mod it to what I like. It's no different than buying a carvin(which physically speaking are very well made basses IMO)and throwing in some nice bartolini or seymour duncan electronics to get better tone capabilities vs spending $5k+ for a custom bass just for "that one tone".
 
#30
According to RMAA, the Eden WT preamp rolls off around ~12 kHz. That should be high enough to allow for a decent slap tone. That said, I modded mine to go up to 20 kHz and think it sounds more open than stock. Might be worth trying the Aural Enhancer mod and see if that gets you closer.
 
#31
12bass said:
According to RMAA, the Eden WT preamp rolls off around ~12 kHz. That should be high enough to allow for a decent slap tone. That said, I modded mine to go up to 20 kHz and think it sounds more open than stock. Might be worth trying the Aural Enhancer mod and see if that gets you closer.
Click to expand...

Yes the newer "B" & "C" models had a higher roll off point...my Highwayman 500 which is "ancient" by todays standards but was also a "true blue(gold)" pre buy-out Eden had a roll of point set much lower. I've already got my tech looking into that AE mod and I think that will get me more of what I'm after. My tech has already gone through and replaced alot of resistors and capacitors and got my amp running quiet and strong...I just hate having 2 EQ around someone elses preset EQ all the time and that mod will give me a flatter starting point.
 
#33
Quote:
Originally Posted by WingKL
The TI TLE2072 is a direct upgrade substitute for the TL072. It cut the noise in my Thunderfunk by at least half if not more and made it clearer. I think this is the opamp upgrade you're looking for.

carvinbassplyr said:
Which sub-model? When I click on that it takes me to a page that has so many different version I can't even take an educated guess...
Click to expand...

Assuming that what you are replacing is in an 8 pin DIP package, it should be a TLE2072CP or TLE2072ACP.
 
#34
Aren't we all getting ahead of ourselves here with talk about swapping or not swapping chips/tubes, selling the head, moving to a high-fi studio preamp, etc?

First, what cab are you using? If your cab isn't capable of producing tones along the lines of what you experienced in the studio, then whatever head/preamp you use isn't going to matter. Is it possible that the tone you were digging in the studio was more a factor of the studio's monitors than the preamp?
 
#35
Kael said:
Aren't we all getting ahead of ourselves here with talk about swapping or not swapping chips/tubes, selling the head, moving to a high-fi studio preamp, etc?

First, what cab are you using? If your cab isn't capable of producing tones along the lines of what you experienced in the studio, then whatever head/preamp you use isn't going to matter. Is it possible that the tone you were digging in the studio was more a factor of the studio's monitors than the preamp?
Click to expand...

I use 2 SWR Goliath III 8 ohm 4x10 cabs daisy chained 2gether for a 4 ohm load with the SM-900 in bridged mono.
 
#36
solarplexus said:
You should look at the NE5532.
Click to expand...

This is an example of something that requires some "design" work...

The TL072 and NE5532 are different..... one is an FET input, the other a bipolar transistor input.

They will have different inherent input impedances, and that may affect how they work, and IF they work.... Significant input current may lead, in some circuits, to a substantial DC offset.

The TL072 has near-zero input bias current, but the NE5532 from TI shows as typically having about 1 microamp. With a high resistance on the input, that may add "flicker" noise, cause a DC offset of a volt or more, etc, etc.

The designers picked a certain type of part, and it is wise to stay within the same general type when trying replacements. otherwise you may have "unforseen" results.
 
#37
Jerrold Tiers said:
This is an example of something that requires some "design" work...

The TL072 and NE5532 are different..... one is an FET input, the other a bipolar transistor input.

They will have different inherent input impedances, and that may affect how they work, and IF they work.... Significant input current may lead, in some circuits, to a substantial DC offset.

The TL072 has near-zero input bias current, but the NE5532 from TI shows as typically having about 1 microamp. With a high resistance on the input, that may add "flicker" noise, cause a DC offset of a volt or more, etc, etc.

The designers picked a certain type of part, and it is wise to stay within the same general type when trying replacements. otherwise you may have "unforseen" results.
Click to expand...

That is the reason why I suggested to use IC sockets and swap the IC's to find the best one. I have used the NE5532 in replacement of the TL072 in some circuits to great results, but, like you said, it can be wrong for others.
 

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