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Standby switch (Sadowsky SA200)

smeet

Gold Supporting Member
Nov 27, 2006
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Sammamish, WA
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I recently bought a Sadowsky SA200 tube amp (sounds great, first gigging it tomorrow!).
I've owned other tube amps, but I've never *really* understood what the standby switch does and how it should be used.

Here's my questions:
  • Do I need to leave the amp on standby for a few minutes even if I'm using it for low/conversational level practice at home?
  • What are the real-world repercussions of not leaving it on standby for the recommended time before playing at medium gigging levels?
  • Is this article to be trusted, and does it apply to this particular amp: https://www.sweetwater.com/sweetcare/articles/great-standby-switch-myth/

Thanks!
 
AFAIK there is no need to wait an extended time to set the amp to operate or let the amp warm before cranking it. However, it does take 15 minutes or so for the tubes to reach full operating temperature and stabilize. So there can potentially be very small changes in performance.

What a standby switch actually does varies by design. I have the schematic for the first production run of SA200s. AFAIK the second production run used the same circuit, but there are some differences in the way they were built.

When the power is turned on, line AC is applied to the primary windings of the power transformer (PT). All four of the PT's secondary windings produce voltage.

The standby switch breaks the connection between the HT secondary windings and the HT bridge rectifier. So when the amp is in standby, the HT supply does not charge up and the preamp and output tubes do not receive plate or screen voltage.

The other three sets of windings go to:
  1. Heater/fan supply
  2. Bias supply
  3. Relay/IC supply
All three of these supplies are powered up as soon as the power is turned on.

I use the standby switch on my SA200s. Whether it's beneficial or not in this particular amp, I can't say. If it makes a difference one way or the other, I doubt it's much of a difference.

I actually use the standby switch in all of my tube amps except the Mesa D180. For this amp I use standby when I power the amp up. But when I am done, I turn the power off first and let the power supply bleed down a bit before flipping the standby switch. With this particular amp, the graphic EQ produces a huge transient if the amp is put in standby with the power on. This produces a loud obnoxious clack. I can avoid the clack by either disengaging the graphic or using the procedure I just described. I believe I could probably mitigate the problem by moving the wire that feeds voltage to the graphic away from the HT wires.

I have several tube amps that do not have a standby switch.

Both of my SA200s are from the first production run. When I put them in standby, they make a whining sound, which I think is normal for the design.
 
What I understand about standby switches (which admittedly might be nothing! ;-)) is that Leo Fender, genius that he was, made a mistake putting standby switches in his amps. They were unnecessary. Tube TVs didn’t have standby switches for example.

Then when manufacturers like Marshall came along, they used Fenders as their blueprint, putting standby switches in their amps too.

Customers then expected them.

Now AgedHorse can come and destroy me! :laugh:
 
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In almost all tube amps, the power tubes get the highest voltage.
From there, there's a string of resistors that decrease, in steps, the voltages provided to downstream devices like the preamp tubes.
And almost always, there's a large capacitor that stores the reduced voltage after each resistor.

For a resistor to drop voltage, some current must flow through it. Otherwise, the voltage remains the same at the output of the resistor.
So if no current is flowing, the voltage remains practically the same all the way to the end of the string of resistors, all the way to the preamp tubes.

Power on:
**********
If the standby switch is not in standby when the power switch is turned on, and the amp isn't already warmed up, and the filaments are cold, the tubes don't conduct = 0.
For a few seconds, while those big capacitors are charging, some current flows into them.
But after that, until the filaments get hot and the tubes start conducting, practically the full voltage reaches the preamp tubes. (It also reaches the storage capacitors for the preamp too, so those had better be rated for that too.)
So, it's safer for those downstream devices to have the standby in standby when power is turned on, until the filaments get hot.

Power off:
**********
This matters a lot less, but I turn off the power switch some seconds before switching to standby. For a while, the filaments are still hot, the tubes are still conducting, and this lets the voltages bleed off, as someone else mentioned. (It matters more for me because my amps are almost never in their cabs, and their circuits almost always exposed.)
 
@Root 5: Designers of tube TVs etc without a standby switch hopefully worked around the problem I described in various ways. One way is to supply the preamp tubes from a separate, lower voltage winding, for example.
In the SVT, the screen voltage (also going to the power tubes) *is* provided from a lower voltage winding, else the power tubes would probably blow in the scenario above.
But unless I'm mistaken, the SVT's preamp tubes are downstream from the plate supply (>660VDC). It matters very much here, unless I'm overlooking something.

EDIT:
-Having a separate winding on the transformer, so the user won't have to operate a standby switch (but they shouldn't be trusted to use the standby switch anyway) costs more. But Leo was famously thrifty, right?
-If not a separate winding, then a big zener diode, somewhere downstream from the plates but probably upstream from the preamp could guarantee that some voltage would go no higher than the zener's rating, by conducting any time the voltage is higher than that. [<< I include this comment to invite anyone to criticize it.] Of course a voltage regulator is possible too, and could even be done with tubes if you're a true fanatic, a word I use with the greatest affection. :-)
 
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I see no differences with them, except for my SVT-AV 2005:

If I immediately switch off the standby, there is a loud « huuuuum » until the current between each half of the output transformer is balanced. If I wait ~1 minute, no unbalanced hum. I know HT isn’t present in standby but in this specific case, the standby is useful.
 
I would start any SA200 (Mk1 or 2) into standby mode every time; simply because those EL34s are operating in quite a bent-over-backwards way. Plus, I believe, based on my half-knowledge of the smallest corner of electrical engineering, that this method lets all the components warm up *a bit* slower which should result in a *somewhat* longer service life (tubes/valves & the rest).
 
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After hanging out in various tube amp communities for a few decades, this is what I have come up with:

When the amp is cold, turn on the power to the amp with the standby off (i.e., no sound) to avoid a big inrush to the tubes before the filaments warm up. After about a minute or so, turn the standby on and play. When it comes time for setbreak, don't turn the stand by to off, just turn down the volume or unplug the input. This is supposedly the best way to ensure long tube life.

Of course, Agedhorse is probably waiting in the wings to correct me.
 
So? How was it?
OK, gig report.
I played 7:30pm to 11:30pm (3 long sets) with "my" funk cover band (vocals/bass/drums/guitar/keys/horns). This is my second gig with them, it's a fun group - nice guys, good musicians, great repertoire (Prince, James Brown, Rick James, Gap Band, Motown, Parliament, EWF, etc), plus extras like Kendrick Lamar and Zappa quotes, La Bamba and Living on a Prayer. Smallish bar with no stage, packed house with people dancing all night. The PA carried vocals and horns only.

As you would expect with a band like this, the bass needs to be fat and prominent in the mix, but without getting in the way of all the other instruments (4 horns last night). There is a tendency for the band to get excited and play too loud, but we kept it reasonably under control and it sounded good.

I played my Sadowsky PJ5 w/Nordstrands and East pre, into the Cali76 and then the Noble to give it some subtle polish. My cabinet was my trusty Audiokinesis 212. Being a cautious guy, I set up the SA200 and then my Mesa WD800 on top of that as a backup.

We "sound-checked" (in front of the full house unfortunately) with Chic's Good Times. I used the SA200 with the fat switch on, cutting 80Hz to about 10:00 and boosting 800Hz and 3k to about 2:00. At home, this gives me a nice mid-present and defined sound with a good amount of low end without boom. We played a couple of minutes, had a few seconds to confer and tweak, and played a couple more minutes. The SA200 was able to get a good volume with the master at noon, gain at 9:00 and volume at 3:00. It was very fat and supportive, but I wasn't getting as much clean definition as I wanted. The drummer commented that I was a bit too loud (probably true), but I was having some trouble hearing my notes clearly.

After soundcheck, I made an executive decision and switched to the WD800 with slight bass cut and low mid bump. This worked well as it always does, so that's how I played the rest of the gig.

Even at home, I noticed an inherent thickness in the sound of the SA200, which is beautiful but may be hard to deal with in some venues. I didn't have the chance to really tweak the low end eq to balance fatness vs intelligibility. Also, although it was loud enough, I felt like at that volume it might have been compressing a bit and thus losing some clarity. I used the fat setting because it gives some punch and extra mids, and also it rolls off some of the extreme lows. I would have to play with that. The WD800 does not have the same beautiful tube thing (the SA200 is inspiring to play through!), but it easily slots into the mix and I can always hear every note clearly without being too loud. Also it has the power and headroom so I can play super softly and get a smooth sound while accenting notes when needed, and it feels easy and natural.

Lessons learned? I'm not sure. The beauty of the all-tube amp is somewhat lost in the sonic chaos of a bar gig. Coupled with a lack of headroom, I feel safer with the smaller, louder, and more versatile modern amp. I'll continue to learn the SA200's eq and features and try it with different cabinets, but for now, given the unpredictible nature of rooms and PA setups, I'll probably do most gigs with the safer bet of the Mesa.
 
I used the SA200 with the fat switch on, cutting 80Hz to about 10:00 and boosting 800Hz and 3k to about 2:00. At home, this gives me a nice mid-present and defined sound with a good amount of low end without boom. We played a couple of minutes, had a few seconds to confer and tweak, and played a couple more minutes. The SA200 was able to get a good volume with the master at noon, gain at 9:00 and volume at 3:00. It was very fat and supportive, but I wasn't getting as much clean definition as I wanted. The drummer commented that I was a bit too loud (probably true), but I was having some trouble hearing my notes clearly.....


Even at home, I noticed an inherent thickness in the sound of the SA200, which is beautiful but may be hard to deal with in some venues. I didn't have the chance to really tweak the low end eq to balance fatness vs intelligibility.
Where did you have the "Bottom:" (40 Hz) set? Check out the SA200 thread for more info, but my "a-ha" moment with the SA200 came when I followed some advice on that thread and cut the bottom completely to start, adding it only if needed. Your experience sounds like mine before I got this advice.
 
OK, gig report.
I played 7:30pm to 11:30pm (3 long sets) with "my" funk cover band (vocals/bass/drums/guitar/keys/horns). This is my second gig with them, it's a fun group - nice guys, good musicians, great repertoire (Prince, James Brown, Rick James, Gap Band, Motown, Parliament, EWF, etc), plus extras like Kendrick Lamar and Zappa quotes, La Bamba and Living on a Prayer. Smallish bar with no stage, packed house with people dancing all night. The PA carried vocals and horns only.

As you would expect with a band like this, the bass needs to be fat and prominent in the mix, but without getting in the way of all the other instruments (4 horns last night). There is a tendency for the band to get excited and play too loud, but we kept it reasonably under control and it sounded good.

I played my Sadowsky PJ5 w/Nordstrands and East pre, into the Cali76 and then the Noble to give it some subtle polish. My cabinet was my trusty Audiokinesis 212. Being a cautious guy, I set up the SA200 and then my Mesa WD800 on top of that as a backup.

We "sound-checked" (in front of the full house unfortunately) with Chic's Good Times. I used the SA200 with the fat switch on, cutting 80Hz to about 10:00 and boosting 800Hz and 3k to about 2:00. At home, this gives me a nice mid-present and defined sound with a good amount of low end without boom. We played a couple of minutes, had a few seconds to confer and tweak, and played a couple more minutes. The SA200 was able to get a good volume with the master at noon, gain at 9:00 and volume at 3:00. It was very fat and supportive, but I wasn't getting as much clean definition as I wanted. The drummer commented that I was a bit too loud (probably true), but I was having some trouble hearing my notes clearly.

After soundcheck, I made an executive decision and switched to the WD800 with slight bass cut and low mid bump. This worked well as it always does, so that's how I played the rest of the gig.

Even at home, I noticed an inherent thickness in the sound of the SA200, which is beautiful but may be hard to deal with in some venues. I didn't have the chance to really tweak the low end eq to balance fatness vs intelligibility. Also, although it was loud enough, I felt like at that volume it might have been compressing a bit and thus losing some clarity. I used the fat setting because it gives some punch and extra mids, and also it rolls off some of the extreme lows. I would have to play with that. The WD800 does not have the same beautiful tube thing (the SA200 is inspiring to play through!), but it easily slots into the mix and I can always hear every note clearly without being too loud. Also it has the power and headroom so I can play super softly and get a smooth sound while accenting notes when needed, and it feels easy and natural.

Lessons learned? I'm not sure. The beauty of the all-tube amp is somewhat lost in the sonic chaos of a bar gig. Coupled with a lack of headroom, I feel safer with the smaller, louder, and more versatile modern amp. I'll continue to learn the SA200's eq and features and try it with different cabinets, but for now, given the unpredictible nature of rooms and PA setups, I'll probably do most gigs with the safer bet of the Mesa.
Great feedback. I haven't tried the WD800 yet unfortunately.
But I guess you might have to try more the SA200. That doesn't mean you will enjoy it but just to make sure you will not miss anything about that great amp.
I usually set everything at noon, then set the bottom and bass at 2:00.
Also, I think you didn't set the gain high enough to really open up the preamp like it should.
But again, maybe in the end, the WD800 is the fits your needs mother than the SA200.
 
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Where did you have the "Bottom:" (40 Hz) set? Check out the SA200 thread for more info, but my "a-ha" moment with the SA200 came when I followed some advice on that thread and cut the bottom completely to start, adding it only if needed. Your experience sounds like mine before I got this advice.
Bottom was set at noon. Good suggestion about adding it in as needed, I’ll try that.

I usually set everything at noon, then set the bottom and bass at 2:00.
Also, I think you didn't set the gain high enough to really open up the preamp like it should.
With bottom and bass at 2;00, the amp is very huge and boomy sounding for my taste.
The gain was set as high as I could go before getting obviously distorted. Turning the fat switch off allows higher settings, but then it’s more mid scooped.

Some interesting suggestions here, I will try them out.

Thanks all!