Variacs and voltage regulators

Discussion in 'Amps and Cabs' started by scottl, Jun 14, 2006.


  1. scottl

    scottl Member

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    I'm thinking of adding a variac to my rig. I am tired of the fluctuating wall voltage. My dog ears can't take any tonal deviation from my standard. The AR1215 in my rack is almost totally ineffective at giving me a regulated output. The range is 120v +/- 5V!!!! Furman told me on the phone that the unit does not switch the transformer taps unless you are less than 115v or over 125v. This is bogus! Why not switch under 117.5 and pver 122.5?? This would tighten the range to +/- 2.5V Acceptable IMO. But no..... They then say the unit is designed for digital stuff and NOT guitar amps. That is why it is not even regulating when the wall is between 115v and 125v.

    ETA systems makes a nice piece that is always regulated to between 117v and 120v This is excellent, but the cost is $700 for the unit! I liek the dig voltmeter right up front on it too!

    My decision therefore is to get a variac. Run it at 113v-114v with my Furman AR1215 between it and the amp. This will filter the RF and junk and step me up to 118v-119v. My tolerences will be much much tighter.

    Any suggested variacs?? I have my eye on this one http://circuitspecialists.com/prod.itml/icOid/7674 5amp should be enough and the unit is only 10 pounds. The 20 amp unit is 25 pounds which is way too heavy to lug around.

    Scott
     
  2. fullerplast

    fullerplast Senior Member

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    Clever solution to increase your regulation, Scott. The Furman has eight taps, so based on their specs each should be at 5V intervals except between 115 and 125. That will give you a new tap at 100, 105, 110, 115, 125, 130, 135, and 140V. As long as your wall fluctuations are somewhat reasonable you should be able to do what you want. I'd keep it even lower than 113 so that upwards drifts won't put you back in the 10V unregulated range.

    The variac you picked out looks fine to me. 5A should be fine for your amp and effects. I have a huge old variac so it's not really suited for gigs but you have me curious now to confirm the regulation steps.....I may need to check that out.
     
  3. Gary Brennan

    Gary Brennan Old cavorting member Gold Supporting Member

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    So how much lower than 113 v should the variac be set to prevent upward drift from getting into that unregulated range?

    gb
     
  4. fullerplast

    fullerplast Senior Member

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    It all depends on how much your wall voltage fluctuates over time. If you set it for 113 and your wall voltage goes up more than 2 volts, you won't be regulated again until you either get up to 125 or back down under 115 (If it works the way Scott/Furman has described).

    If I have the time tonight, I'll run through the range and see exactly where the regulator switches.
     
  5. Jackie Treehorn

    Jackie Treehorn Member

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  6. PaulC

    PaulC Member

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    Scott, there's actually a really cheap and small way of dropping the voltage like you want to without having to get a variac. You can make something called a "bucking transformer". What it is is a 12.6vac fil tranny wired in line with the line voltage in such a way that it will subtract 12.6 vac from the line voltage. If you use a center tapped tranny you can make it select between a 12.6 and a 6.3 vac drop. So for example if you had 124vac out of the wall you could drop it to 111.4vac with the 12.6 tap, or if you had 119 vac you could drop it to 112.7 vac using the 6.3 tap. Then run it into your pwr unit to reg and filter. You can put it into a small box or rack unit to go with your pwr supply - the fil tranny is about the size of a choke. Let me know if you'd like a schematic - it's really easy to wire up.

    Later, PaulC
     
  7. BobbyRay

    BobbyRay Supporting Member

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    Now you post this? I just got an AR1215 delivered to my house today!

    Mainly because at gigs the power can really drive me nuts. My amp always sounds great at home and many gigs. Some places leave my amp sounding like it's starved for power, and my tone is far less than inspiring when that happens. The worst part is, as your tone fades and thins, your instinct is to dig in harder, which only makes the problem worse.

    I guess what I need to know is did I waste my money, or are you just a tone freak listening to things that will be lost on me in live gigging situations? Your ears are freaks of nature aren't they?
     
  8. Campfired

    Campfired Gold Supporting Member

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    Hey, Scott,

    Bob Gilbert here, the guy you talked with about the ODS and Glaswerks amps about a week and a half back.

    I, too, am concerned about differing wall voltage, especially when going from home to gigs. Seeing that I live in CT, the power supply is somewhat consistent from day-to-day, never changing at home from 121 to 124. What concerns me is that this may not necessarily be true when playing out, where there is likely to be a significant voltage drop when there is more equipment on the circuit, namely PAs, other amps, etc.

    How would you say the Furman 1215 holds up there? Does the Furman do the job it's supposed to? I realize that your "Ol Dog Ears" may be more more of a hindrance when compared to earthly humans like ourselves, but would the 1215 be even marginally acceptable for gigging, say to control differing voltage drop less than 115V? If yes, then the 1215 is what I will go with.

    I am hoping others will chime in with their experiences using line voltage regulators and their amps, especially Fuchs. Thanks for getting through this, and I hope your quest for a more consistent tone is found.

    Bob G.
     
  9. fullerplast

    fullerplast Senior Member

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    OK, here's what's actually happening, regardless of the way Furman says it works.

    I set up a variac between the wall and the 1215 so I could characterize the regulator response between 95V and 120V (my max wall voltage). I had an ODS30 plugged in as well to have a realistic load and also to see if I could hear the jumps in voltage.

    The response is basically a sawtooth in terms of voltage levels. At roughly 5V intervals, the regulator would output a low voltage of about 118V going up to about 122V. Every time it hit 122V, it would drop down to 118V and as the input voltage increased, the output would also increase until 122V was hit again. There is a small amount of hysterisis built in to avoid oscillating between the two with an input voltage on the cusp.

    The transition points I measured were at 102.1, 106.4, 110.6, and 115.8. Unfortunately I couldn't get up to the next point which would have been around either 120 or 125. Somebody with a higher wall voltage will need to check that out.

    Overall, it seemed to be better regulated than the +/-5 V spec would indicate as it always was in a 4 volt range. The biggest disadvantage of this type of regulation is that there seems to always be a jump from the max output to the min output at each tap. I could hear the change in the ODS, but I don't think I could identify one voltage from another without listening right at the transition from 122 to 118.

    With regard to Scott's plan, it seems that ensuring that the input voltage is always less than 120V would give him a worst case fluctuation of +/-4V at any point in time. You could not reduce this to no matter what you do, and what's worse, this 4V jump could occur with as little as 1 or 2 V change in input voltage. FWIW, hope this helps.
     
  10. 908SSP

    908SSP Supporting Member

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    I may be misunderstanding about what you guys are talking, but I think you are mistaken if you think a Variac will set a maximum out put it won't.

    A variac sets a ratio. Let's say 120 volts in 115 volts out. If the voltage goes up to 125 in you get close to 120 out. So I don't see how using a Variac will help your issue. It does not regulate or limit. It is a variable transformer.
     
  11. Gary Brennan

    Gary Brennan Old cavorting member Gold Supporting Member

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    Fullerplast,

    Thanks for your research. I am assuming that you did get the described sawtooth response from the 1215 at the 115.8 volts? Would you agree one is unlikely to see voltage higher than 120 at say outdoor wedding gigs or older establishments, and as such the upper portion of the 115-125 range is likely of no consequence? If the 1215 will mostly be keeping the voltage the amp sees at the 118-122 zone, that would seem to justify it considering the alternative of no regulation for most cases.

    gb
     
  12. Gary Brennan

    Gary Brennan Old cavorting member Gold Supporting Member

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    Scott,

    Do you find the 18-22 voltage range makes a significant impact to tone & response? Would you think my bassman 50 mod would also exhibit this, or are the OEM's more sensitive this way?

    gb
     
  13. scottl

    scottl Member

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    118-122 is good. If the unit does that. My concern is for when I record late at night. I frequently have 122-123 at the wall. During the day I can have 116. If I set the amp up for good tone at 120v, then the bias and plate voltages are pretty hot at 123. Amp doesn't sound as good. In the real world, I would guess that voltages don't wind up over 120v. You should be fine!

    Also, Fullerplasts testing did not reveal the presence of a tap at 120v as woudl be expected. He needs more wall voltage and test again. In other words, he may find his unit will volt up over 125v.... I hope there is a 120 tap.
     
  14. fullerplast

    fullerplast Senior Member

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    Hi Gary- I would tend to agree with you, but I know that there are some places that probably get above 125V and that may still be a concern, only in that you could possibly have an output range of 118 to 125 instead of 118 to 122 (if there indeed is no tap around 120-121). I think that's what Scott is concerned about. I'll try it again at some other time of day to see if I can get a transition over 120V. The best thing about the 1215 for practical purposes besides tone is that at low voltages (under 100V), it will still put out 115V or so and at voltages over 125V it will limit the voltage to protect equipment.

    The reason that even tighter regulation is significant for our tube amps is that the turns ratio for the PT multiplies the input AC by about 4, so that a 5V change at the wall is a 20V change at the rectifier and this will affect the amp tone and dynamics to an extent. Scott is trying to minimize this.
     
  15. fullerplast

    fullerplast Senior Member

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    You are correct in your statements, but perhaps misunderstanding what we are talking about. The Furman reportedly has a gap in it's regulation steps between about 115 and 125. Scott is interested in keeping the regulation tight, so by dropping the input voltage he can keep the regulator out of that non-regulated window. The variac would do that for him, provided he kept it low enough to account for any upward drift.
     
  16. TDJMB

    TDJMB Gold Supporting Member

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    I was running off of a 1215. The indicator light goes to yellow - and my lights flicker - often. I got a Richard Gray Power Conditioner over the weekend. I haven't had time to really test it, see how much better things sound, etc. I think my Alessandro sounds better but can't say for sure if it's the placebo effect. I did notice that the "ppp" sound my Analogman chorus puts out even when not on is now barely noticeable. The most dramatic difference has been in the 13-yr-old not-high-end tvs that run on the same circuit but are not plugged into the unit. The pictures are noticeably clearer.
     
  17. scottl

    scottl Member

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    I spoke to Furman this afternoon....again. I explained Fullerplasts results and the guy (same one as yesterday) said he may have been mistaken with yesterdays comments. He is going to bench one on their test gear. He also admitted there is probably a 120v tap. If that is the case, then the unit is +/- 2.5 and not +/-5

    I'll report back. Fwiw, I could live with 118-122v

    ;)
     
  18. jspax7

    jspax7 Member

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    I've been using a 1215 with my ODS 30, and find my tone to be much more consistent than before. I have the same 115-123 variations at home too.

    I'm going to do some further testing as I can. Always interested in better tone here.
     
  19. BobbyRay

    BobbyRay Supporting Member

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    I'm hangin' tight!:AOK
     
  20. jspax7

    jspax7 Member

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    When I was having problems with my ODS 30, it was due to low line voltage. The warehouse/studio was giving me 125, and the amp sounded great. At home I was seeing 115-123. Tone was like a box of chocolates. (You never knew what you were gonna get.)

    I checked the voltage at home with a Furman conditioner, and the meter was reading 116. Tone sucked accordingly, so I plugged in the regulator, then the conditioner, so I could see what the meter was doing.

    When the regulator kicked in, the meter showed 118-119, and occasionally read as high as 122. Never lower than 118, and as I said 118-119, until it settled on 119.

    I discussed this with Andy back in February, and he said;

    [You might be moving the power tubes to a higher bias range at 122, instead of 115. That same effect could be replicated by a minor trimming of the cathode resistor value. Once you make sure, we can see about getting a kit to you with the part or sending it in for the tweak. It's fairly minor, if that's all it is...2-connections. Keep me posted.

    af]

    As I understand it, the tweak can make the amp "see" more voltage than It's getting. Correct me if I'm mistaken. If I'm getting 119, but the amp behaves as though it's getting 122, I could live with that. The regulator would just keep it consistent.
     

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