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Post by kruzty on Dec 18, 2006 10:58:41 GMT -7
Does anyone see any problems with this setup?
Amp -> speaker Parallel out of speaker -> Attenuator Attenuator -> another speaker (or as pure dummy load)
As long as use the appropriate impedance on the attenuator, I can't see any problems, but I thought I should check to make sure I'm not missing anything.
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Post by benttop (Steve) on Dec 18, 2006 11:42:22 GMT -7
Guys do this with the Hot Plate all the time. You get a 3db drop in volume if you run the Hot Plate as a load with no speaker doing it this way. Of course if you have a speaker on there, it's not going to be as loud as your main speaker, obviously, unless you run the Hot Plate with the controls set to "thru" - but that is not your intent.
You could probably do this with the Airbrake too, but there is no "Load" position on the Airbrake.
Watch your impedance though - make sure you have accounted for everything and use the right output.
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Post by kruzty on Dec 18, 2006 12:00:20 GMT -7
Thanks Steve. I have a 50w MiniMASS that I'm pretty sure won't handle a 6545. The master works well on it, but I like the 45 volume as high as I can get it. This might help get a little more from it until I break down and get the standard MASS.
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Post by johnnyl on Dec 18, 2006 13:07:53 GMT -7
Yeah, be careful using the MiniMass. I used one on my SRZ and it got hotter than S*&T! I double-checked w/ Myles and he recommended not too as the SRZ puts out up to 65 watts & sometimes more. I picked up the 100 watt MASS and it worked just fine. Always wanted to try an Airbrake though to see it it'd cut less highs...
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Post by kruzty on Dec 18, 2006 13:22:53 GMT -7
johnnyl, can't you use the tone stack in the MASS to get some of the highs back?
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Post by johnnyl on Dec 18, 2006 13:44:03 GMT -7
Yeah, it did help a little. I've just heard the Airbrake is the top dog.... just GAS getting the best of me I suppose..
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Post by benttop (Steve) on Dec 18, 2006 15:14:29 GMT -7
Yeah, be careful using the MiniMass. I used one on my SRZ and it got hotter than S*&T! I double-checked w/ Myles and he recommended not too as the SRZ puts out up to 65 watts & sometimes more. I picked up the 100 watt MASS and it worked just fine. Always wanted to try an Airbrake though to see it it'd cut less highs... What he's talking about doing here though is splitting the load between the MiniMASS and the speaker, so that half the power goes to one and the other half to the other. So the MiniMASS would see about 30 watts instead of the usual 60. Probably still get pretty hot, but not as bad as the other way.
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Post by johnnyl on Dec 18, 2006 16:20:03 GMT -7
Ohhhhh...... I see. Never thought of that. Cool idea.
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Post by mudskipper on Dec 19, 2006 7:30:14 GMT -7
Does anyone see any problems with this setup? Amp -> speaker Parallel out of speaker -> Attenuator Attenuator -> another speaker (or as pure dummy load) are you describing 3 different setups here? or are you trying to hook up 2 speakers in parallel with an attenuator hooked up to just one of them? i've deliberately mismatched an amp and a speaker/load wired in parallel so that i can get a little more attenuation beyond the -3dB provided by connecting a load and speaker. it also works well. but if you are squeamish about hooking up a mismatched load to your amp, i don't recommend it.
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Post by kruzty on Dec 19, 2006 7:45:46 GMT -7
I'm talking about 2 speakers in parallel with the attenuator only on one.
Which way do you mismatch the impedance? I tried it last night with an 8 ohm speaker, 8 ohm attenuator load, and used the 4 ohm tap.
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Post by mudskipper on Dec 19, 2006 12:44:07 GMT -7
I'm talking about 2 speakers in parallel with the attenuator only on one. so in sounds like you are using your att'er to fade/mix in one of the speakers. i mismatch it downward. for example, i'd have an 8-ohm speaker and a 4-ohm dummy load (MASS, power-resistor, etc...) wired in parallel and hook them up in an 8-ohm tap. you'd get a little more than -3dB attenuation since more power goes to the dummy load. with all things being equal, total load should be within the safety margin. but like i said, don't do it if you don't feel comfortable about deliberately mismatching your amp and load.
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Post by kruzty on Dec 19, 2006 13:08:58 GMT -7
My intention was mostly to safely use a 50w attenuator with my 6545 so I could turn up the volume (45) and master (65) more. But yes, if you used that setup live you could turn up the attenuated speaker as the night went on to get more stage volume.
Isn't the way you mismatch hard on the amp? I thought you could go up, but not down (8 ohm cab on a 4 ohm tap is OK, but 4 ohm cab on 8 ohm tap will make the tranny run hotter). If that is the case, maybe series would be better (8 ohm cab in series with a 4 ohm load, using the 8 ohm tap).
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Post by kruzty on Dec 19, 2006 15:11:40 GMT -7
Maybe I'm just making it too complicated. If I turn the 45 side up about 3/4, I should be OK with a 50W attenuator, shouldn't I? Then if I match the 65 side in volume, it should be about the same wattage.
Also, does anyone know if an attenuator takes all the power from the amp before it goes to the speaker, or does it split the load with the speaker? So if I attenuate 50% and have 50W coming from the amp, is 25W going to the attenuator and 25 to the speaker? If that is the case, then I should be OK if I don't heavily attenuate it.
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Post by mudskipper on Dec 19, 2006 20:47:00 GMT -7
Isn't the way you mismatch hard on the amp? I thought you could go up, but not down (8 ohm cab on a 4 ohm tap is OK, but 4 ohm cab on 8 ohm tap will make the tranny run hotter). If that is the case, maybe series would be better (8 ohm cab in series with a 4 ohm load, using the 8 ohm tap). you don't want to go up. going down is usually OK, though. but you don't want to do any more than 2:1. so don't have a 4-ohm load plugged into a 16-ohm speaker out. Also, does anyone know if an attenuator takes all the power from the amp before it goes to the speaker, or does it split the load with the speaker? So if I attenuate 50% and have 50W coming from the amp, is 25W going to the attenuator and 25 to the speaker? If that is the case, then I should be OK if I don't heavily attenuate it. you know what? wouldn't it be much easier to just pick up a 100w MASS or MASS Lite (also rated at 100W)? it would take a lot of guess work out of the equation.
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Post by kruzty on Dec 20, 2006 7:29:29 GMT -7
Yeah, I should just get the MASS. I was just trying to see if I could make what I have work before spending the money. Plus, I'm sure it will take a few weeks to get one at this time of year. I live about 30 miles south of Weber's shop, so maybe I'll go on a field trip...
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Post by Hohn on Dec 22, 2006 0:17:01 GMT -7
Guys, wouldn't it be easier to just consider the dummy load another speaker?
Hence, my 8 Ohm Hot Plate could go either in parallel or in series with an 8Ohm speaker cab. In parallel, I should just the 4 Ohm tap. In series, I should go with 16 Ohm tap.
It all depends on how your "y" cable is wired. Mine is parallel, so that answers it for me-- 4 Ohm tap.
If you are mismatching impedance between the load and the cab, bear in mind the effects of such a mismatch. Ideally, the cab would have the same impedance as the attenuator (hot plate, in my case). But if the cab is different, it will have the following effect:
-- if cab is HIGHER impedance than the attenuator, then total impedance goes up, and power is shifted from the speaker cab to the attenuator. Hence your load might run hotter, and your speaker will see less power.
-- if the cab is LOWER than the dummy load, then total impedance goes down and power is shifted to the speaker cab and away from the dummy load. This will take some of the heat off your load, but increase the power dissipation (and hence volume) of the speaker cab.
If you are lowering the total impedance below the nominal rating of an output tap, output tranny works harder (which may be what you want, at times). I wouldn't recommend high volume playing like this, though-- if you want to keep your output trans alive.
Raising total impedance above the nominal output tap rating is no doubt safer for the output tranny, but might not give the tone you seek.
jh
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Post by kruzty on Dec 22, 2006 7:03:36 GMT -7
Hohn, I think that's what we're all talking about - condisering an attenuator another load. I just wanted to make sure I wasnt' missing something before I did it.
On another note - I tried it and I swear it took some of the highs out of the non-attenuated speaker. I had the attenuator fully attenuated (a dummy load). If my ears weren't deceiving me, is it possible the attenuator "takes" more of the highs?
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Post by mudskipper on Dec 22, 2006 7:11:40 GMT -7
Guys, wouldn't it be easier to just consider the dummy load another speaker? sure. you can just use an unused speaker in stead of an attenuator. in fact, i'm using an 8-inch speaker in my 1x12 as a dummy load right now. yup, i've used MASS like that. right.... that's why when you hook up a 4-ohm load along with an 8-ohm speaker, you'd get a little more attenuation as you've also stated. you mean, like 16-ohm speaker/cab into an 8-ohm tap of the amp? well, i don't think 2:1 mis-match either way will burn a healthy OT up. for the most part, if you are gonna mismatch, you'd be better off mis-matching it down on tube amps as far as i know. we are, however, working on the assumption that matched load is the optimal solution no matter what. here is an excerpt from the Tube Amp FAQ from the GEO site: "That variation in impedance versus frequency and the variation in output power versus impedance and the variation in impedance with loading conspire to make the audio response curves a broad hump with ragged, humped ends, and those humps and dips are what makes for the "tone" you hear and interpret. Will you hurt the transformer if you parallel them to four ohms and hook them to the 8 ohm tap? Almost certainly not. If you parallel them and hook them to the 16 ohm tap? Extremely unlikely. In fact, you probably won't hurt the transformer if you short the outputs. If you series them and hook them to the 8 ohm or 4 ohm tap? Unlikely - however... the thing you CAN do to hurt a tube output transformer is to put too high an ohmage load on it. If you open the outputs, the energy that gets stored in the magnetic core has nowhere to go if there is a sudden discontinuity in the drive, and acts like a discharging inductor. This can generate voltage spikes that can punch through the insulation inside the transformer and short the windings. I would not go above double the rated load on any tap. And NEVER open circuit the output of a tube amp - it can fry the transformer in a couple of ways."link to the full text here: www.geofex.com/tubeampfaq/TUBEFAQ.htm#matchspkrand here is an exerpt from Ted Weber's Speaker FAQ: " I have heard various views on impedance mismatches between the amp and the speakers. One is that you should always match the impedance (4 ohm amp = 4 ohm speaker or two 8 ohm speakers in parallel), or you can blow your transformer. The other is that it is fine to mismatch, but you may lose power. Should the impedence match? If yes, then how quickly could you damage your amp when you have a mismatched impedence?
Chuck, technically, you should always provide a load that is recommended by the manufacturer of the amp. The designer of the amp chose a particular output device (tube) and specified all of the operating voltages for the output stage so the tube would work at its optimum efficiency while delivering maximum power to the load with minimum distortion. Ok, so let's discuss the problems associated with mismatches. When you use a load that is lower than the intended load, the output has to drive the load (speaker) with more current because it is a lower impedance than is expected. Two inherent problems associated with transformers are flux leakage and regulation. Flux leakage is also referred to as leakage inductance. It is related to the current in the secondary, and these problems increase as the current increases. As the current draw in the secondary increases, the primary has a more difficult time transferring the signal to the secondary, so the secondary signal to the load gets squashed, or 'soft-clipped'. This soft clipping is called regulation. While regulation is desireable in a power supply, it is undesireable in a transformer. In other words, in a power supply, if the input voltage or the output load current changes, we don't want the output voltage to change. In a transformer, we want the output voltage to follow the input voltage and not regulate at all. When you put a heavier load on the output than was intended, it will pull the output voltage down, hence regulation. The leakage inductance problem arises because the current from the heavier load causing the regulation to occur reduces the efficiency of the transformer by not allowing the output to follow the input. Transformer designers simulate or view this problem as having extra inductance in series with the primary. The extension of this idea then, is that with the heavier load, you could affect the efficiency of the transformer, alter the frequency response (due to the extra leakage inductance in series with the primary), and cause other distortions to occur. OK, on to mismatching the other way. A speaker is a current operated device in that it responds to the current through it to generate a magnetic field that works against the magnetic field of the speaker magnet to make the cone move in and out. Thinking in very short amounts of time, when the output charges up the voice coil with current, then the signal goes away or gets reduced, the cone system moves the voice coil back to its home or resting position. As it is moving back, it generates a voltage that is fed back up the line into the transformer and appears in the output circuit of the amp. This generated voltage is often referred to as flyback voltage, because we are charging up an inductor, then when we disconnect or stop charging the inductor, the magnetic field in the inductor collapses and induces this big voltage into itself. This big voltage then 'flies back' to the source of the charging current. There is a mathematical formula to determine how big the voltage is and it is related to the inductance of the voice coil, the amount of time it was fed current, and how much current it was charged with. The bottom line is that the voltage fed back to the output circuit is oftentimes much higher than the voltage that was used to drive or charge up the voice coil initially. This voltage gets transformed up by the turns ratio of the output transformer, and in many cases can be over 1,000 volts. What happens then is that arcing can occur between the pins on the output tube socket. Once this has occured, a carbon path forms on the tube socket between the pins. The carbon path allows a steady current to flow between the pins and eventually burns up the socket due to the heat that is generated. For example, it wouldn't be too uncommon to see a transformer turns ratio of 30:1. If we had a voltage fed back from the voice coil that was around 50 volts, 30 times 50 would be a 1,500 volt spike at the plate of the output tube. This is why you often see designers connect diodes in a string between the output tube plates and ground. They are trying to suppress these spikes and dissipate the energy in the diodes rather than allowing an arc to occur at the tube socket. So, when you use a higher impedance load on a lower impedance tap, the turns ratio is higher and resulting fed-back (flyback) voltage gets multiplied up higher than what it would have been with the correct impedance load. It's just about impossible for me to answer how long an amp would last under these conditions. It all depends on how the designer took these potential problems into account in his or her design with regards to the quality of the tube sockets, the use of stringed diodes, the output circuit operating voltages, etc. "
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Post by benttop (Steve) on Dec 22, 2006 10:16:32 GMT -7
Wow, nice post mudskipper. Very useful information there.
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Post by kruzty on Dec 22, 2006 12:22:17 GMT -7
Problem solved! I ordered a MASS Lite today... Thanks for all the thought and opinions.
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Post by Hohn on Dec 22, 2006 17:35:03 GMT -7
imaginary karma for Muskipper. +100 for you (ha, I don't have that 1-per-hour limit any longer)
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Post by mudskipper on Dec 23, 2006 11:02:49 GMT -7
i'm glad you guys found the post useful.
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Post by skydog958 on Dec 23, 2006 12:29:10 GMT -7
Facinating, but it hurt my eyes (and my brain) a bit
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Post by kruzty on Jan 17, 2007 10:56:01 GMT -7
Well, my MASS Lite came in last week. I didn't like it that well when I was trying to get the 6545 to low levels (when it was just me practicing). Just using the volume/master sounded better. But I thought I'd give it a shot at band rehearsal, and I like it much better when I could turn it up some. I like the 45 volume about half-way, and the MASS let's me do that. Then I just set the 65 master to match. On the attenuator, I have the mid-high side a couple of numbers higher than the low-mid side.
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