I don't recall the site I downloaded it from but there's a schematic for a low powered amp speaker attenuator. The schematic is hand drawn (if that helps anybody to remember) It shows 2 10 ohm 10 watt resistors wired in series going to a 25ohm 3watt wirewound pot. Now here's my confusion- it appears that it calls for another resistor to go over to ground? The pic is labeled 4.7 watt? (I'm not sure because it's hand drawn)I'm also confused as to how to wire the pot. Do I ground the body like on a guitar? My thinking is that the two resistors and the pot plus 2 jacks and I'm good or am I missing something here? This is my 1st project and I found this schematic to be the simplest. I have a decent understanding of electronics and circuits from my work as a hvac technician but we don't repair boards, we replace them. I'd post the schematic but I don't think my phone's capable. Thanks in advance for any help.
Could you post a link to the schematic at least? That would help a lot. Also, most of the attenuators I have seen have been built with light bulbs instead of resistors. Why do you want an attenuator? Have a tube amp that's too loud?
Need more info,
Is it a Valve Amp?
If so how many Watts?
Or What type of power Valves? (i.e. 2x EL84)
If so a 50 Watt HiFi L-pad will do that trick you and save a lot of messing about.
Not the best way but does work for small amps.
Phil.
Blueguitar.org appears to be the site. I got to it via a link on diystompboxes. To answer the questions-yes, it"s a valve amp. It's a crate vc508. 5 watts. single el84 power tube. I know you're laughing but I am getting complaints from family to "turn it down!" so I must quiet it down a bit. She really comes ti life when the master's cranked so I'd like to keep that tone. I'm having a bit of luck running a processor (digitech rp200a or maudio black box reloaded) in front of her and using the level control to turn it down but I really think the attenuator sounds like a better idea. I also own a Radio Shack attenuator but the impedance is too low(varies from 3ohm to 1 ohm throughout its range). I also wonder if I could wire a resistor in series with this? I'm wondering if I need a resistor just in the + wire or both + and -? Just wondering if I'm understanding resistors right or not. I understand that they convert eklectricity to heat, my question I guess is this: can I just run them in series in the + line or do I need something in the - line also?
You can make a *fixed* "keep the Family happy" attenuator with an 8 or 10 ohm, 10 watt resistor, plus a 1 ohm or 0.47ohm, 2 W one.
Wire both in series; connect the free end of the 10 ohm one to the amplifier output hot lead, the free end of the 0.5 or 1 ohm to amp out ground and speaker ground, the midpoint to speaker hot.
Instant bedroom amp.
You can build it into a box with a switch to bypass it, or just with an input and output jack, or on a board bolted to your Crate inside, on a side or bottom.
Anyway you do not need to switch it quickly, it's not an effect, plugging it in/out is quite acceptable.
If you need a drawing, I'll do that later, now i'm sort of busy.
Good luck.
I believe I've got you. Hot lead>>larger resistor>>+ terminal on speaker. Ground lead>>smaller resistor>>- terminal on speaker. I think you can decipher that. Now is it possible to wire a pot in? Or would this be "pissing in the wind" so to speak? As far as switches a dpst should do it I'm presuming? Just can't afford to blow the amp up! If I've got the scheme correct then all I can say is: thanks! I'm looking forward to learning alot here and you my friend, are a very good teacher.
Quote from: will316 on January 07, 2011, 12:49:07 PM
I believe I've got you. Hot lead>>larger resistor>>+ terminal on speaker. Ground lead>>smaller resistor>>- terminal on speaker. I think you can decipher that. Now is it possible to wire a pot in? Or would this be "pissing in the wind" so to speak? As far as switches a dpst should do it I'm presuming? Just can't afford to blow the amp up! If I've got the scheme correct then all I can say is: thanks! I'm looking forward to learning alot here and you my friend, are a very good teacher.
Not quite. Connect the hot lead to the 10 ohm resistor, connect the other end of the 10 ohm resistor to the + on the speaker. Then connect one end of the 1 ohm resistor also to the + on the speaker and the other end to ground.
By "ground" you mean to the - side of the speaker or straight to ground(side of enclosure)? I'm just trying to be sure. I know a bit about electronics but also realize I've got a bit of learning ahead of me. I also plan to look back through the archives here because this site is very informative and everybody seems very knowledgeable. Refreshing to say the least! I am a fast learner so my questions will become less and less in the future(I hope!) Anyway, once again, thank you for sharing your knowledge and answering my noob questions.(you can't learn if you don't ask.)
Quote from: will316 on January 07, 2011, 03:17:26 PM
By "ground" you mean to the - side of the speaker or straight to ground(side of enclosure)? I'm just trying to be sure. I know a bit about electronics but also realize I've got a bit of learning ahead of me. I also plan to look back through the archives here because this site is very informative and everybody seems very knowledgeable. Refreshing to say the least! I am a fast learner so my questions will become less and less in the future(I hope!) Anyway, once again, thank you for sharing your knowledge and answering my noob questions.(you can't learn if you don't ask.)
The negative side of the speaker wire should go to chassis ground. Chassis ground is where you want the resistor heading to, doesn't matter how it gets there.
And you're right about asking questions. When I started doing this stuff I had no idea either, so feel free to ask as many questions as you need to and we will do our best to help.
(http://img716.imageshack.us/img716/7734/fahey3amattenuator.gif)
For a very small amp, like the ruby or a small 5w tube amp, the 25 ohm pot sold at radio shack isn't too bad.
I picked up a pot at Raduio Shack. I would imagine this does have to be used with the resistors, correct? You can't just use the pot alone, can you? I know I'm full of questions, but that's how I learn. My idea was to mount it all in one of their "project enclosures" (metal not plastic). Soon I hope to build a Lead 12 pre amp and mate it with a 50-100 watt power section. *baby steps* lol
In my case, I put a couple of 10 ohm power resistors (rated for 5W each, I think) in series, and put that series in parallel across the outer terminals of the pot. The input jack (coming from the amp) is connected across the outer terminals of the pot as well. So with no speaker plugged into the attenuator, the amp "sees" about 11 ohms of resistance. The output jack (going to the speaker) is connected to the wiper terminal and which ever outer terminal is connected to ground. With an 8 ohm speaker plugged in and the pot turned all the way up, there will be about a 5 or 6 ohm impedance. As you turn the pot down, the impedance "seen" by the amp approaches the 11 ohm resistance seen without the speaker plugged in. And, of course, as you turn down the pot, the current through the speaker is reduced. There might be a better way of doing this, but it is an easy attenuator to make, and allows you to adjust for a trade off between attenuation and good tone. It sounds good with my ruby. Sounds like crap through another homemade amp. Haven't tried it yet with my 5W ValveKing royal 8 yet. You might do better wiring the pot as a rheostat and use it as R2 in JM's schematic.
Or, just wire it like with JM's schematic, where the resistance between the hot terminal and the wiper terminal is basically R1 and the resistance between the wiper and ground terminals is R2. But, of course, the resistance across the outer terminals is more than double the 8 or 10 ohms in JM's schematic.
I believe I've got it. How does this scheme sound: input jack coming from amp>1 10 watt resistor in series to outer leg of pot. Wiper leg of pot to hot side of speaker. Ground leg from amp to opposite outer leg of pot to ground terminal on speaker. If my thinking is correct, this in effect makes the pot r2 as in the schematic shown above. Please show me my error if I'm wrong. Now I also bought one of their in wall speaker faders. The impedence varies from 0 to about 3 ohms when I ohm it out. Could I just wire a resistor across the ter minals on one side of this to also have an attenuator suitable for my needs? I'm also wondering if you can go with "too much" resistor? Example: 20 watts of resistor for a 5 watt amp? I know it's rated at 5 watts but seems to be able to put out closer to 15. It's just as loud as a 20 watt ss amp I also use and itzms quite a bit louder than a 15 watt ss amp I also use.
Surely they sell Lpads in Tandy,, it will make life so much easier as you don't need to mess with any other components. :tu:
5 watts can be done with a simple speaker pot or L pad.
These are *NOT* like a normal pot they are a specialized unit designed specifically for the purpose of attenuation.
Two *Seperate* rehostats with one common wiper.
This might help you to see what goes on inside.
Cheers phil.
I had another pic but keep getting internal server error :'(
I'll try again later.
Phil.
I believe that's what I've got. It's all mounted on a board, has a faceplate and knob so you can mount it in the wall. You've got hot and ground in and hot and ground out to your speaker. I hooked several different 8 ohm speakers to it and put my meter on the other side to get an idea of what my transformer would see. The readings were way too low. I disconnected the speaker and ohm'd it at the terminals and got a normal reading. Is this a case of me taking my measurements incorrectly? I don't understand how an 8 ohm speaker would ohm out correctly but ohm out incorrectly with the attenuator hooked up. Is this a case of the trans will see the correct load with everything in place? I mean how could this control cause the ohm reading to change? I assumed that the speaker's impedence would satisfy the transformer and having the attenuator in line between the two would only raise the ohm reading. I'm kinda stuck here. If someone could briefly explain I'm sure I'd understand. As far as going through all the trouble, it serves to help me grasp a better understanding. My girl thinks I'm crazy, but I would love to be a Jim Marshall, Hartley Peavey, Leo Fender, etc. If anything, I'd be happy as a clam just owning a small shop and keeping garage bands going. I could get so much satisfaction just throwing together little 5-10 watt transistor units that kept music alive for poor kids. You never know, one man's hobby/livelihood could potentially help to inspire the next EVH, Randy Rhoads, Dimebag, etc. Music is most sacred to me but as with all my hobbies(firearms, cars, etc.) I also like to know how it works, build one myself, diafgnose, and repair or modify as needed. I'm sure everyone here's got that in them too.
they look like this;
http://www.amptone.com/wallmountspeakerattenuator.htm
They should state that they are for an 8 Ohm system and wired correctly yes everything will be fine.
If you wire them the wrong way then yes when you turn down to zero the amp gets a dead short,,, not that a dead short matters to a Valve Amp but it sounds crap.
Note the two rehostats are different values.
this maintains a relitive Z load to Amp.
Remember that DC Ohms is not the same as Z Ohms
*Z is AC resistance* which is freq dependant and DC Ohms is exactly that. Ohms
Phil.
Will,
I used that to build an attenuator, it's a Wall Volume Control for speakers. I got the 25w mono model from my local RS. I was advised over at ppwatt forum to use a 4.7uF non-polarized cap across the in and out terminals to preserve highs at lower lower volumes. It seems to work ok except when you turn it way low it tends to lose highs so I might need to use a diff cap. Here's some pics of what I did with it. The schematics are for a different type of attenuator that I never built not for this super simple one.
http://s252.photobucket.com/albums/hh7/spudjds/Public/Builds/MISC%20Projects%20and%20Ideas/Attenuator/?action=view¤t=100_0575_1.jpg (http://s252.photobucket.com/albums/hh7/spudjds/Public/Builds/MISC%20Projects%20and%20Ideas/Attenuator/?action=view¤t=100_0575_1.jpg)
It's in a Radio Shack project box and I put and in 1/4" jacks for in and out and a chicken head knob - I also marked the front with a white magic marker with min/max and a tic for each click of the volume control - mine is stepped and not a continuous volume control/pot - at min it's off (no sound) and max is 0 resistance so wide open. Hope this helps.
Jim
Thanks, guys. Jim, that's the same unit I've got. Looks like I've got some reading ahead of me to completely grasp all this. My job as a tech has taught me alot about electronics and such, but obviouslly I have alot to learn! I assumed impedence was strictly pull the leads, ohm it out, etc. I wasn't aware of differences between ac and dc ohms. Thanks for the info, Phil. Appears I've learned something today, now my head hurts! lol I've gotta lookback through the archives and note reference guides, books, etc. Now my interest is piqued to the max.
Quote from: will316 on January 08, 2011, 05:05:48 PM
Thanks, guys. Jim, that's the same unit I've got. Looks like I've got some reading ahead of me to completely grasp all this. My job as a tech has taught me alot about electronics and such, but obviouslly I have alot to learn! I assumed impedence was strictly pull the leads, ohm it out, etc. I wasn't aware of differences between ac and dc ohms. Thanks for the info, Phil. Appears I've learned something today, now my head hurts! lol I've gotta lookback through the archives and note reference guides, books, etc. Now my interest is piqued to the max.
AC and DC ohms are the same. Ohms are ohms. It is the
impedance that is different. Resistors are measured in ohms and it won't matter if it is AC or DC, it'll be the same. Speakers are measured in impedance and it will be different ohms because speakers not only use AC power, but also the resistance changes depending on the speaker's position in the voice coil.
Now we're getting somewhere. I can grasp that. I wonder how many folks don't understand what a motor is. Many people probably just think of the motor that runs their washing machine, condensor fan motor, etc. In my work I've been put to test trying to explain the fact that a refrigeration compressor is a motor. The folks that don't understand that would probably keel over if I also explained that a speaker is a motor. Seriously, while I do have a basic grasp of circuits, electronics, etc. I don't claim to be an expert. My schooling covered the bare bones basics of electrical theory and focused mainly on diagnosis and repair of refrigeration. I've met other tecnicians that have absolutely no grasp of electronic theory who were spectacular techs. I've also met guys who probably held degrees in electronic theory yet were piss poor techs(they tended to over think stuff). My philosophy kinda falls somewhere in the middle. While I don't doubt electronic theory I also keep in mind that it's just that-THEORY. What I mean is- according to theory, some things I've seen should not work, yet it runs like a champ. I'm sure some of you guys have built or seen projects that on paper, defy all logic and shouldn't work yet you plug it in and it makes beautiful music. I'm probably losing some of you but the ones that understand are probably smiling and nodding their heads.
Well, keep in mind that resistance is a type of impedance.
Sorry I was not very clear;
*Impedance is the Resistance of a component at a given frequency*
Measure the DC Resistance of a 600 Z Ohm microphone,,, the reading will be quite different.
Try Reading this one,,
http://www.teamrocs.com/technical/pages/resistance_impedance.htm
Or just google it ,, "ac resistance vs dc resistance"
Phil.
I think the term impedance includes resistance and reactance. AC resistance is reactance. You've got inductive reactance and capacitive reactance. All are measured in ohms. Both types of reactance and resistance must be considered to figure total impedance.
You will find heaps of related info on the Jensen pages,
http://www.jensen-transformers.com/
Heaps of stuff under *Aplications > White papers and Schematics.*
Also *Rane* used to have a mass of technical terms all laid out in alphabetical order but I can't seem to find it now. :'(
But look here ;
http://www.rane.com/
Under *Support* > Library,
Heaps of stuff to help broarden your knowledge base.
Phil.
Now I've built the unit. I used 1 8ohm 20 watt resistor going from the hot leg coming from the amp going to one side of the rheostat. Wiper leg from rheostat to hot leg out. Ground coming in to opposite terminal on rheostat to ground going out. Tested it witha little Gorilla practice amp. No sound and amp appears to be going out on thermal overload. It dies completely-no led, nothing. After a few minutes, the amp will run fine. Is this a case of bad wiring, way too much resistance in my unit for the Gorilla (10 watter 4 oh I believe), or a case of solid state amps not being usable with attenuators? I just used the Gorilla because I didn't wanna blow up the tube amp. I'm also wondering if I could use 1 10 watt, 10 ohm resistor instead? Also wondering if this scheme would work: 1 10 watt 10 ohm resistor soldered across the outer legs of a 25 ohm 3 watt rheostat with hot wire going in, to outer leg of r'sta. Wiper leg to hot out. Ground coming in to opposite outer leg to ground going out. Also wondering if the r'stat body needs to be grounded like guitar pots are. Any help is appreciated. I also built one with the Radio shack l pad and it works just fine. The only reason I wanna build from scratch is education and possibly financial if I can sell them.
Hi, Sounds like a dead short if Amp is shutting down.
Check your wiring.
BTW, please draw a simple diagram rather that trying to explain it all.
A 50 Watt Lpad as used for HiFi crossovers is all that is needed for Amps up to about 10 Watts.
Adding more is needless complexity and more chance of mistakes.
Phil.
Gotcha. I'm on a phone but with symbols and such I should be able to make crude diagrams. Didn't think to ask-should my input and output jacks be insulated?
Common or Ground is common to both Amp and Speaker,, if you isolate one then there is no circuit path.
You can put it in a metal/ alloy box and ground the box to circuit common and you will be fine.
I make a point of using a short cord from Amp and then a chassis socket for speaker out.
That way it's impossible the plug it in the wrong way.
Amp and speaker Common wires go to pin 1.
Amp Hot to pin 3,, Speaker Hot goes to pin 2.
Datzit.
A 50 Watt Lpad is a bit misleading as it's usually reffering to HiFi system wattage where the Lpad is not passing any low frequency.
Used as a full bandwidth Attenuator you need to derate that wattage,, hence they get quite hot and often self distruct if more than 15 or 20 Watts is passed.
Cheers Phil.