A friends site has a low level line out circuit for use on the speaker output of an amp for reducing the signal to a suitable level for feeding mixing consoles, computers or even a house stereo.
My concern is that the high wattage will fry your run of the mill resistors.
I am assuming if there is a speaker load on the speaker output, you may be safe but if there is not I know for certain the resistors will fry.
I will generally have a load on the speaker line out but if I don't......
Will I need high wattage sand stone resistors or what?
I've worked really hard on perfecting this amp and really want to use it's sound for recording without having to mic the speaker cab.
My concern is that the high wattage will fry your run of the mill resistors.
I am assuming if there is a speaker load on the speaker output, you may be safe but if there is not I know for certain the resistors will fry.
I will generally have a load on the speaker line out but if I don't......
Will I need high wattage sand stone resistors or what?
I've worked really hard on perfecting this amp and really want to use it's sound for recording without having to mic the speaker cab.
Use Ohms Law. Across 8 ohms, 50 watts means 20 volts of signal. Even in the absence of a speaker load, the voltage will not rise in a solid state amp. If it is a tube amp running unloaded, then the line out is the least of your worries.
Remember that amps do not "push out" power, they just make it available and the load DRAWS the power from the amp. So the amp will not be pushing its power into the poor little line out resistor. Wattage per se is not the concern.
So start with the 20v - or whatever voltage your amp might produce. And if you want to use for example a 1000 ohm resistor, you can solve for current and then power. In the case of the 1k resistor you get a whopping 20 ma - .02 amp. That equates to 400mw or .4 watt dissipated in the resistor. A 1 watt resistor would be fine.
But since the line out is high Z, a larger resistor would be fine. The 10k pot suggested above would use even les power. 20v across it yields only 2 ma. That means the 10k pot dissipates only 40mw - .04 watt.
It won't be burning up soon.
Remember that amps do not "push out" power, they just make it available and the load DRAWS the power from the amp. So the amp will not be pushing its power into the poor little line out resistor. Wattage per se is not the concern.
So start with the 20v - or whatever voltage your amp might produce. And if you want to use for example a 1000 ohm resistor, you can solve for current and then power. In the case of the 1k resistor you get a whopping 20 ma - .02 amp. That equates to 400mw or .4 watt dissipated in the resistor. A 1 watt resistor would be fine.
But since the line out is high Z, a larger resistor would be fine. The 10k pot suggested above would use even les power. 20v across it yields only 2 ma. That means the 10k pot dissipates only 40mw - .04 watt.
It won't be burning up soon.
If this is a guitar amp you are talking about, you may be dissapointed with the sound of the "direct out". The sound of the speakers used has a significant bearing on the overall sound of the amp, and a line out will miss that. Also, as most guitar speakers do not use tweeters, the amp usually has a lot of top end boost to compensate, giving a very toppy sound when taking a line out.
Quite often recording studios have a small soundproof room specifically for micing a guitar amp cabinet - the amp can be cranked as far as needed to get the right sound without deafening everyone.
Cheers
Quite often recording studios have a small soundproof room specifically for micing a guitar amp cabinet - the amp can be cranked as far as needed to get the right sound without deafening everyone.
Cheers
...I dunno man, I've fried some resistors already
I've fried some resistors already though......
Centauri, thank you for assuming I'm stupid and don't know any of that common information you shared with me.
If I simply wanted to mic my speakers, I wouldn't be building a line out circuit.......
Yes the amplifier section of a guitar amp has a broad frequency spectrum, the tone stack section of the preamp generally has a treble control set typically somewhere around 7 khz or even as high as 10 khz.
Mine is set at 10 Khz, right where all those sweet 2nd order harmonics primarily are.
In other words, even with a direct out line, you're not going to be getting an abundance of highs that ranges over your amps treble control frequency point.
Even if this is an issue, a treble bleed cap is easily added and can even be wired on a pot to properly cut the treble. Just like your guitars tone control.
I plan to try this circuit with 1/2 watt resistors and use whatever caps necessary to tailor the sound. I'm also going to add a pot to adjust the level of output.
Hopefully the resistors don't fry because in my experiences with high wattage sources, they burn up if the amp is at mid to high volume settings......
I've fried some resistors already though......
Centauri, thank you for assuming I'm stupid and don't know any of that common information you shared with me.
If I simply wanted to mic my speakers, I wouldn't be building a line out circuit.......
Yes the amplifier section of a guitar amp has a broad frequency spectrum, the tone stack section of the preamp generally has a treble control set typically somewhere around 7 khz or even as high as 10 khz.
Mine is set at 10 Khz, right where all those sweet 2nd order harmonics primarily are.
In other words, even with a direct out line, you're not going to be getting an abundance of highs that ranges over your amps treble control frequency point.
Even if this is an issue, a treble bleed cap is easily added and can even be wired on a pot to properly cut the treble. Just like your guitars tone control.
I plan to try this circuit with 1/2 watt resistors and use whatever caps necessary to tailor the sound. I'm also going to add a pot to adjust the level of output.
Hopefully the resistors don't fry because in my experiences with high wattage sources, they burn up if the amp is at mid to high volume settings......
MrCheeks,
Settle down, I am not assuming you are stupid - just sharing my observations taking a speaker line out in live work.
And yes, caps can be added to tailor the output sound. For what its worth, the line out used of Fender "60 Series" amps (tube amp) consists of 560ohm 1/2W resistor from speaker line to hot of line out socket, 100ohm 1/2W resistor from hot to cold of line out socket, and 22ohm 1/2W resistor from cold of line out socket to earth. Even with these relatively low values, they don't seem to have any problem with ratings.
Cheers
Settle down, I am not assuming you are stupid - just sharing my observations taking a speaker line out in live work.
And yes, caps can be added to tailor the output sound. For what its worth, the line out used of Fender "60 Series" amps (tube amp) consists of 560ohm 1/2W resistor from speaker line to hot of line out socket, 100ohm 1/2W resistor from hot to cold of line out socket, and 22ohm 1/2W resistor from cold of line out socket to earth. Even with these relatively low values, they don't seem to have any problem with ratings.
Cheers
The 10 K pot.....
Well, the 10k pot worked great. I already knew it would but guess what.
I cranked the volume a bit and it fried EXACTLY like I said. I mean come on, you're talking about 120 watts running through a 1/2 watt pot.
For what it's worth, I added a 10 uf cap to be switched in and out for giving a cab simulating type effect for when I'd be running straight into a PA or mixing board. It worked beautifully.
So was frying that pot a fluke or what?
I have serious doubts but maybe....
Well, the 10k pot worked great. I already knew it would but guess what.
I cranked the volume a bit and it fried EXACTLY like I said. I mean come on, you're talking about 120 watts running through a 1/2 watt pot.
For what it's worth, I added a 10 uf cap to be switched in and out for giving a cab simulating type effect for when I'd be running straight into a PA or mixing board. It worked beautifully.
So was frying that pot a fluke or what?
I have serious doubts but maybe....
Musta been the electrolytic caps....
I was toying with some different electrolytic cap values so it's likely in doing so I increased the signal draw and smoked it.
Anyway I'm off to rat shack in a bit here to pickup a new 10 k pot being I have no more lying around and don't want to wait to order one.
I am thinking though, can I also use a pot to vary the amount of treble bleed caused by the electrolytic caps?
A 10 uf doesn't quite cut enough and a 47 uf cuts too much unless I crank the 10 k wide open.
....So I imagine I could run a lead from the hot to the input of another 10 k pot then it's output through the 47 uf cap to ground. This is post the 10 k pot for my line out of course.
Wutcha think?
I was toying with some different electrolytic cap values so it's likely in doing so I increased the signal draw and smoked it.
Anyway I'm off to rat shack in a bit here to pickup a new 10 k pot being I have no more lying around and don't want to wait to order one.
I am thinking though, can I also use a pot to vary the amount of treble bleed caused by the electrolytic caps?
A 10 uf doesn't quite cut enough and a 47 uf cuts too much unless I crank the 10 k wide open.
....So I imagine I could run a lead from the hot to the input of another 10 k pot then it's output through the 47 uf cap to ground. This is post the 10 k pot for my line out of course.
Wutcha think?
120 watts was not running through the pot. it was just across something capable of putting that power out. Try a plain old 10k resistor across there as an experiment. I bet it won't burn up. The load determines the power, not the amp. You can run a solid state power amp full out, but if there is no load on it, no power is produced. Even if I had 70V rails, a 10k resistor would still only draw about a half watt. Tube amps have their own issues, so we must load them.
ANy chance the pot arced over? Take it apart and see what the failure mode was.
ALso, when it burned up, was there something connected to it? Or was it just across the output with the wiper unloaded? Point being that if something was connected, there could have been some ground currents finding their way home through the pot.
Another clue would be if it worked OK until the pot was turned close to one end or the other. If some current was allowed to find its way across just the end millimeter of resistive element, it might have been stressed. if the ends of the pot were wired across the amp out and the wiper were turned almost all the way up, and whtever the wiper was connected to was grounded, then the last couple ohms of the pot would be trying to conduct the current of the output stage to ground.
ANy chance the pot arced over? Take it apart and see what the failure mode was.
ALso, when it burned up, was there something connected to it? Or was it just across the output with the wiper unloaded? Point being that if something was connected, there could have been some ground currents finding their way home through the pot.
Another clue would be if it worked OK until the pot was turned close to one end or the other. If some current was allowed to find its way across just the end millimeter of resistive element, it might have been stressed. if the ends of the pot were wired across the amp out and the wiper were turned almost all the way up, and whtever the wiper was connected to was grounded, then the last couple ohms of the pot would be trying to conduct the current of the output stage to ground.
Musta been the elctrolytic I ran before the pot....
I think I spiked the voltage with an electrolytic cap I was toying with to cut treble just before feeding the hot lead into the pot.
Anyway I designed my own circuit around the 10 k pot and have AMAZING results.
It goes like this:
Speaker hot lead into I believe a 560 pf cap( I'm certain it's somewhere between 470-560pf....hell it might be as high as a 680! this suckers HUGE) --> 100 k resistor --> 10 k pot --> 1/4 output jack.
THEN I added a tone pot to kill off the intense amount of treble. A 50 K pot with two .1 uf caps. One just wasn't cutting enough and all the other values I toyed with weren't working the way I needed.
.....I've always noticed doubling the same value caps in parrallel will give just a touch more treble cut and do so more gracefully.
ANYWAY, my line out sounds damn near EXACTLY like my custom built/loaded 4x12 cabinet and it get's even better.
The 560 pf and 100 k resistor I used as an input buffer did something very important it turned out.
The 10 k pot at about 50-60% stops increasing volume and increases the signal density. It's not like a gain effect but it's like the signal has more mass.
It's like increasng cabinet resonation!
All in all I'm really happy and this sure beats any of the line out circuits I've found online.
......I think I'll work on my own D.I. box now and come up with a fixed EQ circuit to use in conjunction with my line out circuit which with the way the 10 k pot works to simulate cabinet resonation.
Only involved about 10-12 hours of experimenting today but it paid off. Hopefully someone else can benefit........
I think I spiked the voltage with an electrolytic cap I was toying with to cut treble just before feeding the hot lead into the pot.
Anyway I designed my own circuit around the 10 k pot and have AMAZING results.
It goes like this:
Speaker hot lead into I believe a 560 pf cap( I'm certain it's somewhere between 470-560pf....hell it might be as high as a 680! this suckers HUGE) --> 100 k resistor --> 10 k pot --> 1/4 output jack.
THEN I added a tone pot to kill off the intense amount of treble. A 50 K pot with two .1 uf caps. One just wasn't cutting enough and all the other values I toyed with weren't working the way I needed.
.....I've always noticed doubling the same value caps in parrallel will give just a touch more treble cut and do so more gracefully.
ANYWAY, my line out sounds damn near EXACTLY like my custom built/loaded 4x12 cabinet and it get's even better.
The 560 pf and 100 k resistor I used as an input buffer did something very important it turned out.
The 10 k pot at about 50-60% stops increasing volume and increases the signal density. It's not like a gain effect but it's like the signal has more mass.
It's like increasng cabinet resonation!
All in all I'm really happy and this sure beats any of the line out circuits I've found online.
......I think I'll work on my own D.I. box now and come up with a fixed EQ circuit to use in conjunction with my line out circuit which with the way the 10 k pot works to simulate cabinet resonation.
Only involved about 10-12 hours of experimenting today but it paid off. Hopefully someone else can benefit........
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.