i have some older analog sources i would like to connect to my mixer (portable record players / reel to reel players) that only have speaker outputs.
when plugging these into the mixer, the signal is way to loud and causes a lot of overdrive - and when i turn the volume down enough to get rid of the overdrive i get some sort of tone that drowns out the signal.
so i figure i must need to create some sort of box that i can plug in-between the units to convert the speaker out into a line level out - how can i go about doing this?
can you make a universal box that i could use with all my units (maybe with a pot to determine how much the signal is attenuated?) - or would you recommend modifying all the units internally somehow?
thanks for your help on this
when plugging these into the mixer, the signal is way to loud and causes a lot of overdrive - and when i turn the volume down enough to get rid of the overdrive i get some sort of tone that drowns out the signal.
so i figure i must need to create some sort of box that i can plug in-between the units to convert the speaker out into a line level out - how can i go about doing this?
can you make a universal box that i could use with all my units (maybe with a pot to determine how much the signal is attenuated?) - or would you recommend modifying all the units internally somehow?
thanks for your help on this
The gain of most amplifiers is in the region of 26dB or x20. Some are a bit higher. The simplest and perfectly acceptable way of doing this would be to make a potential divider. Either a 5k or 10k pot and a resistor 10 or 20x as large. The pot goes to ground with the voltage taken from the other side of it. The resistor connects between +ve and the pot. Put it at the mixer end and use shielded cable after it.
A 10k pot with 100k will give you nominally full output at halfway. If you need more or less gain you can move it eaither way.
A 10k pot with 100k will give you nominally full output at halfway. If you need more or less gain you can move it eaither way.
The problem with that solution is that it depends on the setting of the control. A better idea might be to make a dedicated amplifier with constant gain. This could be very simple and of as high quality as desired.
Another problem is that the output of many amplifiers has more noise and distortion than the signal and your line output will reflect that.
If I knew more details of your setup I could offer a solution. Basically what you'd do is take audio from before the volume control and feed it to a small amplifier (or signal conditioner if you will) to supply a leveled output. You will need one such device for each source, but it could be built into those units.
Something as simple as an emitter follower (or cathode follower if tube) might do it.
Another problem is that the output of many amplifiers has more noise and distortion than the signal and your line output will reflect that.
If I knew more details of your setup I could offer a solution. Basically what you'd do is take audio from before the volume control and feed it to a small amplifier (or signal conditioner if you will) to supply a leveled output. You will need one such device for each source, but it could be built into those units.
Something as simple as an emitter follower (or cathode follower if tube) might do it.
Here is the easy, cheap way. Go to Parts Express. Look for part #269-050
Speaker Level Adapter Costs 75 cents.
Graft a plug or spades onto the end of it and "Bob's Your Uncle."
Speaker Level Adapter Costs 75 cents.
Graft a plug or spades onto the end of it and "Bob's Your Uncle."
I would use a DI box to acheive what you want to do.
Features to look out for would include:-
Switchable attenuation to allow inputs at speaker levels.
Ground lift to avoid any ground loop hum.
A transformer coupled output isolates the balanced signal output, allowing you to use phantom power for any mics that are connected to your mixer.
Active or passive types would be suitable in this case - Active DI boxes are more flexible, as they can also be used with high impedance sources, like an peizo guitar pickup.
Prices vary, more expensive units tend to be more robust for stage use.
Features to look out for would include:-
Switchable attenuation to allow inputs at speaker levels.
Ground lift to avoid any ground loop hum.
A transformer coupled output isolates the balanced signal output, allowing you to use phantom power for any mics that are connected to your mixer.
Active or passive types would be suitable in this case - Active DI boxes are more flexible, as they can also be used with high impedance sources, like an peizo guitar pickup.
Prices vary, more expensive units tend to be more robust for stage use.
thanks for all the advice guys - i have a di box, and while it works, the suggestion from christian for a voltage divider ended up fitting the bill. (i need the di for other purposes)
i put a 10k in series with the (+) and a 100k to the ground - 10:1 works like a charm.
i only worry that i could do damage to the output transformer by not using a speaker... the jack is a closed circuit and subsequently cuts the speaker when anything is plugged into the jack - should i re-wire the jack to be keeping the speaker on?
i put a 10k in series with the (+) and a 100k to the ground - 10:1 works like a charm.
i only worry that i could do damage to the output transformer by not using a speaker... the jack is a closed circuit and subsequently cuts the speaker when anything is plugged into the jack - should i re-wire the jack to be keeping the speaker on?
If you have an output transformer with no secondary load, when the tubes or transistors that drive it go into cutoff with very large signals, there can be an inductive surge that, in rare cases, will cause arcs inside the transformer. And once you have an arc, the insulation has been compromised.
A solution that works well is to use a dummy load. It doesn't have to equal the usual speaker impedance; 50 or 100 Ohms is fine.
A solution that works well is to use a dummy load. It doesn't have to equal the usual speaker impedance; 50 or 100 Ohms is fine.
@ashok good suggestion, that sounds interesting...
@bob do you have any details or schematics for such an approach? i am very interested in learning / implementing as many options as possible - especially what you are talking about - as it sounds like your suggested approach would bypass the volume control and just output an independent and consistent signal.
and what distances are we talking about here? i need about 7' of cable run before i reach the mixer...
thanks guys
@bob do you have any details or schematics for such an approach? i am very interested in learning / implementing as many options as possible - especially what you are talking about - as it sounds like your suggested approach would bypass the volume control and just output an independent and consistent signal.
and what distances are we talking about here? i need about 7' of cable run before i reach the mixer...
thanks guys
Well seven feet of cable, I assume shielded, would be a couple hundred picofarads. A bit much; you will lose some highs.
A buffer can be made simply - for tube, a cathode follower and for solid state a cheap op amp or even emitter follower. Maybe four or five small parts and you are good to go.
What power supply is available? Of course another option you may like would be to build a buffer in its own box with a wall wart and run a short line to the volume control. That would be minimally invasive regarding the amplifier.
A buffer can be made simply - for tube, a cathode follower and for solid state a cheap op amp or even emitter follower. Maybe four or five small parts and you are good to go.
What power supply is available? Of course another option you may like would be to build a buffer in its own box with a wall wart and run a short line to the volume control. That would be minimally invasive regarding the amplifier.
it would be great to have these internal for each unit if i could figure it out - however i have 4 reel to reels i need to mod - three solid state and one tube (and possibly two solid state portable record players).
i don't have any schematics for the solid state players yet, only the tube - all plug into the wall and have transformers (or in the case of the tube, will have an iso transformer soon, 115/230 VAC, 0.7/0.35 A, 80 VA). the solid state players can run off of c or d batteries, but i can't ever think of a time that i would use the line-out buffer only running off of batteries...
also, any places you would suggest looking for a design for an external box? if i can't figure out how to modify them internally - this seems like a good way to go.
i don't have any schematics for the solid state players yet, only the tube - all plug into the wall and have transformers (or in the case of the tube, will have an iso transformer soon, 115/230 VAC, 0.7/0.35 A, 80 VA). the solid state players can run off of c or d batteries, but i can't ever think of a time that i would use the line-out buffer only running off of batteries...
also, any places you would suggest looking for a design for an external box? if i can't figure out how to modify them internally - this seems like a good way to go.
You can make a unit that runs off an internal 9V battery or, as I mentioned, a wall wart. Any unity gain system should work fine. If you have an op amp, especially one that will work off a single supply, you are good to go. Else you can split the supply. That's what I did with my guitar amplifier. It had about 35V single supply so I made a resistor divider to run a quad op amp I had laying around.
My best source of theory has been data sheets and application notes from IC manufacturers. Check National Semiconductor, Analog Devices, Linear Technology, Texas Instruments. Of course they are biased toward their own products but after reading a few of their notes you may gain some perspective.
However, since you are probably going to build a unity gain buffer, nearly any op amp IC will do a good job. The bandwidth and noise considerations are not a problem with nearly any of them. Your main concern is what supply voltage they require. You can find single supply units, capacitor couple the input and output, bypass the power, and you are good to go.
However, since you are probably going to build a unity gain buffer, nearly any op amp IC will do a good job. The bandwidth and noise considerations are not a problem with nearly any of them. Your main concern is what supply voltage they require. You can find single supply units, capacitor couple the input and output, bypass the power, and you are good to go.
Here is the easy, cheap way. Go to Parts Express. Look for part #269-050
Speaker Level Adapter Costs 75 cents.
Graft a plug or spades onto the end of it and "Bob's Your Uncle."
This looks great.
I would like to connect an old Yamaha subwoofer with only one signal input to the 2.0 tpa3116. I think a thing like this should do the trick... I just can't order from PE because the shipping would kill me.
Anyone knows how to achieve this "effect" with ordinary electronic components?