Convertering Speaker Level to Line-Level - Mixer

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digi001

Member
Joined 2015
#1
I have one of these:
Koch Dummybox Home - Koch Amps

Looking to get 2 more channels for an old vintage Stereo Mixer that puts out Speaker Level, but I'd like to convert it down to line-level.

The Koch works well, but I don't need all the bells and whistles, just want Line Output.

So I purchased 2 of these:
Parts Express 8 Ohm 100W Non-Inductive Dummy Load Resistor: Electronic Resistors: Amazon.com: Industrial & Scientific

Question;
Is the setup as simple as, hook up the dummy load and tap off in parallel for line level?
Or any recommended additional resistors or caps for protection/etc? This will be going into a Universal Audio Apollo Recording Interface.

I tried opening up the Koch to take a look, but couldn't tell for sure.
 
#2
> an old vintage Stereo Mixer

Uh. *which* an old vintage Stereo Mixer? Or at least what power?

Speaker level is often ten times line level. So aside from "loading the amp" (not usually needed in transistor amps), you want to pad-down the level a lot.
 
#3
Any DI box with a transformer and pad switch can do this. If you do not need a transformer, a resistor divider is all you need unless it has a tube output stage. For example, DENON PMA1500AE has a line level output made just by a resistive divider after the power stage.
 
#4
Oh yeh ok, I guess I totally missed that.

So in addition to a dummy load of 8 ohms (which some saying might not even need), I also need a voltage divider to reduce the level. Taping in parallel to a dummy load would not convert the voltage and it would still be full. Duh ok. Ha.

Any recommendations on the resistors for the voltage divider? 1k and something else? Does impedance matter here?
 
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#5
This is an old Yamaha 6 channel mixer with built in drum machine and spring reverb. It actually has a line-out, but I’d like to use the speaker out to go about 30 feet before padding it down. In my test that showed to have less noise than when I ran the line-level signal same distance.
 
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#7
You dont need the dummy load, just a divider. The Koch dummy box is for a different application, its for recording a guitar rig. Guitar amps, especially tubes sound different at different power output so that dummy load lets you crank the amp without a cab or your ears bleeding.

If you use a pot you can adjust the level.
 
#12
pelanj said:
Any DI box with a transformer and pad switch can do this. If you do not need a transformer, a resistor divider is all you need unless it has a tube output stage. For example, DENON PMA1500AE has a line level output made just by a resistive divider after the power stage.
Click to expand...

Thanks.
Yes OK I understand now that the LineOutput inside the mixer is likely just from a divider.

But since I want to go some distance with it, I'm going to use my own divider after about 30 feet to get better signal-to-noise on the unbalanced cable.

I dont think I want -28db.

Like I said...I tested at -10db of pad going into +4db Line Level input and that seemed to work nicely.
 
#13
You're also getting all the distortion of an output stage; the line out may have a divider, but its from beFORE the power amp. Typically it has its own buffer, which is driven by the same signal that goes to the power amp.

Better to use the line output, solve the noise problem with a line-level-tolerant DI box (most are), and you probably won't need a pad. The XLR on the DI box will provide balanced.

The notion that *power* might be needed to carry a high-quality, low-noise signal for a distance of 30 feet is false. Microphone level, balanced low-impedance signals travel hundreds of feet when necessary.

Regards
 
#14
Thanks for all the advice here!

Sometimes when it comes to these things I think just gotta try it and see what’s best.

Comparing the following methods:
-Line out of Mixer into Interface
-Line Out out of Mixer into DI then into MicPre then interface
-Speaker out into DI into mic pre Into Interface
-Speaker out into PAD into interface

The last one yielded the lowest noise.
All had the same overall signal (no distortion)
 
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