L122 line out

[dryjoy]

Hello

This is a topic I suspect comes up quite a bit, but I haven't found exactly the answer to my query. Apologies if it already exists somewhere.

My recently acquired L122 has at some point had a 1/4" jack output installed. It's a straight speaker output with no resistor, which cuts out the internal speakers. I assume it must have been used to connect to a leslie or something, although there is no leslie speed switch fitted. That's something I might want to do at some point, if I can find a suitable leslie cabinet that is not too expensive, but for now I would like to convert this into a line out.

I'm thinking of having a go at building the following circuit into an external enclosure, with a jack socket input to connect to the speaker out from the organ on one side, and a line out on the other. Is there any reason this shouldn't work? Are the component values OK for this specific model of organ?

http://www.dairiki.org/HammondWiki/LineOutFromASpinet

Any advice much appreciated.

Thanks in advance.

[Saltech]

The L122 has a valve / tube power amp. With all valve amps it is important to always have a speaker connected for the good health of the amp - also the speaker needs to have the correct impedance for the amp, so you can't substitute a 4ohm speaker if the original is 16ohm. This rule applies to all valve amps but not to transistor amps. The circuit you link to gives a line out along with the internal speaker still sounding, so if you're going to fit it to your organ on the existing speaker out jack socket (which cuts out the internal speaker), then you need to make sure you include the 10 watt resistor which substitutes for the speaker. It will be taking most of the output of the amp so it needs to be heavy duty (not a regular 1/4watt resistor). It will probably get quite hot so allow for this (don't attach it to a plastic box that will melt), also a good idea to use a speaker grade jack cable to connect from the speaker out on you organ to your external enclosure, not a regular guitar lead. The L122 has a bass and a treble speaker wired in parallel (see http://captain-foldback.com/Hammond_...s/L100_wir.gif on the right hand side) if both of these are 16 ohm speakers, then the resulting load for the power amp will be 8ohms, hence the 8ohm 10watt resistor as substitute. Best to check what you have in your organ - I don't know if all the spinets had the same speakers fitted - so you can match your 10watt resistor to the speaker set up in the L (probably 8ohm, just try to confirm it.)

[dryjoy]

Thanks for your advice. Online sources state that the L100 speakers are both 16 ohms, wires in parallel, so 8 ohms should be good. I have a 8 ohm resistor rated at 30 watts, so that should do the trick. It's a lot smaller than I expected, though.

[Saltech]

Looking again at the circuit, the capacitor will filter the very low end (sub 15Hz region) and the potentiometer will tap off the output voltage at a reduced level for the line out. As it stands, this voltage will be between zero and ~95% of the output voltage. This could mean that only the lower region of the pot's range will be useful, after which it's too hot, especially if you are using guitar pedals in the signal path. If so, you can add more resistance on the capacitor side of the potentiometer. e.g. another 20K would mean the potentiometer is going from 0 to 50% of the output level, 60K would give a 0 to 25% range. You can also use other values of pots, if that's what you have available, like guitar pots (500K) and match them with a similar size resistor on the cap side to keep the ratios the same for the voltage divider e.g. 500k pot with a 1meg resistor will give the pot a range of 0 to 33% of the output. Be careful to identify and preserve the earth and signal sides of the circuit from the organ amp's output (e.g. at the organ jack socket, connecting cable and external box jack socket, then internal circuitry), if they get swapped over then you have the potential to short the amp signal to earth (i.e the earth from your external amplifier / mixer), which will not go well for the organ amp.

[Wes]

Sounds to me like your L122 is equipped with a jack for 8 ohm headphones.

The line-out circuit on Jeff's site should work fine. Re. pot selection - this is why log pots are normally used.

If you don't need reverb or EL84 grind, you can just use the RCA output from the expression pedal, where it plugs into the power amp, for your line out.