Line out opinions

[RWood]

I was planning a line out on a 5c3 and was going to lift it from just before the PI grid. If so would I need it to be coupled through another cap...If so, what value?

The second thought was to lift it from just before a Power tube because the PI seems to color and breakup slightly. I am only basing that on my experiences of using different PI tubes in the same circuit.
Which Power tube? The one with NFB loop or the other?

The third thought was to lift it off the NFB loop. I've done it by tapping off the speaker jack with pot/resistor before but it sounded a bit harsh...

[pdf64]

A line out will be used with a cable to connect to other equipment.
Cables have capacitence, eg 1nF.
The equipment will have an input impedance, eg 100k
As I see it, the only place that could connect such a load without noticeably affecting the performance of the amp is to derive it from the speaker output, eg via a 1k - 100 ohm potential divider.
My guess is that the tone is harsher there (than earlier in the signal chain) because the power tube control grids have the least headroom / clipping occurs there at lower signal levels than elsewhere.

[Leo_Gnardo]

What pdf64 said ^^^. A voltage divider across the speaker output was called a "slave" output but maybe that term is no longer "politically correct." Whatever. You can de-harsh it by applying a cap across the lower branch of the voltage divider - some amp manufacturers do exactly that. Some experiments will be needed for you to decide what works for you.

There are some pro-made special DI boxes, for instance the H&K "Red Box", that roll off top end, and do a little compression, maybe some tone shaping besides, to try and simulate the sound of a speaker mic'd up with say, a Shure SM57, commonly used as an amp mic. Maybe a bit complex for the hobby builder.

Long time ago I tried running a DI box straight off the speaker output, and even though the DI had a hell of a pad on it, the tone was, umm, schrecklich (AWFUL!) at the house mix input and I was stuck with it for the show.

If your aim is to run power amps from the "attenuated output", not a line to FOH/monitor mixers, same techniques hold. Tune it to taste, and maybe run the slave, uh.... "assistant"?... output thru an transformer as a DI would, to separate the grounds of guitar amp and power amp(s), keep the hum/buzz to a minimum, and keep that audio transformer well away from all power transformers. How many speakers you want? Look up Grateful Dead's "Wall Of Sound" operating @ 1971-74.

[Firestorm]

An effects loop option you can take from any number of places, if you design it that way. Fender always tapped their line out from the speaker, so the OT is part of the sound. Deluxes get a bit harsh, so that is what you get. If it's your own design, pick anyplace you can get a line level signal. If you want a long run, make it a balanced send.

[labb]

Give this a try:

http://www.jensen-transformers.com/as/as061.pdf

[roberto]

+1 on the speaker output through a voltage divider (or resistor + pot).

[rp]

Anyone got a diagram for how to do this w/ a pot?

[Leo_Gnardo]

Anyone got a diagram for how to do this w/ a pot?

Let's not forget, our OP needs some "signal conditioning" IOW knock off fizzy/shrieky high end, hence cap across lower leg of voltage divider. Gotta try some different values until you get a tone you can live with. This is all so low-impedance, can be breadboarded outside the amp until you settle on circuit values.

Chose 10K R and 1K pot because it's hard to find a smaller value pot, also you'd need a fairly large cap to affect hi freq's as the value of the resistor is reduced. If you used 220R/22R as Dean Jensen Transformer suggests, you'd have to have a thumb-sized cap to roll off hights. I'm also not too thrilled with DJT's ground switch scheme. Let's say, they make excellent transformers and leave it at that.

If you choose to go balanced out, of course you CAN spend $100 upwards for a Jensen transformer, or under $5 for a Mouser. With a Mouser, you won't have all that magnificent bandwidth the Jensen delivers, but they're plenty good for guitar frequencies. I'm just wakin' up and may need to come back and correct the part number, but I' think it's a Mouser TL018 that I've used in DI's I've built along this line.

[labb]

This one from Weber works pretty good. It is $4.00

https://taweber.powweb.com/store/balun.jpg

[pops]

I have tried the 10k/1k speaker out, but felt it was too hot and went up to 30k so do some experimenting to find what works for your amp. These capture the sound of the amp wonderfully and just make a small amp big. It has worked better on a champ for me, as the champ gets a good tone at a lesser volume so going into the P.A. unless you have a input gain won't overdrive the input from the champ. It also works well going into the 2nd input jack (low again)of another amp.

Just looked at the Weber link so guess the resistor size was mentioned sorry i'll get another cup of coffee.

[roberto]

Exactly.
I sometimes use 47k into a 5k pot, but without the cap.

[rp]

Nuts, I don't have a 1K pot.

This is from Hoffman if anyone is interested, I had saved it. As always HBP over there lays it all out, great stuff about the consumer/pro level switch, wish I'd left some room on my Champ.

http://www.el34world.com/Forum/index.php?topic=14664.0

http://el34world.com/Forum/index.php?topic=16792.0

[labb]

This discussion may be of interest

http://music-electronics-forum.com/t25684/

[Leo_Gnardo]

Nuts, I don't have a 1K pot.

No matter, just use whatever pot you may have on hand across another R on the lower leg of the voltage divider. Improvise, improvise, until you have what sounds good to you. Hi rolloff cap optional. I see Weber suggests a hi peaking cap across the upper leg. If the sound is already too obnoxiously bright, as it often is with type of line out, OW, don't do that.

[RWood]

[quote="labb"]This discussion may be of interest

http://music-electronics-forum.com/t25684/[/quote

Great resource.
Ideal line voltage of .775 vac achieved through 470/5k8.
I used 470ohm/10k pot divider off the speaker out with cap across v2 as Leo noted and it works great with no reduction in clarity.