Amp volume reduction - line out question

[Smoke]

Hey guys,

I got my hands on this Fender BXR300 bass amp, and I kinda like the sound of it. Pretty decent for solid state.

It has a preamp out, which I assume is the line out output, but it is very loud. Being post volume and EQ it is affected by the volume knob, and having it on anything over 1 of 10 the signal gets distorted. How can I reduce this volume?

My aims are two: first, plug it into a sound card and record it without distorting.

second, use the power amp/speaker simultaniously with the line out to a mixer desk on live shows. This works, but I either have to have my amp volume on 1, or deal with the sound guy telling my to turn my amp down.
I like my amp to work on around 7-8 volume when playing live. I have connected an XLR to the back on the chassis to use instead of that instrument preamp jack, and I guess I have to place a resistor to reduce the volume... voltage?
Heres a schematic of the amp that I found. 300w power amp.

Any help would be appreciated.

 

[PRR]

> the sound guy telling my to turn my amp down.

The Line Out only makes 2.6V peak at full-blast clipping. Any proper line-input should swallow this with ease. It is rather a lot for a MIKE input, but you shouldn't be jacking lines into mike-jacks, and a good rock-n-roll mike input really should swallow 2.6V peaks. (And while some sound-cards can take 2.8V peaks, an awful lot won't!)

So I dunno if the schematic is wrong, or this is just mis-use.

Whatever. You want less, you can get less.

Change the 1K resistor to the Line Out jack to 2K7 (or add 1K5 or 2K2 in series with the 1K). Shunt a 470Ω resistor across the jack, hot to ground. That cuts the level to about 1/7th the voltage, about -17dB, a good chop.

If some fool insists on plugging into a MIKE input, instead of 470Ω try 47Ω. That should put you in the ballpark of an SM57 on a rock-n-roll stage.

> have my amp volume on 1, .... I like my amp to work on around 7-8 volume

This tells us nothing. The volume control is a Gain control, not a Power control. We don't know how hot your pickup is, whether you brush or yank your strings, or what gain the numbers give.

Hmmm.... this amp has a Limiter, after Line Out, in the power amp stage. Does the limiter LED ever come on while you are playing? If so, then the Line Out may be peaking far higher than the 2.6V peak needed to goose 300 Watts(!) into the speaker. And the speaker output is limited, the Line Out is not, so the Line Out is not what you hear in the speaker. Transients that are limited to 299 Watts in the speaker may be jumping to the virtual equivalent of 2,000 Watts in the Line Out signal.

You might want to tap from the Speaker jack instead of the pre-limiter point. In that case make R85 a 68K or 100K resistor from speaker-hot/CP1 point to Line Out hot, with the 470Ω or 47Ω shunt resistor to Line Out ground.

 

[PRR]

BTW: speaking as a soundman, I think you need to find a soundguy who knows his stuff. You make the music, he takes whatever electricity you give him and deals with it. Yes, negotiation is OK, but being just unable to deal with a very-hot signal is not. And in Fender guitar/bass, the amp and the levels inside of it are very much part of "the sound" and "the music". Would I ask a concert pianist to play on a parlor spinnet because his Concert Grand was too loud for my mikes? Reducing gain is the easiest and most desirable technical "problem". {rant off}

 

[Smoke]

Thanks for your reply PRR
[quote author="PRR"]
You might want to tap from the Speaker jack instead of the pre-limiter point. In that case make R85 a 68K or 100K resistor from speaker-hot/CP1 point to Line Out hot, with the 470Ω or 47Ω shunt resistor to Line Out ground.[/quote]

I guess the above is the formula to the LineOut mod of the amp, the signal being taken from the speaker output jack. Does this load the amp more than normal? Would it be safe to connect to a mixer desk(live) and a soundcard LINEIN?

I thought the preamp out was for the above two purposes... as far as I understood you, on this amp the preamp out has no peak limiting and this could be dangerous. Can that outpot voltage be measured with a multimeter?

Thanks

 

[Smoke]

btw, is this what is called a volume attenuator?

Would it be loading the poweramp more than normal? When running both the speaker (4ohm) and the above mod thing, would it be safe?

Thanks

 

[ebartlet]

[quote author="PRR"]BTW: speaking as a soundman, I think you need to find a soundguy who knows his stuff. You make the music, he takes whatever electricity you give him and deals with it. Yes, negotiation is OK, but being just unable to deal with a very-hot signal is not. And in Fender guitar/bass, the amp and the levels inside of it are very much part of "the sound" and "the music". Would I ask a concert pianist to play on a parlor spinnet because his Concert Grand was too loud for my mikes? Reducing gain is the easiest and most desirable technical "problem". {rant off}[/quote]

Man I delt with this a while back. I had a gig which I almost didn't play because the soundguy had to D.I. my electric guitar. He told me he would put distortion and efx into my monitors! After my band walked off just before we were supposed to play, and much negotiation he agreed to let me play through my amp...

 

[Smoke]

DI a guitar just doesnt work, DI a bass could be alright and in some cases might be undesired.

Is there anyone who can take me out of my misery and help me further with my worries ((((

 

[ebartlet]

[quote author="Smoke"]Thanks for your reply PRR
[quote author="PRR"]
You might want to tap from the Speaker jack instead of the pre-limiter point. In that case make R85 a 68K or 100K resistor from speaker-hot/CP1 point to Line Out hot, with the 470Ω or 47Ω shunt resistor to Line Out ground.[/quote]

I guess the above is the formula to the LineOut mod of the amp, the signal being taken from the speaker output jack. Does this load the amp more than normal?[/quote]

No

[quote author="Smoke"]
Would it be safe to connect to a mixer desk(live) and a soundcard LINEIN?[/quote]

Yes