DIY attenuator

[Zozobra]

If it's for full on bedroom use then I'd go down the load box route with impulse response/cab sims and monitors. Indeed, I have gone down that route and as a bonus I can get great recordings silently too.

[d95err]

I agree that attenuators are useful for taming a high-powered amp for stage and practice volumes, but not really for "bedroom" levels.

For home use, I have a reactive dummy load (a Weber Mass motor I put in a box) and a good digital speaker simulator DI-box (BluGuitar BluBox). I run that to my home studio monitors or headphones. Works better than, for example digital amp simlators.

[Zozobra]

I'm sure this is considered heresy around these parts, but the Mercuriall VST sims are pretty incredible.

This is a quick shoot out I did between Mecuriall Spark and my Laney AOR with a Two Notes Captor load box and Wall of Sound 3 cab sims:
https://app.box.com/s/nnypw4vzortj7a42mtv0rdisx21v01ic

First repetition is Spark, then Captor/AOR, then from the top again.

It's not a particularly fair comparison in a lot of ways as I spent quite a while mixing the Spark takes as part of a forum project and the Captor/AOR parts were done in about 20 minutes. It was also my first attempt at using the captor to record so I've no doubt made a litany of noobish errors in how I have things set up.

[eschertron]

I am building a very crude attenuator...

I haven't built an attenuator yet, so I'm curious to find out what you've discovered. Built one? What do you think?

[catalin gramada]

I built once a very crude fully reactive one to be used for moderate attenuation and like dummy load, simulating an averaged Celestion impedance response as well. If I remembered the Airbrake clone sounds better and also I suspect it blowed one of my Marshall power stage.



Not very impressed with result but slaved through a Palmer into a SS one it was impressive even at low volumes-if you split into a stereo dry/wet rig you.re
in heaven - but the power stage died in the end. I.m not to sure how much sense it have to dime a hundred watter to practice at headphone level...:
It change the feel as speaker reacts it was not even close as real speaker do even the impedance curves are identical but can get nice useful tones and was a nice experiment to do.

[eschertron]

I haven't built an attenuator yet...

So a year later I manage to get curious enough to start my own "crude attenuator" experiments. I have some Ohmite 270 series wirewound resistors (5 Ohms, 225W) laying around, so I took one and paralleled a 16 Ohm speaker to get just under 4 Ohms. I calculate about 12dB attenuation. Enough to notice, anyway. The treble seems to roll off a little, but it could be related to volume difference.

I'm wondering if the wirewound resistor has enough inductance to make a difference at higher frequencies? Anybody have experience with these large resistors?
https://www.ohmite.com/assets/docs/res_270.pdf

[Helmholtz]

No, certainly not. In principle an inductive resistor parallel to the speaker attenuates lows not highs. But generally the inductance of (wirewound) resistors is very low compared to the speaker inductance. No need to use low-inductance resistors in power attenuators.
Your arrangement reduces the source impedance as seen by the speaker and this reduces treble depending on the amp used. You may try an additional resistor (5...100 Ohm) in series with the speaker. But also amp loading changes.
There is more information here:
https://music-electronics-forum.com/...ad.php?t=47723

[eschertron]

I've following that thread with interest.
I've been toying with the idea of a 200uH-ish inductor in series with the resistor (both parallel to the driver) to increase impedance at higher freqs. That's what led me to ask what's already there.

[Old Tele man]

If it's worth DOING, it's usually worth doing RIGHT.

[Helmholtz]

I've been toying with the idea of a 200uH-ish inductor in series with the resistor (both parallel to the driver) to increase impedance at higher freqs

The inductor in series with the parallel resistor may help to re-gain some treble. Its inductance adds to the parasitic inductance of the resistor.

That's what led me to ask what's already there.

This means what?

[eschertron]

This means what?

In terms of parasitic inductance. I couldn't find any mention on the Ohmite website other than "non-inductive resistors available" which sounds suspiciously like the stock resistors DO have some inductance, which in turn leads me to ask if anyone had a ball-park guess of how much parasitic inductance it might have.

edit: and I believe "No, certainly not" was the answer.

[Helmholtz]

I found a 5 Ohm/50W 270 series Ohmite resistor. Its serial inductance is 4.8µH.

[eschertron]

I found a 5 Ohm/50W 270 series Ohmite resistor. Its serial inductance is 4.8µH.

Thank you. Data sourced from Ohmite?

[Helmholtz]

Thank you. Data sourced from Ohmite?

No, measured.

[eschertron]

Excellent!
I built a jig to measure the inductance of an unknown choke out of a donor amp once (a Baldwin organ, so an 'organ donor' amp), but don't expect my instruments to be sensitive or precise enough to measure the parasitic inductance from the resistor. Again, thanks!

edit: thinking about finding an iron core. I might be able to measure the difference in reactance at 100Hz and 10kHz then.