Power attenuators

kennier

Dr J, any idea if you can run one of these on the Roc Pro 1000? Missed out on that 6w cornford but can get my hands on a marshall powerbrake but I don't really know if it's compatible (or any good for that matter!)....

Eoin Madsen

Why would you need an attenuator for a Pro Roc 1000? As I understand it the output stage is entirely solidstate.

It actually won't work properly with an attenuator (they're designed for valve output stages with output transformers). But more to the point, it wouldn't do anything! The purpose of an attenuator is to get the sound of the output stage at high volume - but at a low volume. They work by reducing the volume between the amp and speaker, allowing you to saturate the amp without actually increasing speaker volume in the same proportion. There's no point in using it for a solidstate amp because the volume of the power stage has little or no (desireable) impact on the sound of it. Just turn down the master volume to get less output level.

As an aside, the Marshall Powerbrake is well out of date, and one of the more poorly regarded attenuators. THD and Weber make better ones.

kennier

Cheers Eoin. I wanted to tone down the volume a bit but wasnt sure if it would work on the roc pro.....obviously not! Loud it is so

jcoote

i think the roc pro is brilliant at low levels and high levels.. eoin summed it up by sayin the amp allows saturation at low levels so thats all u need to know...but the thd hotplate is the way to go anyway

Quattroste

Eoin. Where can you get an attenuator. I can drive the preamp in my Laney LC30 with the output volume low but I can't really drive the output valves without smashing windows in my house. Are attenuators expensive?

I'm off on a google search now.

Eoin Madsen

They are expensive. The attenuator of choice is the THD Hotplate or the Weber MASS attenuator. Google them both. The Weber is only available direct from Weber as far as I know. They have a website. The Hotplate you can get in Europe but it works out more expensive that way.

I got a 16 ohm Hotplate via Ebay for about €250. It was a private seller so I never ran into taxes.

(edit) Here's some urls:

Weber - https://weberspeakerscom.secure.powweb.com/weber/mass.htm

THD - http://www.thdelectronics.com/products/hotplate.htm

Quattroste

Thanks Eoin. Nice one.

Quattroste

I like the sound of the Hotplate. Musician Inc has one on their website under used gear for €250 but that's €240 more than I have to spend Dunno how long its there so it's probably gone.

My amp is a Laney LC30 (combo)so I guess its just connect the speaker/cabinet out to the Hotplat and then the Hotplate to the speaker and set to 4 or 8ohms depending on which usit i get. The combo speaker is 4ohm I think.

Eoin Madsen

Quattroste wrote:

My amp is a Laney LC30 (combo)so I guess its just connect the speaker/cabinet out to the Hotplat and then the Hotplate to the speaker and set to 4 or 8ohms depending on which usit i get. The combo speaker is 4ohm I think.

Check Ebay. If Musician are doing one for 240 then there's a cheaper one out there. The Hotplate only comes in set impedance, so find out exactly which you need first. Let us know what the speaker connections on the combo are like too!

Quattroste

Speaker connection is 1/4 inch jack! The amp is switchable between 4 and 8 ohm.

Eoin Madsen

Most amps are switchable, the impedance of the speakers and whether they're wired in series or parallel is what you need to worry about! I'm assuming it's a 2x12 or 2x10?

I take it the speaker wiring goes into a jack and there's a jack input in the amp? How long is the cable coming from the speakers? If you get an attenuator it's going to need to stretch to wherever you put said attenuator.

Quattroste

The apeaker is a 1 x 12 Celestion Seventy 80. I haven't a clue about the series or parallel question. I'd have to check the length of the cable too as I thinks its only long enough to reach the input jack on the upper back of the amp. Thanks for all the info Eoin.

Eoin Madsen

Ah okay. The series/parallel thing doesn't apply if there's only one speaker, never mind. You just need to find out what the impedance of that speaker is. If it's not marked it should be in the specs - if you don't have a manual you can probably google it. But google the amp rather than the speaker first - most types of celestion are available in several impedances anyway, you just need to find out what's been used in your model of amp.

Had a similar problem with cable length using a Hotplate with Tony Fitz's AC30. I had to make up a special speaker extension cable for it - a half metre speaker cable with a jack on one end and a jack input on the other. You could also replace the existing speaker wiring with longer wires and solder on a new jack. Either way, all the parts you'd need are available from Thomann (if you happen to be ordering something more expensive to justify the shipping cost) or Maplin on Jervis Street.