Harley Benton - PA100 Power Attenuator

PiZZaMartijn · Post by **PiZZaMartijn** » 28 Feb 2016, 17:06

I just got my harley benton power attenuator, it comes with a very confusing manual so I opened it up. Can anybody confirm that this thing can run without a cabinet attached while still using line-out?

grrrunge · Post by **grrrunge** » 28 Feb 2016, 18:33

Just saw this thing. It looks surprisingly similar to the "Soldano Designed" Jet City attennuator...
http://www.thomann.de/dk/jet_city_ampli ... l_370975_0

Post by **modman** » 28 Feb 2016, 19:36

Please have a look at the Jen City Attenuator thread...

http://www.thomann.de/be/harley_benton_ ... nuator.htm = €98
http://www.thomann.de/be/jet_city_ampli ... nuator.htm = €148

mirosol · Post by **mirosol** » 29 Feb 2016, 17:20

For the HB's price, that's beginning to look like a proper steal. The rheostat with the same specs (16ohm, 100W) by itself is curretly 78€ plus shipping at mouser. Throw in a few 50W resistors and it's cheaper to buy HB attenuator than the parts to build one like it.

Either way. HB is the same unit as Soldano designed Jet City.

phatt · Post by **phatt** » 01 Mar 2016, 02:17

Regards to no speaker Q;
IF the drawing is correct (and it is not) then yes the resistors are across the load so it would be safe to use without a speaker connected.
The attenuation pot is NOT a normal pot,,hence the name,, L pad.
See the other thread, If I recall?

I corrected that circuit drawing.
Phil.

phatt · Post by **phatt** » 01 Mar 2016, 02:29

Oh yeah to check;
Just insert a cord into say the 8 Ohm input and you should read low Ohms on the tip and Sleeve of the input cable. (with no speaker connected of course)
As long as it reads below ~30 (ish) Ohms you will be safe.

Phil.

gturo · Post by **gturo** » 01 Mar 2016, 06:52

LPAD (made by the italian company CIARE) is an attenuator by itself:
http://www.igtek.it/attenuatore-lpad-ci ... 12582.html
Sorry, the page is in italian... I made my attenuator with two of these in series (in order to shut up a 100W plexi head) and it works well.

PiZZaMartijn · Post by **PiZZaMartijn** » 01 Mar 2016, 12:06

phatt wrote:Regards to no speaker Q;
IF the drawing is correct (and it is not) then yes the resistors are across the load so it would be safe to use without a speaker connected.
The attenuation pot is NOT a normal pot,,hence the name,, L pad.
See the other thread, If I recall? I corrected that circuit drawing.
Phil.

The drawing of the lineout and speaker out part is correct. It just might be different than the jettenuator. The micmod output might have some errors but I'm not using that.

phatt · Post by **phatt** » 02 Mar 2016, 10:55

PiZZaMartijn wrote:
phatt wrote:Regards to no speaker Q;
IF the drawing is correct (and it is not) then yes the resistors are across the load so it would be safe to use without a speaker connected.
The attenuation pot is NOT a normal pot,,hence the name,, L pad.
See the other thread, If I recall? I corrected that circuit drawing.
Phil.
The drawing of the lineout and speaker out part is correct. It just might be different than the jettenuator. The micmod output might have some errors but I'm not using that.

Well obviously you did not read the other posting,,

no matter

Yes your schematic may look perfect but that L pad is not a pot so it's not drawn correctly, therefore,,, it's not right.

A picture might help clear the air;

These Attenuator/ Lpads are a DUAL wire wound pot with a single common wiper. They are configured so that as one turns up , the other turns down.
The idea being to keep the resistance close to 8 Ohms at nearly all points of rotation.
At very low setting (high attenuation) they tend to overheat and often burn out the inside element which is the finer wire. (40 Ohm)

What may be even less obvious is that the Stated 100 Watts is very misleading as these were intended for old style crossover networks where all the low frequency is rolled off and in such a case would only receive mid high frequency signal so the Lpad is not stressed.

In that situation, Yes they can then easy handle 100Watts of system power But asking then to pass full range signal is going burn them out.
That is why those extra resistors are present in the unit as they help to throw off a lot of excess energy and then the Lpad can do the rest without burning out.
Even in such case I would be very wary of over stressing the unit by running high Amplifier volumes with the Attenuator turned down very low.

When they get close to burnout point they let off a very strong odor before they blow up,, no medals for guessing how I know that.

BTW when turned up to full volume (clockwise) the bottom (40 Ohm track) is then disconnected from the wiper so the signal is then direct with no added resistance back to common.
Hope it helps,,Phil.

free photo upload

image upload without registration

PiZZaMartijn · Post by **PiZZaMartijn** » 03 Mar 2016, 13:24

What i meant is that in the harley benton attenuator there are also resistors connected to ground while in the jettenuator they are in series with the L-pad.
My amp is only 15 watts so it should handle it. I've used for a while without cab attached in various settings and the outside of the L-pad doesn't even heat up.

phatt · Post by **phatt** » 04 Mar 2016, 12:58

Although there are slight differences, both units have series and parallel resistors in the signal path before the Lpad.
If you are only pushing 15 watts you have no worries.

Phil.

spoontex · Post by **spoontex** » 08 Dec 2019, 20:02

A strange thing happened to me today with my amp and my attenuator. Usually I use an attenuator at home, and sometimes I like to push up the volume for overdrive. And suddenly, it's like the attenuator bypass him... and don't actuate over the amp... I can't regulate the atteunator volume knob, he goes from no sound to a full sound.

Anybody can explain what happen?

Manfred · Post by **Manfred** » 08 Dec 2019, 21:39

spoontex wrote:A strange thing happened to me today with my amp and my attenuator. Usually I use an attenuator at home, and sometimes I like to push up the volume for overdrive. And suddenly, it's like the attenuator bypass him... and don't actuate over the amp... I can't regulate the atteunator volume knob, he goes from no sound to a full sound.

Anybody can explain what happen?

This is hard to say without further information such as the schematic or wiring diagram.

spoontex · Post by **spoontex** » 08 Dec 2019, 21:52

It's a Harley Benton Power Attenuator. In this web has a schmeatic:

https://blog.brixit.nl/blog/2016/2/harl ... -teardown/

I measured all the amp inputs:

4Ohm:
lpad min: 8.3R
lpad max: 16.6R

8Ohm:
lpad min: 12.3R
lpad max: 20.6R

16Ohm:
lpad min: 16.3R
lpad max: 24.8R

I found that the switched jack from 16R are always open. I replace the jack, and I have this values now:

4Ohm:
lpad min: 4.2R
lpad max: 5.7R

8Ohm:
lpad min: 8.5R
lpad max: 9.8R

16Ohm:
lpad min:16.3R
lpad max: 24.4R

But anyway, this don't attenuate nothing.

Manfred · Post by **Manfred** » 08 Dec 2019, 22:43

If I recalculate the circuit from the link it will give different values than the one you measured, the schematic might not be correct.
Could you trace the circuit of the damping part of your Attenuator.

spoontex · Post by **spoontex** » 09 Dec 2019, 08:20

I disassembled the lpad and it's burned...

https://ibb.co/rf9GbrP

My amp is a Bassman aa864 50W I can use this Attenuator no?

Manfred · Post by **Manfred** » 09 Dec 2019, 09:32

Thanks for the Information.
The attenuator of this kind item is no longer available, what power is the device designed for?
In the article on which the link is referred to a L-Pad power of 100W is mentioned.
But power is voltage times current that says nothing about the maximum allowed current strength
this is determined by the wire diameter of the resistor winding.
Either the L-pad is too weak or there may have been a short circuit at the speaker outputs.

spoontex · Post by **spoontex** » 09 Dec 2019, 14:22

This attenuator is designed to handle 100W power amps. But my amp is 50W. I don't understand why it burned. My amps works normally, seems that nothing is damaged.

Manfred · Post by **Manfred** » 09 Dec 2019, 16:07

My guess is a Chinese product where the Lpad is too weakly dimensioned.

bmxguitarsbmx · Post by **bmxguitarsbmx** » 09 Dec 2019, 19:10

I have read that, because L-pads are typically designed to balance the level of the tweeter to the woofer, the 100watt rating is specified as the rating for the speaker system. Maybe measuring the diameter of the resistance wire could give a realistic idea of power handling. I do know that I immediately smoked this 100watt l-pad with a 20Watt amp. I wouldn't say it sounded all that great either (for obvious reasons).

https://www.parts-express.com/parts-exp ... m--260-261

Harley Benton - PA100 Power Attenuator [schematic]