Tube Cube Attenuator

mangy · Post by **mangy** » 12 May 2011, 08:13

Hey,

First proper post here..

Borrowed a Tube Cube Attenuator (8 Ohm, 80W) from a mate with the intention of building my own for pottering around with. Expected to pop it open and find an l pad or rheostat and a bunch of resistors etc.. But this is a transformer based design..

I'll add a couple more photos later once I've taken the pcb out...

Hides-His-Eyes · Post by **Hides-His-Eyes** » 12 May 2011, 08:29

Any part numbers going?

bancika · Post by **bancika** » 12 May 2011, 08:53

interesting, I wonder what dissipates the heat

DeanM · Post by **DeanM** » 12 May 2011, 09:39

That looks interesting. how does it sound? I have a hotplate but have been tempted to sell it and make somethin.

Also, whats the markings on the PCB? looks like black marker and looks like something is covered over? Maybe they're using someone elses PCBs?

mangy · Post by **mangy** » 12 May 2011, 11:57

No visible part numbers..

Will let you know how it handles the heat and sounds tomorrow when the sprogs are at nursery..

Tried cleaning off the marker pen, but the details have also been scraped... inverted the image to show it better.. any ideas?

Hides-His-Eyes · Post by **Hides-His-Eyes** » 12 May 2011, 12:39

Why scrub your own PCBs? Real odd behaviour.

FiveseveN · Post by **FiveseveN** » 12 May 2011, 13:28

Why scrub your own PCBs?

Unless... it's not.
There's a logo under there. Can anyone make it out? Looks like 4 letters, IMX_G?

bajaman · Post by **bajaman** » 12 May 2011, 21:30

look familiar

http://www.nxgtechnology.com/images/man ... e/vm80.pdf
cheers
bajaman

bajaman · Post by **bajaman** » 12 May 2011, 21:36

...........as he is only using one side of this NXG stereo impedance matching volume control, what is the bet that he connects the left output to the right input, and then takes the right output to the output jack socket for "his" 160 watt version

bajaman

Hides-His-Eyes · Post by **Hides-His-Eyes** » 12 May 2011, 21:37

Fair's fair, turning a component into a product, but the attempt to hide it is hilarious

bajaman · Post by **bajaman** » 12 May 2011, 21:42

............................................ on Ebay - https://cgi.ebay.com/NXG-NX-VM80-Volume ... 6030243019

second hand $11.00

as the blurb says "these retail for US$33.00 but are hard to find" (I wonder why?

)
bootweeaker of the year award????
bajaman

bajaman · Post by **bajaman** » 12 May 2011, 21:44

oh well - I suppose the box and the fancy knob,(and the audio wanker wiring) must account for the dramatic 1000% markup

bajaman

bajaman · Post by **bajaman** » 12 May 2011, 21:47

oh yeah - and the "mutilation" of the switch must be expensive too!!

Hides-His-Eyes · Post by **Hides-His-Eyes** » 12 May 2011, 22:01

Fair's fair here, I had no idea such an assembly even existed. You gotta admire his business sense...

mangy · Post by **mangy** » 12 May 2011, 22:29

Well spotted/sourced bajaman..

..I agree fair's fair on the use of an existing component in another product.. I'd heard of the transformer approach to attenuation before but presumed that all of the hi-fi speaker volume controls were l pads of varying quality..

..still.. will fire an amp up tomorrow & see if this thing cooks..

..so, is the autoformer a reactive load on the amp?..

Steven_M · Post by **Steven_M** » 12 May 2011, 23:20

I like this part of his website the best:

Same sound, same parts and specs, however, this one has a new rugged metal enclosure, additionally, comes equipped with a heavy carry handle. Also, for you DIYers out there, this enclosure can be opened up. Thanks for looking!

http://www.thetubecube.com/component/pa ... /Itemid,1/

Steven_M · Post by **Steven_M** » 12 May 2011, 23:25

Here is the data sheet too:

http://www.nxgtechnology.com/images/man ... e/vm80.pdf

DeanM · Post by **DeanM** » 14 May 2011, 15:30

bajaman wrote:...........as he is only using one side of this NXG stereo impedance matching volume control, what is the bet that he connects the left output to the right input, and then takes the right output to the output jack socket for "his" 160 watt version
bajaman

I saw on another forum after a google search he replied to a customers email and told them that that was how he did it. he said they were in series.

mangy · Post by **mangy** » 17 May 2011, 08:53

Following a couple of sound tests.. my opinion is that this attenuator offers very poor quality sound.. perhaps it might be fine for the intended hi-fi use but it certainly doesn't meet the requirements of an instrument amp..

I ran it through a 50w amp.. popped the clean volume up full.. minimum attenuation on the tube cube and the amp had lost all the spank, thump & dynamics... increasing the attenuation only made the sound quality worse... very thin and squished.. quite like a cheap digital multi-effects unit... or an elevator speaker...

Also, even the minimum setting had quite an effect on the amp... it was very quiet indeed... my amp was louder at 3 on the volume without the cube than at full with the cube on minimum...

phatt · Post by **phatt** » 17 May 2011, 09:00

mangy wrote:Following a couple of sound tests.. my opinion is that this attenuator offers very poor quality sound.. perhaps it might be fine for the intended hi-fi use but it certainly doesn't meet the requirements of an instrument amp..

I ran it through a 50w amp.. popped the clean volume up full.. minimum attenuation on the tube cube and the amp had lost all the spank, thump & dynamics... increasing the attenuation only made the sound quality worse... very thin and squished.. quite like a cheap digital multi-effects unit... or an elevator speaker...

Also, even the minimum setting had quite an effect on the amp... it was very quiet indeed... my amp was louder at 3 on the volume without the cube than at full with the cube on minimum...

Hi mangy,,, Google *Reamping* ideas .

Also the load is wrong,,,,, try a 30 Ohm Sand box and tap a line level from that then send your signal to a second amp.
(simple voltage division after the load resistor,, I use a 470 k series R into a 10k pot,, so simple yet so stunning results)

Yoo hoo

I've never looked back,, ,winky.
Phil.