Tube Cube Attenuator

mangy · Post by **mangy** » 17 May 2011, 09:11

Thanks for the info.. I'm off to do some googling now...

phatt · Post by **phatt** » 17 May 2011, 09:16

Here is something to help you in your endevour.
My original Used a 50k pot but my guess is you only need 10k.
will depend a fair bit on how big the Soaked Amplifier is??
Phil.

DrNomis · Post by **DrNomis** » 17 May 2011, 12:21

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

1000% markup?...the box, knob, and wiring must be made of some rare, and/or, expensive materials....

bajaman · Post by **bajaman** » 17 May 2011, 12:49

the box, knob, and wiring must be made of some rare, and/or, expensive materials

No - just the usual crap

- go with Phil's design

cheers
bajaman

DrNomis · Post by **DrNomis** » 17 May 2011, 13:04

bajaman wrote:
the box, knob, and wiring must be made of some rare, and/or, expensive materials
No - just the usual crap - go with Phil's design
cheers
bajaman

Actually, I might even have a go at building one of these things mate, since I need some way of running a Tube Amp Head in silent mode for recording, one of the other members posted that it doesn't really sound that good, maybe I can improve the design somewhat, if I do get around to it, I'll certainly share it with everyone at FSB....

One question, I happen to have a huge 8 Ohm/50 Watt wire wound resistor, would it be possible to use it in phatt's circuit as a substitute for the 10 Ohm/30 Watt resistor, with a little tweaking of the other resistor values?....

phatt · Post by **phatt** » 17 May 2011, 13:39

Hi DrNormis,
Yes if you just use an 8 Ohm load resistor it will suck the life out of the tube Amp and make it sound like a TS9. I can't remember what Forum but I wrote a whole screed about this stuff back in 09 I think.

The guy that made the UA setup simply explained that you need a load that is the eqivilant of the Z at freq of resonance. (At least I think that's what was meant?) In most situations that seems to be around 30ish Ohms.

Anyway my guess is you might wonder at the wisdom of such claims,, Heck I did!!

So if it helps? I've been belting the living daylights out of a small 10 Watt PP Amp for 3 years and I want for little.
No issues,, I hardly even check it anymore.
Yes you can do totally dry direct recording if you so wish.

I did setout years back to build a King TUt styled powerscaling, Great idea but it finally dawned on me that it is not as easy as it fist looks and does have limitations.
The ReAmping concept allows one to add post power tube effects and additional tone shaping tricks.
As I already had a small Valve rig I figured it was just a simple matter to hang the above circuit off the end of the little Amp. (The advantage is you can take it to another Amp if needed.)

My Amp is a pair of 6GW8's running PP, K biased, no FB, HT is 260VDC. Somehow I think I will die before the Amp.

As I don't have a lot of money I can't justify spending big money on some of the gear that gets talked about on these forums so my second Amps are just SS power Amps but I have no trouble competing with brandname rigs,, winky.

As to soaking really big Amps?? Things may get a little more spooky I just don't have any experience with those.
but it makes sense to soak a little Amp and use the bigger Amps for reproducing an unaltered clean reproduction of the first amp which does the powerstage compression thing.
Phil.

DrNomis · Post by **DrNomis** » 17 May 2011, 13:50

phatt wrote:Hi DrNormis,
Yes if you just use an 8 Ohm load resistor it will suck the life out of the tube Amp and make it sound like a TS9. I can't remember what Forum but I wrote a whole screed about this stuff back in 09 I think.

The guy that made the UA setup simply explained that you need a load that is the eqivilant of the Z at freq of resonance. (At least I think that's what was meant?) In most situations that seems to be around 30ish Ohms.

Anyway my guess is you might wonder at the wisdom of such claims,, Heck I did!!
So if it helps? I've been belting the living daylights out of a small 10 Watt PP Amp for 3 years and I want for little.
No issues,, I hardly even check it anymore.
Yes you can do totally dry direct recording if you so wish.

I did setout years back to build a King TUt styled powerscaling, Great idea but it finally dawned on me that it is not as easy as it fist looks and does have limitations.
The ReAmping concept allows one to add post power tube effects and additional tone shaping tricks.
As I already had a small Valve rig I figured it was just a simple matter to hang the above circuit off the end of the little Amp. (The advantage is you can take it to another Amp if needed.)

My Amp is a pair of 6GW8's running PP, K biased, no FB, HT is 260VDC. Somehow I think I will die before the Amp.

As I don't have a lot of money I can't justify spending big money on some of the gear that gets talked about on these forums so my second Amps are just SS power Amps but I have no trouble competing with brandname rigs,, winky.

As to soaking really big Amps?? Things may get a little more spooky I just don't have any experience with those.
but it makes sense to soak a little Amp and use the bigger Amps for reproducing an unaltered clean reproduction of the first amp which does the powerstage compression thing.
Phil.

I was thinking of using the circuit in a 50 Watt Tube head that I'm currently building, to replace the original line-out circuitry, and I was thinking to myself that surely, a 30Watt wire wound resistor would burn up if it was asked to dissipate 50Watts, I guess the solution, in my case, is to make a 30 Ohm/ 50 Watt resistor, then the Impedance would be correct, but the power-rating would be up-rated...

Or, maybe my understanding is flawed....

phatt · Post by **phatt** » 17 May 2011, 14:13

No I 'd say you've got the idea sorted.
Yes at 8-Ohms you pretty much need to double the wattage of the resistive load or else the R runs very hot.
With this idea you can use a lower wattage and it only gets warm.

Mine has 2 x 10Watts and you can still touch the load resistors after a half hour of playing full tilt.

You'd be luckey if my Amp pushed 10Watts,, probably closer to 7Watts.
To be on the safe side just use a 50~60 Watt load.
The trick is working out what value 10 Watt units will give you close to 30 Ohms.
120 R is a common Value (sold at Jaycar) so 5 x120R will give you 24 Ohm load.

If it runs really Hot and smells like mad then you'll need to recalc.

It's probably safe to run sandbox resistors hot but I don't see the point of running stuff stupidly hot if there is no need to.

You will have a ton of fun,, enjoy. Phil.

phatt · Post by **phatt** » 17 May 2011, 14:19

Whoops forgot

The ground lift is probably needed especially with monster gain stuff.
If both Amp are properly ground in the mains pin then you will need to lift ground to reduce hum issues.
Took me ages to catch on to that but,,,, I got there in the end.
Phil.

DrNomis · Post by **DrNomis** » 17 May 2011, 14:57

phatt wrote:Whoops forgot

The ground lift is probably needed especially with monster gain stuff.
If both Amp are properly ground in the mains pin then you will need to lift ground to reduce hum issues.
Took me ages to catch on to that but,,,, I got there in the end.
Phil.

Cheers for the Schematic, you saved me some design work, I would have had to wind a custom-made Inductor otherwise....

If it's anything to go by, I had the 8 Ohm/ 50Watt resistor hooked up to the amp head as a dummy-load, before I started the rebuild work, and I measured the signal level across the resistor, before the onset of clipping, and it was about 24 V Peak To Peak, the 8 Ohm/50 Watt resistor was getting pretty warm at the time....

bancika · Post by **bancika** » 17 May 2011, 17:50

You can spice it up with an isolation transformer to prevent ground loops. Weber has a tranny for that, I'm sure they are available elsewhere too

phatt · Post by **phatt** » 19 May 2011, 08:11

Hi bancika,
Thanks for the input,, Yep you certainly can use a transformer but you still may need to float the ground.
In your drawing that would mean lifting ground on the CT of the output side. (

I think?)

I did try it that way but in truth unless you have a good quality transformer (and they can get quite expensive) there may be little benifit over a simple resistive divider.
Phil.

dimefan90 · Post by **dimefan90** » 28 Oct 2011, 15:29

Sorry to bump the thread but this seemed better than creating a new one..

I was thinking of buying a Tube cube until i saw this thread and i was wondering if all it takes to build one is to wire the Impedance matching volume control up to two 1/4" sockets?

Also, is this the right part?

https://www.ebay.com/itm/AUDIOSOURCE-AE ... 4ab01248af

phatt · Post by **phatt** » 02 Nov 2011, 09:04

Hi Dime fan90,
Those look like 100volt line transformers and would not work without some mods.
Sorry I took so long

These posts slip under the radar quite often.
Phil.