[dandeurloo]

I used one once and thought it sounded great.  Does any one have one or know what the design is?  Is based on something else like most Tube circuits seem to be.  I'm just curious as it sounded really good and I didn't have time to pop the top and see what was in side.

[Hank Dussen]

I've recently used one and really liked it as well.
There's some info and an inside picture here at Gearslutz: http://www.gearslutz.com/board/high-end/414987-do-i-need-600-direct-box-3.html
Apparently it's got something to do with the preamp of an Ampeg B15...
It has nothing to do with the B15!

and the manual... http://adesignsaudio.com/index_htm_files/reddimanual1_5x.pdf

[dandeurloo]

Interesting.  I love the B15 as well.  Makes sense that they are some how related. 

[joro]

I have one. I opened it up once and traced the circuit. It's really simple. (power supply, 6N1P tube, transformer, a few resistors and capacitors) Unfortunately, I don't have any schematics or images I can share at the moment. I know you are asking because you don't have one, but, if you can get your hands on one, I would suggest opening it up and checking it out. Would be easy to figure out. Sorry this isn't much help.

[abbey road d enfer]

There's some info and an inside picture here at Gearslutz: http://www.gearslutz.com/board/high-end/414987-do-i-need-600-direct-box-3.html
Apparently it's got something to do with the preamp of an Ampeg B15...

That's the type of idiocy you find on GS. The only thing in common with a B15 is the input jack. All the rest is different: not the same tube, SE output instead of push-pull...the list is too long. It's a nice build though, no doubt it should perform well.

[Biasrocks]

There's some info and an inside picture here at Gearslutz: http://www.gearslutz.com/board/high-end/414987-do-i-need-600-direct-box-3.html
Apparently it's got something to do with the preamp of an Ampeg B15...

That's the type of idiocy you find on GS.

Now, watch as the picture complete's itself.

This will be repeated over and over until it becomes the accepted truth.

Did something similar once with the AKG Solidtube over on GS. Althought the info I offered worked great in my application, it got repeated ad nauseum by internet slugs until it became 'the thing to do'.

It always starts with "I heard that...."

Interesting social experiment.

Mark

[Hank Dussen]

I will never quote the GearSlutz again.
I will never quote the GearSlutz again.
I will never quote the GearSlutz again.
I will never quote the GearSlutz again.
I will never quote the GearSlutz again.
I will never quote the GearSlutz again.
I will never quote the GearSlutz again.
I will never quote the GearSlutz again.
I will never quote the GearSlutz again.
I will never quote the GearSlutz again.
...

[dandeurloo]

There's some info and an inside picture here at Gearslutz: http://www.gearslutz.com/board/high-end/414987-do-i-need-600-direct-box-3.html
Apparently it's got something to do with the preamp of an Ampeg B15...

That's the type of idiocy you find on GS. The only thing in common with a B15 is the input jack. All the rest is different: not the same tube, SE output instead of push-pull...the list is too long. It's a nice build though, no doubt it should perform well.

Well that is why I asked here because it's really the only place I trust. 

Any more info would be great.  They do have a very cool sound.  Currently I have a number of solid state DI's but would love to try and dig up some ideas for a nice sounding Tube DI.  Not that I am looking to copy it.  I'm more curious if it was a copy of another design just tweaked to work as a DI.  Seems that many of the tube circuits share a number of the same design ideas just tweaked here and there. 


Hank,  haha.  No worries. 

[Biasrocks]

We could design our own 6N1P based pre.

Here are some design considerations which match the unit in question.

1M ohm input impedance
600 ohm output impedance, transformer coupled, +22dbu output.
16db in hand gain

Tube heater draws about 600 mA, Cathode current 40ma.

6N1P Datasheet

http://www.radiotechnika.hu/images/6N1P.pdf

A single ended line amp



Here's a basic line amp w/20-25db of gain

http://www.arrakis.es/~igapop/russianotes.htm#6N1P%20/6N2P%20How%20to%20use%20them

Tube guru's unite.

Regards,
Mark

[abbey road d enfer]

We could design our own 6N1P based pre.

Here are some design considerations which match the unit in question.

1M ohm input impedance
600 ohm output impedance, transformer coupled, +22dbu output.
16db in hand gain

Are you sure you want that much gain? An electric (passive) guitar delivers about 200mV (-12dBu), resulting in +4dBu output. It's ok if you use a line input, but way too much for a mic input. An active bass would overload it. Most cases, line inputs are not very convenient, do not have enough gain control range compared to mic inputs. In the same consideration, do you need +22dBu output? makes for an unnecessary expensive output xfmr.

6N1P Datasheet...   ...Here's a basic line amp w/20-25db of gain

The tube is only a fraction of the picture. Then you have to choose a topology, single section, two sections in parallels, two sections in cascade (probably with cath-follower output), plate voltage...

[Biasrocks]

Are you sure you want that much gain? An electric (passive) guitar delivers about 200mV (-12dBu), resulting in +4dBu output. It's ok if you use a line input, but way too much for a mic input. An active bass would overload it. Most cases, line inputs are not very convenient, do not have enough gain control range compared to mic inputs. In the same consideration, do you need +22dBu output? makes for an unnecessary expensive output xfmr.

As I understand it, the unit in question is designed to put out line level, not mic level.

So, if we're looking to get something similar that would be the goal.

The tube is only a fraction of the picture. Then you have to choose a topology, single section, two sections in parallels, two sections in cascade (probably with cath-follower output), plate voltage...

Agreed, I'm a babe in the woods as far as tube design goes so your wisdom is welcomed.

I think it was stated earlier that it was a single ended design.

I've posted a rough schematic of what might work, it looks like it has the correct input impedance, is single ended and uses a transformer output. We would need to flesh it out if it's agreed that it's a good starting point.

Regards,
Mark

[abbey road d enfer]

I've posted a rough schematic of what might work, it looks like it has the correct input impedance, is single ended and uses a transformer output.

Apart the fact that a model 145R would be more suitable in terms of ratio, it would work somewhat. You would have to do something in order to regulate the frequency response; simplest way is to load the secondary with a resistor, or better with a Zobel. It wouldn't be super clean, but who cares?

[Travis1000]

Not to side track the design of a sweet tube DI, or the much needed bashing of Gearslutz, but the purveyors of the B15 REDDI myth are A Designs themselves. From their website:

 "Designed and built by former career studio bassists, the REDDI has been hailed by engineer and bassist alike as the best-sounding DI around. Inspired by the glorious sound of the Ampeg B-15 tube bass amp, its 6N1-P tube-driven amplifier feeds signal directly into a hefty custom output transformer, which is key to providing a harmonically rich tone. Its wide-bandwidth design from 20Hz to 60kHz reduces in-band phase shift, which results in greater detail and realism in the audible spectrum."

http://www.adesignsaudio.com/reddi-all-tube-direct-box.htm

Carry on...

[abbey road d enfer]

Pfffff!

[pacemaker]

"Inspired by the glorious sound of the Ampeg B-15 tube bass amp"
they said inspired by the sound,
but not the schematics of the B15
;-)

[alexc]

Interesting project - should be doable.

I'd have to do the calcs for a SE parallel'd 6N1P which is Rp 4400/2 = 2200ohms plate.

So maybe a 8K to 10K SE traffo primary would suit. I like the Carnhill 9600:600 gapped. Maybe some Edcor as well.

With a bias of maybe 3Vdc or so to allow a max input of 5Vpp or so.
Less if you want more crunch and less clean headroom.

Plenty for strong passive pups which I find do 1Vpp easy and 2Vpp on transients.
Actives even more - like 2Vpp average and 4Vpp on transients
Particularly on bass.

So sure - could be very interesting.

I've used the 6N1P parallel'd in parafeed line amps and have been very happy with the result.
I use this in a number of units. Started with an AU7 but felt I liked the sound of better with the 6N1P

My new builds are using 6N1P SE with the Carnhill to mix it up a little.

I do prefer to have an additional input stage to allow driving a volume pot and maybe a little nfb.
But simpler is good too!

Good luck with it and hope to see the design develop.

Disclaimer : I don't know anything about a B-15 sound!

[bernbrue]

Hi,



regards
Bernd

[abbey road d enfer]

I would put some kind of gain control, an input pot perhaps.
Or an output pot, like the REDDI.

[dandeurloo]

yeah, I guess the question is how complicated to make it.  I guess it would be nice to have it be mic pre as well as a DI since it is all basically there.  But I would be happy with just a DIY. 

I like the idea of the output pot however.

[bernbrue]

4 resistor, 2 caps, a single tube and a pot. You should not even think of a pcb. Veroboard for the PSU and you are done.
regards
Bernd

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