REDDI DI

[captainate]

I put the LM317 in backwards  ;D I'm damn surprised it worked at all! All fixed up now, and doesn't she sound purdy! I found an old power supply at the local recycling/resale store, stripped the insides, and (heavily) modified the enclosure. Add one brushed nickel drawer pull, and voila! Thanks to CJ for the output transformer and the schematic. This one goes to a friend, and my two-channel build is next!

http://imgur.com/a/G00bS

 

[mjrippe]

Nice compact build, captainate!  But your photos leave one question - what kind of knob did you use?  ;D

 

[MicDaddy]

Love the small form factor and the case looks nice @captainate! I was going to ask what case you used was before I saw the later photos, looks like something recycled!  \m/  8)

 

[captainate]

Nice compact build, captainate!  But your photos leave one question - what kind of knob did you use?  ;D

Brushed aluminum, small diameter. I couldn't find the right allen wrench for the set screw, so I installed it later! Too excited about the finished product to wait for the pics though  ;D

Love the small form factor and the case looks nice @captainate! I was going to ask what case you used was before I saw the later photos, looks like something recycled!  \m/  8)

Yes sir! I love the beauty of "found" enclosures, even if they're a total PITA to work with. I've put small circuits in prescription pill bottles, built stompboxes out of old amp switching pedals, and all sorts of recycled, reworked old gear. This power supply was an amazing find, not only because it was just big enough for the build, but because it was vented and aluminum. I haven't seen that too often, and I hope I can find more like it since this build was for a friend. My 2-channel is next!

 

[andyfromdenver]

finished my tube DI

came out really nice. kept it simple, and it is super quiet.
working on a nice coverplate and going to scrutinize the bias.
thanks a million to CJ and the OP and the person who traced and drew the scheme.

if interested, I took a ton of pics and was going to do a thread. should it go in preamp, with it's modest little gain  : ?

also, since the triodes were parallel, i left the internal screen disconnected, and don't hear a difference. also also, you can see i nixed the dc heaters with no audible penalty, i used a balance pot, but i think even that can be fixed resistors for further simplification.

i carefully placed the transformers to null them using headphones on the OT, this is key for the new guys.

keep on rocking and stuff.

 

[CJ]

nice job, glad you like it!

 

[andyfromdenver]

Thanks CJ  
I'm still flabbergasted by the beyond quality packing.  You took shipping/ packing to the next level.

I think I am going to tempt fate and build #2 in an even smaller enclosure and put the PT outside...

 

[captainate]

Nice build, Andy!

I've got two more of CJ's transformers just waiting to be strung up, but I've had a thought: what would happen if we added some tone controls to the end of this circuit... maybe another gain stage to counter insertion loss? I'm using this DI for bass almost exclusively, and would love to have a three-band pultec-style passive EQ built in. Wide low shelf inductor-based boost/cut, sweepable mid, hi shelf around 8k. Doable?

Unfortunately, I'm still learning my basics when it comes to electronic design, but I'm really good at building things.

 

[andyfromdenver]

Thanks Nathan!  I just finally logged in to see your super tight build; super tight!  

I have a few more of Cjs transformers too; two are promised already which will be stock w/ added locut (lower cathode cap) and grnd lift and phase flip.

For the last one, I am drawing a scheme for one with tone controls. Nothing as fancy as pultec stuff. I was emailing w/ CJ, cause at first i thought maybe adding a switchable drive stage, but I have decided to nix that.

The current drawing is: input -> 1k grid stopper, 470k grid grnd ref -> another 6n1p wired as a DC coupled cathode follower, biased for half the max gain maybe? (there are some good example circuits in Merlin Blencowes Designing HiFi tube preamps) -> treb mid bass 5f6a bassman style -> then continue on to the original reddi circuit.  I really like the low noise of the 6n1p.  I think using that as the dccf instead of a higher gain 12a_7 will maintain the awesome low noise studio friendly usability.  So I need to experiment with that added stage and make sure it doesn't distort, cause there will be no volume control, just the same end lvl attenuation. 
I am using the Hammond 269ex, in US on the 125v primary tap, this is important cause the circuit is using only a small percentage of the current handling which could make the heater voltage too high (no dc heaters). On our 122vAC nominal wall voltage I am getting 6.7vac on the heaters which is acceptable. 

take care all!

 

[andyfromdenver]

oh yeah, here's the top to my lil baby
the FatBox *makes the devil horns gesture*

 

[captainate]

Looks great, Andy! I was thinking of the Pultec-style circuit because of how great that EQ can sound on bass, and hesitant to go the "guitar amp" direction simply due to the amount of coloration with neutral settings. If my understanding is correct, those circuits tend to muck up the signal a lot more than most "hi-fi" or "studio" gear.

 

[andyfromdenver]

Looks great, Andy! I was thinking of the Pultec-style circuit because of how great that EQ can sound on bass, and hesitant to go the "guitar amp" direction simply due to the amount of coloration with neutral settings. If my understanding is correct, those circuits tend to muck up the signal a lot more than most "hi-fi" or "studio" gear.

Thank you Nathan!
I haven't investigated the pultec eq much, i'm sure it would be awesome.
the dc coupled cathode follower to treb mid bass guit tonestack doesn't suck out as much mid, as say a blackface fender tonestack.
I'm making two more like this picture, for friends, then i can try and experiment with a tone stack version. going to look at the pultec schematic. I am planning to make a cardboard panel with some controls and a tube on it and jack into the power and signal and mess around. sober light of day stuff . There is also a circuit in the RDH4 that has always intrigued me, "synthetic bass". I believe it boosts the harmonics?  need to research. 
*edit in: the synthetic bass is + feedback from cathode of pwr tube (in this case 6N1P) to earlier stage, (w/ attenuation of bass freq, on a switch)  could be an interesting option if it had some pleasant distortion.

perhaps the uber bass box will spring from this forum!

 

[funk1980]

I've been following this thread for quite some time now. Good stuff!! And learning as I go. But I fail miserably when it comes to transformer theory, so I'm more or less bound to of-the-shelve item. But I'd really like to build one of these myself. I like toroids. For their reduced weight, ease of mounting and overall look. Does someone know of such an item? I came across this one:
http://www.amplimo.nl/images/downloads/ds%20vdv/5006see.pdf
Would this work? Inductance, DC tolerance, frequency response and primary impedance all seem ok.

 

[andyfromdenver]

unfortunately that is a no-go, funk1980.  That transformer is suited for a guit speaker type load.

 

[funk1980]

unfortunately that is a no-go, funk1980.  That transformer is suited for a guit speaker type load.

Thanks! But damn . I figured a lower output impedance on the secondary wouldn't be an issue. So a 600ohm secondary is mandatory? Does anyone know of a suited of the shelf toroid?

 

[andyfromdenver]

Thanks! But damn . I figured a lower output impedance on the secondary wouldn't be an issue. So a 600ohm secondary is mandatory? Does anyone know of a suited of the shelf toroid?

the turns ratios are going to be very different between that and the original/CJs

sorry if this has been proposed before group, but how does this measure up?
http://www.sowter.co.uk/specs/9560.htm

 

[kosi]

Thanks! But damn . I figured a lower output impedance on the secondary wouldn't be an issue. So a 600ohm secondary is mandatory? Does anyone know of a suited of the shelf toroid?

Why don't you  buy one from CJ ?

 

[emrr]

Thanks! But damn . I figured a lower output impedance on the secondary wouldn't be an issue. So a 600ohm secondary is mandatory?

It's not really an 'issue' (nor is 600 mandatory), outside of the fact that you have more gain loss through that step-down ratio.  You could use a speaker type L pad with it.  The 'issue' is that this is a bass DI in most peoples minds, and this transformer does not have suitable low frequency response to satisfy the promise of this circuit. 

 

[funk1980]

Why don't you  buy one from CJ ?

Well, shipping (cost) is one thing . So I'd prefer one from a local dealer, but since toroid is out of the window, I'll contact CJ for some more info!

 

[emi2345]

I'm interested to know what are the advantages of this DC-coupled transformer design over much more economical capacitor-coupled one such as the attached?