Rupert Neve Designs - RNDI - DI Box inside photos

[Whoops]

Yes as it is, but if you combine the parts of the circuit and build it into external enclosure (not inside a guitar) and replace the transformer with DI tx (10:1 or so) and J4 with XLR (remove the battery and extra components) , and take the power from the XLR (that's from a console via a mic cable) it could be your proper DI box.

That is highly complicated to achieve something that the free project that's around here for a long time, the Bo Hansen DI, does quite well

 

[mhelin]

That is highly complicated to achieve something that the free project that's around here for a long time, the Bo Hansen DI, does quite well

Thought something like this, not very complicated either:

JFE150 (2N4393 was the FET on Jensen schematics, it should work but no idea on the optimal Idss for this circuit, JFE150 Idds range is closer to that of 2N4392) includes internal protection diodes and has two extra pins which should be connected to clamping nodes (+12V, gnd) not drawn here.

 

[svyet]

I actually have used one. I was running sound for a friend and he had one for his guitar. Next time he played I used my Bo Hansen with Lundahl 1538XL and he wanted to trade for it. I'm sure they both sounded very nice.

I will also prefer to finish my Bo Hansén DI boxes

...

Ps! I know how RNDI design is made because I helped RND in Texas to service their products here in Sweden for a couple of years before they got a dealer with their own service workshop.

It is with some pride to know that I had the same thoughts back in 1975 as Rupert when he made his DI-box 40 years later.

Have any of you, or anyone else here, had a chance to listen to and compare the RNDI/RNDI-S against a Bo Hansen with Lundahl 1538/1538XL?

I've been using a Countryman 85 for a few years and have no complaints, but I'm in need of a 2-channel DI now. I want to use this opportunity to cover some other uses and maybe give DIY a go. My sights were set on the RNDI-S (great reviews, excellent financing, and cost offset by private sale of the Countryman), but I do like the idea of a Bo Hansen just the same. It just depends on actual overall differences, including saturation/distortion/harmonic/compression characteristics, since I will put this to work in a few different ways. Need to keep my setup minimal, mobile, and flexible. If anyone can shed some light on those differences, however subtle, I would appreciate that.

For context, my desired use cases beyond instrument DI are processing line-level signals as follows:

- Having a balanced L/R output for my MixPre (non-10) and other devices
- Outboard analog saturation stage during tracking, driving the DI input for additional harmonics/compression, however subtle, when desired [MixPre preamp ch 1 > ch 1 routed to Stereo Out > DI > MixPre preamp ch 2]
- Passing individual mono and stereo line-level tracks and samples through, again driving the input for desired harmonics/compression, however subtle.
- Passing subgroups, busses, mix bus, and even masters at particular stages. Same reasons as above.

Additional question is: which of the two Lundahls (1538 and 1538XL) would be the most appropriate in covering all the ground I'm attempting to cover? Would the extra headroom and extended high frequency response of the XL work against me in any way? (e.g., unable to achieve desired saturation without lots of gain, or potential issues with source material that might contain digital aliasing however inaudible). I don’t want to over think and over prepare, but I don’t want to under think and under prepare.

Thank you kindly in advance.

 

[svyet]

Another possibility is to forgo the Lundahls and choose instead something from Mr. Hansen's list of transformers with more character and personality. Any suggestions @Bo Hansen ? Something comparable to the RNDI transformer, but most importantly a good all-rounder with some character. Doesn't need to be pristine necessarily, as I do want to take advantage of a transformer's saturation characteristics. But I also don't want to be needing to EQ a bunch of stuff out either.

I'm deferring to your expertise here if you can shed some light on your observations of the various transformers you've tried. Happy to offer more context to narrow things down. Happy to go with the 1538/1538XL unless you think it's worth trying other things. I'm reading yours and other's thoughts on various transformers over here in the meantime.

 

[svyet]

Posting this here since it may be useful information for others, like me, who didn't know:

Focusrite and the Lundahl LL1538 Transformer
Focusrite ISA Two

Turns out the LL1538 is the transformer that Rupert Neve chose for the classic Focusrite ISA pre (and Focusrite has put them in all ISA products since). So in that sense, an LL1538 (and LL1538XL?) can be considered a recognizable and more transparent "Neve" flavor in a very real and popular sense, but of course less "obvious" than the 1078 as the SOS article describes it.

So that gives me some more reference, and it would therefore seem the RNDI and Bo Hansen with LL1538 are likely in a similar sonic ballpark, since the RNDI is not being described as exaggerated, but rather clean and accurate but still "transformy" all the same.

Thoughts?

Really cool bit of history from the first article:

Lars re-imagined the way transformers were usually made, as Per notes. “I have no idea if Rupert Neve ever tested the LL1528 and eventually challenged Lars to improve it, or if the LL1538 was the first of our transformers Rupert Neve tested. As far as I know, already at that time Rupert Neve designed most the transformers in his circuit designs himself. Anyway, for some reason Lars redesigned the LL1528 from a 2+2 section design to a 3+3 section design [this refers to the winding configuration of the transformer]. Each coil now consisted of two low impedance primary sections and one high impedance secondary section. Between each section are Faraday shields. If by luck or by calculation it is impossible to say, but the new transformer, the LL1538, was a success."

 

[jokeramik]

for sure,
I personally don’t like SMD stuff, so now that I know it’s all SMD I will not buy one for myself.
It’s a feeling based on technical arguments, it’s a psychological thing when I see SMD I think it sounds bad and when I see Discreet with standard sized components I think it’s sounds good.
Psychological factors impact a lot on how you perceive the sound of gear, as the brand in the front panel also…

I will also prefer to finish my Bo Hansén DI boxes

SMD components don´t sound...these are not sound generators...)
Look at Neumann and Co. there are a lot of SMD components inside.
Look also at LINN Glasgow....)
The problem is that you must know how these components behave in the circuit.
Best regards!

 

[Ricardus]

If you build a Bo DI you will be happy. You might actually want to use the OEP transformer for your needs.

I have built 4 sets of these with 4 different transformers and for most normal daily usage I don't think too many people would be able to tell them apart.

 

[Philbo King]

With a pair of tweezers, I find that repairing SMD is faster and easier than thru-hole. Even building prototypes, it's faster, all solder from the top, no leads to cut...

Especially simpler if you have 2 soldering irons.

 

[svyet]

If you build a Bo DI you will be happy. You might actually want to use the OEP transformer for your needs.

I have built 4 sets of these with 4 different transformers and for most normal daily usage I don't think too many people would be able to tell them apart.

I appreciate the input, Ricardus. I can see why the OEP would serve my purposes just fine. In my limited experience, I'm wondering about Mr. Hansen's observations (and the spec sheet) that the "OEP have approx. 10 times higher distortion from 100 Hz and down" - what real would effect does that have? Should that be any cause for concern regarding a perceived and possibly exaggerated low frequency bump despite the flat frequency response under 100Hz? Any real world problems when driving the DI hotter, like not being able to drive it without low end problems arising before desired high end saturation? Or is the distortion low enough that it would simply come across as "warmth"? I see in the spec sheet that the low end frequency response is pretty flat up to 100Hz, increasing upwards by .2dB in the midrange, dipping down a little around 10k, then peaking around 30k (almost half a dB over the low end) before dropping off. Basically a very gentle tilt in favor of high end with some extra "air". I would think that a .4dB is audible. In any case, am I reading that right? Would appreciate some insight.

Also, I'm curious - outside of and including normal daily usage - of the 4 different sets you've built, which 2 would you keep and why?

 

[Ricardus]

I appreciate the input, Ricardus. I can see why the OEP would serve my purposes just fine. In my limited experience, I'm wondering about Mr. Hansen's observations (and the spec sheet) that the "OEP have approx. 10 times higher distortion from 100 Hz and down" - what real would effect does that have? Should that be any cause for concern regarding a perceived and possibly exaggerated low frequency bump despite the flat frequency response under 100Hz?

The low end distortion might give you that grunt you're looking for. That's actually why I recommended that traffo.

 

[svyet]

Thanks.

I've been reading more since I last posted, so bear with me as I think out loud and repeat stuff most of you have known for years. I just want to post my thought process to keep it in check with your feedback.

So, looking at the specs of the RNDI-S, I'm seeing similarities with the OEP (flat low end response, similar low end distortion, +/- 1 dB from 12Hz and up) though actual frequency response curve could be different..unless a majority of transformers have a similar response curve. On the RNDI-S, the only thing I can't see is the low end distortion at +20 dBu. They post figures for -20 dBu (0.9% THD @ 20Hz). Is that just marketing to pad the numbers and avoid showing anything over 1% (because for some people think all THD is bad)? Anyway, I assume that the OEP's 2.7% THD @ 20Hz (0.4% THD @ 50Hz) is nothing to worry about..but they use 0 dBm, and I'm not sure if that is also a marketing thing to pad the numbers.

The Lundahl LL1538XL specs come off as maybe too pristine for my application: 10 Hz - 80 kHz +/- 0.3 dB, 1% THD distortion @ 50Hz at +13 dBu. The LL1538 low end figure seems ever slightly more "realistic" in light of other transformers. The LL1578 - a "personality" option according to Mr. Hansen has a similar frequency response range to the OEP, and a little closer in low end distortion performance as well if I'm reading things right. That could actually be a good happy medium for me in terms of Lundahl offerings.

I don't want to live and die by spec sheets, but it does help me to start understanding things a bit better as I shop around.

 

[svyet]

By the way, my MixPre's stereo out has a 500 ohm output impedance and +7.8 dBu max output level.

I should have started there. Obviously that will affect how much transformer headroom I should avoid in order to comfortably push the trafo into saturation (and it seems in that case the LL1578 is still a good option), so that's easy to figure out. I can also understand general distortion characteristics based on the specs. However, the impedence figure and how that might influence distortion and frequency response (and headroom figures?) is a little harder for me to decipher since I'm not knowledgeable enough. OEP use 600 ohms as reference, Lundahl uses 50 and 200.

All that to say, how and to what extent should I be considering the output impedence and level of my MixPre and the Bo Hansen circuit when looking at transformer specs?

I'm happy to simply reach out to a few of these companies with my MixPre specs, Bo Hansen schematic, and ask for recommendations if necessary.

 

[My3gger]

Impedance and frequency response will be fine with OEP, i like Ricardo's suggestion for using it.
Lundahl LL1538 and Cinemag CMMI-5C (i had 7C at hand) will be cleaner, although you might prefer a bit of color from OEP costing a lot less than the other two options suggested by Bo Hansen. Posts #30, #32 and Bo's description of the circuit will help you understand it better.

 

[Newmarket]

for sure,
I personally don’t like SMD stuff, so now that I know it’s all SMD I will not buy one for myself.
It’s not a feeling based on technical arguments, it’s a psychological thing when I see SMD I think it sounds bad and when I see Discreet with standard sized components I think it’s sounds good.
Psychological factors impact a lot on how you perceive the sound of gear, as the brand in the front panel also…

I will also prefer to finish my Bo Hansén DI boxes

But you should be able to get over that tbh. Given that you realise it's a psychological effect. Like for like there are technical advantages to SMT. minimised lead inductance and unbroken 0V planes etc.

 

[Newmarket]

Yeah, but whan you pass 70 years of age and your eyesight is blurry and dim and you can no longer hold your hands steady it is not quite so easy.

Cheers

Ian

I get that and progressively more so. Used to be able to do 0603 okay. Not now But with good magnification it's good and often easier / quicker.

 

[svyet]

Thanks for the extra input.

Since the OEP A262A3E is well regarded here, and seems it could be similar to the RNDI behavior, I will go with that for a DIY build.

Considering the time to source and build - and I need this basically now - I thought this would be a good opportunity to get the RNDI-S risk-free anyway, post some inside pics here, source parts for DIY when I have time, then do some audio A/B for everyone's benefit. If the two are close enough, I can either sell the RNDI-S and keep the Bo Hansen box, or keep both and try a trafo with more (or less) personality for a different flavor. The OEP's are cheap enough that I can either simply gift them, keep them around as spares, or frankenstein a rack DI later on if I need more DI, and want to consolidate everything.

Could be another year or so before I do the OEP box, but I'll be sure to report back. Thanks again, everyone.

 

[svyet]

By the way, at the time of writing this, there are some decent deals on a used pair of RNDI's and one RNDI-S on Reverb if anyone is interested:

Rupert Neve Designs RNDI-S Stereo Active Transformer DI [DEMO] - $395.10 until Oct. 31. ($103.90 off retail)
Rupert Neve Designs RNDI Active Transformer Direct Box 2015 - Present - Black(Pair) - $420 ($178 off retail)

Might be good options for those interested enough and don't mind not having a warranty. The RNDI pair is the better value given the cost and the ability to sell one if you want, or use them separately in different locations for mono stuff. RNDI also has a speaker mode that can handle the "output of a 1000-watt solid-state power amplifier (92 Vrms or 266Vp-p)" whereas the RNDI-S cannot, if that's something you need. I can't speak for their ability to operate together as a stereo unit..I imagine the tolerances are tight enough, but I don't know to what extent wear and tear affects anything.

 

[svyet]

A few years ago I was looking for reviews of this unit, and it's amazing how much magic people assign to it because it says Neve on it. It basically ALWAYS won any shootouts, which were never done double blind.

maybe because it sounds pretty good…

It probably does, but it's not magic.

If the RND-5052 number on the RNDI transformer is any indication, it's possible that it's the same Neve-designed transformer used in the 5088 console preamp/eq modules (incidentally called model 5052). Either way, given the pedigree of the Neve name, the hype is not unfounded, and it's more likely than not to be a very intentionally and well thought-out transformer design. "Magic" is of course subjective. "Better" is also a matter of taste depending on desired outcome. In any case, I think it's fair to say the RNDI is good or even great, and the Neve history and pedigree helps its popularity.

For bass in particular, of all the most popular "professional" models including all-out bass preamps (REDDI, Avalon, Noble), the RNDI is also actually one of the more affordable options, and I would say even less hyped in popularity than the others - at least in some of my circles - simply for a lack of tubes and controls (gain, eq, etc.) if I had my guess. I always think of something like the Noble Bass DI in that regard, which in my opinion does live up to the hype as being incredible balanced, but it is definitely not cheap. For comparison however, I'll link a video below to hear the RNDI and Noble compared. With the Noble settings at flat, both sound similar enough that the extra cost as well as the added hassle of tubes seems much less attractive to me if I'm really just looking for a solid DI.

That being said, from all that you guys have said, the Bo Hansen with a comparable transformer can close that gap even more in terms of price and performance. Still, I think most people including professionals are either going to buy something - or pay someone to build something for them - and just get on with their lives without the risk of trial and error. Could be due to hype and name, could be for specific use case, could be both. In terms of buying, the Neve name and the price compared to most other popular offerings probably plays into some of the "magic" being attributed to it, but it can still be said it's a really good sounding DI. For myself, I would actually prefer to go the DIY route for all the right reasons, but time and convenience push me toward the RNDI until I can source everything and build something.

I'm actually interested in building an unbalanced line to balanced line box as well, so it will be nice to get all my ducks in a row first, buy and build everything, then probably sell off the RNDI for pretty much an even trade. Or, keep the RNDI and just build a line-to-line.

Cheers--

- - -

 

[Whoops]

Just to say I’m pretty confident that the RND designed transformer used in the RNDI is much better and has much higher speced performance than the OEP mentioned transformer.

Bear in mind OEP transformers are budget audio transformers, although some people like them because they say they “color” the sound, which I understand. And the “color” might be to the lower specs and limitations.

But saying this OEP and thr RND transformer are not similar spec wise, being the RND higher quality

 

[Ricardus]

If the RND-5052 number on the RNDI transformer is any indication, it's possible that it's the same Neve-designed transformer used in the 5088 console preamp/eq modules (incidentally called model 5052). Either way, given the pedigree of the Neve name, the hype is not unfounded, and it's more likely than not to be a very intentionally and well thought-out transformer design. "Magic" is of course subjective. "Better" is also a matter of taste depending on desired outcome. In any case, I think it's fair to say the RNDI is good or even great, and the Neve history and pedigree helps its popularity.

If the tests weren't done is SOME sort of blind fashion the outcomes are meaningless. EVERYONE will choose the Neve because we are humans with biases.