Bo Hansen DI layout

[JohnRoberts]

Delete my account …I’m sure an trying to

done...

JR

 

[Rowboat]

"And I would want one to WHOM EVER made this"

= as long as you get what you want, you don't care who violates intellectual property and design copyright.

 

[JohnRoberts]

= as long as you get what you want, you don't care who violates intellectual property and design copyright.

Beating a dead horse?

That member has already been banned as per his own request.

JR

 

[xploited]

I finished my bo DI! tested, and working great. I tried a new way (to me) for the faceplates.. used a pcb service and designed it like a pcb, with silkscreen for the lettering. It worked out pretty great! My most professional looking prject yet, and WAY WAY WAY cheaper then frontpanelexpress or the likes.

Thanks for the kick ass project!

 

[klem]

What transistor parameters are important, especially for stereo matching / 2 channel builds?

Of course, my goal, as far as the transistor parameters can confer, is low noise, good headroom, and very similar output levels. I’ve searched the thread and Bo’s site with various terms, but found limited info on specific ranges / values to realize the above. I also still have much to learn about the parameters of transistors and the implications of the values so maybe I either overlooked something previously posted, or maybe the parameters are not that important for this circuit? I have a Peak Atlas DCA75 and can measure the following values:

hFE
Vbe
VceSat
IcLeak
Vgs(off)
Vgs(on)
gfs
Idss
Rds(on)

Of what I've found on the topic:

Above all, of course, I see repeated emphasis on using a known quality brand from an approved distributor to avoid the knockoffs. That's a given for me.

hFE: I see Bo states hFE should be “at least medium hFE” earlier in thread, I think also said it wasn’t critical but above 200 as minimum.

As an aside, if there's a good overview on the above values geared at a 101/102 level, I welcome the recommendation. I also have a project I'm trying to get these ready for in close to a week, so can't go too deep before making a choice in which ones I solder in...

Thanks in advance,

 

[Whoops]

What transistor parameters are important, especially for stereo matching / 2 channel builds?

As for transistors specifically, I think there's not much you can do besides matching them for HFE measured at the same current the transistors will draw in the circuit.

But if you want to match 2 units then the transistors might not be your first reason for concern,
capacitors can have more than +/- 20% tolerance, so you would need to match capacitors first.

And then how about the transformers?
Transformers will always have a +/- tolerance also, and I really don't see how could someone match transformers without buying a lot of them to measure and select, which would be quite expensive for just a simple DI box build

 

[klem]

What transistor parameters are important

Thanks in advance,

 

[Frdfrode]

Hi,

i've made one too with a Beyerdynamic transformer (5:1). It sounds great. I'm very happy of it!

But, i had an issue when i used it before a Fuzz Face (or a Tonebender). The sound at the output became fizzy. It's because the fuzz overload the source.
I solved the problem by placing an external buffer before the DI, and a "pickup simulator" after the "Through" of the DI.

Hi, I have some beyer dynamic transformer I maybe could use for this project. What are the specs on the one you used?

 

[klem]

HUM in unique (AFAIK) config of the boards. Hopefully if I give a decent overview of how I have this wired and grounded, someone could help me fix this?

I've built a pair of the DIs in a single chassis with an input switch to run the unit as dual mono or parallel. For parallel, input 1 feeds both board 1 and board 2, so I have 2 amp outs and 2 XLRs of the same signal. In dual mode each board works fine with a low noise floor. But in parallel, the amp output of channel 2 has a moderately loud hum rendering the signal unusable. This is not present on channel 1's amp out. I haven't bothered testing the XLR outs yet since this is a show-stopper. Components values are all as specified with the exception of changing 1G R to 2.2G R on both boards

The switch is implemented as follows:
Input 1 jack's tip is wired to both board 1 and a SPST, which also receives input 2 jack tip on other lateral solder lug, and the middle lug of course goes to board 2 input. The grounds of each of the 4 TS jacks stay with their respective 'original' boards. The chassis wire for each board is connected to the case at a standoff with the coating of case scratched to ensure good continuity (verified). Pin 1 of XLR goes to both the board and to the XLR chassis tab (no paint scratched off around the XLR screws).

Some specific and broader questions:
- For the TS jacks, I am using Neutrik NMJ4HC-S, which I saw recommended in the thread, but also see Bo recommends Cliff CL1160A. Both appear to be 'switched', is there a difference otherwise between them? (Mouser doesn't sell the Cliff, but I can get them through DigiKey if this may be the suspected culprit.)
- I also stripped the wire long enough so each each wire reaches both solder lugs for tip and sleeve, respectively. Does this defeat the switching or shouldn't be done regardless?
- Any other ideas why I'd get a hum in this admittedly non-traditional use-case? Tests I should run with DMM?

Here's a pic, but regretfully since I used black wire for the audio signal, it's a bit hard to see the routing against the black faceplate, hence the detailed description above. Yes, the wires are a little longer than necessary because I plan to put this into a reorganized faceplate once I have the time to get the layout right (failing at FPD). That said, since the boards work fine in 'dual' mode, I'm doubtful the extra length of the wires has much detrimental effect. Just trying to cover my bases here with details and head off replies like the one above about transistor parameters.

Thanks,

 

[MidnightArrakis]

I plan to put this into a reorganized faceplate once I have the time to get the layout right (failing at FPD).

>> Should you send me your -- FPD -- file, I can send back to you:

A) A type of CAD-file (called either a "STEP" or "STP") file that you could then send to most any sheet-metal shop and have them fabricate a new panel for you instead, and.....

B) A "Mechanical Detail Fabrication Drawing" as shown below that -- ANY -- basic sheet-metal shop, or a friend of yours who has metal-working tools, would be able to use to create a front-panel of:

(NOTE: The front-panel shown in this drawing is a "GroupDIY 500-Series LVL-LOK" front-panel:



/

 

[guitar4444]

Wondering id anyone is watching this thread that might have had any experience with the Lundahl 1550 for use in the DI? I bought some quite a few years back with a view to using them in some tube mic pres and Di's. I would probably use them in configuration C shown in the spec sheet (attached) so it would be 4:1. I know it will work but i don't really know enough about it to know how well it would work in this circuit. Any help would be greatly appreciated.

 

[Bo Hansen]

guitar4444,

I have measured many Lundahl transformers but not this particular one, so I don't know how it behaves in my DI-box circuit.

The LL1550 has a large core and can withstand about twice the level in the low register compared to the LL1538, and impedance/ratio configuration "C" according to the datasheet is probably the best option.

If you have access to it, try it, but I think it's unnecessary to buy one to take a chance. The LL1538/LL1538XL is hard to beat in this circuit.

--Bo

 

[Bo Hansen]

HUM in unique (AFAIK) config of the boards. Hopefully if I give a decent overview of how I have this wired and grounded, someone could help me fix this?

I've built a pair of the DIs in a single chassis with an input switch to run the unit as dual mono or parallel. For parallel, input 1 feeds both board 1 and board 2, so I have 2 amp outs and 2 XLRs of the same signal. In dual mode each board works fine with a low noise floor. But in parallel, the amp output of channel 2 has a moderately loud hum rendering the signal unusable. This is not present on channel 1's amp out. I haven't bothered testing the XLR outs yet since this is a show-stopper. Components values are all as specified with the exception of changing 1G R to 2.2G R on both boards

The switch is implemented as follows:
Input 1 jack's tip is wired to both board 1 and a SPST, which also receives input 2 jack tip on other lateral solder lug, and the middle lug of course goes to board 2 input. The grounds of each of the 4 TS jacks stay with their respective 'original' boards. The chassis wire for each board is connected to the case at a standoff with the coating of case scratched to ensure good continuity (verified). Pin 1 of XLR goes to both the board and to the XLR chassis tab (no paint scratched off around the XLR screws).

Some specific and broader questions:
- For the TS jacks, I am using Neutrik NMJ4HC-S, which I saw recommended in the thread, but also see Bo recommends Cliff CL1160A. Both appear to be 'switched', is there a difference otherwise between them? (Mouser doesn't sell the Cliff, but I can get them through DigiKey if this may be the suspected culprit.)
- I also stripped the wire long enough so each each wire reaches both solder lugs for tip and sleeve, respectively. Does this defeat the switching or shouldn't be done regardless?
- Any other ideas why I'd get a hum in this admittedly non-traditional use-case? Tests I should run with DMM?

Here's a pic, but regretfully since I used black wire for the audio signal, it's a bit hard to see the routing against the black faceplate, hence the detailed description above. Yes, the wires are a little longer than necessary because I plan to put this into a reorganized faceplate once I have the time to get the layout right (failing at FPD). That said, since the boards work fine in 'dual' mode, I'm doubtful the extra length of the wires has much detrimental effect. Just trying to cover my bases here with details and head off replies like the one above about transistor parameters.

Thanks,

Klem,

Start by showing good pictures of how you have connected these two DI-box cards together with all connectors and switches.

This is a good start for us helpers here on the forum to check if you have done the right thing and not misunderstood anything, and also show the sketch you got from me, when you contacted me privately and got help a number of times.

Also try to describe more clearly how you use this double DI-box when the hum problem occurs.

You describe that everything is completely ok when you try both DI-box channels separately, as if they were two separate units, i.e. with the switch in dual mode and with only a guitar/bass connected to an input jack and out on the XLR output to a phantom powered microphone input on a preamp or mixer.
And then you shift over the input and output cables to the other channel, and you get the same ok result.

But how do you test with the switch in "parallel mode"

Do you only have an instrument connected to input-1, and a phantom powered microphone input on a separate preamp or mixer units to each XLR output, or are there two inputs on the same preamp or mixer unit.
Do you also have something connected to the two "amp output" jacks, for example to two guitar/bass amps.

Why I ask all this, is to find out that you have not run into a "ground loop" with all the external connection with signal ground and mains power ground between preamps/mixers and guitar/bass amps.

Regarding your previous question about matched components.

This DI-box circuit is just an impedance converter without amplification "no gain no pain" so there are no components that need to be closely matched in this case.
Resistor is perfectly ok with normal 5% carbon film resistors, except for the two 6.8k they must be 1% metal film.
Capacitors regular 10% polyester, and electrolytes regular 20% types.
Transistors and diodes do not need to be selected/matched, but they must be known brand types and not "no brand China junk"
Just use the same brand and type on all your DI cards, for example ON-semi BC550C and 560C.

If you stick to the above components and one of our three recommended transformers, you won't notice any level or quality difference between two or more DI boxes.
BUT the condition is that the XLR outputs sees exactly the same load when comparing in terms of impedance and capacitance.

PS! I saw you wrote that you changed the 1 Mohm resistors to 2.2 GR/Gohm, but I hope you mean 2.2 Mohm.

--Bo

 

[klem]

Klem,

Start by showing good pictures of how you have connected these two DI-box cards together with all connectors and switches.

This is a good start for us helpers here on the forum to check if you have done the right thing and not misunderstood anything, and also show the sketch you got from me, when you contacted me privately and got help a number of times.

sketch


faceplate


boards overview

Also try to describe more clearly how you use this double DI-box when the hum problem occurs.

You describe that everything is completely ok when you try both DI-box channels separately, as if they were two separate units, i.e. with the switch in dual mode and with only a guitar/bass connected to an input jack and out on the XLR output to a phantom powered microphone input on a preamp or mixer.
And then you shift over the input and output cables to the other channel, and you get the same ok result.

But how do you test with the switch in "parallel mode"

Before getting to parallel mode hum, I should give a bit more info just to ensure wiring is as it should be. As mentioned in the previous post, the signal wires and chassis are black, which makes tracing wires in any photo somewhat difficult. Lesson learned for future builds. Therefore, in addition to photos of build, I've highlighted the signal wires in the following colors to accompany a written description.



Top-right TS switching jack (top left in faceplate pic, of course): Input to board A (right side), blue lines: A1A, A1B. A1A goes to PCB A Input. A1B goes to the SPST for dual / parallel function.

Top-left TS switching jack (top left in faceplate pic, of course): Input to board B (left side), orange lines: B1 goes to SPST switch, not the PCB, and the middle lug of SPST goes to PCB B Input

Bottom TS switching jacks are amp outs, both signal and ground wired directly to their respective boards (no switch or shared ground).

XLRs and LEDs are easy to see as twisted pairs.

A note on grounds wiring, (as I suspect the switching jacks and grounds are at the heart of the problem):

Each board is connected to the chassis via the "chassis" PCB point, a wire/lug to underneath a standoff, which has the coating scraped away for good contact, good continuity verified from each PCB to chassis

All TS switching jack grounds run directly from to respective grounds on PCB (input and amp out). The dual / parallel switch does not involve grounds.

I realize these pics are not ideal, so if there's a better way to photograph this, please suggest.

When SPST switch is in 'dual', each board works fine when given its respective input and output, akin to a dual mono mode of an outboard compressor

Parallel mode:
When SPST switch is in 'parallel', board A with input and output, still no hum on board A's amp out or XLR.



BUT when SPST switch is in 'parallel', board A input from guitar and board B amp output, hum on board B's amp out and XLR signal as well.
<edit> 5 pics per post it seems, TBC next post...

 

[klem]

<<Something strange with board, can't insert thumbnails at all now, despite relaunching browser and logging out/in of GDIY. I'll try to re-edit the post tomorrow, for now I've referenced pics attached below where they should be in thumbnail position.>>

BUT when SPST switch is in 'parallel', board A input from guitar and board B amp output, hum on board B's amp out and XLR signal as well.
<Parallel B hum.jpg>

Do you only have an instrument connected to input-1, and a phantom powered microphone input on a separate preamp or mixer units to each XLR output, or are there two inputs on the same preamp or mixer unit.

48V for each PCB always came from the same unit when testing. Hum was present whether PCBs received power from a USB-C powered 2 channel M-Audio soundcard, or a Hamptone JFET 2 channel stand-alone preamp.

Do you also have something connected to the two "amp output" jacks, for example to two guitar/bass amps.

I do not have 2 amps at this time to test, but I can borrow one if that would be helpful for testing. That said, in addition the primary use case described at top of this (second) post, <Parallel B hum>, I've tried inserting a TS cord into Input B, and either leaving it dangling in the air or shorting the input to ground. In either case, the hum on board B amp out is unaffected. Here are pics of these additional configs:

<Parallel B-I shorted hum>
<Parallel A-AO shorted hum>

Why I ask all this, is to find out that you have not run into a "ground loop" with all the external connection with signal ground and mains power ground between preamps/mixers and guitar/bass amps.

Regarding your previous question about matched components.

This DI-box circuit is just an impedance converter without amplification "no gain no pain" so there are no components that need to be closely matched in this case.
Resistor is perfectly ok with normal 5% carbon film resistors, except for the two 6.8k they must be 1% metal film.
Capacitors regular 10% polyester, and electrolytes regular 20% types.
Transistors and diodes do not need to be selected/matched, but they must be known brand types and not "no brand China junk"
Just use the same brand and type on all your DI cards, for example ON-semi BC550C and 560C.

If you stick to the above components and one of our three recommended transformers, you won't notice any level or quality difference between two or more DI boxes.
BUT the condition is that the XLR outputs sees exactly the same load when comparing in terms of impedance and capacitance.

PS! I saw you wrote that you changed the 1 Mohm resistors to 2.2 GR/Gohm, but I hope you mean 2.2 Mohm.

--Bo

The explanation as to why transistor specs / tolerances do not matter makes perfect sense, thank you. It is very helpful (for me) to remember there is no amplification.

Re: R values, yes, that was a typo, good catch. The R on these boards measure 2.172M (measured in circuit).

 

[MidnightArrakis]

/

 

[Bo Hansen]

<<Something strange with board, can't insert thumbnails at all now, despite relaunching browser and logging out/in of GDIY. I'll try to re-edit the post tomorrow, for now I've referenced pics attached below where they should be in thumbnail position.>>

BUT when SPST switch is in 'parallel', board A input from guitar and board B amp output, hum on board B's amp out and XLR signal as well.
<Parallel B hum.jpg>


48V for each PCB always came from the same unit when testing. Hum was present whether PCBs received power from a USB-C powered 2 channel M-Audio soundcard, or a Hamptone JFET 2 channel stand-alone preamp.


I do not have 2 amps at this time to test, but I can borrow one if that would be helpful for testing. That said, in addition the primary use case described at top of this (second) post, <Parallel B hum>, I've tried inserting a TS cord into Input B, and either leaving it dangling in the air or shorting the input to ground. In either case, the hum on board B amp out is unaffected. Here are pics of these additional configs:

<Parallel B-I shorted hum>
<Parallel A-AO shorted hum>



The explanation as to why transistor specs / tolerances do not matter makes perfect sense, thank you. It is very helpful (for me) to remember there is no amplification.

Re: R values, yes, that was a typo, good catch. The R on these boards measure 2.172M (measured in circuit).

Klem,

First of all....

When making changes and modifications to a proven and 100% working device, there will always be some form of compromise and deviations from the original specifications, "there is no free lunch"

In order to be sure that a modification I propose will work perfectly, it must first be test built and tested in real conditions, which I normally do not have time or opportunities to do.
That's why I've always hesitated when people want to add extra features to my well-tested and working design, I always regret it afterwards when problems arise.

Ok, I have a few more questions in this case, before I give you a suggestion for a change that might be a solution to your "hum" problem.

When you say "hum" do you mean a dull bass-like sound, or more like a brighter bi-buzzing sound, or some other type of noise.

Regarding the dual/parallel switch.
You call it "SPST" (Single-Pole-Single-Throw) but I think you mean "SPDT" (Single-Pole Dual-Throw) as I suggested in this case, it is hard to see in the picture what type you have used.

--Bo

 

[klem]

Yes, SPST should be SPDT. Specifically I used NKK M2012S3S1W01.

Sound, seems best / most detailed to post quick clips (320k mp3s).

Pic and short description of signal chain for each recording and reference pic

Bass gtr -> Input A, switch on 'parallel', amp output A, both boards receiving P48, Samar MG33 mic near amp -> m audio preamp and A/D. Nice and quiet.


View attachment amp out A - parallel - no hum - mg33.mp3


Parallel B hum.jpg - can't insert no matter jpg, jpeg, gif.... but attached. Note only difference is amp output cord changed from jack A to B.
Bass gtr -> Input A, switch on 'parallel', amp output B, both boards receiving P48, Samar MG33 mic near amp -> m audio preamp and A/D. Hum.
View attachment amp out B - parallel - hum - mg33.mp3


Bass gtr -> Input A, switch on 'parallel', amp out A to amp, XLR output A recorded, no hum
View attachment XLR A no hum parallel.mp3


Bass gtr -> Input A, switch on 'parallel', amp out A to amp, XLR output B recorded, hum
View attachment XLR B hum parallel.mp3

In short (pun semi-intended), the hum happens on channel 2 when in parallel mode, and happens both on the 'amp out' and XLR out.

Thank you for your time and efforts in helping the entire community hopefully gain a new configuration / function of this great device.

 

[Bo Hansen]

Yes, SPST should be SPDT. Specifically I used NKK M2012S3S1W01.

Sound, seems best / most detailed to post quick clips (320k mp3s).

Pic and short description of signal chain for each recording and reference pic

Bass gtr -> Input A, switch on 'parallel', amp output A, both boards receiving P48, Samar MG33 mic near amp -> m audio preamp and A/D. Nice and quiet.
View attachment 128646

View attachment 128641


Parallel B hum.jpg - can't insert no matter jpg, jpeg, gif.... but attached. Note only difference is amp output cord changed from jack A to B.
Bass gtr -> Input A, switch on 'parallel', amp output B, both boards receiving P48, Samar MG33 mic near amp -> m audio preamp and A/D. Hum.
View attachment 128642

View attachment 128646
Bass gtr -> Input A, switch on 'parallel', amp out A to amp, XLR output A recorded, no hum
View attachment 128643

View attachment 128646
Bass gtr -> Input A, switch on 'parallel', amp out A to amp, XLR output B recorded, hum
View attachment 128644

In short (pun semi-intended), the hum happens on channel 2 when in parallel mode, and happens both on the 'amp out' and XLR out.

Thank you for your time and efforts in helping the entire community hopefully gain a new configuration / function of this great device.

Klem,

Here is a suggested change that with a little luck may solve your hum problem.

1. Change the dual/parallel mode switch to a "DPDT" type, i.e. a double version of the "SPDT" one you are now using, which should have six connections instead of three.

2. Connect the new "DPDT" switch according to the attached sketch.

What has been added is drawn in red.

3. Insert a 0.1uF 63/100v polyesterfilm capacitor between the PCB "chassis" connection and the metal box ground, instead of the green wire that is there now, according to the attached sketch. (do this on both circuit boards)

NOTE, for the above to work correctly, it is important that the XLR female cable connector that connects to the DI-box does not have its housing connected to pin-1 and cable screen.

The above changes include that it becomes two thru DI-boxes in "dual mode" but also it should be less sensitive to troublesome ground loops in "parallel mode" when there is a mess of external connections between preamps/mixing consoles and amps.


PS! another thing unrelated to hum.

Since we doubled the value of 1 Mohm bias resistor to 2.2 Mohm, a compromise for the input should keep at least 1 Mohm input resistans even in parallel mode.

To be sure the first transistor bias/operating point is still correct, (as I haven't tried this) it is important that the transistor "hfe" is high enough, so just use BC550C, not A or B, but use a equivalent "C" hfe with typ value around 600, if you use another kind of NPN transistor.

--Bo

 

[klem]

Thanks for the suggestions, I'll get an order in on Monday and report back once it's installed and tested.

As for the switch, with the SPDT I get pops when switching it. For anyone following along, would a 'make before break' / non-shorting switch be the right type of switch function in hopes of minimizing pops? And if so, is a MBB denoted as On-On or On-(On)?
"Sealed" is better quality?
I'm not a penny pincher, I'd rather spend more to get something that is more rugged and robust / lasts longer than I do... so if there are any 'switch aficionados' who care to recommend a specific small footprint switch, please chime in. Otherwise, I will roll the dice come Monday morning.