godwin

Re: Bo Hansen DI layout
« Reply #860 on: March 29, 2018, 03:55:47 PM »
Another picture.


Bo Hansen

Re: Bo Hansen DI layout
« Reply #861 on: March 30, 2018, 04:45:57 AM »
Godwin,

I suppose you have already compared the three working PC cards with the PC card that is not working, that all components are in the right place, are correctly turned and have the correct value.
Also check all voltage test points, as I describe on my DI box DIY page www.hansenaudio.se/techpage.htm

If all this is ok then the next step will be to test if the unbalanced telejack output sounds right.

If it does, then there is something wrong with the Lundahl LL1538 output transformer, or its connection.

Try an additional time to solder all connection pins on the transformer.

NOTE, never cut the pins on a Lundhal transformer, after soldering, these pins are hollow and contain the transformer's thin leads from coils.

--Bo
« Last Edit: March 30, 2018, 05:04:15 AM by Bo Hansen »
I met a man with a dollar, we exchanged dollars, I still had a dollar.
I met a man with an idea, we exchanged ideas, now we each had two ideas.

godwin

Re: Bo Hansen DI layout
« Reply #862 on: March 31, 2018, 02:20:18 PM »
Thank you for your reply. The unbalanced output DOES sound correct. I have another transformer on order. I will reply here after I swap it out.

musika

Re: Bo Hansen DI layout
« Reply #863 on: April 01, 2018, 11:13:43 AM »
I really like your DI box made from thick aluminum rectangular tubing.  Can you tell me what the thickness is that you ordered?  What are the final dimensions and how much length of tubing is necessary to create one DI box?

godwin

Re: Bo Hansen DI layout
« Reply #864 on: April 02, 2018, 11:44:02 AM »
All the tubing is 1/8" thick. The outer case is 2' x 4" x 6". The inner case is 2" x 5" x 3 & 3/4" The supplier cut the pieces to length .
6" long for the outer case and 3 & 3/4" for the inner case. I cut the top of the inner case  off with a hack saw at 1 & 3/4" then filed as needed until it slid inside the outer case. 5 #4-40 countersink 1/2" bolts mount the PC board and ground wire to the inner case.
2 #4-40 countersink 1/2" bolts secure the inner case from the bottom of the outer case. The inner case is tapped at #4-40 to receive those bolts. 

The aluminum is rough when received. I filed the edges square and smooth and polished the outside with fine sandpaper and steel wool.

I purchased the aluminum at Metals Depot online. The approximate case cost per DI Was $22.00.

godwin

Re: Bo Hansen DI layout
« Reply #865 on: April 02, 2018, 11:48:09 AM »
Another picture.

godwin

Re: Bo Hansen DI layout
« Reply #866 on: April 02, 2018, 11:59:11 AM »
Last one.

musika

Re: Bo Hansen DI layout
« Reply #867 on: April 02, 2018, 01:17:13 PM »
Thanks for the info and additional pics...  you did some nice work with those and they look great!   

godwin

Re: Bo Hansen DI layout
« Reply #868 on: April 08, 2018, 10:33:10 AM »
I replaced the LL1538 transformer with a new one and the unit is working correctly. Thank you for your guidance.

godwin

Re: Bo Hansen DI layout
« Reply #869 on: April 08, 2018, 10:40:10 AM »
Added some labeling.


godwin

Re: Bo Hansen DI layout
« Reply #870 on: April 08, 2018, 10:41:12 AM »
other side.

Bo Hansen

Re: Bo Hansen DI layout
« Reply #871 on: April 08, 2018, 11:02:44 AM »
Godwin,

Nice to hear that you solved the problem and that you like my DI box design.

--Bo
I met a man with a dollar, we exchanged dollars, I still had a dollar.
I met a man with an idea, we exchanged ideas, now we each had two ideas.

Whoops

Re: Bo Hansen DI layout
« Reply #872 on: April 16, 2018, 11:32:03 AM »
Hello Bo,
I would like to use your DI box circuit with Piezo pickups that need a much higher input impedance than electric guitars.

Could I change the input impedance of your DI box to 10 Megas?
What components should I change?

Thank you so much

Bo Hansen

Re: Bo Hansen DI layout
« Reply #873 on: April 16, 2018, 01:28:13 PM »
Whoops,

Since the input starts with a BJT transistor, which draws some current on the base, you can not go as high as possible in impedance.

However, it is possible that it runs with a 10 Mohm bias resistor, as there is quite little current through this transistor, but I want to try and do some measurment on this for you and come back later.

It is also possible to replace the first NPN transistor and replace it with an N-channel JFET transistor, such as 2SK30, 170, 246, 2N3819 or 2N4391, 2N5457  series, and then only replace the 1 Mohms bias resistor to 10 Mohm or higher if desired, without having to change something else.

But even this I want to test for you, so everything works as it should.

--Bo
« Last Edit: April 16, 2018, 03:00:15 PM by Bo Hansen »
I met a man with a dollar, we exchanged dollars, I still had a dollar.
I met a man with an idea, we exchanged ideas, now we each had two ideas.

Whoops

Re: Bo Hansen DI layout
« Reply #874 on: April 16, 2018, 02:44:53 PM »


But even this I want to test for you, so everything works as it should.

--Bo

Hi Bo , thank you so much for your help and for caring.

actually having the option of 10Mega input impedance would even make this DI more flexible in terms of uses.

Thanks you

analogguru

Re: Bo Hansen DI layout
« Reply #875 on: April 16, 2018, 03:16:08 PM »
This small modification should deliver you approx. the desired input impedance:
« Last Edit: April 16, 2018, 03:36:46 PM by analogguru »

Bo Hansen

Re: Bo Hansen DI layout
« Reply #876 on: April 16, 2018, 03:42:00 PM »
Whoops,

Sure, lots of choices and features are always fun, but jacks with "make and brake" functions, extra switches and potentiometers, cause poor contact and error over time.

So that's why I chose to present this DI-box design in its simple version, to always work and sound good.

Why did I choose an input impedance of only 1 Mohm, when almost all other active DI boxes have 10 Mohm.

Well, there are three reasons for this, one is that my original design from 1975 has this, the other is that BJT transistors are easier to get with good quality for all of you DIY people, and the third is that 90% of all guitar and bass amps have 1 Mohms input impedance, and then you'll recognize the sound characters and the behavior of your knobs on the guitar.

But wait a while, and I'll come back with some good suggestions for you.

Although I can guess and propose a modification, I'm careful about testing and measuring it, so I do not leave something by chance.
If I suggest something, I want it to work fully.

--Bo
I met a man with a dollar, we exchanged dollars, I still had a dollar.
I met a man with an idea, we exchanged ideas, now we each had two ideas.

Whoops

Re: Bo Hansen DI layout
« Reply #877 on: April 16, 2018, 03:44:03 PM »
Although I can guess and propose a modification, I'm careful about testing and measuring it, so I do not leave something by chance.
If I suggest something, I want it to work fully.


That's totally understandable and I appreciate that

Bo Hansen

Re: Bo Hansen DI layout
« Reply #878 on: April 16, 2018, 04:16:42 PM »
Analogguru,

Yes, bootstrap from emitter to base bias ref. resitors, rise the input impedanse a lot, theoretically about 10 times, what I remember.

But it is also important to see how electronics behave after this modification in reality.

As an example, will the transistors' work point be correct and stable, so the output still clipping nicely with max headroom ?

--Bo
« Last Edit: April 16, 2018, 04:20:31 PM by Bo Hansen »
I met a man with a dollar, we exchanged dollars, I still had a dollar.
I met a man with an idea, we exchanged ideas, now we each had two ideas.

analogguru

Re: Bo Hansen DI layout
« Reply #879 on: April 16, 2018, 04:37:48 PM »
.....
Yes, bootstrap from emitter to base bias ref. resistors, rise the input impedanse a lot, theoretically about 10 times, what I remember.
.....
Exactly - bootstrapping is an old (at least since the 50's) and well established technology.
Here is some easy-to-understand article about it:
http://www.hawestv.com/amp_projects/amp_hi_z_transistor/bootstrap-preamp.htm

.... will the transistors' work point be correct and stable,.....
The DC-"work point" of the transistor will not change with bootstrapping...

....  so the output still clipping nicely with max headroom ?
I doubt that anything clipping will be "nicely" (and I doubt that a piezo pickup will be able to drive this unity-gain-circut into clipping) - but why don't you just try it out if it fits your desires ?  It is only moving one leg of a capacitor from ground to the emitter (the already installed 1µF will be at least sufficient for lo-mid-frequencies and up)

BTW, I also doubt that it is really necessary to have an input impedance of 10M for a piezo pickup, especially when the pickup should have its on impedance converter [think about 5m cable from pickup to the DI-Box with 100pF/m {= 320kOhm @ 1kHz, 32kOhm @ 10kHz}], but....
« Last Edit: April 16, 2018, 06:01:31 PM by analogguru »


 

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