Bo Hansen DI layout

[boji]

Epic retrofit.  All the metaphors!

 

[Whoops]

I'm building 4 units of this DI at the moment.

I will build 1 with 10 mega input impedance using the 2SK170BL for Piezo picukps, and the 3 others with the standard 1Mega input impedance.

Just to clarify something about transistors.
As Bo clearly explains in his page you can use any of this transistors and the DI will perform perfectly:

BC550C = BC550B, BC549B/C, BC548B/C, BC547B/C, BC414B/C, BC337-25/40, BC237B/C, BC184B/C, 2N3391A, 2N3904, 2N4401, 2N5088, 2N5210, MPSA18, 2N3707, 2SC1775-AE, 2SC1815-GR/BL, 2SC2240-GR/BL

BC560C = BC560B, BC559B/C, BC558B/C, BC557B/C, BC416B/C, BC327-25/40, BC307B/C, BC214B/C , 2N3906, 2N4403, 2N5087, 2N3703, 2N4058, 2SA872-AE, 2SA1015-GR/BL, 2SA970-GR/BL


You don't have to select the transistors for HFE but the BC550C is a low noise high HFE type transistor.
the letter at the end of the transistor means:
"B" indicates medium gain (200 to 450)
"C" indicates high gain (420 to 800)

The 550 and 549 are low noise type compared to the 548 and 547 from the same family.
The 2N5088 is also low noise with the same range of HFE as the the "C" letter, it's equivalent to the BC550C.
The MPSA18 probably even lower noise and high HFE

So if you go with the BC550C you already have high HFE and low noise, that's why it's recommended as you dont have much to fiddle around.

The 2N5088 is a great transistor but it's marked as obsolete in most big electronic suppliers, the reason is the TO-92 transistor format is already obsolete. Almost all new industrial productions use SMD so all the through hole components are not used any longer in big quantities so those are obsolete already as far as manufacturing or will be in the near future.
There's still a big enough supply for DIY, but if you see an obsolete transistor it's not because it isn't good but because of the way the market dictated it.
The same happened with BC184C some years ago.

There's still big quantities of BC550C is stock in Mouser and Farnell,
but the BC560C is marked as non-stocked in both suppliers.


If you're in Europe you can get them from Banzai in Germany for cheap:

http://www.banzaimusic.com/BC560C.html

 

[Whoops]

For a 10 Mega input Bo recommended the use of 2SK30, 170, 246, 2N3819 or 2N4391, 2N5457 to replace the first transistor.
Focusing on the 2SK170, there's the GR and BL version, both are recommended, in Banzai the price of the GR version is much higher than the BL, any reason for this?

 

[Ricardus]

For a 10 Mega input Bo recommended the use of 2SK30, 170, 246, 2N3819 or 2N4391, 2N5457 to replace the first transistor.
Focusing on the 2SK170, there's the GR and BL version, both are recommended, in Banzai the price of the GR version is much higher than the BL, any reason for this?

There were a few other components that needed to be changed also. Does anyone remember what they were?

 

[Whoops]

There were a few other components that needed to be changed also. Does anyone remember what they were?

That info is some pages back in this thread.

Bo described the mods and I posted a schematic with the mods also

 

[abbey road d enfer]

For a 10 Mega input Bo recommended the use of 2SK30, 170, 246, 2N3819 or 2N4391, 2N5457 to replace the first transistor.
Focusing on the 2SK170, there's the GR and BL version, both are recommended, in Banzai the price of the GR version is much higher than the BL, any reason for this?

I've tried the 2SK170 as a relpacement for the hard-to-get LSK389 in my MicBooster. The FET's there are in parallels.The BL version cannot be used because the Idss exceeds what the P48 can deliver. The GR version works.
The BL version is the most common; when offers don't specify the grade, it's usually BL that you get.
I would think it's only scarcity that makes the GR type more expensive.
It seems to be the same for LSK170 and LSK389, so maybe the yield of GR/A versions is not as good. However it does not seem to reflect in the manufacturer's pricing.

 

[Bo Hansen]

whoops,

The JFET modifications is far down on side 45
https://groupdiy.com/index.php?topic=36569.880

PLEASE NOTE that my idea with this DI-box design is that it does NOT have a 10 mega ohm JFET input, this is part of the sound character. 
Only do JFET modification if it is to be used for extremely high impedance Piezo pickups/transducers, but do not do it if it is only used for normal instruments such as electric guitars, basses and keyboards.

Regarding the JFET idss when it works as an input transistor in this circuit does not matter much, the transistor only draws about 0.1 mA, so it works well with all idss selections on JFET transistors.

So in the case of the Toshiba 2SK170, all selections like GR, BL and V are perfectly ok.

It is possible to use almost any N-channel JFET general purpose small signal amplifier transistor, there Vds is at least 30 volts.
The only thing to keep in mind is the adjustment of the top resistor in the operating point voltage divider, which is normally 100 k and goes to the plus voltage rail.
For different types of JFET, gm, idss, this resistor can be slightly higher, for example 110k, 120k, 130k, and so on.  This adjustment is made to get the best swing and symmetrical clipping on the DI box's XLR output.  (terminated with a microphone input or a 2k load resistor)

—Bo

 

[Whoops]

PLEASE NOTE that my idea with this DI-box design is that it does NOT have a 10 mega ohm JFET input, this is part of the sound character. 
Only do JFET modification if it is to be used for extremely high impedance Piezo pickups/transducers, but do not do it if it is only used for normal instruments such as electric guitars, basses and keyboards.

Hi Bo,
we've already talked about that before.
I was the one who asked you if was possible to modify it for 10 Mega input impedance for Piezo pickup use.

Thank you so much

 

[Bo Hansen]

I will also comment on your thoughts and questions regarding suitable BJT transistors when you can not find the BC550C and BC560C which I primarily recommend for my DI-Box design.

When we started this DI-Box project almost 20 years ago (yes, time goes by) the BC550C/BC560C were easy to get and were a very good NPN/PNP transistor pair for small signal audio circuit.

But unfortunately, as time has passed, it has become very difficult to get hold of these two types of good quality/manufacturer, especially the PNP BC560C, which began to disappear from the market already 10 years ago.

Since I received lots of requests for suitable replacement transistors that can fit in my DI-Box design, I made a list of both old and new possible types that can be found on my technical help page
www.hansenaudio.se/techpage.htm
With all these listed transistor types, you have a chance to find suitable types from NOS or surplus stock.

In fact, this design is not a ”rocket scince” there are only two cascaded emitter follower, so it is almost possible to use any types of NPN/PNP general purpose amplifier small signal silicon transistors from 1970 onwards.

Below I have listed the most common types today that are still more or less in stock at component distributors.

It is of course possible to use NPN and PNP types in any combination, but beware of pin-out, some types must be twisted half a turn in relation to the marking on the PCB/circuit board.

It is very important that you only buy well known brands like ON-Semi and Fairchild.
Unfortunately, there are far too many fakes and junk sold on the eBay and the internet market today, if you not see any brand, do not buy these transistors.

European type
directly fitting pin-out for the PCB
NPN: BC547B or C         
PNP: BC557B or C

American types
must be twisted half a turn to fit the PCB
NPN: 2N3904                 
PNP: 2N3906
NPN: 2N4401                 
PNP: 2N4403

Good places to buy these transistors are:
DigiKey
Farnell
Mouser
Newark
RS-Components

—Bo

 

[Ricardus]

Mouser in the US does have thousands of 547s and 557s in stock at the moment.

 

[Markus_Krippner]

... But unfortunately, as time has passed, it has become very difficult to get hold of these two types of good quality/manufacturer, especially the PNP BC560C, which began to disappear from the market already 10 years ago.  ...

I bought mine here (Europe):

50pcs Fairchild BC550C... EUR 3.79 + Eur 1.79 shipping (Kessler, Germany):
https://www.ebay.de/itm/BC550C-Transistor-npn-45V-100mA-625mW-TO92-von-Fairchild-Semiconductor/362417060699?hash=item5461bd7b5b:g:NUsAAOSwus5cCGph

50pcs Fairchild BC560C.... about EUR 10.- + EUR 3.80 shipping (Langrex, UK):
https://www.ebay.de/itm/BC560C-FAIRCHILD-PNP-LOW-NOISE-TRANSISTOR-x10PCS/312092114333?epid=1956244962&hash=item48aa23bd9d:g:5nMAAOSwmLFdenj3

...  so 20 Euros for 50 Pairs .... thats ok.    And so I can tell my friends without lying then, that I own "several Fairchilds". 

....markus

 

[Whoops]

Mouser in the US does have thousands of 547s and 557s in stock at the moment.

BC547 and BC557 have higher noise floor so are less interesting than BC550, BC549 and BC559, BC560 which are all Low Noise types.

 

[Whoops]

But unfortunately, as time has passed, it has become very difficult to get hold of these two types of good quality/manufacturer

It's seem it's still pretty easy to find them Bo, I don't think there's any need yet to go for types with an higher noise floor when there's easy sources for the lower noise types BC549/BC550 and BC559/560.

Yes the BC560C is a a litle bit harder to find in big retailers than the others, but it's still pretty easy to find.
All my local Electronics stores (smaller stores) still stock them also.
Anyway if someone doesn't use BC560C I think it's better to go for the BC559C (lower noise type) then the 547.
But like you said Bo, any will work well. There's a lot of choices for transistors

Sources for BC549/BC550:

http://www.banzaimusic.com/BC549C.html
http://www.banzaimusic.com/BC550C.html
https://pt.mouser.com/ProductDetail/ON-Semiconductor-Fairchild/BC550CBU?qs=nEYkbyTNQ5kFgfdWliMJ7Q==
https://pt.mouser.com/ProductDetail/ON-Semiconductor-Fairchild/BC550CBU?qs=nEYkbyTNQ5kFgfdWliMJ7Q==
https://pt.mouser.com/ProductDetail/ON-Semiconductor-Fairchild/BC549CTA?qs=UMEuL5FsraA9pebzi3Uf7w==
http://smallbear-electronics.mybigcommerce.com/transistor-bc549c-ons/
http://smallbear-electronics.mybigcommerce.com/transistor-bc550cbu/
https://pt.farnell.com/on-semiconductor/bc550cbu/transistor-bipol-npn-45v-to-92/dp/2453798?st=bc550c


Sources for BC559/560:

http://www.banzaimusic.com/BC559C.html
http://www.banzaimusic.com/BC560C.html
https://pt.mouser.com/ProductDetail...=/ha2pyFadugI/di3slSIc0GMrYa3BEJ/wv7khBg3L28=
http://smallbear-electronics.mybigcommerce.com/transistor-bc560cg/
https://pt.farnell.com/on-semiconductor/bc559cta/transistor-bipol-pnp-30v-to-92/dp/2453808?st=bc559c
https://pt.farnell.com/on-semicondu...or-bipol-pnp-30v-to-92/dp/2453808RL?st=bc559c
https://www.digikey.pt/product-detail/en/on-semiconductor/BC559CTA/BC559CTACT-ND/4213839
https://uk.rs-online.com/web/p/bjt-bipolar-transistors/5452484/

 

[JohnRoberts]

Whoops your inbox is full....

JR

 

[Ricardus]

BC547 and BC557 have higher noise floor so are less interesting than BC550, BC549 and BC559, BC560 which are all Low Noise types.

I saw this coming and stocked up on about 150 of both 550s and 560s.

 

[Bo Hansen]

Whoops,

I do not think you need to worry about higher NF/Noise Figure in these alternative "general purpose small signal amplifier transistors" I have recommended.

Today's "general purpose" amplifier BJT transistors have lower NF than our normal "low noise" transistors we had in the 1970s, such as BC109 and BC177 which I used in the original of my DI-box design in 1975.

This design is two emitter followers in series and this does not have the same requirements for low noise transistors as for example a circuit with high gain.
”No Gain-No Pain” (think it was my favorite tube man John Broskie who coined this phrase)

But for safety's sake, I'll do a practical noise measurement on different transistors in this DI-box circuit, so we can be sure that this is true as I say.

—Bo

 

[[silent:arts]]

Since I can easily buy BC550C and BC560C for a few cent here in Germany I will add them to the PCBs for free to all people having hard times to find them.

 

[Whoops]

This design is two emitter followers in series and this does not have the same requirements for low noise transistors as for example a circuit with high gain.
”No Gain-No Pain” (think it was my favorite tube man John Broskie who coined this phrase)

Thank you so much for explaining Bo.

I was just following the info you provided in your page:

"It is of course preferable to choose a low-noise type with the best selections of hfe, to ensure
that the transistor is doing a good job in this DI-box circuit."

So I used 550/549, 559/560 for lower noise,
and leter "C" for gain range between 420 and 800

It was not a big deal since there's a lot of this transistors locally

 

[Whoops]

Since I can easily buy BC550C and BC560C for a few cent here in Germany I will add them to the PCBs for free to all people having hard times to find them.

Nice one.
It's pretty nice that you're doing that.

 

[Bo Hansen]

Volker,

This is very generous and kind of you, and I'm sure you choose a well-known brand and not a "no name" type.

—Bo