freestompboxes.org

Hey all!

Usually I use a mic in front of my cab and a DI in front of my pedalboard for live gigs. Now last gig(s) I loaned my friends Red Box MKII as my main DI was in use (still in the studio) and I must say I am impressed by the sound this puppy can bring to the mixing desk. It really mimics my 4x12 I use

(small add-on; I play bass and use a Ampeg V4 through a 4x12 w/ some OD pedals and some modulation)

I found the schematics online at AG's site. Awesome man! As I never heard the difference, can someone tell me the difference between a MKI and a MKII? Can these puppies as shown be powered by phantom power? Are there any mods for these babies (for example bass mod???). I also noticed Pro and MKIII versions???

Second, can someone tell me the difference between these older two models and the newer "Classic" model that has a switch to go between 4x12 and 2x12?

Thanks!

I've got one of the current issue Red Box Classics, it works very well and is a handy tool. I mainly use it as a spare "amp", you can plug a pedalboard into the Line In and use the speaker emulation to get you through a gig. It also works well giving speaker emulation to tube guitar preamps. It has the 2X12 and 4X12 switch, and runs very well on phantom power. From a brief look inside it does not match any of the current schematics I've seen on the net (there are no transformers in it).

I considered building one from the web schematics, but you can buy them used on ebay for around $70 or so, to me it wasn't worth the effort for that small amount of cash.

Thanks!

I build the MKII version and it really adds a nice touch to my playing. I think of adding one to my head as an easy way to get the sound of my amp in a DI format. That mixed with a clean DI of my bass sound would sound really nice!

Shame is that the MKII does not work on phantom power so I would need to feed it........ phantom power addition would be quite nice!

Where did you buy the coils and the xformer ?

I would like to build one too !

Alf

fosnal1950 wrote:Where did you buy the coils and the xformer ?

I would like to build one too !

Alf

I build the active MKII (as can be found here on AG's site). I also build the passive versions which was mentioned above and I like the active version much better!

I'm looking at the schematic for the MKII on analoggurus site (http://analogguru.an.ohost.de/193/schem ... x-MkII.gif) and I see that R6, R7 and C4 are all in parallel with a short from pin3 of IC1 and R5.. so from an electrical POV I can't see how they'd do anything .. is that schem correct/verified? if not, does anyone have an updated one or idea on how it should go?

R6 is connected to pin3 while R7 to pin 2 and i built that version MKII and Classic all working good.MKii darker sounding because no cab switch compared to classic which we can select between combo or 4x12.And between classic 4x12 and MKII, MKII is still a little bit darker but very useable with dirt.

rocklander wrote:I'm looking at the schematic for the MKII on analoggurus site (http://analogguru.an.ohost.de/193/schem ... x-MkII.gif) and I see that R6, R7 and C4 are all in parallel with a short from pin3 of IC1 and R5.. so from an electrical POV I can't see how they'd do anything .. is that schem correct/verified? if not, does anyone have an updated one or idea on how it should go?

I have no reason to assume the schem is incorrect and, as fretburners says, R6 and r7 are connected to different pins.
R4 and R5 make the bias level at half VCC. That's 4.5 volts. This virtual ground biases the opamp at 4.5 volts through R6. R7, together with R8 do an amplification of 1+(R8/R7) while C4 a) ensures the DC level set at the + input (that 4.5 volts again) is not amplified in the same magnitude and b) discriminates the bass response. C5 does the same for the treble.

yup.. I see that now.. must've been too late at night.. I connected the dots where there are no dots to connect thanks all...

fosnal1950 wrote:Where did you buy the coils and the xformer ?

I would like to build one too !

Alf

L1 is a common mode choke using as inductor now.(see image)
For L2 to L4 use high quality audio coils.
I bought the transformer many years ago at H&K,
but that way is not longer possible,
you have to order H&K spare parts at so called H&K main dealers now.
I took a shot of the transformer.(see image)
Manufactured at Haufe a German manufactur.
Part name: HAUFE ST7063
The core sizes are 20 x 20 x 5 Millimeters.
I measured the values as follows.
Transfer ratio 1:1
Primary winding:
Inductance 3,23 Henrys
DC-resistance 50 Ohms
Secondary winding:
Inductance 3,23 Henrys
DC-resistance 62 Ohms
The outcome of this is an impedance of about 20295 Ohms for both sides.

Hey Bernardduur! You said ''Usually I use a mic in front of my cab and a DI in front of my pedalboard for live gigs. ''
You mean you go guitar into> DI >into> pedalboard to your amp which is miked. What do you like about having a DI first in your chain? Just curious

Well, I'm a bass player, so you need more 'clean' to the FOH as it is the driving force behind the band......... with guitar I could imagine quite a use but you need to stick to clean guitar!

Transfer ratio 1:1
Primary winding:
Inductance 3,23 Henrys
DC-resistance 50 Ohms
Secondary winding:
Inductance 3,23 Henrys
DC-resistance 62 Ohms

According to this data Xicon part number 42TM016 which is readily available looks like an exact replacement. 42TM009 is also very close.

here's a layout for the redbox MKII I just finished. not verified , but I think it's right.

I was looking to build something that doesn't have a xformer (so can do it with parts I already have) to be a DI for my acoustic. would this do it?