It's OK how i think to convert Boss BF-2 to Boss HF-2?

[gigimarga]

Hello,

I've just bought an Boss BF-2 and, looking at the schematic of it (http://www.schematicheaven.com/effects/boss_bf2_flanger.pdf) and at the schematic of the (almost very) rare Boss HF-2 Hi-Band Flanger (http://www.schematicheaven.com/effects/boss_hf2_hibandflanger.pdf) i saw that there are almost the same.

If i saw carefully, there are only 4 little differences:

1. HF-2 uses MN3204 instead of MN3207 in BF-2
2. R10  (near the trimpot for tha resonance) is only 22k in HF-2 instead of 39k in BF-2
3. pin 1 of IC4 (MN3102) goes to the "divider" R65/C41 in HF-2 instead of  Vcc/2 in BF-2
4. pin 5 of IC3 (MN3204) goes to the "divider" R65/C41 in HF-2 instead of  Vcc/2 in BF-2

So, before trying to modifiy it, i have some questions (i don't want to damage the expensive and very rare here MNs):

1. Can i use a switch to toggle pin 1/pin 5 of IC4/IC 3 between R65/C41 "divider" and Vcc/2 as in observations 3 and 4 above (i ask that because IC4 is the same, but IC3s are different)?

2. How to set the resonance trimpot? If i'm remebering well, i've read somewhere that you must to turn it (with the resonance pot maximized) until the stompbox starts to oscillate and, after that, to turn it backward a little...

3. After i've set the resonance trimpot, doesn't matter how, can i replace the pair R10 and VR5 with a resistor (in other words, this setting is enough stable)? I ask that because if the answer is affirmative i can switch between BF-2 and HF-2 using a DPDT!

Thx a lot all!

[Mark Hammer]

R65/C41 is for decoupling the supply lines for the BBD and clock chip from the rest of the circuit.  They would probably improve noise performance in the BF-2 as well.

Yes, the way you indicate setting the resonance is the "correct" way.  And yes, if you can identify what the total of R10+trimpot should be, then you can replace it with the nearest common value fixed resistor.

because the delay time in the HF-2 is much shorter than in the BF-2, it will not produce annoying resonances in the bass end of the spectrum when the regeneration is turned up.  That is why R10 can be shorter: the HF-2 circuit "tolerates" more regeneration.

[gigimarga]

Thx a lot Mark, as usually

What i can't understand is where is the difference between BF-2 and HF-2? Only MN3204 makes this difference?

On the www.bossarea.com is written that: "The HF-2 is combining the original signal with a delayed signal that is shifted one octave up to create a flanging effect a bit different but still similar to the BF-2. The effect is brighter and cleaner than the BF-2. The HF-2 may not be as powerful as the BF-2, but for hi frequency flanging it produces a very good result."

Where is made this shifted one octave up???

[Mark Hammer]

The pitch is not shifted up.  It is the delay range that is shifted down by using the same circuit with 512 stages instead of 1024.  With a shorter delay range, the notches occur one octave above where they occur in the BF-2.  Better for bass guitar because it disturbs the fundamental less.

[gigimarga]

Thx Mark!

So, no chance to switch with a DPDT between BF-2 and HF-2...only if i replace the MN3207 with a MN3204, am i right?

I've searched a little and i saw that MN3204 it's hard to find anyway...

[Mark Hammer]

A person can always shift the entire delay range by changing the value of one capacitor in the HF clock circuit.  I do it on every chorus I own.

But remember that the a) the range of clock frequencies needs to be possible for the BBD (above a certain point and you need to add buffering to counteract the input capacitance of the pins on the BBD), and the filtering needs to be adapted to the clock frequency range to keep clock noise out of the audio path.

When Boss produced the HF-2, the only change they needed to make was substituting a BBD with fewer stages, and that one regeneration resistor.  That, and a different paint job, seems like a pretty easy way to make a different "product".  They could have kept the same BBD and changed the delay range, but that would have required changes to the clock circuit.  Easier to make a different delay range by sticking a different chip in the BBD socket.

[gigimarga]

A person can always shift the entire delay range by changing the value of one capacitor in the HF clock circuit.  I do it on every chorus I own.

But remember that the a) the range of clock frequencies needs to be possible for the BBD (above a certain point and you need to add buffering to counteract the input capacitance of the pins on the BBD), and the filtering needs to be adapted to the clock frequency range to keep clock noise out of the audio path.

Thx a lot Mark!
Can you be more clear on how to do that?

[oldschoolanalog]

I've searched a little and i saw that MN3204 it's hard to find anyway...

You just need to know where to look...
A cheap plastic Arion stereo flanger (~$20US) will yield one 3204 and a 3102.

[Mark Hammer]

A person can always shift the entire delay range by changing the value of one capacitor in the HF clock circuit.  I do it on every chorus I own.

But remember that the a) the range of clock frequencies needs to be possible for the BBD (above a certain point and you need to add buffering to counteract the input capacitance of the pins on the BBD), and the filtering needs to be adapted to the clock frequency range to keep clock noise out of the audio path.

Thx a lot Mark!
Can you be more clear on how to do that?

Shifting the delay range involves hanging the small-value cap connected to the 3102 or 3101 chip (whichever is used)  Usually, it will be somewhere between 22pf and 470pf.  Smaller values make the delay range shorter.  Examples of the buffering needed to support very high clock frequencies using Matsushita chips can be found in the Hollis Ultraflanger, the A/DA Flanger, and similar devices.

[gigimarga]

I've searched a little and i saw that MN3204 it's hard to find anyway...

You just need to know where to look...
A cheap plastic Arion stereo flanger (~$20US) will yield one 3204 and a 3102.

Thx oldschoolanalog...i will try to find one

[gigimarga]

Thx Mark...I will try

[Mark Hammer]

Shifting the delay range involves hanging the small-value cap connected to the 3102 or 3101 chip (whichever is used)  Usually, it will be somewhere between 22pf and 470pf.  Smaller values make the delay range shorter.  Examples of the buffering needed to support very high clock frequencies using Matsush*ta chips can be found in the Hollis Ultraflanger, the A/DA Flanger, and similar devices.

They forced a new 22" monitor on me at work, but did not permit me to be able to change the resolution.   So often I cannot see what I have written clearly.  The words highlighted in red should be "changing" and "Matsushita".

I hate LCD monitors.

[gigimarga]

They forced a new 22" monitor on me at work, but did not permit me to be able to change the resolution.   So often I cannot see what I have written clearly.  The words highlighted in red should be "changing" and "Matsush*ta".

I hate LCD monitors.

For my English is the same thing...i understood perfectly )

[trixdropd]

Shifting the delay range involves hanging the small-value cap connected to the 3102 or 3101 chip (whichever is used)  Usually, it will be somewhere between 22pf and 470pf.  Smaller values make the delay range shorter.  Examples of the buffering needed to support very high clock frequencies using Matsush*ta chips can be found in the Hollis Ultraflanger, the A/DA Flanger, and similar devices.

They forced a new 22" monitor on me at work, but did not permit me to be able to change the resolution.   So often I cannot see what I have written clearly.  The words highlighted in red should be "changing" and "Matsush*ta".

I hate LCD monitors.

mark, if you're on windows xp just hold control and use your mousewheel. it will scale the text for you, while maintaining resolution.

[solderman]

Shifting the delay range involves hanging the small-value cap connected to the 3102 or 3101 chip (whichever is used)  Usually, it will be somewhere between 22pf and 470pf.  Smaller values make the delay range shorter.  Examples of the buffering needed to support very high clock frequencies using Matsush*ta chips can be found in the Hollis Ultraflanger, the A/DA Flanger, and similar devices.

They forced a new 22" monitor on me at work, but did not permit me to be able to change the resolution.   So often I cannot see what I have written clearly.  The words highlighted in red should be "changing" and "Matsush*ta".

I hate LCD monitors.

I just love the "sh*t" filter provided by this sites logic. if you type s h i t you vill get sh*t.  I did not put in the * there. The site did that.  the same goes for the company.
It's hard to be Japanees and own the Matsush*ta corp.  So Mark, There is nothing wrong with your monitor. its the little 1:s and 0:s, and that people that put them there that makes the world fall in to sh*tty bits   

[Mark Hammer]

Shifting the delay range involves hanging the small-value cap connected to the 3102 or 3101 chip (whichever is used)  Usually, it will be somewhere between 22pf and 470pf.  Smaller values make the delay range shorter.  Examples of the buffering needed to support very high clock frequencies using Matsush*ta chips can be found in the Hollis Ultraflanger, the A/DA Flanger, and similar devices.

They forced a new 22" monitor on me at work, but did not permit me to be able to change the resolution.   So often I cannot see what I have written clearly.  The words highlighted in red should be "changing" and "Matsush*ta".

I hate LCD monitors.

mark, if you're on windows xp just hold control and use your mousewheel. it will scale the text for you, while maintaining resolution.

Oh I know how to change it.  However, because of the nature of my employer (government) almost every feature that might let me tailor my environment is disabled.  You have to ask fr what you want when things are installed, and they will do it.  But if one wishes to switch back and forth to suit the application (for instance I need smaller fonts when dealing with immense datafiles in SPSS), you can't do that on your own.  Although now that I think of it, Firefox does let me scale font size up and down.  I should probably use that feature more often.

I still prefer CRT images to LCD, though.  At viewing distances greater than 18" from the screen, one's eyes do much of the desired anti-aliasing, so you benefit from the richer colours and greater contrast in an LCD screen.  At workdesk distances, though, I prefer the way in which CRTs soften the edges.  Besides, I don't need the richer colours to work on datafiles.  Sixteen colours is pretty much good enough for work.

[thehallofshields]

Shifting the delay range involves hanging the small-value cap connected to the 3102 or 3101 chip (whichever is used)  Usually, it will be somewhere between 22pf and 470pf.  Smaller values make the delay range shorter.

Sorry to bring up an old thread, but did anyone ever try simply swapping this cap?

http://www.hobby-hour.com/electronics/s/boss-bf2-flanger.php

I'm looking at C30 as the prime candidate. Is the capacitors effect linear in this case? Would 1/2 the value do the 'high-band' trick?

[Mark Hammer]

C30 is indeed the culprit.  The thing to remember is that the MN3101/3102 don't fare especially well driving an MN3007 or MN3207 to very high clock rates.  This is why Boss went the route of using a lower capacity BBD (the 512 stage MN3204) instead of just clocking the MN3207 faster.  It was simply easier to get a shorter delay range by swapping chips that it would have been to use the same chips and add the necessary circuitry to nudge the 3207 to sweep down to shorter delay times.

The obstacle is that the Panasonic chips have a high-ish capacitance on the the clock input pins.  When the clock pulse they receive is low enough (let's say 100khz or lower), that pulse from the MN3102 remains nice and square.  As the clock rate goes higher, that input capacitance changes the clock waveform so that each pulse actualy spends less time above the voltage needed to make all the little FETs in the delay chip switch properly.

So, I think one could probably nudge the clock rate of a BF-2 juuuuust a little higher, by maybe using a 43pf or even 39pf cap for C30.  But I think if one attempted to just go for broke by halving C30 to mimic the delay produced by halving the number of BBD stages with a 3204, you'd probably run into trouble.  Wouldn't fry the chip, but the sound quality may be very poor.

[Fender3D]

+1
don't forget, clock range will change too and will be affected by C31 and D6 capacitance

[thehallofshields]

Mark, thank you so much for the quick informative response.

I think instead; I'll stay simple and try wiring a high-pass filter (2khz maybe) on the input of the first op-amp and rout the lows to the input of the output op-amp.

I expect to get a less disturbed fundamental, but perhaps some 'shrill' highs when I turn the regen up.

Unfortunately I don't have an HF-2 for comparison so maybe you guys could throw in your two cents on the idea while I review the schematic.

I'll report back in a month or so to let everyone know how it goes