Tycobrahe Octavia audio transformer clarification

Mbas974 · Post by **Mbas974** » 30 Oct 2013, 17:18

Concerning the tycobrahe octavia the audio transformer used has a ratio equal to 3:1.
As far as I know an octaver double the frequency....

Is there someone can explane it ?

induction · Post by **induction** » 30 Oct 2013, 17:33

The transformer changes the voltage not the frequency. The frequency 'doubling' is accomplished by using the diodes after the transformer to convert the negative voltage swings to positive voltage swings. This isn't precisely the same as doubling the frequency, which (in addition to crossover distortion from the diodes) is why these octave devices don't sound like a Pog or what have you.

phatt · Post by **phatt** » 31 Oct 2013, 14:11

Agree with *Induction*
Having messed with these circuits a bit, built 2 units for a chap the transformer unit is likely harder to dial in.

My guess is this circuit works best if the phase split is perfect which might be hard to achieve with cheap transformers.

What I did eventually do was use the transistor circuit and this is when it dawned on me that the whole trick to this effect is to balance the phase split which is in front of the diodes.
I simply mounted a pot across the supply to feed the base, and tweaked until it delivered the strongest octave. to easy

But battery voltage drop over time will change this balance so it's still not ideal.
I mounted a small pot at the back of case so it could be fine tuned as voltage drops.
Maybe if I had better transformers it might help but I figured I'd be spending money and get nowhere so went with the other circuit.

As *induction* has noted,
this effect is very sensitive to frequency and only really works best on the higher notes strings, not as much impact on lower notes. But that is part of the magic.
HIH, Phil.

DrNomis · Post by **DrNomis** » 31 Oct 2013, 14:25

In the Tychobrahe Octavia, what the Audio Transformer is really doing is taking the output signal from the transistor circuitry and creating two signals which are 180 degrees Out-Of-Phase with each other, these two signals are then sent to the two signal diodes which Half-Wave Rectify the two anti-phase signals, these two anti-phase signals recombine at the junction where the Cathodes of the two signal diodes join together, the result is a Full-Wave Rectified signal which is double the frequency of the two anti-phase signals and therefore will sound an Octave higher.....

Hope that helps....

HoboRizla · Post by **HoboRizla** » 15 Feb 2014, 12:36

phatt wrote: What I did eventually do was use the transistor circuit and this is when it dawned on me that the whole trick to this effect is to balance the phase split which is in front of the diodes.
I simply mounted a pot across the supply to feed the base, and tweaked until it delivered the strongest octave. to easy

Hi Phatt
I have the same problem...built my Octavia, cool fuzz sound but i can't hear the octave up effect
which transistor are you talking about? Q1?

Thanks,
Rizla

phatt · Post by **phatt** » 16 Feb 2014, 04:40

The Q right before the diodes. Don't have the drawing at the mo but maybe the 3rd Q along.
If the balance is out by a fair bit you don't hear much octave.

Bear in mind that the greatest effect is usually above the 5th fret,, accentuates the higher freq.
Phil.

HoboRizla · Post by **HoboRizla** » 17 Feb 2014, 09:37

phatt wrote:The Q right before the diodes. Don't have the drawing at the mo but maybe the 3rd Q along.
If the balance is out by a fair bit you don't hear much octave.
Bear in mind that the greatest effect is usually above the 5th fret,, accentuates the higher freq.
Phil.

Thank you very much, I'll try that as soon as I can find a 1n34a...saturday I accidentally broke my diode by removing it from the board and I can't find it in town!
DAMN!

phatt · Post by **phatt** » 17 Feb 2014, 12:07

They don't have to be fancy diodes,, it's possible a silicone diode may work better here but by all means try others to taste.

Phil.

HoboRizla · Post by **HoboRizla** » 19 Feb 2014, 13:13

You were right Phatt, that resistor is the key...I'm playing a lot while I'm changing the value of the pot, because it affects the octave up effect but obviously it affects the amount of fuzz too...so you have to find the right balance
Just to know, what was your choice?

Thanks,
Rizla

phatt · Post by **phatt** » 20 Feb 2014, 08:46

Great news,

Well I'll be?? Yes on occasion I get it right.

Umm? I assume you ask about diodes?
Well I never really tested others but mine would have likely been any old 1N4148.
This was all a very long time ago so not even sure I have the circuit on file now.
I do recall playing around with the bass response a bit as it was very sharp
but that is the nature of the effect.
I'd have to build it again to remember what was changed.
Phil.

HoboRizla · Post by **HoboRizla** » 28 Feb 2014, 10:51

Sorry for being so late to answer, I was superbusy...but I did it!

Anyway, I was asking about that resistor! Although in the end I decided to leave the 22k resistor and working on capacitors, like the user soulsonic has brilliantly suggested on this topic:
https://www.freestompboxes.org/viewtopic ... via#p51014

Now I'm really satisfied with my work, I made a little video which you can see here:

Cheers,
Rizla