Bazz Fuss impedance and inductor questions

[Voltzy]

Ok thank you for your explanation I am beginning to understand. I have recorded a couple of different samples, I want to rebuilt it as you described above with just a phase inverter on the clean path and no FET splitter and then record one last sample.

If I build it like that, what can I do to protect  the circuit from low impedance input? For example if I have a seperate buffered-effect pedal before it in the pedal chain (other than always having it first in the chain).

Sent from my SM-G950F using Tapatalk

[Rob Strand]

One side of the 42TM018 transformer has an impedance of 10k and according

Last time I tried to get the Inductance on that I ended up with an estimate of 2.65H and some people on the web were quoting 3H.  Unfortunately I have not measured it.

[Voltzy]

OK I have finally made it sound like the original, with a blend knob.

Here is a video of the different sounds and the parts/layouts I went through:
https://youtu.be/BnGVQvV13M4

I suggest something like this:
(more or less..)

This is exactly the circuit that I went with except I added the mini transformer between the input cap and where the signal splits.

[antonis]

 
Well done, Voltzy..!!

[rankot]

I'm trying to understand this datasheet, so I can decide which of my small transformers can be used here:



So it seems that 10k transformer has inductance of 6H? But why is this called 10k transformer, when it has 45.4k inductance at 1.0kHz???

I have a small GM328A transistor tester which can measure inductances too, and it shows 6H on a small transformer I got from an old modem. Will it be OK for this purpose?

[Rob Strand]

So it seems that 10k transformer has inductance of 6H? But why is this called 10k transformer, when it has 45.4k inductance at 1.0kHz???

The measured impedance of a transformer is always higher than the impedance spec.  If the transformer was an ideal transformer it would have an infinite inductance and an infinite impedance. It would also have zero DC resistance as this represents a loss.   That way the transformer has no effect on the circuit other than the change in voltage at the input and output due to the turns ratio.

For practical reasons transformers do have an impedance.   The measured impedance of the transformer itself is always larger than the specified impedance.     The inductance is usually worked out so it produces 1dB drop or so at the lowest frequency of the frequency spec.   However you might seen anything from 3dB to 0.3dB.  That transformer is 1.5dB.

Another weird thing you might notice is the inductance spec is 5.89H whereas if you calculate the inductance from 45.4k ohms you end up with 7.2H.   I can't explain it.  Normally differences can explained because of losses and DC resistance but it seems a large difference and both tests are done at 1V 1kHz.  Another angle is one spec is typical and another max.  Normally the impedance would be *min* and you would end-up with a smaller inductance than the typical.

[rankot]

God answer as always, Rob, but I'm still unsure about mini TF choice for bass fuzz and similar cirtuits? Is 6.0H OK, or we can go with some other inductance value, to achieve 10k impedance?

[Rob Strand]

God answer as always, Rob, but I'm still unsure about mini TF choice for bass fuzz and similar cirtuits? Is 6.0H OK, or we can go with some other inductance value, to achieve 10k impedance?

The final behaviour of the circuit will depend on the inductance and not the nominal impedance. 

My best information is the inductance of the 42TM018 transformer is about 3H.   That could actually be wrong. 

If you have a 10k impedance transformer which is the same size and same DC resistance as another transformer there's a good chance the inductance will *roughly* be the same.  It's very rough.  Like the transformer you have fits this matching profile but the inductance is 6H which is quite a way off (assuming the 3H is correct.)

So you could just try it but if it isn't quite right it's obviously going to affect the sound.  However that transformer gives you some tricky options.  (Many are the same and there is little reason to choose between them without complicated hair-splitting measurements.)

Connection     Inductance (approx)
1 & 3              6H
1 & 2              6H * (1/2)^2 = 6H * (1/ 4) = 1.5H
2 & 3              6H * (1/2)^2 = 6H * (1/ 4) = 1.5H
3 & 6 but join 2 & 4    6H (1/2 + 1/15.5)^2  = 6H*0.32 = 1.9H  } in all cases
2 & 6 but join 1 & 4    6H (1/2 + 1/15.5)^2  = 6H*0.32 = 1.9H  } we are joining a dot to a non-dot winding
1 & 4 but join 6 & 4    6H (1/2 + 1/15.5)^2  = 6H*0.32 = 1.9H  } and the connection goes
2 &4 but join 3 & 6    6H (1/2 + 1/15.5)^2  = 6H*0.32 = 1.9H  } between the outer dot and non-dot
1 & 4 but join 3 & 6    6H (1 + 1/15.5)^2     = 6H * 1.13 = 6.78H
6 & 3 but join 1 & 4    6H (1 + 1/15.5)^2     = 6H * 1.13 = 6.78H

The 15.5 is an estimate of the turns ratio.  It's some where in the 15 to 16 mark.

So you can get 1.5H, 1.9H, 6H.   You can't get exactly 3H.

So you could try 1.9H and 6H and see if you can hear a big difference.

Beyond that you could tweak the 1n and 2.2uF caps to compensate for the different L
A rough guide is to calculate:   W = 1/(L_old*C_old)   then C_new = 1/(L_new*W)
Hard to know if leaving the C's or tweaking to new ones will make a difference.

I honestly think the 1.9H option and maybe a cap tweak is going to be the closest option.

[rankot]

Thanks Rob, I actually didn't think to use THAT Hammond TF, just used datasheet as an example, but you however described the process in detail. I have few different small transformers, most of them are 600:600 isolation TFs. I will measure inductance and see if there's anything near 3H mark.

[Rob Strand]

most of them are 600:600 isolation TFs.

If you find any have 0.75H on one winding you can connect the windings in series and get 3H.
One series connection will give a high inductance  (~ 3H) but if you flip one of the windings you will get much less than 0.75H.