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An inexpensive audio transformer with DIY projects

Thanks again John for the Trans-Boost pedal!!!

I just was playing with it for about an hour with my Schecter C5 with active EMG’s and my passive Fender Strat. Both the bass and guitar were connected to the Trans-Boost then straight into the SWR 750x amplifier with a 4x10 cab w/tweeter.

I first tried it with the bass with lowest drive and least amount of clipping. It sounded very natural with a subtle little something in the tone that sounded just right. I ran it this way to get a feel for what the transformer was adding to the sound. Very subtle, but very nice!

Then I tried it with the drive at maximum with various clipping levels. This box can get real dirty with my C5! It may be a lot more dirt than I would use in a band setting, but the burpy attack was a blast! I could see myself using these settings for different passages of songs when the keyboard player is busy with his/her left hand on the lower register. With the drive at maximum and clipping at minimum, I could hear a slight loss of HF detail (the tweeter in my cab was on) which I attribute to the transformer beginning to saturate with the low frequencies. So, I don't know yet if I like transformer saturation or not, but I do like the B-H distortions that all transformers have.

I then adjusted the clipping to its max position and dialed up the drive until I had just a little break-up on the initial attack of each note. If I were still playing with a band, I could see myself using this as an always on pedal with these settings. These settings worked well for dynamic dirt… when digging in; there was just enough grit to emphasize the mood/feel. It reminded me of the times I had played thru my friends Mesa combo.

With my Strat, the pedal didn’t have enough drive to go into the heavier distortion territory with this soft clipping circuit. But it had enough to make chords sound thicker/fuller. A very nice tone enhancement for my Strat, but if a guitar player wanted one of these for dirt they may need to add more gain to the drive circuit by changing R6 to 3K3. I like it as is for a clean-ish blues tone and it would be perfect for driving another dirt box or tube amp. It had the same feeling to me as playing thru a clean tube amplifier. This would be a great way for someone to tube-i-fy their sterile SS rig. (My rig is Hi-Fi sterile, even though the preamp is a tube hybrid.)

With a minimum drive setting, the Strat had the same feel as my C5… natural sound with just a little bit of transformer color added to the tone. Very nice!!! This pedal would be great for re-amping tracks in a mix.

When I get more time I will try the Trans-Boost in the effects loop on the amp. This way I can try the bass again with heavier distortion settings on the box and blend some dry signal with it.

BTW, this pedal is even better looking in person! Great job John... THANX!!!!:thumbsup:

-Frank

Yeah, this review made it easier to pass the pedal over...

...or not. Damn, I need to get one of these.
 
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Yeah, this review made it easier to pass the pedal over...

...or not. Damn, I need to get one of these.

It is very different from any dirt box I have tried. The heavier distortion it produces sounds unrefined... open and raw would be a good way to describe it.

-Frank
 
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That's an interesting descriptor for a pedal that at lower gain settings would be well suited as an "always on"!

My original intent with this circuit was to have a transformer circuit that could be adjusted for various amounts of core saturation. John is a dirt addict, so it evolved into something more along those lines. With the type of controls we have on this circuit, I think it covers both territories nicely.

I really like the soft clipping that can be dialed in, because you can keep the transformer from reaching core saturation by clipping the signal at lower amplitudes. Or if you want some core saturation, you would run the clipping at it's minimum setting (highest clipping amplitude) and turn up the drive.

Like I said before, I'm not sure if I like core saturation... And I am wondering if the magic tone that people are referring to with core saturation isn't something else that they are hearing.

-Frank
 
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My original intent with this circuit was to have a transformer circuit that could be adjusted for various amounts of core saturation. John is a dirt addict, so it evolved into something more along those lines. With the type of controls we have on this circuit, I think it covers both territories nicely.

I really like the soft clipping that can be dialed in, because you can keep the transformer from reaching core saturation by clipping the signal at lower amplitudes. Or if you want some core saturation, you would run the clipping at it's minimum setting (highest clipping amplitude) and turn up the drive.

Like I said before, I'm not sure if I like core saturation... And I am wondering if the magic tone that people are referring to with core saturation isn't something else that they are hearing.

-Frank

I think that the only logical next step is to make a new DB-CL variant with a nice transformer, maybe a Lundahl, like the Cali76tx-L with a saturation adjustment. Then, just put me #1 on the waiting list for that. :)
 
I think that the only logical next step is to make a new DB-CL variant with a nice transformer, maybe a Lundahl, like the Cali76tx-L with a saturation adjustment. Then, just put me #1 on the waiting list for that. :)

Do you really think the DB-CL needs more knobs?:D

-Frank
 
the thing with the transboost circuit is that with the drive control turned up and the clip control turned down, you get opamp distortion (the OPA2134 is clipping) which can be a bit harsh and jagged sounding (which i'm not all that fond of) , but when you turn up the clip control, it smooths out the dirt and sounds very nice. the trick to using this one for me is running the clip control at it's higher or highest setting and adjusting the drive to taste.
 
the thing with the transboost circuit is that with the drive control turned up and the clip control turned down, you get opamp distortion (the OPA2134 is clipping) which can be a bit harsh and jagged sounding (which i'm not all that fond of) , but when you turn up the clip control, it smooths out the dirt and sounds very nice. the trick to using this one for me is running the clip control at it's higher or highest setting and adjusting the drive to taste.

I agree on the opamp clipping... it can sound really rough. This pedal has a lot of great sounds, but now I will need to find settings that can saturate the transformer without opamp clipping. Possibly run it with a 12-15V supply for more headroom or change the 2134 with something with a bit more horsepower. Thanks to you, I now can test and probe to my hearts delight!

When I have more time, I will experiment further... because some are claiming that core saturation just sounds awful and others claim a magical tone. I want to hear it for myself and know that what I am hearing is definitely the result of core saturation.

-Frank
 
I agree on the opamp clipping... it can sound really rough. This pedal has a lot of great sounds, but now I will need to find settings that can saturate the transformer without opamp clipping. Possibly run it with a 12-15V supply for more headroom or change the 2134 with something with a bit more horsepower. Thanks to you, I now can test and probe to my hearts delight!

When I have more time, I will experiment further... because some are claiming that core saturation just sounds awful and others claim a magical tone. I want to hear it for myself and know that what I am hearing is definitely the result of core saturation.

-Frank

Hearing this actually makes me think it could be worthwhile to wait a little before getting one of these made, in case you happen to come across some cool modifications to the circuit.

Now I feel good about not being an early adopter! :laugh:
 
the LT1054 chip that supplies the -9V has an input voltage limit of 15V so I wouldn't go past a 14V power supply. that would still be running it at +&- 14 volts. I did try an MC33172 chip there which clips more gracefully than an OPA2134 but it still was a bit harsh when driving it hard.
 
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the LT1054 chip that supplies the -9V has an input voltage limit of 15V so I wouldn't go past a 14V power supply. that would still be running it at +&- 14 volts. I did try an MC33172 chip there which clips more gracefully than an OPA2134 but it still was a bit harsh when driving it hard.

I just looked at the measurements that you made earlier in this thread. You were seeing over 10Vpp of clean signal at one of the primary driver opamps before clipping. That is plenty of signal to easily hit core saturation with low frequencies. This tranny is suppose to saturate with 4mA of primary current, which means that a LF signal with an amplitude of 5.5Vpp out of the push-pull primary opamps (or 2.25Vpp from one driver output) will start to saturate the core. So there is plenty of clean headroom to saturate the core with the 2134.

The opamp clipping may be in the output 4558. Since you can have over 10Vpp of clean signal sitting at the junction of the secondary coil and R10 (with higher frequencies), the 3X gain of the output opamp will cause clipping there. If we change the gain of the output amplifier to unity gain by making R12 10K, then that would guarantee that we can hear more of the core saturation before any opamp clipping occurs.

But the way it sits right now, we are on the edge of core saturation and opamp clipping occurring at the same signal level.

-Frank
 
Here is the R12 revision that I believe will allow for more LF core saturation without opamp clipping. I also changed R6 and R7 for more drive gain available for low output instruments.

***IMAGE REMOVED FOR LATEST CHANGES***

My apologies for the oversight.

-Frank
 
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Hey John, please see if I have R6, R7 and R12 identified properly.
TB R6R7R12.jpg


Thanks!
-Frank