SuperTeddyReg

The SuperTeddyReg is an evolution of the TeddyReg. Like the TeddyReg it consists of two stages, a voltage regulator and a low pass filter. Thevoltage regulator is in charge of providing a stable voltage regardless of variations in the input voltage due to load or mains voltage variations. In addition it reduces the ripple.

The low pass filter stage cleans the mains noise, and noise generated during the AC rectification process. The ripple at the output of the rectification bridge and smoothing capacitors has a saw-tooth form and can reach, depending on the quality of the capacitors and the load, tens to hundreds of mV. A signal with saw-tooth form is actually a combination of sine waves signals at higher frequencies. This ripple is therefore equivalent to noise at all audio frequencies and above, causing coloration and lose of details. The low pass filter stage reduces this noise to a very low level.

The SuperTeddyReg was designed to allow positive and negative versions using the same PCB.

The Circuit

The Regulator Stage

The regulator stage consists of a current source and a bipolar transistor configured as a voltage reference(acting like a Zener). Unlike the TeddyReg, the SuperTeddyReg is no longer using a the LM317 for the regulator stage. Although it provides a good level of voltage regulation, the LM317 is very noisy, and even the following filter stage is unable to completely filter this noise.

The Current Source
Q1 and R1 act as current source (for the positive version Lnk1 should be positioned at the "+" position. Use R1+ and a link instead of R1-). With a 2SK363BL and 100R the current is around 1.5-2mA.

The Voltage Reference
Q2, D1, R2, and R3 act as voltage reference. I have tried various configurations, and found that this configuration performs better than anything else. Zener diodes are extremely noisy, even monolithic voltage references and shunt regulators such as the LM329 were too noisy.

The voltage at the base of Q2 is about 2.42V (the LED voltage + the transistor Vbe), which means that about 0.57mA flows through R3 (when set to 4.2K). The voltage on the Collector of Q2 is equal to the Vb + Ir3 x R2. Using 42K for R2 we get 2.4 + 0.00057x42000 equals around 27V. In practice the voltage varies and a 10K trimmer is recommended for fine tuning.

Comparing to a Zener diode or monolithic voltage references, a transistor based voltage reference has high output impedance, but since there is no current through the gate of Q3 the output impedance has no effect in this circuit. On the other hand this voltage reference has a significantly lower noise level which is much more important in this context.

The voltage reference is followed by a first order low pass filter Gyrator that cleans part of the ripple. R6 is a bias resistor, it should be set to allow 1-3mA through Q3. The purpose of this resistor is to force Q3 into its linear region where it performs better.

The diode is used to accelerate the charging of C1.

The Filter Stage

The filter stage is a first order low pass filter consisting of R7, C3 and C4, and Q6 and Q7 acting as Gyrator.

R7 and R8 make a voltage divider and should be calculated to allow a minimal dropout of  2V on the filter stage. The negative Vgs of Q6 is approximately equal to the positive Vbe of Q7, which means that the output voltage is approximately the same as the voltage of the voltage divider.

R7a, R8a, and Q5 are optional and act as accelerator, that is, they charge C3 rapidly and disconnect as soon as C3 reaches the final voltage defined by R7 and R8. The accelerator circuit is required when powering DACs, clocks, and other CD circuits where start time is critical.

Short Circuit Protection

A 2SK363BL has a current limit of about 12mA, and the D44H11 has a hfe of about 200, the combination of the two allows a maximum current of around 2.5A. The D44H11 can withstand up to 10A and 50W so in practice the circuit is protected against short circuits at the output (I have tried it...). Note however that using jfets with higher Idss will allow higher currents.

Negative Version

The SuperTeddyReg PCB was designed to allow implementation of either positive or negative version on the same PCB. For the negative version:

- Use a wire link instead of R1+
- Use a wire link in the "-" position of Lnk1
- Reverse the polarity of all electrolytic and Tantalum capacitors
- Reverse the LED polarity
- Reverse Q1
- Use P channel  jfet for Q3 and Q6 (e.g. Toshiba J74). 
- Use BC560C for Q2
- Use D45H11 for Q4 and Q7
- Use BC560 for Q5

Sound Quality

The sound of the SuperTeddyReg is better than the TeddyReg, and better than anything else I have tried so far (I keep saying so with every new version...). The effect is all over the spectrum but, as could be expected from the measurements, especially in low and mid-low frequencies. Piano has more presence and sounds more natural, drums have even more punch and dynamics, and everything is more focused and involving.

The SuperTeddycap can be ordered as built and tested modules or as PCB, ordering info.

Construction Tips

The SuperTeddyReg is extremely sensitive to component choice, I therefore strongly recommend buying the built-and-tested version. The following tips may help you select the right components in case you decide to built it yourself.

JFET Transistors

I have seen several series of defective/poor quality jfet transistors, and discovered it only while using noise measurement equipment. These transistors usually had an Idss outside the specifications. Test the voltage between the gate and source of the jfet transistors, it should be negative and between 100-300mV.

Capacitors

C3 is the most critical capacitor. Although you are welcome to experiment, I have found that mil-spec axial Tantalum perform the best, you need the Dry type, not the Wet (all the Wet the I've tried are more expensive and have higher leakage current).
Here again, not every dry mil-spec axial capacitor performs the same, and you need low leakage capacitors. I have measured the leakage current of many capacitors and found that the blue Vishay M39003 perform very well. Alternatively, a pair of 10uF Tantalum SMT can be used, one on top of the PCB and another below.

For the electrolytic capacitors I often use Rubycon ZLH.

The ceramic capacitor should be X7R or COG/NPO. I often use SMT capacitors in this position.

Don't use unbranded Tantalum capacitors (unless you can measure their leakage voltage). Not only that they don't sound good they can explode and blow other components. AVX are my preferred, and AVX SMT are very good.  

Resistors

I use good quality 1% 0.25W metal film resistors. Since the calculation of R3 is quite complex, I recommend using a 10K trimmer to set the exact value.

Assuming a 10K trimmer, R2 should be calculated as follows:

- For output voltage between 20-30V use around 50K
- For output voltage between 10-20V use around 25K
- For output voltage below 10V use around 10K

R8 and R8A should be calculated to allow at least 2V dropout.

The dropout on the second stage (Vdo) can be calculated using the following formula:

Vdo = Vout / ((R7+R8)/R7) -1)

Using 100K for R7

Vdo = 100 * Vout / R8

 or

R8 = 100 * Vout / Vdo

For a dropout of 2.5V

R8 = 40 * Vout

Where R8 is in Kilo Ohm 

 

The SuperTeddyReg design is the property of Teddy Pardo and is published for non-commercial use only.