6Э6П-ДР driver tests

Here is a quick test I did today that the 6e6p-dr is a promising valve as a driver. I’ve used 6e5p and made several tests with these fantastic valves. Anyway, looking at a single sample from my stock:

The 6e6p-dr can do well and provide a nice 0.17% @ 200Vpp. Not many valves can do this in triode-mode.

Now, let’s look at the harmonic composition:

Edit (28th July 2014): The harmonics should be read: K1=H2, K2=H3, K3=H4 and so on.

Harmonic level is very low and dominated by H2 with raising H4 above 120-130Vpp. An interesting dip takes place in H3 closer to maximum swing level. This may be due to CCS FET load interaction and harmonic cancellation I guess. Beyond 205Vpp my CCS is limited by its HT supply. It can be boosted, but for a quick test, here is were it ends 🙂

This will be another valve to try as a driver in my next 300B project.

Orval and whole lotta love

Starlight: discrete DAC boards

Added the set of decoupling SMD low ESR capacitors for each board

Starlight Discrete DAC: more progress

I used a aluminium bar structure to hold both LL7903 transformers and the Russian PIO output capacitors. The LL7903 will be wired in 4:1 and the capacitor will prevent the DC current from the DAC to shunt to ground. Also used some silicon rubber to protect the mu-metal can of the LL7903:

Here are the DAC boards mounted on a PTFE board with a set of copper strips that will be used to solder 10 x 100μF SMD low ESR capacitors to improve decoupling of DC rails:

I think all fits in the box I’m planning to use 🙂

Starlight discrete DAC boards finished

After testing the accuracy of the R and 2R network, thanks to Jon managed to complete my discrete DAC boards for the Starlight CD player. Not very keen to solder SMD ICs but couldn’t get away from the tedious task of soldering 10 ICs:

Now need to continue with the DAC (or the transport). Lots of work to do still…

814 SE Amplifier: measurements

It was time to take the 814 SE Class A2 amplifier measurements. The challenge though, is that the amp is so heavy that I will never take it up to the workshop. Therefore, I decided to take my workshop PC down from the loft this time to see how the 814 really responded.

First test was to do a THD analysis as a function of the total output power. As you don’t want to do this with your speakers, and also the classic wire wound resistors (Alu-clad) are inductive, you want to use non-inductive resistors like this test jig:

I bolted on to a large heat-sink an array of resistors to form 8Ω in value by using a pair of 10Ω in parallel and three 1Ω in series. I added a set of binding posts and connectors for the speaker cables. this way you can easily wire your speakers and connect your audio test set to take the measurements.

Continue reading “814 SE Amplifier: measurements”

JFET RIAA Phono: Battery Charger

After enjoying the RIAA phono preamp for several weeks with the new battery pack, I decided to build the battery charger just not to be surprised by the lead-acid battery pack running out unexpectedly.

The lead-acid battery pack is formed by a 12V and a 6V 1.3Ah batteries. Between both batteries there is a total of 6 +3 cells = 9 cells. Each cell requires 2.27-2.30V of charge at 15-24C. Therefore the charging voltage should be 20.43-20.7V. Exceeding this voltage will reduce the battery life. The charging circuit has to be constant voltage, not current.

Rod recommended me a simple but very effective design based on the TL431a. The regulator output voltage is set by R1 and R3. 0.1% precision resistors are needed, otherwise a trimpot should be used as R1. R3 should provide at least 2mA for both Q1 and TL431a operation:

A simple PCB was built in less than 1 hour. You need to place the BD439 in a heatsink as it will get hot when charging the battery:

In a question of 2 hours the battery was charged back fully. I used it for around 20 days so far I think. The initial current is as high as 370mA and drops as the battery charges and the voltage goes up. The residual charged voltage was about 19.4V. This drops quickly after some current starts to flow through the preamp.

Fresh pilsner

Not music related, but it has to do with my other passion: brewing
Straight from Czech Republic, brought on a flight from Prague today, a nice pint of Pilsner lager!

4P1L DHT Preamp Siberian (Gen3) finished!

Introduction

Building a new version of the venerable 4P1L “Siberian” was very encouraging. This belated project finally came to life after some recent work on a new set of power supplies. So why 4P1L again? I always found the 4P1L sound to be unique. Great detail, overall tone and fantastic treble. What it makes it well suited for pre-amplifiers is not just its linearity (probably being the most linear valve out there) but the fact that it has a low anode resistance and current capability to ensure any challenging load can be handled effectively without any sound degradation. This can be heard particularly on the treble where the input capacitance of the amplifier is more evident and it is translated into treble loss. Other DHTs like 26, 01A, 30sp can only handle a few milliamperes of anode current and is not enough to charge and discharge the parasitic capacitance at high frequencies. More importantly, the 4P1L has filaments which aren’t demanding. This is a unique feature amongst DHTs that is rare and very useful. Having low-current filaments that can be either configured at 325mA or 650mA, low grid voltages and high transconductance in a valve is very useful. This mean that filament bias can be easily implemented without burning unnecessary power by swinging many volts to perform the desired level of amplification.

Continue reading “4P1L DHT Preamp Siberian (Gen3) finished!”

4P1L Siberian DHT Preamp (Gen3)

Recently I finished the filament supply for the latest incarnation of my 4P1L pre-amplifier. Here is the next instalment of this project. The HT power supply was refined after builiding more than 7 stacked HT supplies for the 814 SE Amplifier.

The supply design is very simple. Perhaps the selection of components and the refinement of some aspects of it is what makes the difference to me: Continue reading “4P1L Siberian DHT Preamp (Gen3)”