Category: RIAA

DHT LCR RIAA preamp by Salvatore Aragona

Here’s a very interesting project worth sharing to all, hopefully will inspire some of you on the same journey. Achieving a quiet and good sounding LCR phono stage is not a simple project:

Hi,

I wanted to share with you the satisfaction of completing the most challenging project I’ve tackled so far, and I wanted to thank you and Rod Coleman for the fantastic PCBs you provided. It is a phono stage built entirely around DHT triodes and SITs, featuring LCR RIAA equalization. Here are the key details: 1) First stage: two 3A5 sections in parallel with a UTC A-30 anode choke and 0.15µF Miflex KPCU capacitor; filament bias using a Pathaudio resistor; 45V anode, 2.2mA. 2) Second stage: 2SK79 SIT with a Tamura A8713 interstage transformer and SiC diode + resistor bias; 58V, 5.8mA. 3) LCR RIAA network with Noguchi Finemet-core inductors, Teflon capacitors, and Charcroft Z-Foil resistors. 4) Noguchi 600:50k Finemet-core transformer. 5) 01A tube with mu-output gyrator, direct-coupled (capacitor-less) to a MOSFET source follower PCB regulated at 15mA; 0.33µF Miflex KPCU output capacitor. 6) Four power supplies, each with an independent transformer, diodes, and CRC filter. 7) Anode power supply with a Telefunken mesh-plate vacuum rectifier and cLCLC filter; the first capacitor is 2.39µF, composed of a 2µF military-grade 800V polystyrene unit (actually two 4µF/400V units in series) plus a 0.39µF Audio Note copper-foil PIO capacitor; Tango TC160-35 choke; other capacitors include polypropylene types and Tentlabs MEC50s. 8) The anodes of the 3A5 and 2SK79 are fed by Linear Audio T-Reg V5 series regulators. I’m posting a few photos here; I’d be happy if you published them on your site (feel free to decide whether or not to do so).

The system is extremely quiet and, in terms of sound quality, far superior across all parameters to the Audio Note M5 Signature I previously owned.
Best regards
Salvatore Aragona

LCR by Salvatore Aragona

Credits

Salvatore wished to mention the following people who inspired him and helped to realise this project: Rod Coleman, Antonio Maggio, and Giovanni Giorgianni and myself 🙂

Excellent job Salvatore.

Tuning the system for ETF

This year I entered the shootout competition and will bring my DHT system to the European Triode Festival in France. It’s comprised of the ER801a stage plus the 01a (if extra gain is needed) and the 4P1L PSE output stage

I will have to swap out the amorphous OPT for the Monolith Magnetic ones as the speaker load is 5R.

It’s going to be interesting!

DHT Phono Stage Test

High gain stage with DHT

Some time ago a colleague  (Shawn Fox) contacted me to find out whether I could test some rare high-mu DHTs. I didn’t have them in my stash, so he offered to send them across for testing. He was quite keen to find out the performance with a gyrator load due to the particular characteristics of the DHT in question. The valve in question is the CX-340. There isn’t much information about this valve am afraid and coincidentally, Thomas Mayer (Vinyl Savor) wrote not long ago a review of this valve.

Tracing the curves, the first step

The high anode resistance as well as the low anode current in which this valve operates makes it a real challenge to implement successfully. Hence, this is why the gyrator load plus an output follower stage comes into play as the best companion for this valve. Before we look into the circuit itself, I submitted the 40 valve to the mercy of my tracer:

Continue reading “DHT Phono Stage Test”

LCR Phono: design notes (Part III)

My previous design wasn’t good for two reasons:
  1. Input capacitance was too high due to Miller effect.
  2. Overall gain wasn’t enough: 55dB was marginal as 60dB would be ideal for an MC stage. Obviously this doesn’t apply to an MM cartridge where 40dB should be more than ok.

Continue reading “LCR Phono: design notes (Part III)”

LCR Phono: design notes (Part II)

Introduction

This is a continuation of my previous blog post. I will try to share my experience through the design process of this RIAA stage through these individual posts with an attempt to spark some interest in others and in return to get some valuable input from the experience and knowledge of others. Hope this works!

First stage

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Here is the initial design version for analysis. I’m working through this step by step and refining the circuit in every iteration. The initial circuit is very simple. The first stage is key. We want to achieve as much amplification as possible from this stage before we hit the LCR network. The choice of the 6S17K-V valve may appear as a surprise to the ones not familiarised with this valve.  Here are some notes from Wavebourn around this valve:

Continue reading “LCR Phono: design notes (Part II)”

LCR Phono: design notes (Part I)

Introduction

A phono stage is probably one of the most challenging circuits to build in audio. Clearly not for beginners, many make the mistake in adventuring in building one. There are several designs which are simple, albeit many are poor ones. In addition to the challenges related to high-gain and very low noise design, audio enthusiasts really overlook the fact that you need to be able to measure and adjust the RIAA curve for a successful phono stage build. This means that you need an IRIAA signal source and also an accurate LCR bridge to adjust the network. I personally built a great IRIAA box and procured several LCR meters including this one as part of my learning journey of phono stages.

Continue reading “LCR Phono: design notes (Part I)”

RIAA Preamp Power Supply

Introduction

I ran my JFET folded-cascode RIAA preamp for more than a year with batteries. Charging the batteries has been painful enough for me to decide to look for alternative supplies

A DC supply for an MC stage is not an easy task to accomplish. My battery pack ran out to a point that frequent recharging periods became a real nuisance, so decided to build a DC supply.

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The new power supply (far left), the Lenco turntable (right) and the RIAA JFET stage (middle)
Continue reading “RIAA Preamp Power Supply”

Merry Christmas!

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It is so great to have another Christmas. It gives us an opportunity to wind down and spend proper time with our loves ones. The ones who are physically with us, and remember the ones who are no longer here, but still very present in our memories.

In fact, we all look forward to the holiday period to crack on with our projects. We all have a pile of endless projects and ideas and no better time than Christmas to start working on them.

Continue reading “Merry Christmas!”