The Symphonies Plus Vacuum Tube Pre-amp is made and sold by YS audio as a level 2 product for around £490 + duty and taxes in the UK. YSA have a scale of 1 to 4 for their products and they sell a number of pre-amps and power amps at various levels of internal parts quality and upgrades.
This pre can be upgraded to level 4 by some mods and tweaks recommended by the original designer. It needs some changes to get the very best out of it and in some set-up's without a few critical mods it could sound mis-matched. It uses 3 x Ecc83 (12AX7) tubes with global feedback in the circuit. Sound of the unit before any upgrades or mods is fast, dynamic with bite and edge without being overly sharp, not at all fat, slow, coloured and mushy like some other tube amps can be. Construction quality as standard is excellent with a full non magnetic anodised black metal chassis, thick brushed aluminium face plate, anodised aluminium knobs, C core mains transformer, regulated power supply, tube rectifier, circuit screening and tube dampers etc. Dale resistors are also used throughout the circuit.
This model includes the following part upgrades :-
- 14 x WBT Gold RCA sockets
- Silver Teflon Wire on CD and AV input
- CCC Wire on other inputs, audio ground and output
- Power Supply cap upgrade
- SCR Tin Foil and Ansar capacitors in the main circuit
- Russian Glass Silver Mica By-Pass Caps on Output Caps
- Silver Mica By-Pass Caps in Input and Center Stage Caps
- Dale Resistor DACT step attenuator
On some power amps that are a very difficult load (Low Z Input) seem to cause a mis-match were the coupling caps fitted are a little too small in value resulting in some bass roll-off making the pre sound thin. I suspect the manufacturer has tuned this preamp to drive their own easy load tube power amps were it would never be a problem. Therefore the most important upgrade you can make if you find your unit sounding a little lacking in weight or body is to change the coupling caps not only to better quality types but to slightly larger values. The input cap on this unit was increased from 0.22uF to 1uF. The middle stage cap from 0.22uF to at least 1uF and the output cap from 1uF to 2uF or higher. This alters the character of the pre and adds more flesh to the sound even if the pre manages to drive your power amp fine to begin with.
The next best upgrade to make is add a good NOS tube at the input, this being the middle tube in the chassis. For example adding a single Mullard 12AX7 gives the pre some lushness and warmth but using all Mullards can make the amp sound too soft, lazy and laid back. Just a matter of personal taste here; but I would certainly replace the input tube at least for more refinement. I found a Brimar a good compromise here.
After changing the caps and input tube the next recommended mod is to change the input wire for some unscreened single core, either copper or silver. The standard screened cable fitted is ok wire but it does not need to be screened at all with zero noise or hum when un-screened. The screen just increases the cable C resulting in loss of detail in the treble and mid band. I replaced all the screened wire throughout with high grade un-screened Teflon coated wire with no problems of noise or hum pick-up as the psu is ultra quiet to begin with.
Cathode By-Pass Addition
This pre has no cathode by-pass caps in the circuit. It is quite fashionable to omit these in many tube designs when possible as most think they degrade the sound. However without the cap you get local negative feedback and reduced gain in the lower frequencies. The sound is generally cleaner and mid focused without a cap but sometimes an amp can sound tonally in-accurate without it. Adding small quality cathode by-pass caps can be a compromise. In this pre I tested a 47uF 25V to the centre stage cathode resistors (outer tubes in the chassis). This altered its tonality and it takes on a more organic warmer sound throughout the frequency range. Connect these across resistors R6 (1K8) for both sides. Again, maybe a matter of taste here. I later removed the cap as I think the cleaner sound is better.
This is a super quality preamp to begin with but after some mods it puts it in the higher end category. This pre (before the cathode mod) was in a shoot-out with the upgraded DiyHS EZ-Pre, a £2000 croft pre-amp and a light speed attenuator. The Symphonies Plus did not let the side down and had the widest bandwidth, fastest most dynamic sound in the bunch with a deep controlled sound. It did not give up anything to the expensive croft in terms of imaging and detail, but the croft did have the cleaner purer mid band.
** Main circuit inside zip file download below **