[traynor-amps] Traynor Mod Thread (Long) Date: Thu, 31 Jan 2002 22:04:06 -0000 From: "cronerror" I started a thread about a month ago asking for peoples experiences with mods to Traynor amps. I thought I would share a couple of my own. I will offer a couple examples of my favourite circuits I have put into various amps in future posts, but thought that a post on "best practices" would be helpful. There are a couple of things that I now do to all my amps, Traynor or otherwise, that I mod. First, the disclaimer. I feel pretty strongly that early to mid sixties Traynors sound pretty good stock. My sense of history determines that any tweaks I do to these amps, is reversable and doesn't involve chassis drilling, or defacing the amp in any way. Since the seventies versions of these amps are 1) less rare (I feel), and 2) use lower quality parts in some cases (ie. Output Transformers, etc.), I have done most of my "mad science" projects on these amps. My favourite patients are Voicemasters, Bassmasters, and MKIII's. I have worked on MKII's and Custom Specials to a lesser extent. That being made clear, two mods I do to all amps that I am using as "mules", are 1) Buss/Star grounding, and 2) tube filaments referenced to an elevated DC voltage. These mods affect the noise performance of your amp. They assume you are making other changes to the circuit board, and are usually implemented "while you are in there". BUSS/STAR GROUNDING Most Traynors have the input jacks and speaker jacks grounded to the chassis. In lower gain circuits like most Traynor ones, this can work fine. With this approach, ground loops can be a particular problem if you implement an effects loop, and are plugging into AC powered rack effects. If you want to install a ground lift switch in order to eliminate ground loops with other gear, or are concerned about noise levels when modding to higher gain circuits, better results can be had with a buss/star ground. An interesting implementation of this can be seen in the last models of MKIII amp (around 1977/78). Traynor implemented a buss ground on the eyelet board, in the form of single length of #14 buss wire soldered into an eyelet at one end of the circuit board on the pot side. The length of wire then spanned the length of the board on the same side and was soldered into the last eyelet at the other end of the board. Traynor then soldered all ground-connected board components to the buss wire, rather than the individual eyelets on that side of the board. A single wire from this ground buss is then connected to the ground lift switch, which gives a choice of grounding direct to the chassis, or thru a 10nF cap. In order for this switch to work properly, the ground lugs of all pots on the front (or rear) apron,as well as all PS caps and speaker jacks, have to be on their own busses, and then attached to the same ground lift switch on their own separate wires. If you then isolate all jacks from the chassis, using fiber shoulder washers, and attach their grounds to one of the busses, you have the ability to lift your circuit grounds completely from chassis ground. The results - a vastly noticeable improvement in noise performance and NO ground loop potential. This is a bit of work to do, but gives a great payback. FILAMENTS REFERENCED TO AN ELEVATED DC VOLTAGE One of the most common forms of noise injected into tube audio circuits is AC line noise coming into the tubes via the filament supply. In Traynor amps this supply is always AC, and so you have 60Hz noise being injected directly into your tubes. This is especially noticeable in the smallest signal tubes (the first preamp tube position, for example) because the signal to noise ratio is so low there. One of the ways to avoid this is to rectify & filter your filament supply, and run the tubes off DC heaters. No AC equals no noise. This mod can be a pain to implement, though, and requires a higher current from your filament supply. This can lead to thermal stress on your filament winding. I don't do it for these reasons. A simple and effective alternative approach, is to reference your AC filament supply to an elevated DC voltage. Before you run shreiking in terror from the room, this is REALLY easy and gives HUGE results in terms of noise performance. Here is what you do. (Disclaimer - unplug your amp and drain your filter caps before you do any of this!!) 1) Get a schematic for your amp and find out if your filament(heater) supply is a) centre-tapped, or b)balanced to ground thru 2 (usually 100 ohm) resistors. Locate either the centre-tap wire or resistor junction in your amp. 2) Find the point in your power supply, where the choke or 470ohm 10W resistor meets with the second filter cap. 3) Install a 4 lug terminal strip in a convenient place at the PS end of the chassis. 4) Run a wire from point "2" above to an end lug of the terminal strip. 5) On the terminal strip, solder a 330K 2W resistor between the lug with the wire and the next lug. 6) Solder an 82K 2W resistor, with a 10uF 160V cap in parallel (postive terminal of the cap toward the 330K resistor), from the "bottom" of the 330K resistor to the last lug of the terminal strip. 7) Solder a wire from the last lug of the terminal strip to your star ground point. What you now have is a voltage divider to ground with approximately 1/4 of the screen grid voltage or somewhere ~75 volts, at the junction of the 330K and 82K resistors. The actual voltage at the junction is a function of your supply voltage, and can be anywhere between 40 and 100VDC volts to be effective, so don't agonize over it too much. The 10uF cap just provides additional filtering. The final step is to lift either the centre-tap wire, or the ground end of the two balance resistors for your heater winding from ground, and solder it to the junction of the two resistors on the terminal strip. You have then effectively "raised" your filament supply ~75 volts above ground and lowered the noise floor significantly. If you were to measure across pins 4 or 5 to pin 9 of any preamp tube you will only read 6.3 volts - what the tube "wants" to see. The tangible result though, is that you will hear only ... silence. These two mods are the most easily integrated, most effective ones I do for noise reduction. More to come. Have fun. Craig If you can't gig with your YBA-1 because of volume problems, try using your volume control. On all of my guitars, there is a 150k resistor and a .001uf cap across the input and wiper of the volume controls to keep them bright at lower volume settings. It sounds ten times better than using a Tube Screamer IMO.