Metropoulos Forum

Yeah, I've tried the transistors; it's more of a tamed saturation, not as grindy as the diode clipping. Also depends on the size of capacitor you use before the Jose master.

The custom turret boards I make are designed to fit more of the components on-board, so none are installed over the preamp tube sockets. There are also shield location turrets for the shielded wires.

Best to use shielded wire that has at least a 22AWG conductor. The RG-174U coax is crap, IMHO.

I like to take Belden foil shield wire, remove the pvc coated wire from it and run silver plated teflon 22-20 AWG in place of it.

You may want to have the preamp ground buss, terminate at the first filter cap ground under the turret board if you have ground noise issues. I haven't noticed any problems grounding it at the screens/mains star ground thus far, but standard practice is to have it grounded at the first preamp filter star ground.

Experiment with different gain pot values as well, usually 300k to 500k will tame the higher gain if it's too much for you. I sometimes add a 2.2M on the input lug to the ground lug with a 1meg pot.

Can you shoot us the part number for those low noise carbon film résistors? (Green ones)...! thx

http://www.koaspeer.com/catimages/Products/SPR/SPR.pdf

The 1 watt and 2 watt versions work best for plate resistors. 1 watt versions have color codes and the 2 watt versions are all green with black alpha-numeric markings.

5150loveeddie wrote:Mike, for the transistor, is that the mod Chris was talking about? using one for more gain and less noise??

I think that the one:
The transistors were MPSA06 ....
Wired like this: BE--EB----BE--EB

Exactly where you use them as a Diode, but Hardriver Mark said he prefers the Zenerd and that he's seen amps that MarK C has built using the Zeners so go figure

mightymike wrote:

5150loveeddie wrote:Mike, for the transistor, is that the mod Chris was talking about? using one for more gain and less noise??

I think that the one:
The transistors were MPSA06 ....
Wired like this: BE--EB----BE--EB

Exactly where you use them as a Diode, but Hardriver Mark said he prefers the Zenerd and that he's seen amps that MarK C has built using the Zeners so go figure

Chris came here a few years ago (Ski vacation with his lady) we went to eat at a good restaurant in Montréal, was the first time I actually met Chris in person (we talk on phone a lot) anyway, he then start explaining me that the most you can get from a 12ax7 is 55-60% of the gain more then that that is «noise» he has a mod/way to go up to 100% using a transistor....I don't have a clue how you do it still!! lol maybe it is a «diode clipping» thing a la C e rrem, it was still is experimental he says, might not sound right ...I don't know.....

xenrelic wrote:http://www.koaspeer.com/catimages/Products/SPR/SPR.pdf

The 1 watt and 2 watt versions work best for plate resistors. 1 watt versions have color codes and the 2 watt versions are all green with black alpha-numeric markings.

Cheers dude

Notice the heaters on V1-2 are hooked differently.... your using dc there, pin 9 is not used (heater)? why, sorry for the ignorance...also the part number of that transistor comming from the dc transformer is hard to read.....didn,t see it on the shcematic..!

5150loveeddie wrote:Notice the heaters on V1-2 are hooked differently.... your using dc there, pin 9 is not used (heater)? why, sorry for the ignorance...also the part number of that transistor comming from the dc transformer is hard to read.....didn,t see it on the shcematic..!

You can run the heaters with dc, two different ways.

1. Rectify the 6.3vac heater supply with a bridge rectifier + a 4700uF cap and then connect the filaments in parallel with pin 9 positive and pins 4 and 5 negative. Make sure to also connect a 100 ohm resistor from the positive and negative lines to ground.



2. Build a regulated 12vdc power supply and connect the filaments in series with pin 9 disconnected, pin 4 positive and pin 5 negative.



If you heat sink the LM7812 Voltage Regulator to the chassis, make sure to disconnect the center ground terminal to prevent a ground loop. You can also isolate it with a mica spacer and use heat-sink compound instead of removing the center ground terminal. A TO-220 heat-sink should work also, if you don't want to drill the chassis.

thx man, didn't know that stuff, been away from here...!!

This won't damage the tubes? 12ax7 pin 9 not in use ?, question of proper heat

How about lifting the heaters up? (ex.50v above) I do that to all my amps and it works pretty well....VDC must be better even? I guess..!!

5150loveeddie wrote:thx man, didn't know that stuff, been away from here...!!

This won't damage the tubes? 12ax7 pin 9 not in use ?, question of proper heat

How about lifting the heaters up? (ex.50v above) I do that to all my amps and it works pretty well....VDC must be better even? I guess..!!

You can run heaters in series with 12V, no problem, that's what they are designed for. Just don't run them in parallel with 12v, use 6v in parallel.

Lifting the heater potential works great as well. It's just my personal preference to run V1 and V2 on DC, seems to work the best (noise wise) for me. You could probably go dc + lifting and get even better results.

Something like this:

This is good stuff thx for all the insights!!!

5150loveeddie wrote:This is good stuff thx for all the insights!!!

You're welcome, man.

Now we need some clips bro.... One I really dig is the Atomica, was never able to find an accurate layout/schematic for....

http://www.youtube.com/watch?v=0zaEnTNoLx8" onclick="window.open(this.href);return false;

1. Rectify the 6.3vac heater supply with a bridge rectifier + a 4700uF cap and then connect the filaments in parallel with pin 9 positive and pins 4 and 5 negative. Make sure to also connect a 100 ohm resistor from the positive and negative lines to ground.

Photo #1 above:

So can I tap off the PI tube? and how much current does the rectifier have to handle? I tried something similar once and had a smoke show.
Will this quiet a normal 4 stage hiss more than just the 6.3ac heaters.

ezs wrote:

1. Rectify the 6.3vac heater supply with a bridge rectifier + a 4700uF cap and then connect the filaments in parallel with pin 9 positive and pins 4 and 5 negative. Make sure to also connect a 100 ohm resistor from the positive and negative lines to ground.

Photo #1 above:

So can I tap off the PI tube? and how much current does the rectifier have to handle? I tried something similar once and had a smoke show.
Will this quiet a normal 4 stage hiss more than just the 6.3ac heaters.

It won't do jack shit for Hiss, it will only help reduce low 60hz hum, and possibly spew 120hz noise all over the place if your not careful.

If you want to do it with simple rc filtering, check out how Marshall employs it in their amps. The dsl is one popular example.