Synthacon, how to increase ouput level?

Lorenzo · Joined: Nov 09, 2008 Posts: 375 Location: Trieste - Italy

Hi

How can I increase my Synthacon ouput audio level?
I mean, now it sound very low/flat... in the PCB, where is write "level" I put a jumper, and 10k resistor just close...

thank you

andrewF · Posted: Mon Mar 08, 2010 9:31 am Post subject:

hi
just replace that link with a resistor.
maybe 100K would be a good startpoint.

or you could replace the link with a pot:

Ken's page describes what to do -
The final stage is a simple gain stage, as I found the original was too quiet for my needs. In the first version of the PCB, this stage was inverting, while on the Rev 1 PCBS, this stage is non-inverting. The LEVEL pads are to allow for a level pot to be installed. Use a pot with a value of 50k or 100k (going even higher if needed, e.g. 250k), depending on the overall gain required. Alternatively, a fixed resistor could be put here, or even a link, if the 47k in series with it is increased to compensate.

Lorenzo · Joined: Nov 09, 2008 Posts: 375 Location: Trieste - Italy

... ehmm

Lorenzo · Joined: Nov 09, 2008 Posts: 375 Location: Trieste - Italy

Hi,
just now I notice that Ken Stone has update the shematic of this filter!!!
v1.2

He corrects a "crack-click" problem of the resonance... (using a 10uf cap)!! Idea

and in reference to the topic
... adds a 47pf; an 330 ohm take the place of a 1K and a 47k resistor (in series with the volume pot) is now connect directly to OUT, instead of at previous 1k resistor!!! Exclamation

so I have to change my connections!
No problem with the resonance mod, I have already done it some time ago ... it was necessary
47pf is not a problem too ...
but I don't know what is the best way to put the level pot in series with 47k resistor directly to the out.

any ideas?

thank you very much in advance for your kindly reply!

andrewF · Posted: Wed Mar 24, 2010 2:29 am Post subject:

you do not have to do this mod.
Many Steiners work perfectly well with the feedback loop connected directly to the op amp output.

If you really want to do it:
put the 330R in the 1K position
the 47pF cap where the 47k resistor should go
install the link, with a nice little loop sitting up so you can solder a wire to it.
From the 'out' pad connect a 47k resistor, the other end gets connected to a wire that goes to your level pot.
Another wire goes from the level pot to the link, attach it to the top of the little loop you made when you installed the link.
The level pot will only have two wires connected to it.
one wire to the centre pin and an outer pin, the other to the remaining outer pin.

Lorenzo · Joined: Nov 09, 2008 Posts: 375 Location: Trieste - Italy

andrewF · Posted: Wed Mar 24, 2010 4:22 pm Post subject:

The resistor and level pot are for gain, but the capacitor is for stability to prevent unwanted oscillation. I think that is also the idea of the feedback loop starting after the output resistor. Ken did write about this once but I can't remember where or exactly what he wrote

This is original article on the steiner, by N. Steiner at Yusynth:
here