elkulon wrote:Actually, about the mistic IC, Tech21 uses TLCs (CMOS rail-to-rail opamps, from Texas Instruments) often in their designs.
I believe that's the reason to go for +-5V, since those opamps get fried above +-8V (or 16V, whatever you want to name it). Otherwise, I believe that there should not be reasonable to supply a regular 072 with that low voltage. Unless "that" would be the real trick of the "machine".
Anyway, thanks for taking the time and share.
Hope you'll feel better.
av500 wrote: but maybe the real secret is only in the magic box
SansAmp products rely strictly on such “heresy” as overdriving OpAmps.
There is no universal “SansAmp circuit” and thus the insight is limited to SansAmp GT2. However, what are universal are the approaches and methods of tone shaping used in the concerned circuit
DimebuGG wrote:Schematic redrawn...
teemuk wrote:From that to another topic: Those diodes... In back-to-back configuration like that they pretty much have to be Zener type. What's the Zener voltage? Close to supply rails or much lower? It's a somewhat important detail.
teemuk wrote: From that to another topic: Those diodes... In back-to-back configuration like that they pretty much have to be Zener type. What's the Zener voltage? Close to supply rails or much lower? It's a somewhat important detail.
Am trying to repair a PSA1. Any hints would be appreciated.
PSA1 given to me to look at after a replacement transformer burnt out within 2 minutes of powering on. Trying to troubleshoot with 2 multimeter's and a basic level of electronics understanding, so is not very effective at all, want to repair it so that I can buy it.
Secondary winding to the analogue power supply side burnt out. Digital side appears to work OK. Guitar plugged into input and output taken to valve amp produces sound akin to an earthed connection.
Fix attempts to date
Have replaced all power supply circuit caps, diodes, and voltage regulators (except for small 79L05 reg), and added new transformer.
Powering is done with no inputs or outputs and all pots turned full to the left.
Two symptoms have presented. Initially the transformer secondary winding became too hot to hold after 20-30 seconds of power on. Digital side of device appeared to work OK. No other heating effect was observed. After troubleshooting one night device was left unpowered. Upon switching on the next morning the voltage regulator feeding the +15 volt rail became too hot to touch after 20 seconds and the transformer is now no longer overheating. Transformer has been checked and its AC outputs are OK.
Repairer wrote:Further question, av500, on your sketch of the amplifiers circuits you list the unknown IC's (ones with the code ground off) as DS1267.
I'm sure that somewhere else on a forum (perhaps this one) I saw that conjecture was that these "unknown" IC might be opamps.
Can you expand on how you determined what these chips were, i.e. were you lucky enough to have a still decipherable code on one of your IC or did you figure it out by testing inputs and outputs; if so how confident are you that you are correct.
I ask because one of the things that atttract me to this device is the ability to be able to secure any future repairs caused by failures by sourcing its cheap component spares whilst still available (as well as its alleged great performance (yet to hear for obvious reasons)).
This is a little aside. On this model I don´t see the "amp model" switching circuitry you mention in your book. I wondered where the 1k notch comes from on the "Tweed" model. I found no reference for that whatsoever.