From: Steve A. (steve_ahola@yahoo.com) Date: 8/1/2000 3:46 AM Subject: Re: what is dumble about... [text] Steve Ahola P.S. I have been wondering about the improvements to the power supply mentioned by certain cloners... I bet it has to do with an added filter stage ahead of the power tube plates (which will reduce the ripple factor considerably). Am I close, Andy? * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * From: andyfuchs (FuchsAudio@nettaxi.com) Date: 8/2/2000 5:52 PM Subject: Re: what is dumble about... Steve: I'm really not too keen on starting a dialogue on specifics about what I'm doing in my modified amps or the production stuff, only because it (enevitably) leads to MORE questions. As we've discussed privately, I do suffer constant angst about trying to be both an Ampage "team player" and yet, be able to produce products that remain outside the forum. (I'll share some things from my bag of tricks, I just would rather not let you look inside it.) Rather than open the proverbial "can-o-worms", I will say that my general power supply philosphy is lots of reserve capacitance at the start. I know many feel that power supply sag is an inherent part of an amps sound (and I agree), but I prefer to induce this by switching to triode, or knocking down output power in other ways. I also think hi-speed rectifiers are very beneficial to the sound as well. The modified amps have fairly traditional R/C filters w/mylar bypasses. My choke filtering is usually "beefed" as space permits. Yes there is a practical maximum before there are no more returns. Yes, it increases the load on the P-former (mostly the turn-on surge), but I haven't lost a tranny yet, and I did this to over 2,000 Dynacos, and to a least few hundred Fenders over the past 20 years. The production amps have significant differences in both the power supply and audio circuit's (particularly in the preamp), which I choose to not discuss. I know you understand, and I hope the other forum members do as well. AF * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * From: Steve A. (steve_ahola@yahoo.com) Date: 8/3/2000 5:25 AM Subject: Re: what is dumble about... Andy: Well, if my guess was totally wrong your reply would have been much briefer... ;) From time to time people here have wondered about the power supply improvements mentioned on your web site... "what is Andy talking about?" I was looking through the Dan Torres amp book the other night and ran across one of his suggestions to reduce the ripple factor from 0.0214 to 0.000000000000044. Take a typical SS rectifier feeding a pair of 100uF/350v caps in series to ground (this node goes to the OT CT and on to the output tube plates). Well, add in an extra stage ahead of this consisting of another pair of 100uF/350v caps in series to ground followed with a 10 ohm 10 watt resistor. This results in a loss of perhaps 2 volts in the B+ but as mentioned above reduces the ripple factor considerably... Sounds like an interesting experiment to try if you have a few extra caps lying around and plenty of room on your power supply board. Maybe someone who has tried this trick can let us know if it is a worthwhile mod. As for "tube sag", it seems like most of the modern high-gain amps (except Boogie!) are using ss rectifiers and humongous power supply filters. IMHO it is the older amps that were designed for tube rectifiers in which the "tube sag" is a critical part of the cranked sound...) Adding "tube sag" to a modern high gain amp isn't always desirable. It's like driving on the freeway and you want to punch it to switch lanes... all of a sudden, the "tube sag" kicks in and your vehicle is not accelerating fast enough to avoid the 18 wheeler that rear ends you. In the hospital you brag to your friends about replacing the solid state ignition module with one that uses a tube rectifier... Steve Ahola * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *