Hey guys,
I've been hunting for this but I've came up dry. I just got an ppp 6550 amp. Its a audio research d115. When I turn it off I get a click then a loud thump out of the speakers. What is the usual cause for this? I'm guessing its carted by a cap discharging but I'm not sure where to begin to find it. Its a loud enough thump to get me worried about my GPA 416's its driving.
Any help would be great.
Thanks,
Nick
I've been hunting for this but I've came up dry. I just got an ppp 6550 amp. Its a audio research d115. When I turn it off I get a click then a loud thump out of the speakers. What is the usual cause for this? I'm guessing its carted by a cap discharging but I'm not sure where to begin to find it. Its a loud enough thump to get me worried about my GPA 416's its driving.
Any help would be great.
Thanks,
Nick
I bet the B+ voltage goes down to near zero way-fast. Add a bigger filter cap and see what happens. Inthe best case you should turn off the power and the amp continues to make music for a second or so then fades out. For that level of performance you might need another RC stage prior to where the power goes into the output transformer's center tap. But try an experiment with a bigerr cap rigged in parallel using wire with clips.
its normal.
its called counter emf of the output transformer.
get a 5A dpdt relay and switch the speaker in and out.
I used 115V aircraft ones ( cheap and lower dropout) and connected it to the violet wire off the power transformer primary (100V tap).
I took a 100 ohm 12W resistor and went across the nc circuit to speaker common so when the relay is de-energized, the transformer had a load. when the relay closes, it switches to the speakers.
Try temporarily disconnecting the gNFB loop. The schemo looks to have two capacitor couplings, and these are possible culprits for LF instability. From Nyquist theory, it is possible to have too little A_vol. Insufficient A_vol can cause that Nyquist plot hit the forbidden -1 + j0 point, even if more gain causes a miss.
Power down a tube amp, and voltage and cathode temp drops, and with it, A_vol. Then you get that burst of oscilation when it goes unstable. With no power, the finals will pull down the remaining charge pretty fast, and you get that loud bang.
Yes, but isn't the reason for this the voltage at the center tap going to zero nearly instantly? If you can prevent that then you don't need the relay.
The relay is not hard to wire, power the coil with the 6.3v heater supply. Better to have timers control relays for power and speaker but that gets real complex. I think better to try and fix the root of the problem and not use any relays
For safety of the transformer I always place a 470R resistor across the output. Then een if a voice coil fails the secondary never sees an open circuit. The 470 does not waste much power but saves the OPT if the speaker cable comes loose or whatever. I'd rig a failsafe like that before messing with relays
It may not necessarily be any shortcoming or poor design. While powering down the working points of the various stagers change drastically in random order, so that temporaray imbalance or NFB trying to maintain the status quo could result in some transients depending on what the loop gain is at any specific remaining ht.
If it is large enough to worry you or generate visible large travel of drivers' cones on the loudspeakers then decoupling them immediately at switch-off, as said above, is a cure.
My question would also be, is the same thing happening on turn-on?
If it is large enough to worry you or generate visible large travel of drivers' cones on the loudspeakers then decoupling them immediately at switch-off, as said above, is a cure.
My question would also be, is the same thing happening on turn-on?
I Know what it is...due to a crazy design were the tube regulated voltage are used both to the screen-grids (output) and the 1. stage amp. The regulator tube is controlled by an op-amp and its loosing its power long before the rest of the amplifier. It causes an impuls from 1. stage and the solution is to cut the supply line (for the opamp) and insert a diode + 10.000uF whish hold the supply long enough. Then thére is no more bump.
Last edited:
Thats right...I have made it and it works. I was a little dissepointed that they mix voltage supply which run the input stage and output screen grid. There will be much fluctuation due to power modulation at the output tubes. It seems its been an 'oops'...then they made the exstra solid state regulation. I would newer mix anything in the output with anyting in the input. I always run theese things at seperate supplys.
Just my 10cent
Just my 10cent