I have an old PCB from Old Colony for the Bride of Zen (BOZ) preamp by Nelson Pass. Schematic is available on the PassDIY website (I cannot find directions in FAQ on how to post a link to the page).
I understand that the BOZ has a start-up thump as the output capacitor charges up to the bias voltage for the gain transistor. I would like to avoid the thump by having a slow ramp-up of voltage - say 1 minute. Is there any easy way to do this on the PCB, perhaps by cutting traces and adding additional components. I am not really a "designer😕," but I can follow a schematic and figure out how to modify the board (I've done similar things on other projects in the past).
I understand that the BOZ has a start-up thump as the output capacitor charges up to the bias voltage for the gain transistor. I would like to avoid the thump by having a slow ramp-up of voltage - say 1 minute. Is there any easy way to do this on the PCB, perhaps by cutting traces and adding additional components. I am not really a "designer😕," but I can follow a schematic and figure out how to modify the board (I've done similar things on other projects in the past).
just use the correct startup/shutdown procedure.
startup: source, pre amp, power amp.
shutdown: power amp, pre amp, source.
problem solved. or you can use output relay with a timer.
startup: source, pre amp, power amp.
shutdown: power amp, pre amp, source.
problem solved. or you can use output relay with a timer.
BOZ will be used in an integrated amplifier
The BOZ and the power amp will be in a single chassis - as an integrated amp. I want to use only a single power switch so that it will be foolproof (wife-proof). If I put two power switches - one for the pre and one for the amp, it will likely be mis-used).
The fallback will be to use a mute on the pre output before the power supply ( I think I have a mute board from Old Colony as well - a Curcio design), but I would prefer the slow startup on the pre-amp (I will be using a DIY board on the amp as well).
Thanks for your suggestions, but I did consider them before posting.
I also considered running the preamp constantly and only switching power to the amp on the front (power disconnect for the preamp on the back, for safety).
The BOZ and the power amp will be in a single chassis - as an integrated amp. I want to use only a single power switch so that it will be foolproof (wife-proof). If I put two power switches - one for the pre and one for the amp, it will likely be mis-used).
The fallback will be to use a mute on the pre output before the power supply ( I think I have a mute board from Old Colony as well - a Curcio design), but I would prefer the slow startup on the pre-amp (I will be using a DIY board on the amp as well).
Thanks for your suggestions, but I did consider them before posting.
I also considered running the preamp constantly and only switching power to the amp on the front (power disconnect for the preamp on the back, for safety).
SoundHappy: Thanks: I actually have purchased a set of the boards from another DIY member for another project. This is not my first choice to address the turn-on thump, however.
if your volume pot is at the output of the BoZ, you can it turn down to zero before you start up.....( probably not foolproof) ;
or you try out to increase some of the electrolytic caps:
e.g. C2 in the power supply........C102/202 in the BoZ........
or you try out to increase some of the electrolytic caps:
e.g. C2 in the power supply........C102/202 in the BoZ........
or you look at the Aleph P1.7 Service Manual.
look at the part for the Startup delay and a fast turn off.
This circut Switch relays to mute Output at start and at turn off.
But i dont know, whether you can Switch the Output to ground at boz, to do that.
look at the part for the Startup delay and a fast turn off.
This circut Switch relays to mute Output at start and at turn off.
But i dont know, whether you can Switch the Output to ground at boz, to do that.
Increasing Capacitor and Resistor
>>>or you try out to increase some of the electrolytic caps:
e.g. C2 in the power supply........C102/202 in the BoZ........<<<
Thank you, MJF, for this suggestion. I will increase C2. I think I will also increase R-1 to decrease the current to C2, with the intent that this will also slow down the charge up of C2 and there more slowly ramping up the gate of the transistor regulating the downstream power smoothing capacitors. I will breadboard it first and plot the increase in voltage over time before settling on final values for use in the circuit board.
Geary
>>>or you try out to increase some of the electrolytic caps:
e.g. C2 in the power supply........C102/202 in the BoZ........<<<
Thank you, MJF, for this suggestion. I will increase C2. I think I will also increase R-1 to decrease the current to C2, with the intent that this will also slow down the charge up of C2 and there more slowly ramping up the gate of the transistor regulating the downstream power smoothing capacitors. I will breadboard it first and plot the increase in voltage over time before settling on final values for use in the circuit board.
Geary
or you can use an input mute/unmute that is automatic.
or you can use an output mute/unmute that is automatic.
Both these can use signal relays, or FETs and both can be controlled by a simple RC delay, or a 555 timer.
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