I've built a few B1 buffers, but have become concerned about the initial level of DC offset since I bought an SVS SB-3000 with its 800 watt amp.
Initially, the units output about 150mv of offset, which dies down to nearly zero within a few minutes.
It is that first few minutes that worries me, particularly with the sub.
I know that I can just wait to turn on the amps, but this negates the ability to use the automatic turn on and, more importantly, annoys my wife who just wants music without any annoying complications.
Is there any way to block this DC offset from the get go?
Initially, the units output about 150mv of offset, which dies down to nearly zero within a few minutes.
It is that first few minutes that worries me, particularly with the sub.
I know that I can just wait to turn on the amps, but this negates the ability to use the automatic turn on and, more importantly, annoys my wife who just wants music without any annoying complications.
Is there any way to block this DC offset from the get go?
What would the impact of the 1M resistor be on output impedance and/or sound quality?
Qwertyl's suggestion is interesting, but the delay would be far too short. It is probably a good three minutes before the offset drops to insignificance.
In looking at other B1 threads, I ran into a post by the late, great AndrewT on offset in a B1 that seems related. Any thoughts?
Qwertyl's suggestion is interesting, but the delay would be far too short. It is probably a good three minutes before the offset drops to insignificance.
In looking at other B1 threads, I ran into a post by the late, great AndrewT on offset in a B1 that seems related. Any thoughts?
I should have mentioned that I have two outputs (but offset is the same whether they are plugged in or not).
clarify - what is original B1
original FW product, or first DIY schematic, with single rail and caps on input and output?
pictures could help, also
original FW product, or first DIY schematic, with single rail and caps on input and output?
pictures could help, also
@Hamett: the original Pass B1 has no DC offset as it has output capacitors. For some reason people use wrong names when asking questions which leads to misunderstanding and a lot of noise. It is also not respectful to people that want to help out. Probably it is about a DC coupled DCB1/Mezmerize but the latter should have a muting relay which of course is the only good solution to prevent power on/off phenomena. So which B1 did you build? If it is either one of the mentioned versions you forgot something 😀
Your (apparently) DC coupled device must have power on/off muting and there should be at least 1 cap per channel in the chain either at the input of the power amplifier or at the output of the DC coupled B1-like device.
And for gods sake, it is mV and Watt.
Your (apparently) DC coupled device must have power on/off muting and there should be at least 1 cap per channel in the chain either at the input of the power amplifier or at the output of the DC coupled B1-like device.
And for gods sake, it is mV and Watt.
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My experiences are very different (this counts for many others as well) and this thread subject speaks for itself. The first post speaks of 150 mV DC offset and the OP and his wife having annoying power on/off phenomena. What more reasons do you want? The PLOP alone is annoying and simply solved with a 5 $ circuit. Therefor the Diyaudiostore Hypnotize and Mezmerize do have a muting relay which is simply good design practice, certainly with DC coupled devices and it is a very adequate prevention of completely unnecessary issues.
Comparison:
Pass B1: single power supply, input and output capacitors so no DC offset but power on/off phenomena.
DCB1/Hypnotize/Mezmerize: symmetric power supply, DC coupled, possible slight DC offset (no caps) depending on matching JFETs, muting relay in design so no power on/off phenomena.
OP either built a Pass B1 without output caps or the better DCB1/Hypnotize/Mezmerize without muting relay 🙂 Or ...OP uses wrong terms and means only power on/of phenomena of the Pass B1 and calls it DC offset. In that case the muting relay (omitted in the original B1) still is the solution. Or an upgrade to a Hypnotize/Mezmerize.
Comparison:
Pass B1: single power supply, input and output capacitors so no DC offset but power on/off phenomena.
DCB1/Hypnotize/Mezmerize: symmetric power supply, DC coupled, possible slight DC offset (no caps) depending on matching JFETs, muting relay in design so no power on/off phenomena.
OP either built a Pass B1 without output caps or the better DCB1/Hypnotize/Mezmerize without muting relay 🙂 Or ...OP uses wrong terms and means only power on/of phenomena of the Pass B1 and calls it DC offset. In that case the muting relay (omitted in the original B1) still is the solution. Or an upgrade to a Hypnotize/Mezmerize.
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Ha ha that is clear and convincing information 🙂 Some say the same but they switch the power amplifier on after the buffer. Also input impedance of the power amplifier will have some influence.
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proper switching on and off sequence must be second nature, at least for someone making own amplification ........ even when there is no need for care (no plops)
as I said - if there is no need for delay mute circuit, I'm not including it
if there is need, of course it must be included
as I said - if there is no need for delay mute circuit, I'm not including it
if there is need, of course it must be included
Nonsense (the second nature item) as it can be done randomly when issues are prevented with a 5 $ circuit and like it was already done in good designs since the eighties. One can not force laymen to have a specific power on/off sequence certainly not in a family.
Also not appropriate in this thread. If we read and interpret rightly what OP means we can conclude that muting is needed in this very case. I assume the SVS SB-3000 subwoofer to be the active and "auto on" type which likely reacts quite fast as it is Class D and this will give a truly nasty PLOP. So I can not think of any other solution for the sub at least.
Also not appropriate in this thread. If we read and interpret rightly what OP means we can conclude that muting is needed in this very case. I assume the SVS SB-3000 subwoofer to be the active and "auto on" type which likely reacts quite fast as it is Class D and this will give a truly nasty PLOP. So I can not think of any other solution for the sub at least.
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you're reading what is written, or what you want that is written?
"as I said - if there is no need for delay mute circuit, I'm not including it
if there is need, of course it must be included"
is that, in any sense or way, dispute of what you wrote?
or - say it this way - if there is no need for anti-plop circuit, then nonsense is including it
"as I said - if there is no need for delay mute circuit, I'm not including it
if there is need, of course it must be included"
is that, in any sense or way, dispute of what you wrote?
or - say it this way - if there is no need for anti-plop circuit, then nonsense is including it
My B1s are all from Pass DIY boards (non-First Watt) with Pass supplied JFETs PassDiy
This means they have input and output capacitors. One uses K75-10 1uf as input and k73-16 10uf as output and another uses Vishay 1839 1uf and 10uf caps.
Both measure some degree of DC on the start up.
There are a few references do offset in the big B1 thread: B1 Buffer Preamp
I normally do not have a pop upon startup, but I have gotten a pop occasionally.
This has been a concern because the reason I have a new sub is that my old Dayton 1200 amp died within a couple of months of putting the B1 into that system.
This means they have input and output capacitors. One uses K75-10 1uf as input and k73-16 10uf as output and another uses Vishay 1839 1uf and 10uf caps.
Both measure some degree of DC on the start up.
There are a few references do offset in the big B1 thread: B1 Buffer Preamp
I normally do not have a pop upon startup, but I have gotten a pop occasionally.
This has been a concern because the reason I have a new sub is that my old Dayton 1200 amp died within a couple of months of putting the B1 into that system.
Please do read the suggestions. Also use correct terms. DC offset is the unwanted slight + or - deviation from 0V during operation and in general only a few mV when we talk DC coupled preamps/buffers/sources. Devices with output capacitors can have no DC offset... Some call the capacitors even "DC blockers". So... a Pass B1 has 0.00V DC offset. However the circuit needs to "settle" after power on and the capacitors will be charged (they will discharge at power off as well). This causes a temporary DC voltage at the outputs and this is called power on/off plop, pulse or similar. Some devices even "fart" annoyingly at power off as the caps discharge! If it are not the ears that don't like it maybe the speakers may not like it.
Your issue is power on/off phenomena as the devices you built lack an essential protection against power on/off phenomena to which your ready made devices react. The solution is.....(post #9, last alinea).
Your issue is power on/off phenomena as the devices you built lack an essential protection against power on/off phenomena to which your ready made devices react. The solution is.....(post #9, last alinea).
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If a muting circuit with a relay will be used please note that the "shorting output to GND" type muting causes that it only will take a few seconds (or less really) to charge the capacitors. At power off they will be discharged in a very short time as well.
BTW I am sure some will advise to change output resistors or output cap values but I think the power amplifiers you have are very high input impedance (tube?) types and you might change those one day to standardized stuff. I would not change too much circuitwise then.
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It appears my definition of DC offset was too broad. I assumed any DC measured between positive and negative on outputs would be considered DC offset.
I have a DCB1 board populated, but have not had time to test or otherwise hookup.
Thank you for clearing things up.
I have a DCB1 board populated, but have not had time to test or otherwise hookup.
Thank you for clearing things up.