| David Farber <farberbear.unspam@aol.com>: Nov 10 05:02PM -0800 On 11/9/2020 8:06 PM, Phil Allison wrote: > Using a Variac slowly may be an issue, but nothing will happen until the +/- 15V rails appear, then it should ramp up the PWM in about 1 second. > .... Phil I hadn't realized that the ramp up occurred within 1 second. I powered it on without the Variac and sure enough, the waveform made a gradual change within that 1 second timeframe. Everything seems to powering up OK. Checking the audio will be next. I'm still curious about the power supply question I asked in my previous post (see below) regarding how the two bridge diode circuits seem to be adding voltage in a series circuit. ============================================ At this point I could reassemble everything and see if it actually will perform properly. But before I do that, I would like to figure out the operation of the power supply circuit that is rectified by diodes D805-D808. It's easy to see that when pin 20 of T3 goes positive, D805 conducts and becomes the V+ line. From that point, it feeds the load and then I imagine it ends up going through ground via the terminal marked HI RAIL on T3 and also through the other ground circuit which is in series with the array of capacitors, C811-812, C849-850, and C34, C36, and C51. Apparently there is also a connection to the bridge circuit, D809-D812. Is there some voltage adding going on there with the secondary transformer windings interacting with the two bridge circuits? This is not a configuration that I have come across before. At the very least I'd like to know where ground is for the V+ supply coming from the cathodes of D805 and D806. I am measuring 90 volts individually across capacitors C850 C852. Thanks for your reply. -- David Farber Los Osos, CA |
| Phil Allison <pallison49@gmail.com>: Nov 10 08:48PM -0800 David Farber wrote: ================== > it on without the Variac and sure enough, the waveform made a gradual > change within that 1 second timeframe. Everything seems to powering up > OK. Checking the audio will be next. ** So far - so good. > post (see below) regarding how the two bridge diode circuits seem to be > adding voltage in a series circuit. > ============================================ ** Yep- it sure is complicated !!. The DC supply is *series stacked* with a low an high voltage components. Then a pair of IGBTs for each channel is used to *regulate* the voltage to the main BJT amplifiers so it TRACKS the incoming audio. Maybe not perfectly but reasonably close to demand and just a lite more volts than needed by the load at any moment. The low voltage DC supply sets a fixed lower limit. Look up "class H" on Wiki. I only know of one other amp maker doing this, Lab Gruppen. Crazy complicated - why not go Class D an keep it simple ?? ..... Phil |
| Phil Allison <pallison49@gmail.com>: Nov 10 09:22PM -0800 David Farber wrote: ================== ** FYI Dave, The marketing for this model (B2000) is totally wrong. 1. It is not a "mono block"- it has two distinct power channels that must drive two different speakers. 2. It sure as HELL ain't "class D" Either. The PSU tracks so it is "clearly class H" WTF ??? .... Phil |
| David Farber <farberbear.unspam@aol.com>: Nov 11 08:27AM -0800 On 11/10/2020 8:48 PM, Phil Allison wrote: > I only know of one other amp maker doing this, Lab Gruppen. > Crazy complicated - why not go Class D an keep it simple ?? > ..... Phil Hi Phil, My experience with commercial(?), high powered audio gear with switching power supplies is almost nil. I'll check out class H on Wiki and while I'm there, I'll check out any other classes that I haven't come across. Yesterday, I installed the PC board into the chassis and connected the front panel connectors. The result was the earth ground became tied to the power supply ground which should have made voltage testing much easier except for the fact that I could no longer access the bottom of the PC board. It's next to impossible to accurately put a probe on anything from the component side. Many parts are covered in epoxy(?) or hot glue(?) and the power transistors are totally obscured by the heat sinks that surround them. Thanks for your reply. -- David Farber Los Osos, CA |
| David Farber <farberbear.unspam@aol.com>: Nov 11 08:30AM -0800 On 11/10/2020 9:22 PM, Phil Allison wrote: > .... Phil Hi Phil, When I was still trying to figure out if the schematic matched the pc board, I mentioned in passing that the second channel audio amplifier components were not installed. There are however marked out spaces for them. In summary, any components that refer to CH2 do not exist. As to whether it is class D or class H (I don't think my electronics training from the 1970's went past class C), I'll leave that up to you and in the meantime, I'll turn to the internet to update my knowledge about the alphabet soup of amplifier classes. Thanks for your reply. -- David Farber Los Osos, CA |
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