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Chip Amps Amplifiers based on integrated circuits

Another BPA200 post: Need some advice on finalizing design
Another BPA200 post: Need some advice on finalizing design
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Old 8th February 2018, 05:28 PM   #11
sr2002 is offline sr2002  United States
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And the reason i’m being lazy is that I have not touched analog design since my senior year and I’m completely out of touch with most design practices.
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Old 8th February 2018, 06:07 PM   #12
tomchr is online now tomchr  Canada
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Re. mute: You need to ensure that all LM3886es have at least 500 uA flowing in their respective mute pins. If you connect all the mute pins together, you'll likely find that you need to run significant current to get the chips fully out of mute. I suggest adding an external series resistor of about the same magnitude as the internal resistance of the LM3886. Then drive the mute pins with a common RC.

When the LM3886es are not fully out of mute, the THD of the amp will suffer.

Note that the BPA architecture has an interesting little quirk. If the negative supply (VEE) starts up before the positive (VCC), the amp can latch up. It's a soft latch-up in the sense that the amp will draw a lot of current until it recovers and starts up in a few seconds. So make sure your supplies turn on at the same time or add a bit of circuitry to disable the chips until both supplies are up.

Tom
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Old 8th February 2018, 06:10 PM   #13
tomchr is online now tomchr  Canada
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Quote:
Originally Posted by sr2002 View Post
Do you have a better reference design that you suggest ? I already ordered parts for BPA200 ... but most of the expensive stuff should work any any design.
You can always build my soon-to-be-released Modulus-686.
I'm not giving out the schematics, though.

Tom
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Old 8th February 2018, 06:33 PM   #14
00940 is offline 00940  Belgium
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Quote:
Originally Posted by sr2002 View Post
Do you have a better reference design that you suggest ? I already ordered parts for BPA200 ... but most of the expensive stuff should work any any design.
I liked the shine7 design but the schematic on their website is incomplete and I can’t patch the holes they left out.
If I were to embark on something like that, I'd build 4 identical pcb with Cordell's supergainclone (without the input buffer). Tie their input/output 2 by 2 (with balancing resistors of course) and drive each group from a balanced line driver.

You'd need a total of 4 lm3886 and 5 dual opamps. With all the opamps involved, it'd be easier to draw a pcb than going p2p imo.
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Old 8th February 2018, 07:05 PM   #15
tomchr is online now tomchr  Canada
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That would be a good way to go. The modular approach is a lot simpler in many ways. You could build and test each module independently and once you have four working modules, couple them together to form the BPA200.

Tom
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Old 8th February 2018, 07:22 PM   #16
sr2002 is offline sr2002  United States
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The problem with schematics from the internet on the LM3886 is that there is very little support available on the designs. Some of them are partially shown and require additional components not mentioned on the schematic etc. So its hard for me to know what wall i'm going to hit at what point. With An-1192, I have already build the BA100, with two identical p2p boards and it sounds great. So I kind of have some faith in that document. However, its been 13 years since I build that one and I am keen to know if things have changed or if design choices in the document have been debunked or improved upon and I am open to experiment, but its just that I have very little access to T&M equipment (all i have is a DMM) and very little time to invest in the design part (my day job takes up quite a lot of time from my week, I work in Cloud software now ... so nothing related to my old Analog EE knowledge). I am still planing to make my own PCB using the toner transfer method .. unless I run out of patience for the layout design
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Old 8th February 2018, 07:58 PM   #17
sr2002 is offline sr2002  United States
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So, conning back to the discussion, and thanks a lot for your inputs Tom and 0940. Using the exact BP200 schematic so far I understood I need to do the following:
1) mute: if I’m not able to get a unified RC. network calculated, I am planing to put individual 33kohm resisters in series from pin 8 to -V for each chip with a 100uf cap in parallel to GND. Any issues with this approach?

2) power on delay: I might try to put together a 1 or 2 second delay circuit with a relay between the PSU and the amp boards

3) transformer selection: i’ve Not used a toroidal track before and am a little confused with the dual secondary tracks from Triad. They say you can’t use the secondaries individually. So my plan is to connect the center two secondary terminals together (series combination) and use the combined center secondaries as a center tap. Please let me know if I am thinking of this wrong.

Any thoughts on the above and are there any additional components needed for that particular design? Thanks
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Old 8th February 2018, 10:23 PM   #18
00940 is offline 00940  Belgium
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PCB layout is kind of a stress relief exercise for me and I had a layout already close to what I was thinking of so...

Here is what I meant exactly. Four of these, driven by a drv134 or something similar. The pcb are 7*5cm and made for easy daisy chaining of power supply lines.

I don't think a power on delay is really necessary however a dc protection scheme might not be stupid considering the power involved. I wouldn't trust mechanical relays for that, better use solid states ones here.

Would you have the reference of the triad transformer ?
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Old 8th February 2018, 11:13 PM   #19
sr2002 is offline sr2002  United States
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Thanks Ben. That does look nicer. But I don't know if I will be able to etch my own board with double sided trace, not to mention I dont have the skills to make such a nice PCB layout myself. And for P2p, the difficulty seems to be similar to the reference BP200 design.
With the BP200 I was infact planing to assemble the circuits in 2 separate modules, one with U1 + U2 + U5 and the second with U3 + U4 + U6. Granted I wont be able to test each sections individually.

The transformer I was planing to use was either of the two options:

Single 1kVA for both channels: Mouser #: 553-VPT48-20830; Mfr. #:VPT48-20830 =>
Parallel connection on the Primary for 115VAC; Series on the seconday. Center Tap from Red+orange connection. I'll then use a single Bridge with beefy enough forward current rating

2 330VA one per channel: Avel Lindberg Y236750 330VA 25V+25V Toroidal Transformer
Use the same arrangement as above for Center tap and bridge.

What do you think ? Reason for the 1KVA is it costs $140, if I get two 500VA they cost about $90 each. The 330VA costs $70 each ... so I'm trying to keep the cost down as much as I can
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Old 8th February 2018, 11:24 PM   #20
sr2002 is offline sr2002  United States
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Second question about the DRV134, is there a reliable kit out there that anyone has experience with?
Also, I dont get why converting an unbalanced signal to balanced for such as short journey (from RCA jacks to Amp PCB) be necessary? From my understanding atleast the benefit of balanced is to have more gain and to have the diff amplifier eliminate interference from long signal cables
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