Help with LM3886 + Crystal PGA2311 pre-amp kit! - diyAudio
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Old 4th January 2011, 10:03 AM   #1
Hubba is offline Hubba  Sweden
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Default Help with LM3886 + Crystal PGA2311 pre-amp kit!

Hi,

I've got a chipamp.com LM3886 and I have connected it to a cheap e-bay pre-amp kit. It's a Crystal PGA2311 based kit (Crystal PGA2311 Volume remote control preamplifier kit on eBay (end time 05-Jan-11 04:52:06 GMT)) with a remote and an LCD. The LM3889 is powered by a toroid, and the pre amp circuit is powered by a 6-0-6V @ 5A transformer.

Now to the problem: When I turn the power off, i get a really bad "thumpf" from the speaker. The solution right now is to turn off the power amp befoe the pre amp, which eliminates the thumpf, and also tells me that the problem lies in the pre-amp section.

Does anyone have any experience with a similar setup, or even better any ideas on what might cause this...

During operation the amp sound fine....but I do not trust myself enough to always remember to turn off the power amp before the pre-amp.....

Cheers,
Fredrik
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Old 4th January 2011, 10:06 AM   #2
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Why not use the Power Amp PSU to drive a relay and use the relay contacts to power the Pre.

Alternatively you could power a relay from the Pre PSU and use the contacts to disconnect the speakers.
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Old 15th January 2011, 08:01 PM   #3
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Default Ebay PGA2311 kits

With no programming experience I was considering one of these unassembled kits for the controlling the PGA2311 chip only. My thought was to use the control bits and remote only within a design similar to either the Elektor or Mark Hennessy design. If you cannot fix your problem maybe this is a way forward?
By the way, do these kits include Balance control as well as volume?
Thanks
Martin
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Old 18th January 2011, 09:42 AM   #4
Zoodle is offline Zoodle  Australia
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Hubba,
Do you have the two connected directly together, with nothing between? The advert states "600 Ohm directly without buffering."
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Old 18th January 2011, 03:09 PM   #5
Hubba is offline Hubba  Sweden
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Hi all!

Martin:
No, the kit only has a volume control (and selector).

Zoodle:There's nothing in between; CD->PGA2311 kit->chipamp->speakers. I fail to find "600 ohm directly without buffering". And honestly, even if I did see it I'm not fully sure what it means..
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Old 18th January 2011, 11:24 PM   #6
Zoodle is offline Zoodle  Australia
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Quote:
Originally Posted by Hubba View Post
And honestly, even if I did see it I'm not fully sure what it means..
I think it means you can connect directly to a power amp, as you've done. How is it sounding? Have you compared it to something else?
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Old 19th January 2011, 05:57 AM   #7
Hubba is offline Hubba  Sweden
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Quote:
Originally Posted by Zoodle View Post
How is it sounding? Have you compared it to something else?
The sound is quite good given the low price. As i have had problems with the thump, I have now removed the PGA2311 and put a passive volume control before the LM3886 and that is the only thing that I have compared it to. The LM3886 is driving a pair of DIY TQWT (TQWT-) which has an efficency of 95dB, so while easy to drive they are also quite picky on the quality of the signal delivered to them.

With those speakers hooked up some of the details are lost with the PGA2311 kit, it kind of sounds like putting a cloth over the speaker. If this would have been a kithcen or bedroom system it would have been acceptable, but for this setup the PGA2311 is not giving the LM3886 a chance to perform as they should. Still, I'd recomend the kit to anyone who are searching for a simple remote controlled solution (given that they do not get the same turn off thump problem that I had).

Cheers,
Fredrik
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Old 19th January 2011, 06:13 AM   #8
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Many opamps does weird things when the VCC and VEE voltages drop.

I would put a relay between the pga2311 kit and the lm3886 amplifier.

This relay would run off the 5v (not sure what regulators are on the pga2311 kit). As soon as power is cut the relay will disconnect before voltages drop to "thump" level.

you could even add a small resistor to relay coil to limit voltage so that relay is "just" on to speed up off switch time when power is removed.

if pga2311 has output current limiting resistors ( those 600 ohm ones) then the relay can just short to ground the connection between the preamp and lm3886. Then connection does not run through relay but is just grounded.

hope this makes sense
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Old 19th January 2011, 07:15 AM   #9
Zoodle is offline Zoodle  Australia
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Quote:
Originally Posted by Hubba View Post
The sound is quite good given the low price. As i have had problems with the thump, I have now removed the PGA2311 and put a passive volume control before the LM3886 and that is the only thing that I have compared it to. The LM3886 is driving a pair of DIY TQWT (TQWT-) which has an efficency of 95dB, so while easy to drive they are also quite picky on the quality of the signal delivered to them.

With those speakers hooked up some of the details are lost with the PGA2311 kit, it kind of sounds like putting a cloth over the speaker. If this would have been a kithcen or bedroom system it would have been acceptable, but for this setup the PGA2311 is not giving the LM3886 a chance to perform as they should. Still, I'd recomend the kit to anyone who are searching for a simple remote controlled solution (given that they do not get the same turn off thump problem that I had).

Cheers,
Fredrik
Which passive are you using? Have you looked at the 'lightspeed' method?

Thanks for your comments on the PGA2311. I was looking at this for myself, but a couple of other user comments made me wonder if it was 'too good to be true.'

Maybe it's better for 'mid-fi' use(?)

I'm also interested in the LM3886, so I hope you'll update this thread with your future experiments.
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Old 19th January 2011, 07:20 AM   #10
jerryo is offline jerryo  Isle of Man
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There is an alternative:

just leave the amp and volume control "on" all the time; unless obviously when on holiday or away from your house for a long period of time. This way you avoid the stressing of components with the power-on, power-off cycle and your amps will be warm and ready to go all the time. I know there is a cost implication for electricity used whilst on stand-by, but it is not that great.
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