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Old 10th April 2009, 08:54 PM   #1
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Default Salvage value?

OK, on an earlier post, I complained about bad HISS in my HLLY tamp-90.

What about replacing the board in this with a known good one from say, 41hz or chipamp.com, and keeping the HLLY's transformer, case, fuse, switch, etc.?

My question is this. I don't know what the transformer in the HLLY puts out. Is is 2 x 25VAC or 2 x 35VAC, or just what?

If no one really knows, well, can you tell me how to measure this? Do I simply unhook the secondaries, turn the thing on and set the VOM to AC and measure?

Chipamp.com for instance wants their LM3886 to have around 2x35 VAC.

Thanks,
Mark
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Old 10th April 2009, 11:46 PM   #2
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Default I wanted to edit but..

..couldn't figure out how. Geeze........

I meant to say chipamp.com board needs to see about 2x25 VAC.

Mark
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Old 11th April 2009, 04:18 AM   #3
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Location: Reston, Virginia
Default Re: Salvage value?

Quote:
Originally posted by Mark2727
OK, on an earlier post, I complained about bad HISS in my HLLY tamp-90.

What about replacing the board in this with a known good one from say, 41hz or chipamp.com, and keeping the HLLY's transformer, case, fuse, switch, etc.?

My question is this. I don't know what the transformer in the HLLY puts out. Is is 2 x 25VAC or 2 x 35VAC, or just what?

If no one really knows, well, can you tell me how to measure this? Do I simply unhook the secondaries, turn the thing on and set the VOM to AC and measure?

Chipamp.com for instance wants their LM3886 to have around 2x35 VAC.

Thanks,
Mark
The TA2022 uses a maximum of +/- 40V with "typical" +/- 31V, so the transformer should be compatible with National Overture series amps (LM3886, etc.). However, you would have heatsinking to deal with, plus the lower efficiency of the LM3886 means most of the power from that transformer is going into heating up the heatsink rather than into your loudspeakers. So the transformer may be undersized for the LM3886's.

Did you try the capacitor fix that HLLY recommends? It adds a 20-47pF capacitor across R7 and R5, which correspond to the Rf resistors in the Tripath circuit.

Also, please read the numbers on R5/R7 and R11/R12 and post your results. The capacitor value that HLLY recommends suggests that R7 is around 150K, and if R11 is around 20K then the gain will be over 7. That may be too much gain if the op amp inside the TA2022 is not a low noise design.
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Old 11th April 2009, 03:29 PM   #4
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Default Resistor values

Hi there Neil,

Thanks for your reply! I hope you will continue to help me.

To answer your first question, I personally have not tired the 20-47pF caps across R5 and R7. But, a fellow I am corresponding with has -- he reports no change in his hiss problem.

Also, you asked about the values of R5,R7,R11, and R12. I don't know what the values are, but after looking at them with my jeweler's loup --- all four read "1962".

So, what else can you tell me from this information?


Oh, one more thing. The transformer reads: output 2 x 24V. So, if I cannot get the noise out of this HLLY is there some suitable board I could substitute; basically drop in to make a usable chip or digital amp?

Mark
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Old 11th April 2009, 04:46 PM   #5
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Default Re: Resistor values

Quote:
Originally posted by Mark2727

Also, you asked about the values of R5,R7,R11, and R12. I don't know what the values are, but after looking at them with my jeweler's loup --- all four read "1962".

So, what else can you tell me from this information?

Mark
Ri and Rf are 19.6K, which means the gain of the input opamp is 1. So the noise is probably not coming from the input stage. You'll need to look elsewhere for the source of the noise. Sorry--I'm not familiar enough with the amp to make any other useful suggestions.
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Old 11th April 2009, 05:49 PM   #6
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Default What about other boards?

Hi Neil,

Hmmm...not good.

Well, do you have any suggestions about scrapping this board and substituting another? Couldn't I keep the enclosure, and this 2x24vac transformer?

Mark
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Old 12th April 2009, 02:25 PM   #7
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Location: Reston, Virginia
Default Re: What about other boards?

Quote:
Originally posted by Mark2727

Well, do you have any suggestions about scrapping this board and substituting another? Couldn't I keep the enclosure, and this 2x24vac transformer?

Mark
I've reused a number of enclosures and power supplies, so, sure, it is possible. However, it typically requires a lot of drilling, custom brackets and rewiring that can be challenging. I have no idea what your capabilities are, so I am reluctant to recommend any project that may end in frustration or be unsafe.

You might want to look at the UDC modules fron Hypex, but my preference would be a design based on the TDA8950, which is now sampling.
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Old 12th April 2009, 09:26 PM   #8
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Hi Neil,

Well, mechanical stuff is no problem. What I was getting at is can you point me towards an appropriate kit or pre-assembled board which would be compatible with my 2 x 24 volt transformers in the HLLY?

It's the electrical stuff that's more mysterious to me.

To my layman's eye, looks like the LM3886 stereo kit from chipamp.com might work. They, I think, call for 25 v.

Mark
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Old 13th April 2009, 12:53 PM   #9
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Location: Chicago, IL
Have a look at 41hz.com for affordable, high quality class D kits. Looks like the Amp5 would suit your package as long as it fits your box.

--Buckapound
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Old 13th April 2009, 05:32 PM   #10
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Hey, thanks!

Yeah, I have written both 41hz and chipamp.com. No response from either yet.

I will consider the Amp5. Looks OK!

Do you have one?

Mark
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