What kind of amp do I need

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gfre...@aol.com

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Dec 8, 2020, 1:44:58 PM12/8/20
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I bought a new TV and like most now, they don't have a line level
output. I bought a digital to analog adapter to drive my remote
amplified speakers but the line level out of the converter is so low I
need to run the amps at full volume and they are still marginal. I
think a small pre amp would work but the "turn table" amps might be
too much of a good thing and they don't seem to have a gain pot.

Adrian Caspersz

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Dec 8, 2020, 5:50:51 PM12/8/20
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You are not the first person to spot this.

I wonder if the digital to analog adaptor is hackable? Could be a
resistor change be all that is required in the ADC setup?

What's the chip in there?

BTW, you may get a better response posting elsewhere TV hardware
related. Yeah, I know your TV runs on electricity, but ...

--
Adrian C

Dimitris Tzortzakakis

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Dec 19, 2020, 9:58:22 AM12/19/20
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you're right a turntable preamp is no good because these have had and
have what is called a RIAA curve de-emphasis because the records used to
(and are) being compressed in the bass, I think. basically what you need
is an op amp to boost your signal, surely there are pres or even kits
that fulfill your needs? when I did for my thesis (in EE) an AM
transmitter I needed an 60 W audio amp so I picked a ready PCB, it just
needed a PSU and box.HTH.

gareth evans

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Dec 19, 2020, 1:22:20 PM12/19/20
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On 19/12/2020 14:58, Dimitris Tzortzakakis wrote:
> ...what is called a RIAA curve de-emphasis because the records used to
> (and are) being compressed in the bass,

The (apparent, only) compression of the basis was an attribute
of magnetic pick-ups but not of crystal pickups.

Simple electromagnetics, the faster the movement between conductor
and magnet, the higher the induced voltage.

High frequencies entail faster movements than low frequencies!



Dimitris Tzortzakakis

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Dec 29, 2020, 7:31:45 AM12/29/20
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right, I never thought of that. likewise dolby was also an analogue mode
of compression, I still have a working tape deck!that can do dolby b and
c. short before analogue tape became obsolete there was also dolby s.
the best tape decks were the 3 headed ones, where you could listen to
your recording on the fly, while it was recorded! they could fit a
record/play head on one piece, mine is a regular auto reverse, twin
deck. one of the last good quality to be made.

Anthony Stewart

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Dec 30, 2020, 9:55:49 AM12/30/20
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Do they have a useable earphone jack?

gfre...@aol.com

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Dec 30, 2020, 10:46:28 PM12/30/20
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No. The only out is digital/fiber.

When I get little time I will get back to it. I am looking at LM324
circuits and I have a few chips already. I am not looking for
audiophool quality, just reasonable sound I can hear. A couple I saw
look reasonable and I am just looking for line level inputs to an amp.
I think a 324 can do it. Since I have 4, I might double them up. I saw
that trick too.

Anthony Stewart

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Dec 31, 2020, 12:40:18 PM12/31/20
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It is possible new TV's do not have an isolated DC supply, so you might be best to use a transformer off the audio.

gfre...@aol.com

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Dec 31, 2020, 3:50:16 PM12/31/20
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On Thu, 31 Dec 2020 09:40:15 -0800 (PST), Anthony Stewart
Since the audio output is optical, it is not much of an issue but I
did need to put an isolation transformer on the output of the DAC.
That may be part of my low level problem .

Michael Terrell

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Jan 13, 2021, 10:58:35 AMJan 13
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What kind of audio connectors are used? A set of computer speakers with an earphone jack would work, if your adapter uses 1/8" stereo headphone connectors. Turn the volume way down, before turning it on.

Those mag phono preamps had the gain set to match the expected level of a cheaper cartridge. Some cheap cartridges put out up to 2V P-P. I used one over 45 years ago to bring the level up on the Network feed at a Military radio station. That allowed a simple switch from local to network without adjusting the gain at every switchover.

gfre...@aol.com

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Jan 13, 2021, 12:18:57 PMJan 13
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Easy enough to try. Thanks.

gfre...@aol.com

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Jan 22, 2021, 9:50:43 PMJan 22
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On Wed, 13 Jan 2021 07:58:33 -0800 (PST), Michael Terrell
<terrell....@gmail.com> wrote:

>On Tuesday, December 8, 2020 at 1:44:58 PM UTC-5, gfre...@aol.com wrote:
>> I bought a new TV and like most now, they don't have a line level
>> output. I bought a digital to analog adapter to drive my remote
>> amplified speakers but the line level out of the converter is so low I
>> need to run the amps at full volume and they are still marginal. I
>> think a small pre amp would work but the "turn table" amps might be
>> too much of a good thing and they don't seem to have a gain pot.
>
>What kind of audio connectors are used? A set of computer speakers with an earphone jack would work, if your adapter uses 1/8" stereo headphone connectors. Turn the volume way down, before turning it on.

It is not elegant but it works.
It turns out the earphone jack must be attenuated because I had to
turn the volume way up but it fixed my problem.

Thanks.

Michael Terrell

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Sep 1, 2021, 3:37:01 AMSep 1
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On Friday, January 22, 2021 at 9:50:43 PM UTC-5, gfre...@aol.com wrote:
> On Wed, 13 Jan 2021 07:58:33 -0800 (PST), Michael Terrell wrote:
> >
> >What kind of audio connectors are used? A set of computer speakers with an earphone jack would work, if your adapter uses 1/8" stereo headphone connectors. Turn the volume way down, before turning it on.
> It is not elegant but it works.
> It turns out the earphone jack must be attenuated because I had to
> turn the volume way up but it fixed my problem.

You're welcome. It's easier than building a custom amplifier, and it was designed for the right signal input levels. Some of the PC speakers that I've scrapped had a 220 ohm resistor in series with each earpiece when using headphones.

You can buy small headphone amp boards on Ebay, but most are overpriced.
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