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 Post subject: Re: Attenuator to Match Line Level to Vintage Amps Question
PostPosted: Jun Thu 22, 2017 2:30 pm 
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Most likely it is somewhere between 10K and 50K.

Definitely will affect tube sources.


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 Post subject: Re: Attenuator to Match Line Level to Vintage Amps Question
PostPosted: Jun Thu 22, 2017 2:39 pm 
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tonality ?

steve

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 Post subject: Re: Attenuator to Match Line Level to Vintage Amps Question
PostPosted: Jun Thu 22, 2017 3:17 pm 
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Think what is meant is that feeding a tube circuit into a lower than designed load impedance will cause at minimum a loss in bass response, but if the impedance mismatch is large enough it will cause low output and distortion.


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 Post subject: Re: Attenuator to Match Line Level to Vintage Amps Question
PostPosted: Jun Thu 22, 2017 5:08 pm 
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Tube Radio wrote:
Think what is meant is that feeding a tube circuit into a lower than designed load impedance will cause at minimum a loss in bass response, but if the impedance mismatch is large enough it will cause low output and distortion.
That's what transformers are for.

- Leigh

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 Post subject: Re: Attenuator to Match Line Level to Vintage Amps Question
PostPosted: Jun Thu 22, 2017 6:02 pm 
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Agreed transformers are good for that, but often older tube sources with a line level output expect a higher impedance than most transformers are made for plus if going from for example a 220K source impedance to 50K load impedance there would be a good bit of signal loss using a transformer.

The best way is to use an OP-AMP configured for unity gain.

Makes it real easy as it has a real high input impedance and a real low output impedance. Plus there's no loss in signal level.


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 Post subject: Re: Attenuator to Match Line Level to Vintage Amps Question
PostPosted: Jun Thu 22, 2017 6:26 pm 
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I've never heard of any power amp remotely approaching 220K source impedance.

Any decent transformer should handle a 4:1 impedance ratio, and much higher than that.

- Leigh

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 Post subject: Re: Attenuator to Match Line Level to Vintage Amps Question
PostPosted: Jun Thu 22, 2017 6:29 pm 
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Leigh wrote:
I've never heard of any power amp remotely approaching 220K source impedance.

Any decent transformer should handle a 4:1 impedance ratio, and much higher than that.

- Leigh


This is what I said

Tube Radio wrote:
often older tube sources with a line level output


as the discussion was about line level sources.


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 Post subject: Re: Attenuator to Match Line Level to Vintage Amps Question
PostPosted: Jun Thu 22, 2017 7:33 pm 
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Tube Radio wrote:
This is what I said
Tube Radio wrote:
often older tube sources with a line level output
as the discussion was about line level sources.
This is the 220K source impedance statement I'm questioning.
I've never encountered a 220K source impedance for a line level output, nor anywhere close to that value.
Tube Radio wrote:
Agreed transformers are good for that, but often older tube sources with a line level output expect a higher impedance than most transformers are made for plus if going from for example a 220K source impedance to 50K load impedance there would be a good bit of signal loss using a transformer.


- Leigh

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 Post subject: Re: Attenuator to Match Line Level to Vintage Amps Question
PostPosted: Jun Thu 22, 2017 10:42 pm 
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I've encountered it once in a Scott amp where it specified that the load on the record out jacks could be no lower than 220K otherwise it would affect the EQ networks for the tape head and phono inputs.

I can also judge by the value of the output coupling cap what impedance the source is more than likely expected to see for flat response to the higher end of the low frequency response portion of the HI-FI standard which I think is 40Hz best I can remember.

Ceramic phono cartridges which are line level are 1 meg impedance or more.

That said a lot of the vacuum tube sources often had higher output levels because a lot of devices back then such as console radios expected the external input to have a higher level like the AM detector in the radio puts out if only to save a tube.

In cases like that a transformer may be beneficial, but often an OP-AMP or a resistor divider would cost less than the necessary transformer.


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 Post subject: Re: Attenuator to Match Line Level to Vintage Amps Question
PostPosted: Jun Thu 22, 2017 11:35 pm 
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Tube Radio wrote:
I've encountered it once in a Scott amp where it specified that the load on the record out jacks could be no lower than 220K otherwise it would affect the EQ networks for the tape head and phono inputs.
...
Ceramic phono cartridges which are line level are 1 meg impedance or more.
You need to decide what you're talking about.

Neither "recorder output jacks" nor "ceramic phono cartridges" are "line-level outputs".

Not by any stretch of the imagination.

- Leigh

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 Post subject: Re: Attenuator to Match Line Level to Vintage Amps Question
PostPosted: Jun Thu 22, 2017 11:44 pm 
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But often the voltage output is at the typical consumer line level which would make them line level outputs that can plug into a line level input.


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 Post subject: Re: Attenuator to Match Line Level to Vintage Amps Question
PostPosted: Jun Fri 23, 2017 2:33 am 
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Dutch Rabbit wrote:
...all that is needed is to chalk off about 10% of the audio. there is no distortion, but a small edge of audio input needs to be removed.
It is not possible to overdrive the amp shown in the schematic that was posted since the volume control is placed before the input stage. Perhaps it is the "loudness" compensation circuitry that, when the volume control is set at the low end of its range, is causing too much bass boost that you are trying to overcome. In this case, that little attenuator should be effective. Personally, I don't like non-defeatable loudness compensation.

On another topic...since the record output on some amps comes from the output of the phono and/or tape preamp stages, a lower than recommended load resistance at the record output can, indeed, affect the feedback loop used for the RIAA or NARTB playback EQ curve. I have run into this problem on my Scott and other tube integrated amps and preamps.

Dave


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 Post subject: Re: Attenuator to Match Line Level to Vintage Amps Question
PostPosted: Jun Fri 23, 2017 3:28 am 
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thanks guys.

i will try this little guy out, probably next week or so. lots going on for the next week or so.

i will definitely do a test where i can switch between the attenuator and a direct connection to compare the difference.

also, thanks dave for clairifying the "impossible to overload". now that you mention it, that loudness compensation is what is probably making it "too loud". now, the bass does not boom and it is not overbearing. this unit just pounds like a juke box with deep oomp-paah.

i just want to take the edge off the program source (line level) to give me a bit more play of the volume control at lower volumes.

thanks guys.

steve



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 Post subject: Re: Attenuator to Match Line Level to Vintage Amps Question
PostPosted: Jun Fri 23, 2017 9:00 pm 
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i just had to try it.

this little guy works like a champ with NO tonality differences.

it certainly has taken the edge off and all is just fine and dandy.

I believe I will order more.

https://www.amazon.com/PAC-LC-1-Remote- ... attenuator

steve

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 Post subject: Re: Attenuator to Match Line Level to Vintage Amps Question
PostPosted: Jun Fri 23, 2017 10:16 pm 
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Very nice.


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 Post subject: Re: Attenuator to Match Line Level to Vintage Amps Question
PostPosted: Dec Thu 07, 2017 3:22 am 
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hi guys,

I've resurrected this thread b/c I might build my own little attenuator box and try a 1 met pot between the input and source.

I would like to try it and compare it to the 50K control that was purchased from amazon b/c I believe there has been some tonality adjustment.

I have more time now this time of year.

so, my question is:

shall I use a 1 meg Linear or Log pot for this "set it and forget it" application ?

I will be using the amplifier's volume control as normal and NOT use this attenuator to control the daily volume. it will just be a variable attenuator to adjust once and then forget its existence.

log or linear ?

thanks.

steve

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 Post subject: Re: Attenuator to Match Line Level to Vintage Amps Question
PostPosted: Dec Thu 07, 2017 4:48 am 
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It does not matter much in this application. Log will allow you easier volume adjustment since it will use more of the control's range of motion.

-David


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 Post subject: Re: Attenuator to Match Line Level to Vintage Amps Question
PostPosted: Dec Fri 08, 2017 2:46 am 
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thank you for the answer.

steve

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 Post subject: Re: Attenuator to Match Line Level to Vintage Amps Question
PostPosted: Dec Fri 15, 2017 6:27 am 
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If you shunt the wiper to ground via a resistor of about 40% of the linear pot value you get a good audio taper. Easier to set levels. Source has to be of lower resistance than the shunt... usually it is.
Cheers,
Roger

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