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PostPosted: Wed Oct 12, 2011 12:19 pm 
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Wondering what the optimum input voltage is for vintage preamps and integrated amps?

With a 1990's CD player to my 1970's Marantz receiver, I noticed that the maximum output before distortion was occurring around 11:00 o'clock on the Volume control.
I did some experimenting with simple resistor networks at the input to drop the CD player's voltage to around 20%.
I heard less distortion at all levels and the Volume control would now go to abround 2:00 o'clock.

So, could it be that the newer signal sources are overloading the inputs on vintage equipment?
Anyone done any measurements?


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PostPosted: Wed Oct 12, 2011 1:24 pm 
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Without measurements off hand, I concur that overloading older inputs is common.
A few old Mac's (MX113, 111) peak at .6V and others are similar.
If you did a resistor network, you didn't record voltage values?

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PostPosted: Wed Oct 12, 2011 3:58 pm 
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yournamehere wrote:
Without measurements off hand, I concur that overloading older inputs is common.

I've never given this any thought, but I have a vintage Sansui integrated amp, so I just checked the specs. The input sensitivity for the aux input is rated at 250mV, 27k ohms. However, the HRT Music Streamer DAC I have connected to it has an output of 2.25Volts RMS. I just looked at the specs for a few other DACs and they are also around 2V.

So is this a problem?


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PostPosted: Wed Oct 12, 2011 4:30 pm 
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yournamehere wrote:
Without measurements off hand, I concur that overloading older inputs is common.
A few old Mac's (MX113, 111) peak at .6V and others are similar.
If you did a resistor network, you didn't record voltage values?


No recording of voltages on that effort. My goal was to see what attenuation I needed to bring the Volume control pot back to approximately the same position as it did with inputs from vinyl.
If no one has such info I will see if I can use my scope to see what input voltage does cause distortion or clipping in the pre-amp section of a couple of vintage Marantz's.


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PostPosted: Wed Oct 12, 2011 4:35 pm 
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jst_canuck wrote:
yournamehere wrote:
Without measurements off hand, I concur that overloading older inputs is common.
A few old Mac's (MX113, 111) peak at .6V and others are similar.
If you did a resistor network, you didn't record voltage values?


No recording of voltages on that effort. My goal was to see what attenuation I needed to bring the Volume control pot back to approximately the same position as it did with inputs from vinyl.
If no one has such info I will see if I can use my scope to see what input voltage does cause distortion or clipping in the pre-amp section of a couple of vintage Marantz's.


Gotcha. What was the last value that you had for the circuit?

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PostPosted: Wed Oct 12, 2011 4:40 pm 
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I was just doing some searching on this topic and I found this quote on audiokarma from a thread titled "Amplifier Sensitivity, Decibels, and You!" :

"If these units are typical of most vintage gear then there is nothing at all to worry about when connecting the 2volt output of a CD player into the line level inputs of a vintage amplifier - simply exercise some restraint with the volume control and all will be well."

Read the full post here: http://audiokarma.org/forums/showpost.p ... stcount=49


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PostPosted: Wed Oct 12, 2011 4:45 pm 
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arossphoto wrote:
yournamehere wrote:
Without measurements off hand, I concur that overloading older inputs is common.

I've never given this any thought, but I have a vintage Sansui integrated amp, so I just checked the specs. The input sensitivity for the aux input is rated at 250mV, 27k ohms. However, the HRT Music Streamer DAC I have connected to it has an output of 2.25Volts RMS. I just looked at the specs for a few other DACs and they are also around 2V.

So is this a problem?


Using this audio level conversion site http://www.sengpielaudio.com/calculator-db-volt.htm
the 2.25 V rms spec for that DAC is equal to 6.37 V peak to peak!

Now I do wonder what the Sansui 250mV input spec. really means?

I can overload the input to my 5 year old Onkyo with my M-Audio card if I set the output menu bar above 100%.
Is that distortion within the card or at the Onkyo pre-amp?

Hope we get some interest here in checking out iPod connections and other digital sources.
Maybe they are blamed for crappy sound with some equipment because of signal overload?
Long live vintage..................


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PostPosted: Wed Oct 12, 2011 5:30 pm 
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jst_canuck wrote:
Wondering what the optimum input voltage is for new and vintage preamps and integrated amps?

With a 1990's CD player to my 1970's Marantz receiver, I noticed that the maximum output before distortion was occurring around 11:00 o'clock on the Volume control.
I did some experimenting with simple resistor networks at the input to drop the CD player's voltage to around 20%.
I heard less distortion at all levels and the Volume control would now go to abround 2:00 o'clock.

So, could it be that the newer signal sources are overloading the inputs on vintage equipment?
Anyone done any measurements?


In one word ..... yes. In the pre-CD era, nominal output voltages for sources (tuners, cassette and RTR tape decks, phono stages) were pretty much standardized in the 0.5V range and input sensitivity and input overload levels were set accordingly; CD players and most newer gear are rated in the 1V to 2V range, so about double. If your vintage preamp has a maximum input voltage spec of 2V and your CD player with a 1V nominal output has a maximum output voltage of 6 to 7V on peaks, then you have a distortion problem. Modern preamps were designed for these higher output voltages to avoid such problems but this is also why so many people complain about their CD players always seem to play so much louder than their phono sections (coincidentally one of the only components that still seem to adhere to the same vintage era voltage standards). This difference in input sensitivity/output voltage is what the whole '"Digital Ready" marketing thing was all about back in the day.

Has absolutely nothing to do with the volume control. Think of a volume control as being a faucet. The faucet knob position depends on how much pressure is on the other side of the faucet. If the faucet is rated to be used in a 50psi water system and you use it in a 100psi warer system, the knob position is going to be much smaller to get the same amount of water flow and the faucet's gaskets will blow or wear out a whole lot faster that they would when used in the proper water system.


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PostPosted: Wed Oct 12, 2011 5:30 pm 
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they sound crappy because they are. no one ever said that you can't use your vintage equiptment with the new cd format when it first came out, only that it was perfect sound for ever and ipod ain't gonna sound any better.


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PostPosted: Wed Oct 12, 2011 5:41 pm 
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I've seen receivers with an active buffer before the volume control, but this is rare. In most cases the volume pot trims the voltage to a safe level that avoids overload (including your Sansui, Andrew).

Older equipment was more gain oriented as the input signals in most cases were very small, especially for record players which were the most common source of input. Other devices were matched for user convenience. Today the signals are much greater owing largely to the software capability.

With digital, it's never a good idea to apply gain to a small signal. Digital relies on full bit usage for fidelity...this is probably the reason modern cds are recorded very loudly.

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PostPosted: Wed Oct 12, 2011 6:32 pm 
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you said you can do the same thing with your 5 yr old onkyo. that's not vintage that's why we lock menu's.


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PostPosted: Thu Oct 13, 2011 4:36 am 
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So, is there agreement that a simple way to have vintage , or not so vintage, equipment have the same approx. sensitivity at the same position of the Volume control for different inputs, could do so with some passive resistor networks to reduce the input voltage? Maybe $0.20 worth of parts soldered at the RCA connector.

-- 13 Oct 2011 12:39 --

416 huff wrote:
you said you can do the same thing with your 5 yr old onkyo. that's not vintage that's why we lock menu's.


I like the idea but don't see that on the VLC Media Player software.
Are you talking about a menu on my receiver or on my PC?
Not obvious that I can lock either one.


-- 13 Oct 2011 12:53 --

ripblade wrote:
I've seen receivers with an active buffer before the volume control, but this is rare. In most cases the volume pot trims the voltage to a safe level that avoids overload (including your Sansui, Andrew).
.


A lot of of newer equipment uses semiconductor switches to do the input selection instead of mechanical contacts. In these designs the front panel switches that you operate do not handle the input signals directly. There may also be an active buffer ahead of the switch in there too.
All of this is before the Volume control, so one could generate distortion by exceeding the design limit for these components.
Not sure where to look for some helpful specs on this?

I'd guess that these circuits came into common use by the mid 80's with the most popular consumer brands.

A little winter experimentation is called for................


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PostPosted: Thu Oct 13, 2011 5:01 am 
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Not to mention the extreme amount of compression used in many of todays C.D.'s. Due to the ear fatigue, makes me run to the volume control very quickly. With the loss of dynamics, the music tends to sound very harsh. I am wondering whether this may play a part in what your hearing as well. :?:

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