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Way to go for vinyl through SHD 2 years 5 months ago #49560

  • entripy
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A simple hardware inline attenuator should be high quality. The tricky part is knowing how much attenuation you need.
As you found, altering the cartridge loading will not do what you want.

You will neecd no more than 20 log (50/2) or 28dB attenuation maximum. That would guarantee that even if the RIAA pre was creaking at the seams with 0.5% THD and 50V RMS output the SHD would only see 2V RMS. In practice it is unlikely the pre is giving anywhere near this much out so less attenuation should work. 15dB and 10dB attenuators tend to be most common, it is rare to find higher attenuation required because it is rare to find anything that outputs 50V RMS because that's enough to damage some equipment. Inline attenuators may be found in unbalanced RCA and balanced XLR forms.

The good news is that it can be a very good quality solution. Any noise and distortion from the pre will also be reduced by the same attenuation so there's isn't really any compromise involved. Worst case the load will see a slightly wrong source impedance or the source will see a slightly wrong load impedance but that is usually not critical.

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Last edit: by entripy. Reason: correct typo

Way to go for vinyl through SHD 2 years 5 months ago #49565

  • rodrigaj
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The gain of the ARC PH5 is spec'd at 57.5 dB. That seems about 10dB too high for MM cartridges and about right for most MC cartridges. Strange that they offer no built in attenuation to handle MM - a jumper or DIP switch or some other means to change that.

Edit: Rothwell Audio makes some very decent inline attenuators (-10, -15, -20 dB) balanced and unbalanced:

www.rothwellaudioproducts.co.uk/html/attenuators.html

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Last edit: by rodrigaj.

Way to go for vinyl through SHD 2 years 5 months ago #49570

  • lukaszstefaniak
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Yeah, attentuator seems really suitable solution for me. Thanks a lot!!
I found only MONACOR ILA-1020 is available in my country, but it didn't buy my trust. What do you think about it? It has changable attenuation.

I could build one by myself, construction is child's play. But I can't figure out what resistors I should use to reach -15dB attentuation.

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Way to go for vinyl through SHD 2 years 5 months ago #49576

  • mvs0
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I could build one by myself, construction is child's play. But I can't figure out what resistors I should use to reach -15dB attentuation.


-15dB = 10^(-15/20) = 0.1778

So the ratio of your divider needs to be R2/R1=0.1778

Given the max load of your pre-amp of 10k and the input impedance of the SHD of 47k a good choice would be:

R1 = 8.45k and R1 = 1.54k (R1 is corrected for the 47k load here)

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Way to go for vinyl through SHD 2 years 5 months ago #49584

  • lukaszstefaniak
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So, to make things clear.



Upper vector is a signal line and bottom vector is ground.
R2 (1,54k Ohm) stands for input impedance of SHD and R1 (8,45k Ohm) is a load for source. Am I right?
Attachments:

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Last edit: by lukaszstefaniak.

Way to go for vinyl through SHD 2 years 5 months ago #49585

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Just thinking. Maybe just connecting phono pre to SHD by using RCA to XLR cable would solve my problem?
In the end, XLR input has higher voltage tolerance.

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Last edit: by lukaszstefaniak.

Way to go for vinyl through SHD 2 years 5 months ago #49590

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So, to make things clear.



Upper vector is a signal line and bottom vector is ground.
R2 (1,54k Ohm) stands for input impedance of SHD and R1 (8,45k Ohm) is a load for source. Am I right?


You placed R1 and R2 correctly.
The load/impedance story is a little more complex:
The load your pre-amp will see is R1 plus R2 in parallel with the input impedance of the SHD so:

Rload = R1+ 1/(1/R2+1/Rin) = 8.45k + 1.491k = 9.941k ~=~10k

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Way to go for vinyl through SHD 2 years 5 months ago #49591

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Just thinking. Maybe just connecting phono pre to SHD by using RCA to XLR cable would solve my problem?
In the end, XLR input has higher voltage tolerance.


In theory this would give you 6dB extra headroom.
You said you needed 15db reduction?

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Way to go for vinyl through SHD 2 years 5 months ago #49592

  • lukaszstefaniak
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In theory this would give you 6dB extra headroom.
You said you needed 15db reduction?


I thought it is worth trying. Signal peaks at -1, -2dB on a signal strip, but I don't know if it wouldn't reach higher, because top area is excluded, if you know what I mean.

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Way to go for vinyl through SHD 2 years 5 months ago #49668

  • mollie
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Hi,
It looks like that there is a missmatch. Make sure that you have choosen for "Moving Magnet" (not Moving Coil) and a "load impedance 47K.
The output given output voltage is not 50V but .50V as you can see at the A.R. manual.
See copy manual at
www.manualslib.com/manual/803861/Audio-Research-Ph5.html#manual

MM elements give for instance something around 2,5-6mV as output voltage and an MC element something in between 0,050-0,250mV

I think that you now have connected a MM true the MC stage wich will give a lot of to high gain, which will overload the SHD analog imputs and the low output choosen with MC is loading the MM element to much too.!!!

So check and try again !!!
Succes

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Way to go for vinyl through SHD 2 years 5 months ago #49669

  • mollie
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Forgot to say that my written story is all about RCA connections.

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Way to go for vinyl through SHD 2 years 5 months ago #49672

  • entripy
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The manual you linked clearly states 50V RMS output capability. Also it states 57.5dB gain which is supposedly compatible with MM and MC but no way to change gain depending on MM or MC so I'm not sure what your point is. Other than the output will be rather hot with MM input compared to MC which is the exact problem the OP has.

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Way to go for vinyl through SHD 2 years 5 months ago #49673

  • mollie
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Hi again,
Be carefull to read the specs in the manual the right way!!!
This is what is written:
RATED OUTPUTS: . 5V RMS 10Hz to 60KHz at100KOhm load(=0,5V RMS !!!!!)

(output capability is 50V RMS output at 1/2 percent THD at 1KHz)
Which only means that the output stage of the phono amp can handle this voltage.!!!

There is only given one figure about the gain, but i am shure that this figure is only used for the MC cardridges and not for MM.
For MM it will be for instance something like 37,5 dB gain.

Example gain stage specs for Phono stages with RIAA corrections:
Low level M.C. has f. i. 0,1mV output and needs about 3160x gain (which is G=70dB)
Standard Level M.C has f.i. 0,5mV output and needs about 630x gain (which is G=56dB)
Moving Magnet M.M. has f.i. 5,0mV output and needs about 63x gain (which is G= 36dB)
That is quite different as it "looks like" in the A.R. specs, but shure closer to the truth as is written in A.R.
(they only forget to tell you that the given gain is only for M.C. applicable)

Hopefully you understand my story and handle accordingly to find out what is happening in your case.

You could start to take down the level of the inputs of the SHD to let's say -10dB to start with.

Succes

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Way to go for vinyl through SHD 2 years 5 months ago #49676

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But the A.R. has one pair of inputs and no way of selecting gain depending on whether you use MM or MC. So there's no way for MM to have lower gain than MC. I know it would normally on a typical RIAA preamp, but this A.R. is anything but a typical RIAA preamp.

Although the nominal output level with 57.5dB of gain for some input input level may be 0.5V RMS at decent distortion amounts it would appear that there is nothing that prevents the output rising to 50V RMS with huge distortion should the input be large enough. That's to be expected for a valve circuit, they commonly run on voltage rails of hundreds of volts. As your figures point out, an MM output could easily be 50 times bigger than an MC output.

Perhaps they just never expected that anyone would use MM with it :)

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Way to go for vinyl through SHD 2 years 5 months ago #49678

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Hi again,

I am allmost shure (as you are going to use a MM cartridge) if you switch on the front to the 47KOhm position. (for MM cartridge), that the A.R. unit will switch automaticly to the right gain usefull for the MM cartridge. If input is still overloading lower the SHD input level by 12dB

You should never make a choice for 100 or 200 Ohm position(s), because these are only for use in conjuction with M.C. cartridges.

If thiis is not of any help, you'll have to let check the A.R. unit by a proffesional in combination with your SHD.

Succes again!!!

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