Any RCA jack/plug attenuator ?

Thread Starter

Externet

Joined Nov 29, 2005
1,873
Hi. Do you know of a vendor for an attenuator and RIAA equalizer to use 'line' level audio into 'phono' input jacks ? -About 100-to-1 attenuation + reverse RIAA-
Or an empty female-to-male adapter shell to fit a passive circuit in it and make my own ? The ones found are bulky boxes.

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This one has the right idea, but only a tiny board with surface mount components would fit in there...
1653247874970.png
 
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LowQCab

Joined Nov 6, 2012
2,180
This is a bad idea right from the start.
It's likely to be very noisy and distorted
no matter what You do, or how much Money You spend.
.
.
.
 

MrSalts

Joined Apr 2, 2020
1,845
This is a bad idea right from the start.
It's likely to be very noisy and distorted
no matter what You do, or how much Money You spend.
.
.
.
Bad is a relative term.
In this thread, for example, your claim that "this is a bad idea from the start" can only be true if someone (especially you) proposes a BETTER idea. Without a relatively better idea, the OPs plan is just an idea (not good or bad).

At this point, the only alternative is to do nothing and the OP's "bad" idea is better than nothing. It gets him closer to his goal without damaging any equipment, burning down his house or hurting anyone.
 

AnalogKid

Joined Aug 1, 2013
10,098
Turns out, this is not all that rare a request. Lotsa web sites, and many kits.

The RIAA curve is not capacitor-friendly. No matter how you scale the resistor values, one or more of the cap values will require two or more high-precision caps in parallel. Also, the RIAA curve spans a 40 dB (100:1) amplitude range. The good news is that for an inverse curve it is all attenuation. Note that both the source and destination impedances will have a direct affect on the accuracy of the equalization.

Intro article with component values: https://ttradio.net/riaa-network-phono-amp/

This sounds exactly like what you want to do: http://diystrat.blogspot.com/2015/04/making-reverseinverse-riaa-attenuator_21.html

Lotsa links to pages:
https://images.search.yahoo.com/sea.../RIAA_and_Inverse_RIAA_Graph.gif&action=click

Kits:
https://search.yahoo.com/search?n=1...vst=0&vf=all&vm=p&fl=0&p=inverse+riaa+kit&vs=

ak

RIAA_inverse_std.jpg
 
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MisterBill2

Joined Jan 23, 2018
12,441
The tiny adapters shown in post #1 will certainly hold two small leaded resistors for a very low power attenuator, but not any equalizer. .

Now for the bigger question: what is the purpose or goal of the inverse RIAA compensation? I am guessing it is to use a phono input on some legacy equipment for a more current audio input. My solution to that goal is to internally bypass the phono equalization stage, and feed the signal , at the higher level, to a point beyond the EQ segment. Been there and done that and it worked quite well.
 

AnalogKid

Joined Aug 1, 2013
10,098
what is the purpose or goal of the inverse RIAA compensation? I am guessing it is to use a phono input on some legacy equipment for a more current audio input. My solution to that goal is to internally bypass the phono equalization stage, and feed the signal , at the higher level, to a point beyond the EQ segment.
If MB is correct, then age (and photos) matters. The older the gear is:

a) the larger and fatter the parts

b) the less dense the pc board layout, making for easy re-work

c) the easier it is to find a service manual with schematics, parts layouts, etc.

Often in home entertainment gear, the line level inputs (Tuner, Tape, Aux) go straight to the selector switch. Isolating the photo preamp stage so it can be bypassed might be as simple as clipping or floating one component lead per channel.

ak
 

KeithWalker

Joined Jul 10, 2017
2,409
I have made loads and attenuators with the connector parts from RCA jacks and plugs and thin walled brass tubing from an old telescopic TV antenna. They are labelled and covered with transparent heat-shrink sleeving. They work well for audio frequencies.
 

MrSalts

Joined Apr 2, 2020
1,845
I have made loads and attenuators with the connector parts from RCA jacks and plugs and thin walled brass tubing from an old telescopic TV antenna. They are labelled and covered with transparent heat-shrink sleeving. They work well for audio frequencies.
And now, the old style RCA connector is sold for pennies at overstock electronics stores because nobody wants them. I have a case of 288 three-channel through-hole mount jacks if anyone wants them.
 

AnalogKid

Joined Aug 1, 2013
10,098
I have some Switchcraft, one-channel, panel-mount RCA jacks that have a bypass switch like an earphone jack or DC power jack. When you unplug the plug, the jack center-pin contact is switched to another pin. This has a variety of uses for both inputs and outputs. And, the plastic body keeps the shell from making contact with the panel in case you want to float the signal GND from the chassis.

Hey, guess what I found on the innergoogle:

1653314719016.png 1653315026354.png
ak
 
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MrSalts

Joined Apr 2, 2020
1,845
I have some Switchcraft, one-channel, panel-mount RCA jacks that have a bypass switch like an earphone jack or DC power jack. When you unplug the plug, the jack center-pin contact is switched to another pin. This has a variety of uses for both inputs and outputs. And, the plastic body keeps the shell from making contact with the panel in case you want to float the signal GND from the chassis.

Hey, guess what I found on the innergoogle:

View attachment 267853 View attachment 267854
ak
Is there a switch on the image you posted or just a spring-tensioner for the tip of the RCA plug?
Edit: never mind, I can see it when looking at a bigger screen. If I am old, that patent number will soon be old, too.
https://patentimages.storage.googleapis.com/40/bb/21/0c521e7a881aa6/US3356800.pdf
 
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MisterBill2

Joined Jan 23, 2018
12,441
@Mr.Salts: There is a switch indeed. The two sides that contact the center pin also contact a tab above that in the photo, when the pin is not present. So not only is there a transfer switch, it is a redundant contact transfer switch. Very good engineering and a really low-priced scheme.

And K.W. must be a very skilled master tech to assemble circuits in a package that small. I am truly impressed. Small stuff takes more planning and better magnifiers and tiny parts. It is complex and tedious based on my efforts.
 

AnalogKid

Joined Aug 1, 2013
10,098
@Mr.Salts: There is a switch indeed. The two sides that contact the center pin also contact a tab above that in the photo, when the pin is not present. So not only is there a transfer switch, it is a redundant contact transfer switch. Very good engineering and a really low-priced scheme.
And they last. I got mine in the 80's, and the tabs still are perfectly solderable.

Peavey and others use shorting jacks to reduce noise pickup in unused amp channels. Recently I borrowed the idea when resurrecting my brother's small mixer/amp, changing the input connectors to these guys. Made an audible difference.

ak
 

MisterBill2

Joined Jan 23, 2018
12,441
OK, off-topic stuff vanished. We still do not have the details about the application. And external lossy frequency response adjustments do tend to increase the noise level no matter how well made they are.
 

KeithWalker

Joined Jul 10, 2017
2,409
OK, off-topic stuff vanished. We still do not have the details about the application. And external lossy frequency response adjustments do tend to increase the noise level no matter how well made they are.
That may not be an issue. It all depends on how they are being used. The ones I made have no apparent adverse effects on signals in the applications I have used them in. I don't have the ability to measure very small noise levels.
 

MisterBill2

Joined Jan 23, 2018
12,441
If the assemblies are well made then the noise may not be a problem. But if the desired signal is reduced but the noise is not reduced then the signal to noise ratio is worse, problem or not..
 

AnalogKid

Joined Aug 1, 2013
10,098
Headphones and ear buds - definitely yes. I run mine for two weeks.

Electrolytic capacitors - yes, but 72 hours is way more than necessary.

Everything else in a preamp (and transformers - ?!?) - not in my opinion. And I checked with a couple of golden-eared wonders - they think not.

ak
 

MisterBill2

Joined Jan 23, 2018
12,441
I have seen inverse RIAA filter circuits and never considered that I would find them useful.
But the claim about needing to "burn in" electronic circuits is so very fake that all credibility is destroyed. Probably the same organization sells those oxygen-free copper" speaker leads for some high price, for those with better trained hearing who can detect the different (distorted) sound from speakers connected with ordinary #14 lamp cord instead. I would expect to find that the insulation in that gold plated housing has been treated with some higher quality "snake oil" to further reduce distortion products.
Newly constructed equipment often is given an initial operating period to catch early component failures. But that is quite different.
And certainly, after I repair a measurement device for a client and verify the calibration, I do keep it on for at least 24 hours and verify that the calibration does not shift.
 
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