Connect preamp to amplifier

N

nrgeti

Audiophyte
#1
I was just given a A/V system without some of the cables. I need to connect the preamp to an amplifier. The preamp has a set of amp output connector posts: red and white, green and black. The red and white ones are marked "right side", the green and black are marked "left side". Also there is a "C" marked on the white one and on the black one. I assume these are the ones that will connect to the amplifier.

The amplifier only has two RCA jacks marked Amp Input. One is also marked "Left" the other "right". I assume that each cable must have two wires in it; one being a common or ground that connects to the "C" connector.

Nick Geti
 
WaynePflughaupt

WaynePflughaupt

Audioholic Field Marshall
Ratings
615
#3
What TLS said. I’ve never seen a pre-amp with anything but red and white, or red and black outputs. We’ll need some documentation to help you.

Regards,
Wayne A. Pflughaupt
 
N

nrgeti

Audiophyte
#4
I tried sending pictures but got a message that the file is too large for the server to process. But here are the model numbers:
McIntosh Preamp Model C26 Solid State Stereo Preamplifier. I am pretty sure that my initial request stated that this unit has the Red/White right outputs and the Green/Black left output.

McIntosh Amplifier Model MC2505 -2. On the right hand side there are two RCA jacks, one marked "left" and the other "right". Above them is a marking, "Output".

I assume that the two sets of colored outputs indicated above from the preamp will feed these two jacks.

Nick Geti
 
TLS Guy

TLS Guy

Audioholic Slumlord
Ratings
7,339 17 25
#5
Is this what you have?



I downloaded the manual but I'm none the wiser. Mac refer to those connectors as L connectors. They are nothing like modern L connectors. I never saw preamp outs like those ever and that is in over 60 years.

You will have to make you own leads. I would bet that in the RF environment of the modern home they will hum like the Devil.

Also I can tell they are the old style RCA connectors which are slightly out of spec with the modern ones. They do not make good connection with modern RCA plus.

If it were me I would replace those RCA sockets with modern gold plated ones. I would also convert those preamp outs to RCA sockets as well.
 
TLS Guy

TLS Guy

Audioholic Slumlord
Ratings
7,339 17 25
#7
You will have to take an RCA to RCA lead and cut the plugs off one end. Then strip a bit of insulation from the live connection. I would tin the live and screened wires with some solder.

I guess from everettT's link you push on the ends of those connectors which exposes a hole in the side you poke a wire in. They seem similar to old receiver connections. I have never seen those used as an unbalanced line out from a pre/amp.

I still think in this era of LED light bulbs and lots of other sources of RF in the home, they may not be the most silent connection. There is just too much exposed that will not be shielded. If it works fine, if not you will have to convert to a fully shielded connection.
 
highfigh

highfigh

Audioholic Warlord
Ratings
2,778 9 5
#8
Is this what you have?



I downloaded the manual but I'm none the wiser. Mac refer to those connectors as L connectors. They are nothing like modern L connectors. I never saw preamp outs like those ever and that is in over 60 years.

You will have to make you own leads. I would bet that in the RF environment of the modern home they will hum like the Devil.

Also I can tell they are the old style RCA connectors which are slightly out of spec with the modern ones. They do not make good connection with modern RCA plus.

If it were me I would replace those RCA sockets with modern gold plated ones. I would also convert those preamp outs to RCA sockets as well.
Where are the non-RCA-style preamp outputs that you're seeing? The jacks at the lower right of the photo are all RCA jacks.

http://www.roger-russell.com/c26pg.htm
 
highfigh

highfigh

Audioholic Warlord
Ratings
2,778 9 5
#9
You will have to take an RCA to RCA lead and cut the plugs off one end. Then strip a bit of insulation from the live connection. I would tin the live and screened wires with some solder.

I guess from everettT's link you push on the ends of those connectors which exposes a hole in the side you poke a wire in. They seem similar to old receiver connections. I have never seen those used as an unbalanced line out from a pre/amp.

I still think in this era of LED light bulbs and lots of other sources of RF in the home, they may not be the most silent connection. There is just too much exposed that will not be shielded. If it works fine, if not you will have to convert to a fully shielded connection.
Those spring terminals are to be used for speaker connections, as marked. The Main comes from the power amp and the others are connected to two sets of speakers, with a selector on the front of the C26.

Yeah, it's weird, but it was the late-'60s.
 
highfigh

highfigh

Audioholic Warlord
Ratings
2,778 9 5
#10
Where are the non-RCA-style preamp outputs that you're seeing? The jacks at the lower right of the photo are all RCA jacks.

http://www.roger-russell.com/c26pg.htm

BTW- commercial/industrial power amplifiers, line amps and preamps mostly have Euro-style connectors, often called 'Phoenix' connectors. Three wires, three terminals in a piece of plastic, designed for LowZ balanced audio, sometimes with plenty of exposed wire and still, low noise.
 
TLS Guy

TLS Guy

Audioholic Slumlord
Ratings
7,339 17 25
#11
Where are the non-RCA-style preamp outputs that you're seeing? The jacks at the lower right of the photo are all RCA jacks.

http://www.roger-russell.com/c26pg.htm
There are no RCA pre amp out puts except the tape loop. I never said they were. The main preamp outputs are speaker connectors, which I have not seen used as line outs before. Never saw that even pre RCA connectors. Very odd.

That unit is late sixties, so as I said the RCA jacks will have a different physical speck from modern ones. They are a little smaller and that make for connectivity issues.
Best thing to do is clean them well and then crimp the outside of the RCA plugs a little.
 
highfigh

highfigh

Audioholic Warlord
Ratings
2,778 9 5
#12
There are no RCA pre amp out puts except the tape loop. I never said they were. The main preamp outputs are speaker connectors, which I have not seen used as line outs before. Never saw that even pre RCA connectors. Very odd.

That unit is late sixties, so as I said the RCA jacks will have a different physical speck from modern ones. They are a little smaller and that make for connectivity issues.
Best thing to do is clean them well and then crimp the outside of the RCA plugs a little.
At the lower right in the photo, it has four jacks labeled 'Main'- those are the preamp output jacks. They're to the left of the ground screw and to the right of the center Channel output jack. As I wrote, it was the late-'60s and we all know what was going on at that time- lots of new ideas. The speaker terminals are for connecting the speaker wires from the power amp and sending the output to two pairs of speakers, with the selector on the front determining which will be used. The photo of the front shows the Main and Remote buttons in the row of six switches.

http://www.roger-russell.com/c26a.jpg

As for the RCA jacks, I agree, but they were never intended for the plugs we have now- most had four thin metal tabs that were easily bendable, to make better contact and weren't rigid, as many are now.
 
TLS Guy

TLS Guy

Audioholic Slumlord
Ratings
7,339 17 25
#13
At the lower right in the photo, it has four jacks labeled 'Main'- those are the preamp output jacks. They're to the left of the ground screw and to the right of the center Channel output jack. As I wrote, it was the late-'60s and we all know what was going on at that time- lots of new ideas. The speaker terminals are for connecting the speaker wires from the power amp and sending the output to two pairs of speakers, with the selector on the front determining which will be used. The photo of the front shows the Main and Remote buttons in the row of six switches.

http://www.roger-russell.com/c26a.jpg

As for the RCA jacks, I agree, but they were never intended for the plugs we have now- most had four thin metal tabs that were easily bendable, to make better contact and weren't rigid, as many are now.
That is a preamp. It has no power amps. I do note those main outs now. Its odd though as he manual tell you to connect the power amp to spring loaded speaker type connections.
 
highfigh

highfigh

Audioholic Warlord
Ratings
2,778 9 5
#14
That is a preamp. It has no power amps. I do note those main outs now. Its odd though as he manual tell you to connect the power amp to spring loaded speaker type connections.
It's a preamp, but it has speaker selection switches on the front, as I posted. Their power amps never have those, AFAIK. I have seen this model, as well as many others from McIntosh- they definitely had their own ways of doing things.

It's odd, but then, it's McIntosh.
 
N

nrgeti

Audiophyte
#15
I checked the wiring diagram for the C26 preamp and discovered that the 3 sets of spring clips on the back are not connected to any wiring inside the box. They are only connected to each other and act as a switch to distribute programming from the set marked "Amplifier Output" to the other two sets marked "Main Speaker" and "Remote Speaker". In other words the "Amplifier Output" is for accepting speaker outputs from an amplifier somewhere. There is nothing to be gained by using them since speakers can instead just be wired directly from an amplifier without going through the preamp.
 
highfigh

highfigh

Audioholic Warlord
Ratings
2,778 9 5
#16
I checked the wiring diagram for the C26 preamp and discovered that the 3 sets of spring clips on the back are not connected to any wiring inside the box. They are only connected to each other and act as a switch to distribute programming from the set marked "Amplifier Output" to the other two sets marked "Main Speaker" and "Remote Speaker". In other words the "Amplifier Output" is for accepting speaker outputs from an amplifier somewhere. There is nothing to be gained by using them since speakers can instead just be wired directly from an amplifier without going through the preamp.
Not connected? You might want to look at it again- the two switches in the row of six on the front (immediately to the left of the headphone jack) are marked 'Speakers Off' with 'Main' and 'Remote' and if there's no connection inside, there's no reason to have switches for selecting the speakers to be used.

The benefit of this is that the user doesn't need an external speaker switch, in some kind of box.
 
one more time

one more time

Enthusiast
Ratings
2
#17
I'm a bit late to the show, but my Marantz 7C pre-amp had those same speaker connections. This allows the output of the power amp to be fed back into the speaker inputs and allows the user to select between two sets of speakers. IOW, it has a built in speaker selector if you chose to avail yourself of this feature.

Of course, use of this feature is entirely optional, One could simply connect their speakers directly to the power amp's output.
 
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