MC 754

[Kingsin7]

Does anyone have thoughts about leaving these 754s powered on all the time? They do not have power switches and the manual claims leaving them always on is fine as long as they are used frequently. When I press my ear to the ribbon tweeters on my speakers I can hear a very (very) low hiss when my pre is off and the 754s running.

When I had just the one 754 I had it plugged into a Mac CR7 Remote Receiver that allowed me to turn it on/off with a clicker. Now that there are two in the mix that isn't an option (or is it?).

 

[TSmith8605]

Does anyone have thoughts about leaving these 754s powered on all the time? They do not have power switches and the manual claims leaving them always on is fine as long as they are used frequently. When I press my ear to the ribbon tweeters on my speakers I can hear a very (very) low hiss when my pre is off and the 754s running.

When I had just the one 754 I had it plugged into a Mac CR7 Remote Receiver that allowed me to turn it on/off with a clicker. Now that there are two in the mix that isn't an option (or is it?).

My thoughts would be to defer to the advice of the engineers who designed the amps as quoted: "They do not have power switches [hint] and the manual claims [actually says] leaving them always on is fine as long as they are used frequently."

 

[62caddy]

I guess it depends upon how McIntosh defines "frequently". Call it habit but leaving equipment powered up and unattended just doesn't sit well with me personally.

In any case, the CR7 has two switched A/C outlets which can be safely used to power both amplifiers. The total maximum capacity of all 3 outlets of 1750 W is well in excess of the maximum power consumption of a pair of MC754s.

 

[techguy0192]

Does anyone have thoughts about leaving these 754s powered on all the time? They do not have power switches and the manual claims leaving them always on is fine as long as they are used frequently. When I press my ear to the ribbon tweeters on my speakers I can hear a very (very) low hiss when my pre is off and the 754s running.

When I had just the one 754 I had it plugged into a Mac CR7 Remote Receiver that allowed me to turn it on/off with a clicker. Now that there are two in the mix that isn't an option (or is it?).

You have to keep it in context with the time period these amps were released. McIntosh designed the preamps of that time with a switch AC outlet, that they expected the MC754 (& 752) to be connected to. This in effect did facilitate a power switch for the amp. I have always switched my amps off when not in use. This is a good practice, especially for NON McIntosh amps that might not have as good or any safeguards against a run away DC offset. Too much DC down the speaker cables will fry speaker. While the Mac amps do have excellent safeguards again too much DC getting to the speakers, I still keep the amps switched off. Additionally, there's the increased risk of lightning damage or other damaging electrical surges. Overall, these amps sound great cold and don't require an extensive warm up time. A power strip can be used to power the amp on/off. I recently had a MC752 overhauled and the AC outlet was replaced with a power switch....search the McIntosh section if you're interested in seeing how this turned out.

 

[Kingsin7]

I guess it depends upon how McIntosh defines "frequently". Call it habit but leaving equipment powered up and unattended just doesn't sit well with me personally.

In any case, the CR7 has two switched A/C outlets which can be safely used to power both amplifiers. The total maximum capacity of all 3 outlets of 1750 W is well in excess of the maximum power consumption of a pair of MC754s.

Thanks Caddy - Should I hook the two power amps into those CR7 outlets and the pre into one of the power amps?

Last thought, and thank you everyone for being so helpful:
Does passing the signal through the CR7 unit diminish fidelity in any significant way?

 

[62caddy]

Thanks Caddy, I forgot that the CR7 has two AC outlets marked 'tuner' and 'CD' as well as the single 'power amp' outlet and an unswitched one. I can just hook the other amp into the tuner or CD outlet as you suggested and problem fixed - I Don't know how I did not think of that when hooking up amp #2 this weekend...

Last thought, and thank you everyone for being so helpful:
Does passing the signal through the CR7 unit diminish fidelity in any significant way?

Actually the outlets are labeled "Unswitched", "Power Amp" and "Preamp" (switched) but the labeling isn't so important as the total capacity of 1750 watts not being exceeded. Preamplifiers draw very little current so plugging the preamp into either of the MC754s should pose no problem.

I am using a CR7 inserted through the tape monitor loop in each of my systems and found it impossible to distinguish between the signal processed through the CR7 or directly. CR7 is essentially a very basic C31 preamplifier and utterly quiet.

 

[Kingsin7]

Actually the outlets are labeled "Unswitched", "Power Amp" and "Preamp" (switched) but the labeling isn't so important as the total capacity of 1750 watts not being exceeded. Preamplifiers draw very little current so plugging the preamp into either of the MC754s should pose no problem.

I am using a CR7 inserted through the tape monitor loop in each of my systems and found it impossible to distinguish between the signal processed through the CR7 or directly. CR7 is essentially a very basic C31 preamplifier and utterly quiet.

Thanks Caddy, you're telling me everything I want to hear!
I edited my post regarding the CR7 after I checked the unit and was reminded it had CD + Tuner labelled inputs, not AC outlets...

 

[c_dk]

PSSS don't tell anybody but the CR-7 is just about the most minimalist Mac preamp you can do. No phono.....need external one, no tone or loudness, volume is controlled by using the Toshiba chip set, but the switching scheme uses JFETs just like it's contempory preamps. The next generation, led by the C37, went to relays just like they use now.

 

[Kingsin7]

PSSS don't tell anybody but the CR-7 is just about the most minimalist Mac preamp you can do. No phono.....need external one, no tone or loudness, volume is controlled by using the Toshiba chip set, but the switching scheme uses JFETs just like it's contempory preamps. The next generation, led by the C37, went to relays just like they use now.

The gentleman I bought my first 754 from threw in the CR7 too for $500 total. I was skeptical about that little guy when I first got it, but it sounds like a gem from what I'm hearing.
I plugged a DAC directly into it some months back, but noticed enough loss of clarity to continue to run a pre instead. It still sounded good, though - just not good enough to forego a preamp.

 

[c_dk]

Have no idea what good adding another layer of electronics could add but would love to see some unity gain scope shots with and without your preamp whatever it is.

The only problem we ever had with the Toshiba volume control chip set was you could sometimes hear the precison resistor ladder network tick as it switched up and down the ladder.

It was used in the MCD7007 cd player, the MAC4300 and the first run of the C31. It was replaced in the C31 2nd gen by the motor controlled amps volume control. Might have been used in later products also but I am not sure.

 

[62caddy]

I'm guessing the main preamplifier doesn't have remote.

I ran the CR7 alone in my main system for a month when the C32 preamp was out for service and the system was none the worse for it other than not being able to play records or make tone adjustments.

For the minimalist user having no need for tape faculties, phono section or tone controls, I would not hesitate to recommend the CR7 for the pittance they sell for and never want for better. Seriously it's that good. Only small complaint is the clicking that occurs with changing volume.

 

[Kingsin7]

Have no idea what good adding another layer of electronics could add but would love to see some unity gain scope shots with and without your preamp whatever it is.

The only problem we ever had with the Toshiba volume control chip set was you could sometimes hear the precison resistor ladder network tick as it switched up and down the ladder.

It was used in the MCD7007 cd player, the MAC4300 and the first run of the C31. It was replaced in the C31 2nd gen by the motor controlled amps volume control. Might have been used in later products also but I am not sure.

No phono for one and unfortunately no remote for any preamp I own.

I A/B'd both scenarios and I heard a distinct difference. CR7 alone was flat sounding but I'm not able to describe audio in any proper technical way - it just sounded okay - but I do like the concept of a Spartan setup with no preamp as an option for a future configuration...

I was using a fully rebuilt Marantz 1060 at the time as a preamp. I'll be hooking up a Threshold pre this week. I will mostly be listening to vinyl with this system and occasionally use it for movies.

Anyone foresee an issue using a 3 prong to 2 prong AC plug adapter to plug my Threshold SL-10's external power source into the AC outlet on the 754? Too much..?

 

[c_dk]

There are any number of members who love to debate the value of changing the "color" of their sound system by rolling tubes etc. so if you find that adding a preamp improves the sound go for it.

Will be interesting to hear what a different preamp does.

At somepoint you should really invest in a sequential or similar controllable power strip.

 

[Kingsin7]

Everything is hooked into a power strip. The CR7 allows me to use a remote control for the whole system. That is why I ask about the 3 prong to 2 prong adapter for plugging this particular preamp into my power amp. If foregoing the CR7 for a controllable power strip is better, I may do so, but I got the CR7 pretty much for free...

 

[Kingsin7]

I guess I am going out of my way to keep the CR7 in the mix but it says "Mcintosh" on it and I have a Mac remote for it, so why not?

 

[techguy0192]

I guess I am going out of my way to keep the CR7 in the mix but it says "Mcintosh" on it and I have a Mac remote for it, so why not?

Just because it has the Mac logo on it, doesn't provide enough justification to have it in the single chain. I have found simplicity and the less is more approach typically leads to better sound. Unless some thing it needed it should be left out.....just my opinion.

 

[c_dk]

There was a Panamax strip that had a relay that was switched by the control units switched AC outlet, triggering relays that would turn on the strips sockets. Next step up had a sequencer added.

 

[Kingsin7]

Just because it has the Mac logo on it, doesn't provide enough justification to have it in the single chain. I have found simplicity and the less is more approach typically leads to better sound. Unless some thing it needed it should be left out.....just my opinion.

I was kinda joking, but in the end I do need the volume control function the CR7 grants me.

I'll have to A/B the new pre vs running my source through the CR7 tomorrow and report back my thoughts.

 

[62caddy]

In order for A/B comparisons to be of any use, it is imperative the listening comparison is made instantaneously. The tape monitor loop is the ideal means to this end.

Sources must be connected (and selected) at the main preamplifier and volume setting of the CR7 should be set so that loudness is unchanged whether the CR7 is in the loop or bypassed. (Do not connect sources directly to the CR7 - as the results will be nullified)

Then play the source and switch the tape monitor in/out as desired to determine whether any differences can be heard. Even better would be to have someone else do the switching for you on your command.

I hope the experiment proves enlightening and informative.

 

[62caddy]

There was a Panamax strip that had a relay that was switched by the control units switched AC outlet, triggering relays that would turn on the strips sockets. Next step up had a sequencer added.

That's exactly how I have each of my systems set up: CR7 switched outlet>Panamax trigger control>power to equipment. Two of the outlets are on a delay on the Panamax model I have.