#163392  by nuthatchwinters
 Fri Nov 16, 2018 5:00 pm
hello all. just had preamp tap done on Twin to accomadate Mac power amp and "Healy Mods" and upon completion my tech states he is unhappy with the performance of the preamp signal output level and also the Macs input reaches saturation and clipping extremely quickly with a very hot signal coming from the Twin which defeats the whole purpose of having a very clean amp and preamp. also was concerned there is no input sensitivity level on the Mac to compensate for a hotter signal and that the Mac seems to struggle with the signal from the Twin and the gains are not matched very well. I am not panicking though because he feels that with a little more work he'll have it all ironed out. I trust him. just curious if any of you who have had the same work done ran into the same issues. any feedback appreciated. thank you. MK p.s. (its a Mac 2505 and 71 silverface Twin)
 #163395  by lovetoboogie
 Fri Nov 16, 2018 6:10 pm
There is no need to govern the Mac input sensitivity... If you are distorting early or it is too gainy at all points then the preamp signal isn't tapped at the right point or the McIntosh driver stage is faulty. Did you try and run a regular hi-fi signal through the Mac and out to a known set of good speakers....

A well oiled McIntosh power amp does one thing, and does it well. It reproduces the signal coming in with little or no coloration(within reason).
 #163423  by waldo041
 Sun Nov 18, 2018 7:38 am
The input sensitivity of an MC2505 or 2105, whichever you have, is dictated by the Macs Volume control. The twin preamp first sees it! If you turn that all the way to zero, is the twin preamp still over-driving the mac?

Turn the Mac volume down! Or did he Bypass it?

I have had 110 volts slamming the front end of a Mac from a Twin. And thanks to Brad Sarno's teachings to me, the McIntosh Volume control absorbs the majority of the voltage drop. So not sure how or why your Tech is over-driving the mac.

Sounds to me like he bypassed the macs volume control. BUT i have been wrong before!

~waldo
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 #163486  by nuthatchwinters
 Fri Nov 23, 2018 9:57 am
and you were not wrong this time Waldo! precisely the issue. once again thank you! right on the mark as always.

MK
 #163504  by nuthatchwinters
 Sat Nov 24, 2018 5:20 pm
One final question. I have HT cab with 2 jble120s wired with black wire going to red input port and red to black as was recommended. Now when I tap speaker cab to rear of Mac am I connecting to “4” spot or “8” spot. Have it on 4 currently.
 #163505  by nuthatchwinters
 Sat Nov 24, 2018 5:33 pm
Correction: White wire (not red) to black input port, and black wire to red input port. But anyway, the 4 and 8 Spot on rear of Mac is where I need clarification. Thanks. MK
 #163529  by waldo041
 Mon Nov 26, 2018 4:29 pm
nuthatchwinters wrote:
Sat Nov 24, 2018 5:33 pm
Correction: White wire (not red) to black input port, and black wire to red input port. But anyway, the 4 and 8 Spot on rear of Mac is where I need clarification. Thanks. MK
2 - 8 ohm speakers wired in parallel will give you a 4 ohm speaker load. You can use the 4 ohm output tap for a 1:1 match, or increase the drive of the amp by using the 8 ohm output tap which will give you a 2:1 mismatch. Both will work fine, You can also use the 16 ohm tap for even more drive. Research the McIntosh Sentry Monitor here when playing with mismatch's.

~waldo
 #163892  by Pointclear
 Sat Dec 22, 2018 11:53 am
waldo041 wrote:
Mon Nov 26, 2018 4:29 pm
nuthatchwinters wrote:
Sat Nov 24, 2018 5:33 pm
Correction: White wire (not red) to black input port, and black wire to red input port. But anyway, the 4 and 8 Spot on rear of Mac is where I need clarification. Thanks. MK
2 - 8 ohm speakers wired in parallel will give you a 4 ohm speaker load. You can use the 4 ohm output tap for a 1:1 match, or increase the drive of the amp by using the 8 ohm output tap which will give you a 2:1 mismatch. Both will work fine, You can also use the 16 ohm tap for even more drive. Research the McIntosh Sentry Monitor here when playing with mismatch's.

~waldo

I have, just this past week, tapped my twin and fender concert to run through a Harman Kardon citation 16 (unbelievably beautiful sound) pushing a k and e 120 in a 4 ohm can. The amp has an 8 and 4 ohm switch, running it on 8 ohms gives so much more fullness to the notes!