McIntosh ma6100 sounds muddy

[Deezel]

I just recently recapped the electrolytics in a ma6100 about 3 weeks ago and have noticed a slightly muffled sound now. Playing it through JBL L100Ts and have an audio research sp9 as reference. The lows are great, mids very slightly muffled which is made more apparent by the rolled off highs. I have to turn the treble knob 3/4 of the way to make it sound right. Then it sounds really good. But I'm sure this isn't what its supposed to sound like at neutral. Thoughts? Possibilities?

 

[c_dk]

A typical restored MA6100 will measure + - 1 dB from 20 to 20k through all inputs and out all outputs when properly restored......spot checking at 5 or 6 frequencies is usually adequate to determine if you unit is within this basic spec.

We would do, and I still do, this with a Soundtech analyzer, scope and a 8 ohm dummy load or via the tape out or preamp out with a line level switcher. The phono EQ gain stage is measured with a reverse RIAA circuit.

Without the proper test gear to attempt to reset the frequency/gain ratios is not a good idea.

 

[Deezel]

A typical restored MA6100 will measure + - 1 dB from 20 to 20k through all inputs and out all outputs when properly restored......spot checking at 5 or 6 frequencies is usually adequate to determine if you unit is within this basic spec.

We would do, and I still do, this with a Soundtech analyzer, scope and a 8 ohm dummy load or via the tape out or preamp out with a line level switcher. The phono EQ gain stage is measured with a reverse RIAA circuit.

Without the proper test gear to attempt to reset the frequency/gain ratios is not a good idea.

I guess I need to build reverse riaa, I have the other equipment

 

[c_dk]

Do a line level spot frequency check......20,100, 500, 1000, 10k, 20k would be a series of good basic frequencies to check the output. If your readings are different between the main out and speaker level it could be a amp issue. Most likely though a tone circuit out of alignment in the preamp.

 

[Deezel]

Do a line level spot frequency check......20,100, 500, 1000, 10k, 20k would be a series of good basic frequencies to check the output. If your readings are different between the main out and speaker level it could be a amp issue. Most likely though a tone circuit out of alignment in the preamp.

Will do, thanks. Seems weird that the muffled sound will go away with 1/4 turn of treble knob, like the blanket is completely lifted

 

[c_dk]

My second and third McIntosh sales were MA6100s in 1978, these were the last of our demo units which opened shelf space for the new MA6200.

That makes the youngest of these units 40 years old, yours could easily be 45 years old.

Caps dry out, resistors values vary, transistors get noisy....all reasons why these units need complete restorations before subjected to " subjective " judgements. I would expect all these vintage units needing restoration by this time.

Have you cleaned the switches with D5, the potentiometers with Faderlube?

A European member while restoring a similar vintage C26 reported substantial measured improvements on his unit after doing DEEP cleaning of his badly corroded switches.

You need to establish a performance baseline and compare it to your preferred setting with added treble gain to make sense of what you are hearing.

 

[twiiii]

By your description you have a unit that needs an over haul. But a lot of listeners originally thought Mac amps from that period were not capable of producing fine detailed sound. With the right speaker the 6100 can reproduce detail with the best of them. Yes it will be a well controlled presentation. If you are looking for a Krell or Threshold type sound you will never be happy. But I bet the 6100 just needs to be reconditioned.

 

[seacliffe301]

I just recently recapped the electrolytics in a ma6100 about 3 weeks ago and have noticed a slightly muffled sound now. Playing it through JBL L100Ts and have an audio research sp9 as reference. The lows are great, mids very slightly muffled which is made more apparent by the rolled off highs. I have to turn the treble knob 3/4 of the way to make it sound right. Then it sounds really good. But I'm sure this isn't what its supposed to sound like at neutral. Thoughts? Possibilities?

Are you saying that it sounds worse since you re-capped? It may just be the nature of the beast.
I had a friend that had a 6100 back in the early 80's. That made the unit not very old when he was using it. At that time, it did not sound as detailed as either a 1700 that he had, or C28/2505 combo that I was using. I was actually quite disappointed with the SQ of that particular unit.

 

[jayvis]

I was tempted to buy a very clean used MA6100 back in 1980. Our local dealer had just gotten it in on trade. Fresh out of coIlege and with a new job, I was ready to treat myself to my first dive into higher end audio with my first McIntosh. After listening to that fine piece of McIntosh engineering, I asked the store manager what it was traded for. He smirked and pointed to a new Pioneer SA-8800 on a shelf across the room. So, out of curiosity, I listened to the Pioneer through the same speakers just for the heck of it. Guess what I went home with? A brand new Japanese integrated amp and some money left in my pocket. Never really regretted it either.

 

[c_dk]

The OP started his questions about this MA6100 in the solid state forum with a very dead unit.

We got him thru the basic repair stages to get it up and running and the first steps of restoration have been taken.

At this point I have no idea if the unit has had the now almost certainly needed recap but I do believe the know issues of the ground drains have been taken care of.

As to the sound, without establishing a series of basic benchmark frequency tests any repair or modifications would be strictly guess work. I am looking forward to the OPs measured results.

Of coarse a Pioneer should have sounded different than a MA6100 back in 1980......I know they sounded different than their Sansui and Technics completion also.....

 

[Thocom]

Any change with the “loudness” engaged? I have always thought Mac loudness makes it sound muddy. At least on my MX110, MX113 and C39

 

[c_dk]

The Ma6100 loudness raises the volume of the bass at 20 Hz aprox. 12 dB, not quite the amount needed at 60 dB listening level.

If you speakers can not handle 20 Hz with low distortion, and few speakers can, I would expect using the loudness at any level but for background listening to be muddy.

This all or nothing approach to loudness compensation issues is the best arguement I can think of to support the variable loudness concept Mac introduced with the MAC4100 receiver. The subtractive method used in the C26 and some Yamaha units I always found clunky.

 

[BilboBaggins]

The OP doesn’t mention what speaker he is using. I’ve noticed big differences depending on what speaker I’m using on my leestereofied ma-6200. I tried a pair of Kef 103.2s and they didn’t sound good with it. Tried a pair of KLH-17s and they sounded good, but not as good as the EPI M100s I’ve decided to pair with my MA-6200. They sound excellent together!

Here are 3 different speakers about the same size that sound completely different on the same amp. The right synergy is essential to get the best out of your system.

 

[Deezel]

I have been through this unit and recapped everyelectrolytic, reflowed grounds, replaced transistors, cleaned every connection, checked voltages, everything looks good. It even sounds good when I make big adjustments to bass and treble knobs. It sounds dull almost muffled and really rolled on the highs. Got me thinking, I didn't do anything to volume and tone control board. Do you think I need to make tone adjustments via the variable resistors r227 , r228 ect. And if so how do I go about it? I do have a good signal generator and oscilloscope.
The speakers I'm using are JBL L100T. Has great 20hz response and considered to have bright highs

 

[c_dk]

Have you taken measurements of how linear the output of the unit is at different frequencies?

If you have a reverse RIAA circuit you can check both the phono eq and the tone circuits alighnment at the same time, which we would do at clinics because back then the turntable was use as the source most often. Ultimately you need to measure both low and high level inputs at at least 5 or 6 spread out frequencies.

For example a friend of a friend asked me to check oit his Onkyo integrated. At 2k it barely made it's rated 50 watts, but was down to 42 at 200 hz and 35 watts at 20hz. Down close to 2 dB it was out of spec and maybe could "sound thin" but in reality few speaker systems come close to being + or - 5 dB so general statements defining sound are often questionable.

However, if you do not do correlating measurement how would you know.......muddy makes me think of either a excessive amount of bass or a speaker problem. The height of the waveforms on your scope will let you know how close to linear your amp is. Passing a square wave through the unit will let you see how well your tone circuits are tracking.

 

[SA7I]

I just recently recapped the electrolytics in a ma6100 about 3 weeks ago and have noticed a slightly muffled sound now. Playing it through JBL L100Ts and have an audio research sp9 as reference. The lows are great, mids very slightly muffled which is made more apparent by the rolled off highs. I have to turn the treble knob 3/4 of the way to make it sound right. Then it sounds really good. But I'm sure this isn't what its supposed to sound like at neutral. Thoughts? Possibilities?

Are you sure it’s not your speakers?