MC-2505 / Chorus I

[mcsylklipsch]

I've had a pair of Klipsch Chorus (I / front ported) for about ten years now.

On a regular basis (let's say once per day for 5-10 minutes) I enjoy listening at a fairly generous volume. I'll ramp it up until I start getting nervous or the turntable starts feeding back. Better than coffee.

Recently, I started noticing a "flapping" sound when trying to reproduce certain [lower] frequencies at high volume. I pulled the grille, and sure enough there's physical damage to the surround. I've resolved to have both drivers rebuilt locally by an individual who comes highly recommended.

I'm interested to know if there's a general consensus as to whether the McIntosh MC-2505 is an appropriate amplifier to drive the Chorus speakers.

I've been pleased with the sound of this combination over the years and am generally not motivated to make any changes. However, I understand it's better to use an amplifier with a wattage rating at least equal to the wattage rating of the speakers (or am I mistaken here?).

I certainly don't need the capability to generate more volume, but I would like to optimize the speakers' performance at the high volumes I already enjoy. I don't really have existing problems with distortion but I am concerned an amplifier -> speaker mismatch could shorten the life of the drivers once they're repaired.

Thanks very much for any thoughts/opinions you all care to share!

[rcarlton]

The McIntosh should work well with the Chorus. I have 2 MC250's that have powered Heresys, Cornwalls, LaScalas and K-horns.

[stormin]

With a solid state amp of 50wpc with .25% distortion and with only a damping factor of 27 at 8 ohms I would think it would be very easy to overdrive the K-48 woofer with distortion and all the other drivers if you like to throttle the volume.

Just to give you a comparison I am driving a Chorus II which has a K-48-E with an amplifier that has 500wpc with .1% distortion with a damping factor of over 3,000. When I throttle the volume it becomes a nightclub environment in the listening room. The K-48 just loves watts. I dont have a hint of distortion and talk about headroom.

Mac makes some great equipment but if you love volume you might want to look at that their more powerful lines.

[artto]

That MAC should be fine for the Chorus but it also depends on the size of the room and how absorbant/reflective it is ~ as well as how loud you like it ~ and the condition of your ears.

I believe Klipsch used the "pro" driver in the Chrous so you would have to be driving them pretty hard for the surrounds to be coming apart. The MAC's are usually not direct coupled, instead using a transformer coupled output to the speakers. In my experience (both as a listener/audiophile, and a bass player) the transformer coupled amps tend to be softer, less controlled, not as solid in the bass department. IMO this is at least partially due to the lower damping factor with transformer coupled output which provides less control over the woofer. (just some food for thought)

[djk]

Lack of a sub-sonic filter destroys woofers in ported speaker systems.

"IMO this is at least partially due to the lower damping factor with transformer coupled output which provides less control over the woofer. (just some food for thought)"

Incorrect.

McIntosh bass can be rock-hard by just adding some bypass caps at various points in the amplifier.

You may be able to repair the K48 surrounds with Weldbond (I have repaired many JBL cloth surrounds with Weldbond).

[artto]

"IMO this is at least partially due to the lower damping factor with transformer coupled output which provides less control over the woofer. (just some food for thought)"

Incorrect.

McIntosh bass can be rock-hard by just adding some bypass caps at various points in the amplifier.

You'll have to do better than that to convince me otherwise. I've played the bass for 40+ years. Tranny output coupled amps always sound softer to me, especially in the bass. A quick look at the amp's specs always confirms a low damping factor. On top of that I also have to disagree that simply adding bypass caps anywhere would make it more solid sounding in the bass. If anything, I think the opposite is true.

My Luxman MB3045 have the most solid state sounding ( as in good ~ I like it it) bass of any tube amp I've ever heard. They are transformer coupled but are quadrafilar wound (instead of bifilar as in MAC) and cross couple the driver/output tubes with this unique output trans. They have a low damping factor too. And. of course, they are not as "solid" and clean on the low end as say, anything Crown or Mark Levinson.

[djk]

"You'll have to do better than that to convince me otherwise. I've played the bass for 40+ years. Tranny output coupled amps always sound softer to me, especially in the bass. A quick look at the amp's specs always confirms a low damping factor. On top of that I also have to disagree that simply adding bypass caps anywhere would make it more solid sounding in the bass. If anything, I think the opposite is true."

Try it before you complain, you certainly haven't as you would have never made that statement otherwise.

"Which caps are they DJK? I'll try them in my 2125."

Add one 47µF across each ±42V rail at the main filter caps

Add a 0.01µF~0.1µF film cap in parallel with C239, 240 (little board on the input jacks, very tight for space)

Add a 0.1µF film in parallel with C203, 204 (input coupling cap to impedance buffer)

Add a 0.1µF film in parallel with C207, 208 (output coupling cap from impedance buffer)

Add a 0.1µF film in parallel with C219, 220 (feedback cap)

Add a 0.1µF film in parallel with Q215, 216 (bias transistor)

Add a 0.1µF film in parallel with C305, 306 (±15V regulator outputs)

Add a 0.1µF film in parallel with D304, 305 (reference diodes for regulators)

I cut off all the push on connectors in the power supply and speaker relay and soldered them direct. I soldered a pair of 0.1µF film across the speaker relay contacts and cleaned the relay contacts with a sheet of paper and applied De-oxit.

I sprayed De-oxit on the RCA jacks, cleaned the input sensitivity selector switch (very important), and the edge connectors for the L and R amp boards.

I removed the 10-32 screws on the main filter caps and used De-oxit before replacing.

Do not move the chassis with the bottom off, the glass could crack. Put it on a small piece of carpet to help turn at different angles.

The 47µF are under a lot of stress, I used 100V caps even though they only run at 42V.

Even though this changes no measurable performance specification, it will change the sound more than you can believe.

Jackhammer bass from an amp with a DF of only 14?

[Invidiosulus]

"IMO this is at least partially due to the lower damping factor with transformer coupled output which provides less control over the woofer. (just some food for thought)"

Incorrect.

McIntosh bass can be rock-hard by just adding some bypass caps at various points in the amplifier.

You'll have to do better than that to convince me otherwise. I've played the bass for 40+ years. Tranny output coupled amps always sound softer to me, especially in the bass. A quick look at the amp's specs always confirms a low damping factor. On top of that I also have to disagree that simply adding bypass caps anywhere would make it more solid sounding in the bass. If anything, I think the opposite is true.

My Luxman MB3045 have the most solid state sounding ( as in good ~ I like it it) bass of any tube amp I've ever heard. They are transformer coupled but are quadrafilar wound (instead of bifilar as in MAC) and cross couple the driver/output tubes with this unique output trans. They have a low damping factor too. And. of course, they are not as "solid" and clean on the low end as say, anything Crown or Mark Levinson.

Artto,

What bass amps are you fond of?

[stormin]

Add one 47µF across each ±42V rail at the main filter caps

Add a 0.01µF~0.1µF film cap in parallel with C239, 240 (little board on the input jacks, very tight for space)

Add a 0.1µF film in parallel with C203, 204 (input coupling cap to impedance buffer)

Add a 0.1µF film in parallel with C207, 208 (output coupling cap from impedance buffer)

Add a 0.1µF film in parallel with C219, 220 (feedback cap)

Add a 0.1µF film in parallel with Q215, 216 (bias transistor)

Add a 0.1µF film in parallel with C305, 306 (±15V regulator outputs)

Add a 0.1µF film in parallel with D304, 305 (reference diodes for regulators)

I cut off all the push on connectors in the power supply and speaker relay and soldered them direct. I soldered a pair of 0.1µF film across the speaker relay contacts and cleaned the relay contacts with a sheet of paper and applied De-oxit.

I sprayed De-oxit on the RCA jacks, cleaned the input sensitivity selector switch (very important), and the edge connectors for the L and R amp boards.

I removed the 10-32 screws on the main filter caps and used De-oxit before replacing.

Do not move the chassis with the bottom off, the glass could crack. Put it on a small piece of carpet to help turn at different angles.

The 47µF are under a lot of stress, I used 100V caps even though they only run at 42V.

Even though this changes no measurable performance specification, it will change the sound more than you can believe.

Jackhammer bass from an amp with a DF of only 14?

Sounds like the son of Frankenstein. LOL!

[djk]

"Sounds like the son of Frankenstein. LOL!"

Why, it's just sound practice. I'm just bringing it up to the standard of a well designed amplifier like a Leach.

http://users.ece.gatech.edu/~mleach/lowtim/graphics/ckt.pdf

With a copy of the manual it is very easy to do, and the McIntosh will sound much, much better.

Here is the list for the older 250/2100/2105 series:

I own a MC2100 and two MC2120s.

Caps wear out.

Even when not in use.

This list is for the MC2100, electrically it is the same as the MC2105, just without the meters.

Even though your old amp is still working, you have no idea how much of the music you are missing.

The parts are inexpensive.

Digi-Key is good, Mouser has no minimum order.

Posted by djk (M) on July 11, 2004 at 04:29:36
In Reply to: Re: MC2105 @ $ 100 even @ 20 yrs old is a best buy for me. posted by julian4@telkomsa.net on July 06, 2004 at 14:58:04:

The sound would benefit greatly from replacing a few dried out electrolytics, and adding a few film types here and there.
C301, 302 is the main input coupling cap. It is a Mylar type so it is likely to be OK, upgrading it to a Polypropylene type with give a smoother sound to the high end (0.47µF).

C307, 308 are emitter bypass caps, 100µF 15V. Replace with same type and add a 0.1µF film bypass.

C309, 310 are the output coupling caps for the pre-driver section, 10µF 25V. While a film type would be better, size is a problem. The DC bias across this cap also helps out with its being an electrolytic. Replace with same type and add a 0.1µF film bypass.

C303, 304 are the DC power supply caps for the front end, 470µF at 25V. Replace with same type and add a 0.1µF film bypass.

C1, 2 are the feedback loop caps, 330µF at 3V. The signal goes through these so replacing these with new ones and adding a 0.1µF film bypass really opens up the sound. Go with as high a voltage as what space permits.

C11, 12 are the DC supply caps for the voltage gain stage, 150µF at 50V. Replace with same type and add a 0.1µF film bypass.

C201, 202 are the main filter caps, 39,000µF at 40V. These may be quite expensive new, although I have seen them surplus for very low prices. I would use then unless signs of leakage or amplifier hum are there. Add a 47µF at 50V cap in parallel with each.

C203 is a multi-section cap that will be very hard to find a fresh date code. New caps are small enough that they may be wired to the terminals of the old one, leaving the old one in place. This cap is important as it provides the current for the diff pairs and the VAS. The sections go 80/80/150/50µF with the voltages being 200/200/150/150V. If you measure the voltages 100/95/90/80V are typical, so 200V caps are not really needed, but 100V is not enough.