Looking good, anytime i replace any 3watt resistors like those, i raise them off the board a few mm so they stay cooler and don't burn the board..( i know they are just bleeder resistors but..... )

That was originally my preference, but there is so little clearance between them and the top cover, it was impossible to measure without mocking it up in the lab. Which, i couldn't do because i just brought the PCB board and not the entire chassis to the lab at my office. I was out on calls assisting detectives all day (on my day off, mind you), so having my entire amp in my car was a no go. Especially since i was in some of the most dangerous parts of the city ref to some very violent crimes. Explaining that my agency vehicle got burglarized because i left my Adcom in the back seat is not on the list of conversations i want to have with my Lieutenant. Lol

However, been playing for about two hours now and the bass is substantially improved. Problem solved!

Got about 50 hours of on-time, with about 30 with music. Bass has been transformed. The 105 C Nichicon caps took longer to burn in than expected, but the results are excellent.

Update January 2017:

In late November I began to, again, experience a loss in bass output. I checked in a friend's pro portable RTA and I was seeing a gentle roll off in bass and mid bass, beginning at roughly 480hz. This wasn't present after the previous cap replacement earlier in the thread.

So, I ordered ELNA Silmic II caps in the appropriate values and replaced C3, C7, and C9 on both of the channel boards after testing the 4 main filter caps, disconnected, and they are still yet just fine.

Bingo! Problem solved!



Old caps.



Old caps, different angle.



New caps.




@Jon Lane , you might get a kick out of this.

Alright, the Elna Silmic II's have been amazing. Much more depth in the soundstage and all grit/grain has disappeared. However, the main caps started to reach end of life so I swapped them out with some TDK/EPCOS 22,000uf/100v caps from Mouser. Slightly shorter (leaving room for an air gap under the bottom of the cap) but the same diameter as the CD caps that came out. Went from 72,000uf of main filter capacitance to 88,000uf (about the upper limit without changing other parts). Finished assembly around 1:30 this morning and adjusted bias/DC offset before turning in for the night. Leaving the amp on for the next few days and will recheck bias and DC offset closer to the weekend.

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Hi BufordTJustice


As long as I cant send PM...
I would like to know about your 5500.. are you running it yet?
How was the changes after you changed the main caps?
Much better? I'm thinking about follow your steps... I have a 555 mkII that I modded, sounds nice btw.

Thanks, from Brazil


Rafael

Interesting, I am puzzled C3, C7 and C9 were changed less than a year and you have to change them again. Something doesn't sound right to me. I looked at the schematic, those are filter caps for the preamp section that is low power. If I were to do it, I'll buy a higher value cap to replace those. try a 2200uF or even 3300uF that can fit the pcb and the headroom. Then tag on something like a 22uF cap at the bottom if space permit. You have 0.1uF C1, C6, C7 and C10, that's good, a 22uF will bridge the gap between 0.1uF and the big cap.

He didnt change twice the signal caps, this time he changed the main filter caps, the big ones (black TDK/Epcos), and kept the signal caps. (its what I understood)

I am talking about the filter caps. See post #30 , he changed them.

Problem is not the brand, 1000uF is not big enough. No matter how "good" the cap, it's only 1000uF. Change to 2200uF or 3300uF will definitely improve the performance even if you get the cheapest of the cheap caps. I always use the cheapest of the cheap components that can do the job. I don't believe in using expensive parts if I can help it.

This is filter caps, it is ONLY for the preamp stage, it's low current, ESL and ESR is not important. The new caps are smaller than before, I am sure he can find 2200uF or 3300uF caps that can fit the original footprint on the pcb and not too tall.


Honestly, I don't even think it is that important to change the caps. Unless the top is swelling or leaking, I tend not to tough the caps. The key is to have enough caps, not new caps.

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C3/7/9 were only changed once.

There is zero room for taller caps on the top board. Possibly only 3mm-5mm between then and the top cover. Forget squeezing a bypass between the base of the Caps and the board. Not going to happen.


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I paid $16 shipped for 10 of the Caps I used to replace those. Nelson Pass's hinted that the uf rating of those aren't the weak link in the chain.


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I ended up also replacing the four main filter caps with larger TDK/Epcos 22,000uf caps as one of the original CD caps had started to leak.

Been using it non stop since I did that. Loving it.

I'm considering having John Hillig at Musical Concepts do a package on it. But that's another level.


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I am glad you are back, I am interested in this amp also. I almost made an offer on the GFA5800 that was burned. I withdrew my offer after I saw the picture that it uses some really old transistors that are obsoleted and are hard to find. Now I am waiting for a broken 5500 for cheap.


That I disagree with Pass, this is an unregulated supply, the larger the cap, the smaller the ripple. This is particular true in this case as it's for preamp and it's low current.



I can assure caps don't go bad in a year and degrade the sound like you described. You'll get less ripple if you use 2200uF or 3300uF.

Thanks!

Changing the main caps.. did the sound change too? Or we just can say its only a maintenance?

When I bought my Nakamichi PA-7 ( also designed by Nelson Pass, a slight improved version of his famous Threshold S300), I did change the filter caps. It did nothing. I actually looked at the overshoot of the sawtooth wave on the cap with a oscilloscope, the old cap has somewhat more overshoot. But I did not hear any improvement in the sound. I consider it's a waste of money.


Let's just say, if the cap is 10 years old, go ahead and change it ( I won't) if that make you happy. Cap definitely don't go bad in one year unless it's defective to start with.

Where did you see he changed cap within a year? He changed original caps w/ around 30 years old!
Post 30 (Feedback network cap replacement)
Post 34 (signal stage cap replacement)

Nothing went bad in a year.

The eight original feedback network caps were replaced. Then, in a completely separate event, the four original beer can sized main filter caps were replaced. Then, in another event, the pre-amp/driver board caps were replaced with Elna Silmic II caps. Noting that I have done has needed to be redone.

Yeah the 5800 isn't necessarily better in terms of being able to keep it running. And it's VERY DIFFICULT to work on. That's why I passed on one as well. The clutch play would be a 5500 with an IEC outlet. Only the later production models had this. Though, to be fair, the attached power cord of mine has a LOT of copper in it. It's very heavy for its length and feels like other 10-12awg 2 conductor stock I have laying around. It's definitely heavier than 14awg. So it's no slouch and very likely not the low hanging fruit.

But the sound. It's got essentially zero grit or grain to it. In fact, I rarely get out of the Class-A region.

Not to overstate it's performance, but it's REALLY smooth and dimensional. Pairing perfectly with the Chane magnetic Planar ribbon, the Ascend RAAL in the Sierra 2, or true compression drivers from Italy. Delicate, airy detail with no bite.

I've decided to send the amp to John at Musical Concepts for further enhancement. Likely the Elite + Platinum package. He addresses the few weak points and upgrades a bunch of resistors as well as adding some strategic bypass caps and a few proprietary tweaks.

I have a local buddy with a Macintosh and a Krell. The Adcom GFA-5500 Is currently dangerously close to them. But I think the 5500 has even more in the tank.

As far as ripple reduction, I am not going to argue with you. However, there's just not much additional room in the chassis for taller caps. Diameter must remain the same because the caps are touching each other on the side.

I did an exhaustive search and it was heard enough just to find quality caps that met the spec and fit. The ones I found happened to have the 105C rating, which is nice for an ammo that runs warm. No sarcasm; if you can find better that actually fit, please let me know. Really.


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Mostly to keep from hosting an electrolyte sauna in the bottom of the amp chassis. Lol.

The new caps added a dark character initially. After leaving the amp on for about a month everything was back to normal.

But, with four lightly stressed 22,000uf beer can sized caps, that's not entirely unexpected.


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Nice, looks like a maintenance lol

This characteristic of a darker sound reminded me of when I made a series of several modifications on my 555 MKII ... after more than a week the sound began to become more interesting.

Worth every penny. And now that I'm with the 5500, I want to do the same as you did on your amp and I'll probably add an IEC (removing the original power cord)

Post 30 showed those filter caps like C4, C16 and C19 got pulled out and show pictures of those bigger caps. Those are the filter caps that are together with C3, C7 and C9. See the schematic I posted in post 39, you can see those are all filter caps.

No caps were changed twice, at any point.

That should settle it.


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Amp update. I did go through with the full boat at Musical Concepts; LX Mod with Elite mod upgrade. I added the mini Platinum mod as well. Also upgraded to Cardas RCA input connectors and an IEC power input (used with a Pangea AC-9Mk 2 IEC cable).

I received it back on Thursday (8/8/19). Took about three months.

Bottom line: it's worth every penny i spent and every day i waited.

Every aspect of acoustical performance has been enhanced. This with less than 48 hours of run time on it, of the 300 John Hillig recommends.


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Happy to learn the amplifier is back and performing so well.

Having an Adcom GFA-5503, I am interested in the specific sonic changes you have noticed. Also, what was the cost of the modifications?

No tricks from John Hillig. I got charged exactly what was quoted to me. To the literal penny. It was literally the opposite of getting work done on your car.

EDIT: All prices are exactly as stated on his website except for shipping which is quoted based on actual freight charges.




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Preliminary listening impressions. All observations are made for stereo listening:

I don't have speakers anymore. Virtually every source is now presented as a large, cohesive, 3D acoustic hologram. Even garbage while watching YouTube videos. Spatial cues have been exploded and stratified in all 3 dimensions.

The detail and texture in the mid-range and highs are now really exceptional. Zero sibilance and MOAR detail, but the additional sonic info is somehow less fatiguing.

Bass impact (not level) is heightened and bass texture is even more tightly defined at low and high SPL output. Upright bass performances are something you both feel in your feet and you also get the sense that you can see the player's fingers at work.

The sense that you can just get up and walk around inside the soundstage is palpable. I've got sonic sources literally dancing around my entire room, depending on the track and source (all CD rip or HR FLAC or Tidal MQA via my Bluesound Node 2).

The sense of depth of the Soundstage (both closer to you and further away behind the speakers and even far-past the back wall) is now very pronounced.

In sum, digital sounds smooth and full of body like vinyl. But also better than vinyl because you're swimming in detail and information.

I'm struggling to explain this but it's like a hybrid of a tube amp and class A solid state amp. All the smoothness and body of a tube amp, without any of the occasionally tubby or bloated/flabby bass. And seemingly unlimited current. But that smoothness carries across at as loud of a volume level as i dare. As do all the other things described above.

This thing is playing with the big boys now. No price caveats required.

Also, note that I'm using a Van Alstine Humdinger on John Hillig's and EddyZ's recommendation. This is a non-current-restricting DC blocker. My transformer is now SILENT even when i press my ear against the top grate. Confirming my suspicions that DC was present on my AC line.

Oh, and many thanks to @Eddy_Z . He and i have shared many enjoyable PMs and he led the way with sending his GFA-5500 to John at Musical Concepts first. So he's just been fantastic and a truly open book. Thanks Eddy!!


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List of actual mods from Musical Concepts website:


*************************************
"LX Series Modifications

Modification Strategy: Our venerable LX mod for your Adcom amplifier has changes in feedback circuitry which improves bandwidth, dynamic range and bass solidity/power. The bias circuit uses a new and better bypass capacitor with an added high quality bypass capacitor. Input and output filters are improved with far better parts. Some critical resistors are upgraded. Each small-value (p high frequency stabilizing capacitor is optimized for audio quality. Each power supply capacitor has an added bypass capacitor. Elite and higher models have superb power rectifiers in the main power supply. We use the finest soft-recovery diodes superior in naturalness and dynamics.

The Sound: LX is much more natural, sweet and liquid. Soundstage is much more open. Imaging from top to bottom is more predictable, i.e. instruments come from stage locations that seem more accurately positioned. Gone is the brightness, etched quality and bass inaccuracies. Perceived dynamic range soars! The Elite version is even more refined/defined with solid bass extension and silky extended high-end detail, a definite improvement in resolution and definition. The mids have superior timbre, texture, clarity and musical naturalness. Highs are more natural and clear.


We no longer support all Adcom power amps. Some of the newer mosfet amps, GFA-5800/5802 plus several others and multi-channel amps are not serviced.



LX Mod
LX mods are for all the earlier classic stereo or mono Adcom amplifiers, including all “535”, “545”, "555", "585", “565", etc.

Features of the LX Mod*

Superior coupling caps - better sound top to bottom with great bass, tonal purity, 3D qualities of focus and transparency
Feed back(FB) loop tech mods - better phase response - tight, deep, clean bottom, even more 3D sense of sound space
Superb cap used in Zobel network(output load) - more open
High quality resistor replacements in several locations - smooth and silky yet great clarity and intonation
Better bypass caps in power supply, FB loop, Bias circuit - dynamics with control, big soundstage

$399 installed for early Adcom stereo and GFA-5500 amps
GFA-565 LX mod is $599/mono pr
*Will vary with different Adcom models



LX Elite Mod
The Elite mod includes all the features of the LX Mod…

Plus More Features*

Premium grade Audio specific electrolytic capacitors - more transparency, quickness, clarity
Premium power HiperFred rectifier - smooth, transparent, rich majestic sound stage and dynamics
Select bypass capacitors - dynamic, silky, open stage

$599 installed for all early model Adcom stereo amps, other items listed below
GFA-5500 $529 - rectifier replacement not included for GFA-5500
GFA-565 $799/pr
*Will vary with different Adcom models



LX Mini-Platinum Upgrade
While you could apply this to the standard LX mod it clearly makes the most sense to add it to the ELITE version.

Takman CF resistors in strategic locations offers superior naturalness and clarity, plus a very elegant proper warmth.
Some added larger bypass caps are used in critical locations
Additional power supply tweaks

Add this upgrade to an ELITE mod for even more natural sound. Add $200 to stereo ELITE mods, $300 to ELITE mono pair pricing."


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Oh, and if you've ever wondered what it looks like inside a Belkin PureAV PF30 power conditioner, here you go:





EDIT:

Here's the inside of a Panamax MAX 5100:







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Thank you for the detailed reply.

So, not much of a sonic difference at all...

Actually, I am now intrigued and considering the modification. The price is quite fair. (The three-channel 5503 will obviously cost more than the two-channel 5500.)

What preamp are you utilizing?

No problem on the reply. Easier than journaling. Hehe.

Oh, and yeah... hardly noticeable.

Parasound Halo C2 is the preamp.


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Again, thank you.

Please keep us updated after you acquire more run-in time on the amp.