GFA-555ii - Need some advice on bias and static. Gurus?

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Background

New-to-me GFA-555ii, in great cosmetic shape. Listened to in earnest for the past 11 days, hours a day. Sounds fantastic. Really impressed with how it matches up in my system.

The problem(s)

- Over the past 4'ish days, the 'turn on the amp thump' got worse. It went from a 'clunk' from the switch and a 'thump' from the amp to a 'clunk and THUMP'.

https://www.youtube.com/shorts/raD4PP4k0T0

- If you have good hearing and stand close to the left channel, there's a little bit of static in the drivers at silence. It's definitely noticeable if you put your ear close. Doesn't manifest in the music, as far as we can tell.

- Power output seems... high and too quick. Meaning, my preferred listening level with this thing isn't quite at 1-out-of-10 on the dial. If I push it to 3 to 4? Too loud for me, my room, the house, the neighborhood...

What I checked

- I swapped/disconnected cables/wires. The thump increase and static is definitely amp.

- I read Google until I thought I'd have a stroke. Watched some videos. Still not sure exactly where to clip the meter to test the bias level... but I don't have clips for my meter, so I need to order some anyway. Amazon, here I come.

Thoughts?

I looked at the manual and service manual. Electricity scares the [insert swear word here] out of me. I blame my Dad's control room warnings when I went with him to work on Saturday mornings, and a shorted tv at my Granny and Papaw's house in 1978...

- It looks like the obvious 1st stop is making sure the caps are where they should be and checking/adjusting the bias. Correct?

- The static could also be a loose solder point, a wire, or... other things?

What advice from the Hive Mind?

The amp only cost me $250 + $40 in gas. Not cheap for me, but not awful if I need to save to have more done to it. If I hit the lottery, Hoppe's Brain upgrades/refurb sounds neat. But, I'd rather try to fix with zero money spent right now =\

audioluvr

If it's all original, it's probably way past due for a recap. Get it done before it destroys your speakers.

Gardenstater

So service manual isn't clear on how to adjust bias and DC offset huh?

One thought I have is to post the same question on diyaudio.com forum.

Also, I don't know if this is a reasonable deal or not but $170 $275 for a restoration/recap service kit.

https://www.ebay.com/itm/155126510432

https://www.ebay.com/itm/155126491073

Oops!

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Also:

I saw people discuss 'the Adcom thump' on the models w/o DC protection.

I'm not 100% on that, but even the Hoppe's Brain guy seems to accept that (in likely a much smaller amount than I see) as normal.

Just seems my thump is much stronger, and... with the volume issue, makes me wonder about the bias.

A lot of Adcom folk talk about the longevity of the caps, but I'm curious to see what's in the case.

pitdogg2

audioluvr wrote: »

If it's all original, it's probably way past due for a recap. Get it done before it destroys your speakers.

This ^^^^ it is WAY past due.

Spend the money wisely and you'll get another 30yrs of problem free good sound.
If I was going to do it this is my recommendation, I tried very hard to get him to tear into my Adcom 5802. He did a few and swore off doing any more regardless of the money thrown at him, trust me I really tried hard

Sure you can get many techs to do the work

https://hoppesbrain.com/2022/09/26/another-tour-of-a-hoppes-brain-adcom-gfa-555-restoration-5-years-later-with-better-technology/

He is the best.

boston1450

When I owned my 555 I was told there is upgrades as well. Perfect time to do that

plastic_avatar

Brief follow-up = [sadface]

O.k., Hive, I disconnected the 555, taped some protection around it, and will pack and store while I figure out when (and if) I can afford to talk to the Brain guy... Ima hafta save some pennies for a spell, and the world is simultaneously on fire and under water.

The debate is now:

Good G/god(s)! $1500 for a full custom job.

His work is amazing, and we know the soldering iron and I have a complicated relationship =(

Is it worth it to save up for that, or sell it to someone handy and look for something newer, much cheaper?

If it sounds this good now... will it compete with other amps in the $1500-2000 range after a refurb/upgrade?

DaveHo

https://forum.polkaudio.com/discussion/198980/beast-of-an-amp-parasound-a21#latest

I wouldn't sink that kind of money into a 555.

audioluvr

DaveHo wrote: »

https://forum.polkaudio.com/discussion/198980/beast-of-an-amp-parasound-a21#latest

I wouldn't sink that kind of money into a 555.

Totally agree here. You'd never recoup your investment. Unless you just like spending money on restoring vintage electronics or you absolutely love it's sound in your system, I wouldn't bother. Once in a while there are excellent amps that come up for sale here but they won't be $250.

As for the cost of refurbishing it, that's not a bad deal.

plastic_avatar

I hoped it was a $250 score, and maybe I'd be o.k. putting another $350 into it, if it needed caps. I still don't know if I should attempt to repair on my own (if it's just caps and bias, I can do that), or sell to recoup.

The faint static in the left channel... I don't know that is a cap issue.

But the DC driver thump. I imagine caps and bias would put that back where it should be

[thinks]

No, outside of the 1C for me and the 5(B) for my Dad, I won't be diving into any more 'just for fun money sinks' [laughs]. I had a plan, it's been wonderful, I continue to get my fun and satisfaction from those, but I am a thrifty person and my cap (after Christmas) will be around $700 for an amp that works.

xschop

Is there a list/spreadsheet of all the electrolytic caps somewhere?

plastic_avatar

Well, forget me doing the work myself.

The words 'if you slip... lethal voltage' = guy-with-the-nerve-condition-will-not-do-it-on-his-own

https://youtu.be/fRzTHxyQWQI?si=P4VLc6UG_R4039OG

Gardenstater

I have no experience but I wonder if you could use a 100W light bulb in a fixture with wires and well insulated alligator clips to discharge the capacitors in the power supplies for each channel.

The adjustments and checks of course you would have to have it powered up for so I know this doesn't help tremendously.

audioluvr

The refurb process is quite involved and unless you have an oscilloscope and a frequency generator, and the skill set how to use one you will probably just end up blowing yourself up. Second thought. Go for it!

Gardenstater

@plastic_avatar I don't know if you saw this in the comments of that vid:

heiney9

Don't spend $1500 on that amp. Perhaps you can find someone local (a repair shop) that can at least trouble shoot it for you. For a good tech, it's probably something routine and common for this age piece of electronics.

That would be my suggestion, even if you have to ship it a few states over, it's worth it to put $300 or so into it. But I wouldn't spend much more than that.

H9

daddyjt

Turn on(off) thump is usually caused by a difference in the speed at which the positive and negative “rails” charge at turn on, and discharge at turn off. Aging(failing) capacitors are almost always to cause, due to the fact that the caps don’t fail at the same rate.

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daddyjt wrote: »

Turn on(off) thump is…

Great to know.

Showing my novice nature here:

Could I get the whole cap-and-kaboodle kit from eBay (Gardenstater found for me^), touch up solder points, and install everything… without going the oscilloscope and tests route, with good odds that this will fix the problem(s)?

Possible activity with a friend.

That would keep things at $300 to repair… blindly =/

Probably crazy, but if the odds of success are in my favor because the issues are normally fixed by X-Y-Z…

Yes, I often do things in a frustrating way to people with deeper pockets and/or more time, but such is the thrifty life of learning new things [smiles weakly].

heiney9

Just randomly replacing things is never the best approach. Especially if you have no knowledge beyond soldering. I suppose you *could* do that, but it might be a huge waste of time and money.

It's your adventure, your gear. I'd still at the very least get a diagnosis before I went down the path you suggest. Is the seller no help? Did he state it was in good working condition? Did you pay with a means you can dispute the purchase? That would have been my first route.

Good luck

H9

Gardenstater

A complete recap kit doesn't equate to "randomly replacing things", at least not in my mind, and there are many who say that it is an advisable thing to do if you want to use a vintage amplifier. I'd purchase a tester like he had in the vid, so that you can verify that each new cap has better ESR values than the old one it is replacing.

I don't think it is a bad idea to get it tested by a tech but they don't come cheap.

I would do the DC offset and bias checks myself before doing anything else. Carefully.

plastic_avatar

I'm in a bit of a tech desert.

The owner said there was nothing wrong with it. Paid cash. The faint static and yuge thump showed up over hours of listening each day for over a week. I don't believe he was trying to pull one over on me. For the first... probably 7 days... the thump was small and within what I read about for Adcoms. It got more intense over the next 4 or 5 days, and that's when I noticed the background noise popped up. It was quiet when I first hooked it up =(

Wasted money = yeah, this one hurts a tad. If I can recover the loss for $300 more, I'd take the bet if it was in my favor by enough.

Maybe.

The debate is real.

And my oldest is sad. She really liked how it sounds.

Electrically insulated gloves? Anyone use them? I should probably get a pair for myself, just to have in the toolbox as a just-in-case the next time I replace an outlet or something...

daddyjt

I am not a fan of the “shotgun” approach of just replacing parts and hoping for the best - it almost always turns out to be a waste of both time and money. The problem with simply installing a “recap kit” is that when a capacitor fails, it exposes parts of a circuit to voltages that they were intended to be shielded from by said capacitor. So when a capacitor fails, there is often a cascading failure of resistors, transistors, etc…

You really need to diagnose the problem, fix it, then move on. I would only perform a recap on a correctly functioning unit.

On the topic of insulated gloves - there is NO WAY (from my personal experience anyway) that I would be able to perform the needed actions for repairing electronics, in any kind of glove. Best practice is to stand on a thick rubber mat, and only put one hand in the amplifier at a time when it is energized, and keep your other hand behind your back (or at least not touching anything).

bcwsrt

Based on the replies here, I’d send that thing down the road. There’s nothing “thrifty” about throwing good money after bad.

Gardenstater

Voltmeter probes are electrically insulated and safe to pretty high voltages. If they weren't repair technicians would be dropping like flies 🤣

But I get not trusting oneself to something you're not experienced at.

Can you test the DC offset, as an initial step? You don't have to open the case for that.

PS - If you open the case, make a big posterboard sign for on the table that says DON'T TOUCH ANYTHING!

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You guys are great.

Thank you for the help.

It's on the 'sell-or-store' shelf next to my Yamahas now.

There is Galaxie in Pittsburgh that does work. 2 hours from door to door. A guy I know spent... I think... $750 for a Marantz receiver de-ox, lamp replacement, check-over, and caps. So, if it would be that much... likely not a go.

There's a place in Washington PA that's closer, good reviews, but not sure if they do the work on amps anymore. Just sent an inquiry.

Will report back.

invalid

Gardenstater wrote: »

I have no experience but I wonder if you could use a 100W light bulb in a fixture with wires and well insulated alligator clips to discharge the capacitors in the power supplies for each channel.

You can discharge the main power supply capacitors by turning the amplifier switch off and just continue playing music until the music stops playing.

Gardenstater

That makes sense. It wouldn't have applied to that tech video Steven posted because he had a bias DC voltage that would've destroyed the voice coils in any loudspeaker connected to it, until the fault was repaired. I think if you're a tech you have backup solutions to be safe and verify things.

audioluvr

You could ship it to Stargate Electronics

VR3

Make sure they are not a gould

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100 Stargate points, Team @VR3

VR3

Huge Stargate fan, not gonna lie