Adcom GFA 555 Internal Protection Update and Correction

[@johnny7254]

Seeing the mistakes made by persons of your experience level gives hope to us all. Thanks for that.

[@raygianelli3612]

That's really good to hear. I think we sometimes wind up with unrealistic expectations from heavily edited videos. My main concern was not showing that I make errors (and I make plenty; just ask the ex's) but rather that no one follow along and end up with protection that really wasn't.

[@Edisson.]

@@raygianelli3612 Hi Ray, I don't know how it is in your country, but here in the Czech Republic, Murphy's laws work perfectly, if you care about not making a mistake, you will do it 100% even if you check it a hundred times - that's how it works for me. Because we are humans and not machines (even though they make mistakes too) we make mistakes and we will make them, but it is important to learn and it is amazing that thanks to technology we can point out mistakes to others. Nice day🙂 Tom

[@roroseppel2077]

Hello Ray, now the amp is really protected ! Exchanging all sorts of comments and experiences, that's what the community is for. I really enjoy your channel, you are so kind and so honest with all of us

[@raygianelli3612]

Thanks RORO. The generosity of the viewers on this channel never ceases to amaze me! Once you asked the question about grounding it clicked... like a ton of bricks. 😁

[@Trucam2020]

Thanks for sharing this video.

[@billzumwalt324]

Ray , you are awesome !

[@raygianelli3612]

Bill, checked out the Shuffle Dawgs. You guys have a good thing going!

[@billzumwalt324]

@@raygianelli3612 Thank you kindly , sir .

[@bobisyouruncle1]

Hi Raj - your tutorials are excellent. Remember, we all make mistakes. That does not make you a lesser excellent technician.

[@raygianelli3612]

Thanks Erwin. It does give me pause, but I recently received comments that my screwups actually give aspiring techs the confidence to dig into a repair, the thought being if this guy who's been doing this work for decades can make mistakes, I'm not going to be discouraged if I do. Who'd have thought it?

[@rajoconnor]

Glad you figured it out! Keep it going.

[@raygianelli3612]

Thanks Randy! Mistakes like that are what kept me from being a brain surgeon. 😁

[@stanmyers5994]

Gotta love people that admit mistakes

[@raygianelli3612]

We all make them. The only thing that bothers me about them is the frequency at which they occur.😁

[@daffyduxxx]

Ray, kudos to you for showing your mistake.

[@raygianelli3612]

Thank you. While it wasn't what I set out to do, I've come to see the importance of showing errors, to let people see that even techs who have been doing this for decades can still screw up. The comments here show that. And ironically, some have commented that it gives them the confidence to try to work on gear. I also learned that failure and mistakes are only failure and mistakes if you give up. That's been a good lesson for me.

[@g.fortin3228]

@@raygianelli3612 yes Sir ! and it helps to prevent us from copying the error as well. But your teaching is very much appreciated.

[@andymouse]

Nice one Ray, I learnt something today....cheers:)

[@raygianelli3612]

I did too, Andy. And learning is what it's all about. At least I don't repeat my mistakes, having learned from them. I come up with new, improved ones. 😜

[@sretchko]

Hi Ray, I love your videos and the knowledge you share with the Community! I am rebuilding a Technics SA-300 that I picked up cheap and want to add speaker protection to it. I was wondering if I could use a speaker protection board with isolated grounds. It looks just like the one you used here, just has 4 terminals for the speaker connections (instead of 3 terminals) and they are isolated. FYI,the Technics SA-300 has common negative L/R speaker terminals and they are grounded to chassis. I have spend a lot of time rebuilding it and it sounds nice and don't want to blow it up :) Thanks again, Steve

[@1320pass]

Good catch! There is some serious talent in the audio tech yootoobs. In awe. Ray you mentioned DC offset and the lack of adjustability on that Adcom. As i understand it, high offset can damage speaker voice coils. So with my collection of amps I rotate in something different for a listen, but before it (in this particular instance a B&K ST-202 plus) gets wired I checked the offset and found some difference between L-R channels. Left was nice and low at -1.3MVDC and right channel is little higher at -50MVDC. This is an early 90's amp and as far as I can tell, it's all original on the boards and even the 2 big 15600uf Philips caps in the power supply. I can't find a schematic anywhere and Hifi engine website isn't accepting any new accounts. At what point do I get concerned? Thanks and I really like learning about this stuff from anyone who takes the time to read my post.

[@raygianelli3612]

Way past the 50mV mark.Most protection circuits will happily pass over 1 volt, and it doesn't seem to adversely affect speakers. My bench amp probably has around 600mV of offset, and if I ever get a chance to address it I will. But it's a low priority.

[@1320pass]

@@raygianelli3612 Gotcha, thanks bud.

[@raygianelli3612]

drive.google.com/file/d/136Nmw1i_Lcm-wmimd3rpC9ixRJ5ZTc1p/view?usp=sharing

[@1320pass]

@@raygianelli3612 That's my ST-202+...! I downloaded a copy here locally. Fan freakin Tastic. Thanks Ray. On edit; downloaded to my tablet PC locally.. you know what I was trying to say..😅

[@raygianelli3612]

@@1320pass 😬

[@poormanselectronicsbench2021]

They most likely plated the through holes for a bit more durability instead of just mounting to the fiberglass substrate. I was wondering if you were going to test the module once installed, now we know.👍

[@raygianelli3612]

Yes we do. Really stepped in it with this one. 😁

[@RanTausi]

@@raygianelli3612 Thanks a lot Ray for this correction, Would this be apply to The GFA 555 MK2 Model ?

[@raygianelli3612]

@@RanTausi Yes.

[@g.fortin3228]

Great update Ray.. I just watched the original vid last night and left a question. I need to make sure that the newer (still old but newer) version GFA-555ii is the same type, non float to use this mod. I'd like to do this in the next few weeks. I believe they would be similar but will check anyway. My question on the other comments list was can I use this same module on the smaller amp as well, the 100w version 545ii ? I want to order a few of these and get my and my brother's amps protected. You do a great service here showing us how, and why. Thank you !

[@raygianelli3612]

An amp will state clearly on the back not to ground the negative terminals if it's floating(balanced) topology.

[@g.fortin3228]

@@raygianelli3612 Thank you ! I'll be doing both 545ii and 555ii models.

[@RanTausi]

@@g.fortin3228 Hi , did you installed the speaker relay protection board inside the 555mk2 and 545mk2 ? Thank you

[@g.fortin3228]

@@RanTausi Yes I did.. worked out very well on the 545ii but not so well on the 555ii (which is not the same design as 545ii), I ended up removing it from that unit and going back to stock with that one.

[@RanTausi]

@@g.fortin3228 Many thanks for the reply, I have both MK2 555 and 545 and I'd like to install speaker relay board by myself. What did wrong with your 555 ? Do you have pictures that you have taken in the upgrade ?

[@Drekkag]

Thanks for putting up the video. Helps me learn alot. Keep em coming and I will keep watching. Hoping to sometime just put up videos eventually of the different projects I will be doing. I am into ham radio and electronics so I can have a lot of subjects to put on. Still into basic stuff in electronics. I need to get my feet wet and get the courage to buy a broken item and just fix it. When I do I will start posting videos for some fun. 73, Adam Rennison ad0am

[@raygianelli3612]

Adam, get something you don't care about and dive in. I used to pick up broken CRT tV's on the side of the road. That way, if it didn't survive my attempts to fix it there it was no great loss. Learned a lot by doing that!

[@victormihai3929]

Ray, I'm not sure how this was a grievous error - it never had DC protection anyway, no? I'm a novice but did wonder how it would stop DC without 'original circuitry. I dont fully understand how it only needs a ground to accomplish that but now it's even better! I ordered same relay online. Yes, there are two models of this amp and mine will shut off if I over heat it. My other one has some higher DC offset - maybe one day you can explain 'the frontend.' Are those the transistors on the board? Thanks and keep them coming!

[@raygianelli3612]

Victor, the module I installed monitors the outputs for DC offset. When it gets around 2 volts, it opens the relay. But it needs to "see" that voltage, and without being tied to the chassis it never will. To better understand what I mean, take a digital multimeter set to DC volts and a battery. Take the red lead and put it on the battery's positive terminal. Leave the black lead laying on the bench. See the issue here? It was a grievous error because if you followed my first video you might think you had protection against this, but you wouldn't. Kind of like taking out an insurance policy, then after making a claim the company tells you they're not paying it because you didn't sign the policy.

[@victormihai3929]

@@raygianelli3612 Ray, understood - I'm not THAT novice LOL. My opinion was that I know everyday I dont have DC protection so perhaps nothing gained, nothing lost and I would still get the soft start with a cheap easy fix. Maybe the only mistake was not showing the before and after as in the second video which was an A+ illustration of the added DC protection. I guess it could be different for someone who would NEVER use an amp without DC protection. Thanks again.

[@raygianelli3612]

@@victormihai3929 Sorry Victor. It can be difficult to ascertain someone's skill level from a brief interchange!

[@g.fortin3228]

Hi Ray. Did you use 14 OR 16 GA wire ? solid wire ? I'm getting ready to do one soon thanks again very much for covering this topic :-)

[@raygianelli3612]

I used 14 gauge stranded. But the lengths are so short that it shouldn't really matter. 14 is just what I had on hand. 😬

[@g.fortin3228]

@@raygianelli3612 Thank you Sir .. hopeful to get these started in the next week or two. I gotta clean the workshop for the new year first. The modules just arrived.

[@mooishi1398]

A common lament you hear about retrofit speaker protection on this amp is the +/- 80 V rails might be enough to weld the contacts on the speaker relays together. Also people suggest that MOSFET may be the better option over mechanical relays re: speed and reliability. What's your thinking on these points, Ray?

[@raygianelli3612]

While I have heard of relay contacts welding after a catastrophic failure, I have yet to see it myself. While MOSFET's would be faster, it would also entail quite a bit of expense. For speedy protection that won't break the bank a crowbar circuit is hard to beat.

[@mooishi1398]

@@raygianelli3612 Thanks for the insight, Ray.

[@mooishi1398]

@@raygianelli3612 I just thought of one more question: how long does it take for the dc current to shutdown the relay?

[@raygianelli3612]

@@mooishi1398 Once the DC voltage rises to about 2 volts the relay opens.

[@t1d100]

Maybe crimp a ferrule connector onto the end of the stranded ground wire going into the screw terminal? And, a squirt of thread lock on the clamping screw?

[@raygianelli3612]

Yeah, I'm not crazy about those green terminal blocks. The ground bar screws did have lock washers.

[@t1d100]

​@@raygianelli3612 I don't know if you are familiar with the crimp of which I speak. I can't imagine not, but for others... They have plastic shoulder insulators, very similar to the ones that are used on eyelet, Y and blade type crimp terminals. However, all that extends from the insulator is a round, metal tube. You trim the wire's insulation and insert the wire strands through the insulator and into the tube. Then, you use a special crimping tool to squeeze the tube (not the insulator.) The crimping tool compresses the wires and deforms the tube into a nice square shape that the screw in the terminal block can get a perpendicular bight on. I would post an example link, but KZbin has nixed commenter posted links. "Ferrule Crimping Tool Kit" seems to be a good search term. A trick that I discovered is that you can trim the new square tube to a shorter length that allows a proper bight for the block terminal screw, but does not allow any extra length of the square tube to be an exposed shorting hazard. I hope I said all of that well enough to be understood. Cheers.

[@g.fortin3228]

personally.. rather uses a toothed lockwasher on a ground, than a chemical on threads

[@jimromanski2702]

Where can I find the speaker relay circuit board that you used? Will it work with an Adcom GFA-5400 amp?

[@raygianelli3612]

Jim, go to eBay and search for speaker protection board. Make sure it works on AC199V-220V. Electrically it will work with the 5400, but having never seen one I can't say if it will fit.

[@keithtrauner1738]

Not sure I understood your comment about 2 modules - if ground is common, wouldn't dc be detected on either output? (since you offered me one of these, figured I need to ask 🙂.

[@raygianelli3612]

Keith, this only applies to balanced outputs, which are not too common in amplifiers. You do not have the negative speaker terminals tied to ground in those, everything is balanced (AKA floating). If you tie the negative terminals together on one of those amps it will be damaged.

[@DewaldV84]

I've made the same mistake with such a protection unit.

[@raygianelli3612]

Dewald, these things just come in a box with no instructions. I made some erroneous assumptions, which I would not have realized if I didn't read the comments here. Nice to know I wasn't the only one!

[@kernalkorn1514]

I've put together a dual mono amp (2 transformers, 2 capacitor banks, 2 mono amps) and it has a floating voltage. I only have the speaker positive leads being switched by the speaker protection unit (no power ground connected). I guess that means I'm without DC protection. Is the only way around that to use 2 separate speaker protect units and connect each amp's speaker out AND its corresponding ground to the speaker protect for that channel? Thanks for the upload mate!

[@raygianelli3612]

There may be variants made for balanced/floating topologies. Frankly I never looked, as the vast majority of amps aren't.

[@kernalkorn1514]

@@raygianelli3612 Thanks Ray! I guess I'll keep trawling through ebay and squinting at the ground traces until I find a unit with separate left and right channel grounds :-)

[@salvadorrodenas3071]

We are glad you didn't lead the Manhattan project 😅, it is just a bad joke😉

[@raygianelli3612]

On the contrary, it's a great joke! 😁😁😁

[@salvadorrodenas3071]

@@raygianelli3612 thanks 😊