I have a new to me adcom gfa 5500...plays loud and clear, just has weak bass responce, is this normal or is there something wrong with it...my other amp it replaced is lower power but has more bass responce than the bigger Adcom, this is my first Adcom amp is this normal for these amps?
looked around on here, found someone with simular problem...but cant get anywhere with this...any help is appreaciated,thanks
Are you able to do any measurements? Weak bass can be caused by an electrolytic in the feedback loop losing value, or perhaps the input capacitor. It could also be caused in the output cap in a preamp went down a lot in value, or if it is kind of small to begin with. What kind of preamp are you driving the amp with?
Akitika GT-101
Update My Dynaco
Akitika GT-101
Update My Dynaco
I jave measured the dc offset at the speaker terminal...was (L) 30mv...(R) 66mv...and the input source is good, swaped another amp in place to make sure and its a lower power amp, and the bass output was better...so Im thinking its the amp.
it just seems to lack (the punch ) in the bass dept!!, other than this..plays loud and clear...no humm, no pop's or anything else strange..Im at a loss...could it be since the DC offset is a lil high that it maybe needs a (tune up)..I really had high hopes for this amp, it looks so good on paper!
Hi, get your Offset issues dealt with (and check Bias while you are at it), then see about next steps such as re-capping.
Offset should be within +/- 10 mv of zero.
Example of a happier camper at this link here
Also - what speakers are you driving? Just curious.
Offset should be within +/- 10 mv of zero.
Example of a happier camper at this link here
Also - what speakers are you driving? Just curious.
speakers are cerwin vega VS150..thanks, I have a nice volt meter, are these things I can do myself...or do I need other equipment to do this sort of stuff
Ok..checked the bias...was within the limits 45mv and 47mv and the offsets are 4.5 mv and 8.0mv....and played it again last nite...and then immediately swap in two other amps just to see...both other amps have more low end(kenwood basicM2/onkyo M504)...what to check now??
C03 and C09 are likely candidates to have lost capacitance. That's a guess of sorts...HiFiEngine had parts list for the amp module, but not the schematic.
A question still remains...do you have the equipment that would be needed to measure the frequency response? Function generator, meters, scope? That would help.
Akitika GT-101
Update My Dynaco
A question still remains...do you have the equipment that would be needed to measure the frequency response? Function generator, meters, scope? That would help.
Akitika GT-101
Update My Dynaco
Measuring is good advice as djoffe has brought up, or get someone to do an evaluation for you.
There is little satisfaction if you start part swapping unless you have much dollars and time. If you do have dollars and time - get it to a reputable shop for assessment. (Two weeks since you noted as such on AK)
Standard warning for safety - Not knowing your capability / skills I strongly advise you to exercise great care with such a powerful source of energy. No offense meant. Just standard reminder that people are more important than things....
There is little satisfaction if you start part swapping unless you have much dollars and time. If you do have dollars and time - get it to a reputable shop for assessment. (Two weeks since you noted as such on AK)
Standard warning for safety - Not knowing your capability / skills I strongly advise you to exercise great care with such a powerful source of energy. No offense meant. Just standard reminder that people are more important than things....
I have the parts list from the service manual, and no schematic, and I dont have any of the other tools u speak of, but just found something fishy, if Im looking at this correctly...the C03 on the parts list states a cap value of 47uf 50v..mine are 1000uf ( there is 8 of these)and 100v..the C09 is the correct value of 47uf 25v...only going by what is on the cap, have not taken any measurements of the caps yet.
very true... It has just been sitting all week with me pondering what to do...it is looking like I have surpassed my capabilities on this now...was hoping it was something simple(like just some adjustments) ..oh well now to figure out where to send it!...I found a place that has a flat rate for repair since its in working condition for $240.00..is this a fair price if power supply and amp caps and such has to be replaced?
Adcom GFA-5500 weak bass
Hi Rselby,
Did you ever fix the Adcom GFA-5500 with low bass output? I have the same exact problem and was wondering if you ever got it fixed.
Thanks,
Hi Rselby,
Did you ever fix the Adcom GFA-5500 with low bass output? I have the same exact problem and was wondering if you ever got it fixed.
Thanks,
not yet but will soon be sending it to here Adcom GFA-5500 Repair Service
guess the heat of 20 yrs of use has dryed out or for whatever reason made the (8) caps above the (4) large ones need to be replaced
guess the heat of 20 yrs of use has dryed out or for whatever reason made the (8) caps above the (4) large ones need to be replaced
update...amp is in repair waiting to see what it needed to have replaced and adjusted, should know something next week or so....will report back on what was done, and how it sounds compared to before, now that it has been serviced.
ok...got the word today, here is what was wrong....R-channel: low bias, 25mV DC (high)
L-ch: ok
Both channels need new electrolytic caps
so should get it back in a few days....will report back with how it sounds
hope this sheds some light on this subj for some other people that runs into this similar problem
L-ch: ok
Both channels need new electrolytic caps
so should get it back in a few days....will report back with how it sounds
hope this sheds some light on this subj for some other people that runs into this similar problem
and here are the results...the bass is back! and does run warm, but has ( what seems to be ) TONS of more power than before, so looks like the 8 caps on top of the 4 BIG ones is the ones that made the bass get really weak when they dry out or whatever goes wrong with them, anyway $240 later...and its all good
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