Replacing adcom 5500

[Rick DeSonia]

I should start with what I had. Adcom gfa 5500. Adcom gtp 450. Bowers and Wilkins nautilus 803’s(not the diamond- b4 that). The toroidal transformer shorted out. Can’t find one. It’s actually 4 transformers in 1 and quite unique with multiple voltages.

So here I’m looking for an on the cheap(for now) amp. I’ve found 2 carver cubes(m400) to bridge for mono for $400 or a hafler pro 500 for $325 all used of course. I picked them because I like the warmer sound of MOSFET amps.

Which shall I go with? I found the adcom gfa-5500 slightly underpowered. The 803’s are quite power hungry and I may like it loud sometimes. The room is big at 24x20.

Any help or a “don’t buy that junk” would be appreciated.

 

[Mayank]

Rick: Welcome to AudioKarma !

I had a Carver M400t. Wonderful "little" amplifier which was in our main living room set up. If I recall, it did not sound as good in bridged mono mode. I do not have any experience with the newer Hafler.

Given your setup, my advice is that as your B&W 803's require a fair amount of power, you should look out for a pair of Adcom GFA-565 mono-blocks. They are solidly built (assume the pair has been serviced/upgraded with new capacitors) and can handle the load comfortably.

Best Rgds
Mayank

PS Another "temporary" option to consider could be to replace the transformer on your Adcom GFA-5500. Affiliated Electronics has them in stock for $210
https://www.teve21.com/841-1162/xc/xd/ADCOM/MECHANICAL_ADCOM/xa/xb/TRANSFORMER-GFA-5500-MV.aspx (NO AFFILIATION)

 

[pauljh]

The Hafler would have no problem driving the 803s. Though the DH500 pro does have a fan which you might find annoying.

 

[Rick DeSonia]

Rick: Welcome to AudioKarma !

I had a Carver M400t. Wonderful "little" amplifier which was in our main living room set up. If I recall, it did not sound as good in bridged mono mode. I do not have any experience with the newer Hafler.

Given your setup, my advice is that as your B&W 803's require a fair amount of power, you should look out for a pair of Adcom GFA-565 mono-blocks. They are solidly built (assume the pair has been serviced/upgraded with new capacitors) and can handle the load comfortably.

Best Rgds
Mayank

PS Another "temporary" option to consider could be to replace the transformer on your Adcom GFA-5500. Affiliated Electronics has them in stock for $210
https://www.teve21.com/841-1162/xc/xd/ADCOM/MECHANICAL_ADCOM/xa/xb/TRANSFORMER-GFA-5500-MV.aspx (NO AFFILIATION)

May I ask a second question. The transformer circuit output voltages are supposed to be 1 at 60v and one at 73v for each of the 2 channels(4 total). All are slightly more than 25% high which is indicative of some shorted out windings on the primary side of the transformer. I came to this conclusion because all are wrong at the same ratio. BTW that makes it sound extremely "tinny".

Do you believe that that damaged other circuitry? Is that likely or unlikely? Is buying a new transformer just going to reveal the first of many other things damaged? Is it worth going down that road or just call it a loss? Thank you in advance.

 

[Mayank]

May I ask a second question. The transformer circuit output voltages are supposed to be 1 at 60v and one at 73v for each of the 2 channels(4 total). All are slightly more than 25% high which is indicative of some shorted out windings on the primary side of the transformer. I came to this conclusion because all are wrong at the same ratio. BTW that makes it sound extremely "tinny".

Rick: If you are measuring +/-75V on the 60V rails and +/-92V on the 73V rails on both channels, then I would concur with your diagnosis and estimate about 1/5 of the common primary windings in the transformer have shorted out (resulting in 1.47:1 instead of 1.83:1) which are causing the secondary voltages to increase by 25%.

Do you believe that that damaged other circuitry? Is that likely or unlikely? Is buying a new transformer just going to reveal the first of many other things damaged? Is it worth going down that road or just call it a loss? Thank you in advance.

The output devices in the GFA-5500 are RFP9240 which are rated at 200V so these should be OK if you have not run the unit for long and if there has not been any thermal protection/fuse blowing. The unit would be drawing higher current and getting rather warm, ultimately causing serious damage to the amplifier. The logical way to confirm if the rest of the amplifier is working would be with an external power supply and slowly bringing it up with a variac.

If you do not have access to these, then buying the new transformer would be a $210 gamble.

You could always sell the unit with full disclosure for someone to try and repair it and use the $ towards new gear.

Good luck.
Mayank