Here is the decision I am facing and would appreciate your collective wisdom.
My speakers will be a two-way system with a horn tweeter and a 15 inch woofer in a vented box. The horn will be driven by a Pass DIY (First Watt) F5. A separate amp will be used for the woofer. The woofer is only about 92 dB efficient and will need more wattage (100 - 200 Watts).
My choices are narrowing on the woofer amp.
1) Use an Adcom GFA-555 ii amp (at least 25 years old & stashed in a closet). I would spend about $100-200 refreshing the capacitors (especially the big ones in the power supply). The amp is old but it is working. The bias is fine, there is negligible DC offset, but there are some on/off thumps and noises. So it is a working amplifier showing some signs of age, but I have always loved the way it sounds, especially in the bass regions.
2) Use an old case/heatsinks from a gutted Adcom GFA-545 (stashed in the garage) and build a Pass "AB100"
3) Use an old case/heatsinks from a gutted Adcom GFA-545 (stashed in the garage) and build a Honey Badger.
The costs are all close enough to one another (with some scrounging on the transformer and power supply parts). So cost is not a deciding factor.
Are there any other choices? Note: tubes are out, chip amps are out, anything less than about 100Watts is out, the power requirement also probably prevent any reasonable Class A amps. Also, I am a cheap son of a gun and also an avid DIYer that likes to learn a bit in the process (I have some experience with electronic projects). I am interested in your comments.
Thanks in advance,
-Tom
My speakers will be a two-way system with a horn tweeter and a 15 inch woofer in a vented box. The horn will be driven by a Pass DIY (First Watt) F5. A separate amp will be used for the woofer. The woofer is only about 92 dB efficient and will need more wattage (100 - 200 Watts).
My choices are narrowing on the woofer amp.
1) Use an Adcom GFA-555 ii amp (at least 25 years old & stashed in a closet). I would spend about $100-200 refreshing the capacitors (especially the big ones in the power supply). The amp is old but it is working. The bias is fine, there is negligible DC offset, but there are some on/off thumps and noises. So it is a working amplifier showing some signs of age, but I have always loved the way it sounds, especially in the bass regions.
2) Use an old case/heatsinks from a gutted Adcom GFA-545 (stashed in the garage) and build a Pass "AB100"
3) Use an old case/heatsinks from a gutted Adcom GFA-545 (stashed in the garage) and build a Honey Badger.
The costs are all close enough to one another (with some scrounging on the transformer and power supply parts). So cost is not a deciding factor.
Are there any other choices? Note: tubes are out, chip amps are out, anything less than about 100Watts is out, the power requirement also probably prevent any reasonable Class A amps. Also, I am a cheap son of a gun and also an avid DIYer that likes to learn a bit in the process (I have some experience with electronic projects). I am interested in your comments.
Thanks in advance,
-Tom
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I have a bi-amped system using old JBL 2445/2397 horns with 2225 woofers. My experience has been that every time I improved my low frequency amplifier, the sound got better. I guess it's not surprising since with my 900 Hz crossover point, it is approximately right in the middle of the musical frequency range, and a lot of the midrange is reproduced in the low frequencies.
I would try as an experiment, driving the low end with the F5 and finding a nice low power amp for the horns. Or use your 555 and F5 and experiment.
I would try as an experiment, driving the low end with the F5 and finding a nice low power amp for the horns. Or use your 555 and F5 and experiment.
the adcom 'cause
Which, by the way, is spot on...but if you have to do something with the case and heatsink a DIY S/200 or S/300 with the new stasis front end?
Which, by the way, is spot on...but if you have to do something with the case and heatsink a DIY S/200 or S/300 with the new stasis front end?
Best to overhaul the Adcom 555.
Brute of an amp when working right.
If it doesn't have the optional cooling fan, I'd recommend designing one into it, as well as installing tiny heatsinks on the driver transistors - and go over the soldering in case the heat weakened any connections.
I did one a while back for a customer, and he was so grateful.
Brute of an amp when working right.
If it doesn't have the optional cooling fan, I'd recommend designing one into it, as well as installing tiny heatsinks on the driver transistors - and go over the soldering in case the heat weakened any connections.
I did one a while back for a customer, and he was so grateful.
No need to replace the big filter caps in the Adcom, save your money. They're not that old. I've refurbished at least 20 GFA-555 II's and haven't encountered a single bad filter cap. I've only encountered a handful of bad ones in GFA-555 MKI's.
But if you want to replace them anyways the Kemet ALS series is excellent. Don't go over 18,000uf without a soft-start. These amps sometimes weld their power switches shut.
Your turn-on thump is normal, as are the funny noises it might make on power-off. Some make a sort of "squeeee" noise, some a "mrrrrrp!" or "bup bup bup bup".
This is just because there are no speaker relays. The amp is connected to the speakers, even as the power supply slowly drains to zero. At some point, some low voltage, there is no gain left in the amp, and no negative feedback, and things get all wobbly and you hear an oscillation out of the speaker. No worries, there's not enough energy left in the amp to do your speakers any harm.
No relays, and yes, no speaker protection beyond rail fuses. But the 555 is extremely reliable when maintained properly, so just do meticulous work and don't worry.
But if you want to replace them anyways the Kemet ALS series is excellent. Don't go over 18,000uf without a soft-start. These amps sometimes weld their power switches shut.
Your turn-on thump is normal, as are the funny noises it might make on power-off. Some make a sort of "squeeee" noise, some a "mrrrrrp!" or "bup bup bup bup".
This is just because there are no speaker relays. The amp is connected to the speakers, even as the power supply slowly drains to zero. At some point, some low voltage, there is no gain left in the amp, and no negative feedback, and things get all wobbly and you hear an oscillation out of the speaker. No worries, there's not enough energy left in the amp to do your speakers any harm.
No relays, and yes, no speaker protection beyond rail fuses. But the 555 is extremely reliable when maintained properly, so just do meticulous work and don't worry.