What Adcom amp for my SDA/SRS’s?

bbmhmt1grudn.jpeg

So I have finally purchased the “dream speakers” of mine from back in the day when I was a young man just becoming interested in high-end audio. I had planned on powering them with some Adcom amps run in mono (either vintage GFA-565’s or new GFA-555se’s), but have read some posts that gave me the impression that running mono amps with these speakers doesn’t work because of the IC cable. Any help would be much appreciated. Thx...Randy

Answers

  • ClipdatClipdat Posts: 3,578
    I can't answer your question, but that picture is awesome. Those speakers look amazing.
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  • I think Jesse is one of the resident experts on common ground amps. Maybe he'll see the post and chime in. Personally, I use two Yamaha stereo amps and have them bi-amped. Not quite the same effect as running mono but it seems to reduce stress on the amps.
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  • codycatalistcodycatalist Posts: 1,373
    edited December 2017
    In regards to Adcom GFA 565 amps
    F1nut wrote: »
    Anyway, there are two circumstances when you can use mono block amps with SDA SRS speakers. One is if your serial numbers are above 5001 on both speakers. If so, you can use the special AI-1 interconnect cable, which you'll have to make as it's no longer sold. The other is if you can tie the negative outputs of the amps together to create a common ground. You'll have to check with Adcom to see if that can be done with those amps.
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  • westmassguywestmassguy Posts: 6,020
    Those appear to be the original 2nd/3rd Generation SRSs. You MUST use a common ground amp. You cannot use an AI-1 or Dreadnaught, with mono-blocks, with that model.
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  • gudnoyezgudnoyez Posts: 6,163
    The GFA 555 and the 555II are common ground amps.
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  • A GFA 5802 works great too as will a 5500. I have both in storage and have used them with blade-blade SDA's. They just need a jumper between the grounds at the amp.

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  • Viking64Viking64 Posts: 2,543
    I asked a similar question when I first posted here 7 years ago. The first 10 responses or so were very informative.

    http://forum.polkaudio.com/discussion/108053/bi-amping-2-3tls-with-adcom-555-ii/p1
  • slendaslenda Posts: 2
    edited January 3
    bbmhmt1grudn.jpeg

    So I have finally purchased the “dream speakers” of mine from back in the day when I was a young man just becoming interested in high-end audio. I had planned on powering them with some Adcom amps run in mono (either vintage GFA-565’s or new GFA-555se’s), but have read some posts that gave me the impression that running mono amps with these speakers doesn’t work because of the IC cable. Any help would be much appreciated. Thx...Randy

    I have Polk SDA-1Bs on Adcom GFA-555 amp (circa 1989) with a Adcom GTP-500 II pre amp and the sound is incredible. I can play records all day the sound is that good.
  • i0armxsalnxl.jpeg

    I added a pic of the serial number, if that helps. I was really hoping to run GFA565’s, in keeping with the vintage theme. I guess even a 5802 would be ok, but I’m not sure about jumping the grounds. Would that be the same as the negatives? Anyone else have a suggestion? Thx again
  • twochanneltwochannel Posts: 171
    I have GFA-565's connected to my SDA-SRS's since 1991. The grounds can and must be jumped together. I have a GFA-5802 that I have used intermittently with the same speakers. The 5802 is not common grounded internally, so you will need to also jumper the grounds. If you decide to go with the 565's. I would have them serviced by an Adcom repair facility to make sure the leaky cap issue has been addressed and bias adjustments are correct before connecting them to the SRS's. They are great amps, but due to their age, components due fail and can destroy speakers. Mine have already been serviced twice and will do it again if needed.
  • Thanks for all the feedback. I'm still not sure what jumping the grounds means. Is this done internally or externally? Any chance someone could post a pic to clear things up for me??
  • TNTsTunesTNTsTunes Posts: 754
    Thanks for all the feedback. I'm still not sure what jumping the grounds means. Is this done internally or externally? Any chance someone could post a pic to clear things up for me??

    On my GFA 5802 I just wire the speaker grounds together at the amplifier.
    "Make a man a fire and he'll be warm for a day. Light
    a man on fire and he'll be warm for the rest of his life."

  • F1nutF1nut Posts: 39,622
    In regards to Adcom GFA 565 amps
    F1nut wrote: »
    Anyway, there are two circumstances when you can use mono block amps with SDA SRS speakers. One is if your serial numbers are above 5001 on both speakers. If so, you can use the special AI-1 interconnect cable, which you'll have to make as it's no longer sold. The other is if you can tie the negative outputs of the amps together to create a common ground. You'll have to check with Adcom to see if that can be done with those amps.

    It should be noted that tying the negative outputs does have a negative effect on the sound quality.
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  • headrottheadrott Posts: 5,250
    F1nut wrote: »
    In regards to Adcom GFA 565 amps
    F1nut wrote: »
    Anyway, there are two circumstances when you can use mono block amps with SDA SRS speakers. One is if your serial numbers are above 5001 on both speakers. If so, you can use the special AI-1 interconnect cable, which you'll have to make as it's no longer sold. The other is if you can tie the negative outputs of the amps together to create a common ground. You'll have to check with Adcom to see if that can be done with those amps.

    It should be noted that tying the negative outputs does have a negative effect on the sound quality.

    Absolutely agree with this.
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  • TNTsTunesTNTsTunes Posts: 754
    F1nut wrote: »
    In regards to Adcom GFA 565 amps
    F1nut wrote: »
    Anyway, there are two circumstances when you can use mono block amps with SDA SRS speakers. One is if your serial numbers are above 5001 on both speakers. If so, you can use the special AI-1 interconnect cable, which you'll have to make as it's no longer sold. The other is if you can tie the negative outputs of the amps together to create a common ground. You'll have to check with Adcom to see if that can be done with those amps.

    It should be noted that tying the negative outputs does have a negative effect on the sound quality.

    It has no negative effects on a GFA 5802 or 5500 however.
    "Make a man a fire and he'll be warm for a day. Light
    a man on fire and he'll be warm for the rest of his life."

  • F1nutF1nut Posts: 39,622
    TNTsTunes wrote: »
    F1nut wrote: »
    In regards to Adcom GFA 565 amps
    F1nut wrote: »
    Anyway, there are two circumstances when you can use mono block amps with SDA SRS speakers. One is if your serial numbers are above 5001 on both speakers. If so, you can use the special AI-1 interconnect cable, which you'll have to make as it's no longer sold. The other is if you can tie the negative outputs of the amps together to create a common ground. You'll have to check with Adcom to see if that can be done with those amps.

    It should be noted that tying the negative outputs does have a negative effect on the sound quality.

    It has no negative effects on a GFA 5802 or 5500 however.

    Have you tried those amps strapped and then with the AI-1 or Dreadnought?
    Political Correctness'.........defined

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  • TNTsTunesTNTsTunes Posts: 754
    F1nut wrote: »
    Have you tried those amps strapped and then with the AI-1 or Dreadnought?

    Yes. Both have been used strapped with a pin/blade interconnect and then with my 1000VA Dreadnought when strapped and unstrapped plus used strapped with blade/blade SDA's too.
    "Make a man a fire and he'll be warm for a day. Light
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  • F1nutF1nut Posts: 39,622
    Very good. I don't recall the model of Adcom I heard strapped and then with the AI-1, but the improvement was not subtle.
    Political Correctness'.........defined

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  • TNTsTunesTNTsTunes Posts: 754
    On the 5500 or 5802 you can measure resistance between the grounds before they are strapped unlike two separate mono amps.

    Here's a good post about it.
    stogie wrote: »
    My Adcom 5802 has the neg terminals strapped and plays my SDA SRS's without a problem. Before strapping the resistance was 200ohms, after strapping .3 ohms. Below is some information I saved from a post by DK- in quotes.
    "My email to Adcom on 11/12/2000:
    Subject: Adcom GFA-5802 with Polk Audio SDA-1B speakers
    "Is the GFA-5802 a "common ground" amplifier? My speaker specifications state that only common ground amplifiers must be used. I just purchased a GFA-5802. The sound from the speakers seemed "echoey" and out of phase. When I removed the interconnecting phase array cable from between the speakers, the sound was normal. I was previously using an Adcom GFA-555 amp and never experienced this problem. Any ideas on what is causing this?"

    Adcom's response on 11/14/2000:
    "There are 2 options for you to do. You can get a cable from Polk for those speakers, the AI-1 cable. This connects the 2 speakers and deals with the common ground problem. The other option is to take a piece of speaker wire and run it between the 2 negative terminals of the amplifier that you are using. This will not hurt the amp at all so dont worry about that. This a problem that has been common with the 5800, 5802, and 5500, all our newer amps and those model speakers.
    Thanks and good listening Adcom" "

    In my case the AI-1 cable was not an option but strapping worked fine. According to Adcom's reply, it is ok to strap the 5800 too.
    "Make a man a fire and he'll be warm for a day. Light
    a man on fire and he'll be warm for the rest of his life."

  • Leaning towards a 5802. I'm in the Milwaukee area. If anyone has one they are interested in parting with, let me know. Thx
  • TNTsTunesTNTsTunes Posts: 754
    PM sent.
    "Make a man a fire and he'll be warm for a day. Light
    a man on fire and he'll be warm for the rest of his life."

  • 250GTLusso250GTLusso Registered User Posts: 158
    To each his own, but I prefer the authority (bass) and detail (highs) of the Adcom GFA-585 (Big Sky Audio upgrade) with my SDA SRSs. I use the Adcom GFA-565 mono blocks (currently traveling to Big Sky Audio for their upgrade) with my 2.3TLs, but unfortunately I cannot use them with the SDA SRSs as they are not common ground, and I don't like tying the negative terminals together.
    HT
    Adcom GFP-565 Pre-amp, Adcom GFA-565 Mono Block Amps (Front), Adcom GFA-585 Amp (Side), Adcom GFA-555 Amp (Rear), Adcom ACE-515, Pioneer CLD-3070 Laserdisc, Sony CDP-605esD, Sony BluRay BDP BX59, Samsung 50" Plasma, Polk Audio SDA SRS 1.2TL Front (Walnut), Polk Audio SDA SRS Side (Walnut), Polk Audio SDA SRS Rear (Walnut).
    2 Channel (Living Room)
    Adcom GFP-565 Pre-amp (w/Big Sky Audio Upgrades), Adcom GFA-565 Mono Block Amps (w/Big Sky Audio Upgrades), Adcom ACE-515, Sony CDP-705esD, Magnum Dynalab FT-101A Etude, Polk Audio SDA SRS 2.3TL (Walnut), Polk Audio SDA SRS 2 (Walnut), STAX SR34 Electret Earspeaker System.
    2 Channel (Office)
    Adcom GFP-555 Pre-amp, Adcom GFA-555 Amp, Sony CDP-605esD, Adcom GFT-555 Tuner, Polk Audio SDA 1C (Walnut).
    2 Channel (Garage)
    Hafler DH-110 Pre-amp, Hafler DH-220 Amp, Sony CDP-505esD, Hafler DH-330 Tuner, Polk Audio SDA 2B (Walnut).
  • Think I may have been talked into a 585...lol.
  • I need to pull the trigger on a 5802 or 585. 585 seems to be more fitting in my vintage setup. Any feedback?? Thx
  • 250GTLusso250GTLusso Registered User Posts: 158
    I prefer the GFA-585, paired with the GFP-565, or preferably the GFP-750. Definitely will provide excellent sonic character with that classic vintage look and vibe. Later you can send the amp and pre-amp to Big Sky Audio for their outstanding upgrade, to take it to the next level. You will not regret it.
    HT
    Adcom GFP-565 Pre-amp, Adcom GFA-565 Mono Block Amps (Front), Adcom GFA-585 Amp (Side), Adcom GFA-555 Amp (Rear), Adcom ACE-515, Pioneer CLD-3070 Laserdisc, Sony CDP-605esD, Sony BluRay BDP BX59, Samsung 50" Plasma, Polk Audio SDA SRS 1.2TL Front (Walnut), Polk Audio SDA SRS Side (Walnut), Polk Audio SDA SRS Rear (Walnut).
    2 Channel (Living Room)
    Adcom GFP-565 Pre-amp (w/Big Sky Audio Upgrades), Adcom GFA-565 Mono Block Amps (w/Big Sky Audio Upgrades), Adcom ACE-515, Sony CDP-705esD, Magnum Dynalab FT-101A Etude, Polk Audio SDA SRS 2.3TL (Walnut), Polk Audio SDA SRS 2 (Walnut), STAX SR34 Electret Earspeaker System.
    2 Channel (Office)
    Adcom GFP-555 Pre-amp, Adcom GFA-555 Amp, Sony CDP-605esD, Adcom GFT-555 Tuner, Polk Audio SDA 1C (Walnut).
    2 Channel (Garage)
    Hafler DH-110 Pre-amp, Hafler DH-220 Amp, Sony CDP-505esD, Hafler DH-330 Tuner, Polk Audio SDA 2B (Walnut).
  • TNTsTunesTNTsTunes Posts: 754
    I like the nelson pass design GFA 5802 sound better then the GFA 585 but I've never heard a 585 after big sky does there thing to it. I'm local so if he wants to hear a 5802 power his speakers that could probably be arranged.
    "Make a man a fire and he'll be warm for a day. Light
    a man on fire and he'll be warm for the rest of his life."

  • 250GTLusso250GTLusso Registered User Posts: 158
    I am a fan of the NP designs as well. I have a GFA-555 that was my second amp ever (it replaced my Hafler DH-220 some 28 years ago!) and I still use it today. Its an exceptional sounding "budget" amp IMO. NP always endeavored to minimize what was in the signal path, and he achieved it in spades with the GFA-555.

    I find that the Class A GFA-585 (triple Darlington design) has a lower noise floor than the GFA-5802 (MOSFET design). The GFA-585 also has the capability to provide up to 60amps at its output stage.

    Signal to Noise ratio:
    GFA-585 - 110dB
    GFA5802 - 105dB
    (Per ADCOM's spec sheet)

    I find that the GFA-5802 sounds grainy at times.
    HT
    Adcom GFP-565 Pre-amp, Adcom GFA-565 Mono Block Amps (Front), Adcom GFA-585 Amp (Side), Adcom GFA-555 Amp (Rear), Adcom ACE-515, Pioneer CLD-3070 Laserdisc, Sony CDP-605esD, Sony BluRay BDP BX59, Samsung 50" Plasma, Polk Audio SDA SRS 1.2TL Front (Walnut), Polk Audio SDA SRS Side (Walnut), Polk Audio SDA SRS Rear (Walnut).
    2 Channel (Living Room)
    Adcom GFP-565 Pre-amp (w/Big Sky Audio Upgrades), Adcom GFA-565 Mono Block Amps (w/Big Sky Audio Upgrades), Adcom ACE-515, Sony CDP-705esD, Magnum Dynalab FT-101A Etude, Polk Audio SDA SRS 2.3TL (Walnut), Polk Audio SDA SRS 2 (Walnut), STAX SR34 Electret Earspeaker System.
    2 Channel (Office)
    Adcom GFP-555 Pre-amp, Adcom GFA-555 Amp, Sony CDP-605esD, Adcom GFT-555 Tuner, Polk Audio SDA 1C (Walnut).
    2 Channel (Garage)
    Hafler DH-110 Pre-amp, Hafler DH-220 Amp, Sony CDP-505esD, Hafler DH-330 Tuner, Polk Audio SDA 2B (Walnut).
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