Adcom preamp question

[SEAWOLF97]

.
recently switched over to an Adcom GTP-555 mk2 preamp ...nice features , great build quality, BUT , it felt like something in the sound was missing ..:eek:

now a little BG..I run 2 separate systems from the 2 MAINS OUT jacks on the preamp ..well 1.5,
I guess...

OUT #1 goes to the BGW amp connected to the 250Ti's and daisy chains (yes , its designed this way) to a second BGW amp that pushes the Ohm speakers...

OUT #2 goes to an old NAD receiver that runs the subs

PROBLEM WAS : The 250Ti's didnt seen to have the full range & sparkle that I know they are capable of ....I tried everything to correct this EXCEPT reading the Adcom owners manual...on every preamp that I've used that has 2 mains OUT jacks , they are identical , in desperation , I downloaded the manual and started reading ...

surprise surprise :blink::blink: , they aren't the same ...swapped cables to the opposite way that they were and all the sound that the JBL's are famous for have returned...




from the manual:

[Robh3606]

Hello Seawolf

Well even so you shouldn't have a clearly audible difference between them. Thats odd. Might want to get it checked out.

Rob:)

[DavidF]

Which output number you mentioned is associated with the 'Normal', cap coupled output?

Is there a switch to designate the preferred output or does it seem both outputs are full on, all times?

[MikeBrewster77]

Interesting. I'm guessing Rob's thought (as would be mine) is that the manual seems to indicate that the primary difference between the LAB and NORM setting is that ...the NORM outputs...roll off frequencies below 10Hz.

Which would lead one to believe that the difference wouldn't really be audible -- unless maybe the capacitors used to achieve that roll off degrade the sound quality? :dont-know:

[SEAWOLF97]

unless maybe the capacitors used to achieve that roll off degrade the sound quality? :dont-know:

mebbe the caps have degraded and now all frequencies are affected on the cap coupled outputs ?

the NORM outputs are fine for running the subs...:o: as both sets are always ON.

[DavidF]

mebbe the caps have degraded and now all frequencies are affected on the cap coupled outputs ?

the NORM outputs are fine for running the subs...:o: as both sets are always ON.

The caps would be there to suppress DC coming out of the upstream components but may have some adverse influence from the daisy chain setup you mentioned.

[clmrt]

Would the amplifier's input impedance cause the f3 to rise if it were too low?

Adcom GFA-535II, for example, has an input impedance if 100Kohms. The BGW (750?) shows 15k.

[Hoerninger]

Would the amplifier's input impedance cause the f3 to rise if it were too low?

My thought too.
____________
Peter

[SEAWOLF97]

but may have some adverse influence from the daisy chain setup you mentioned.

the BGW 750D is a pro amp that takes XLR & 1/4TRS inputs and just below that has XLR & 1/4TRS outputs....mebbe "pass through" is a better term ....the second amp (BGW 250d) on the chain can be working even if the first is OFF , and they can both play together .... cannot see how this would affect preamp , but I'm not an EE.

Re-reading my own posts in this thread and the replies, it seems obvious now that the capacitance connected MAINS output (NORM) is not up to spec ..... and with the current config of the NORM outputs running the subs & the JBL's happy on the LAB outputs, I think things are OK....wasnt obvious to me until this thread.

BUT if I wanted to run 2 amps and did not have the chain feature for the BGW 250D , then a fix would be needed.

Thx all. :D