2 channel; 3 amps 6 channels 2250watts

disneyjoe7 · January 2008

There's not many on this board understand transistor bias when it comes to A A/B or B, and you wish them to post back on a 1 volt offset issue.

You're in your own league

tonyb · January 2008

Some how I have this vision of Ben,looking like Doc from Back to the future.

Systems · January 2008

Congrats on getting it working.Does that amp have a pot for nulling offset?1 volt offset is high , are the + and - DC voltages feeding the input stage fairly close.

disneyjoe7 · January 2008

tonyb wrote: »

Some how I have this vision of Ben,looking like Doc from Back to the future.

Some how I don't think you're too far off

jakelm · January 2008

GV#27 wrote: »

Congrats on getting it working.Does that amp have a pot for nulling offset?1 volt offset is high , are the + and - DC voltages feeding the input stage fairly close.

Should have a pot for each channel, right?

jakelm · January 2008

ben62670 wrote: »

:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D:D
No smoke!!! None!!! I have output!!! all systems go!!!

Damnit, I should have quoted the excitement from last night...:p:p

Congrats Ben, way out of my league.

Systems · January 2008

jakelm wrote: »

Should have a pot for each channel, right?

Yes if it has adjustments for offset then it will have one for each ch .Some amps don't have them relying instead strictly on component matching and allowing some offset(50mv or so) to exist.

ben62670 · January 2008

The problem is the inputs are receiving some sort of dc feedback from somewhere in the system, and amplifying it to 1vdc on the speaker outputs. The output from an amp is AC only. DC output kills speakers. There is no adjustment for DC out(self biasing). I am going to try to locate where the DC is leaking into the input stage. I can't DC couple the inputs, because there is DC present even with no source hooked up.

Systems · January 2008

ben62670 wrote: »

The problem is the inputs are receiving some sort of dc feedback from somewhere in the system, and amplifying it to 1vdc on the speaker outputs.

Are the + and -DC voltages feeding the input stage close to being the same.?If one is lower than the other this could be the source of the offset.

DC output kills speakers

Yep if you feed them enough,been there done that,a wiring error in one of my projects sent 40 or so volts of DC to a 6.5" woofer and destroyed it in seconds.

ben62670 · January 2008

GV#27 wrote: »

Are the + and -DC voltages feeding the input stage close to being the same.?Yep if you feed them enough,been there done that,a wiring error in one of my projects sent 40 or so volts of DC to a 6.5" woofer and destroyed it in seconds.

The Adcom service manual doesn't tell ya much. Its funny you mention the dc for the input stages. When tracking the problem before I found something amiss with the power at the OP amp. The DC output is .2 watts at idle which make the cone jump just a hair. I ran it like that for a year, but I would like to get it right. I am listening to some Allison Krause on it right now driving some custom monitors, and it just sound so sweet. I am going to play a little, and enjoy before I let problem hunting annoy me. I am so pleased that I have this amp going. These are a special product in the Adcom line up;)

ben62670 · January 2008

Well I rewired my SDA's for one amp for now. I don't need 2000+ watts in my office. They are wired for 2.6ohms on the MM. I have driven them to 116db with this amp, and a pot as a pre today. Sounds good. The highs are too much though. They were controlled by another amp with less watts. I'll have to tame them a bit;)
Another ugly pic:D
DSCN0923.jpg?t=1201405714

tonyb · January 2008

Jeez Ben....when's the Death Star going to be fully operational?

ben62670 · January 2008

HeHe I just reached 125db with Fleetwood Mac's worlds turning bass riff:D:D:D Nice and clean. The only problem is the bass made the CD skip:( Those transistors are getting better, and better. No more distortion lights flickering at high levels anymore! Whoo Hoo!!!

disneyjoe7 · January 2008

ben62670 wrote: »

HeHe I just reached 125db with Fleetwood Mac's worlds turning bass riff:D:D:D Nice and clean. The only problem is the bass made the CD skip:( Those transistors are getting better, and better. No more distortion lights flickering at high levels anymore! Whoo Hoo!!!

Dud you're just F'ng mad.

BTW did you ever get juiced working for the "Electric Company" :eek:

ben62670 · January 2008

disneyjoe7 wrote: »

Dud you're just F'ng mad.

BTW did you ever get juiced working for the "Electric Company" :eek:

Nope I never hit more than 1 wire at a time:D
The scariest thing though was when I touched a wire with the tree, and the butt was in a wet swamp. Me drop saw and run:eek: Hair stood up, and it wasn't just cause I was scared:p
My buddy took out the power in six towns once, and it happened to be just before Luke and Laura's wedding on that popular soap in the eighties:D
Thousands of house wives wanted to kill him:D

tonyb · January 2008

125 db's Ben? I had such high hopes you could do better.:p;):)

tonyb · January 2008

I use to be able to make a cd skip with the SRT's and 3000p's bringing up the **** end and I swear,drywall has cracked loose around nail heads in the ceiling from it.Those speaks you have there are awesome.Now,how you gonna get them to conyers?

ben62670 · January 2008

tonyb wrote: »

I use to be able to make a cd skip with the SRT's and 3000p's bringing up the **** end and I swear,drywall has cracked loose around nail heads in the ceiling from it.Those speaks you have there are awesome.Now,how you gonna get them to conyers?

I know that is not just a story. I have done it. I can't believe this amp is just getting better, and better. I have a rat shack meter, and it goes to 126... well I just pegged it, and had a hair more. Slow response, A weighted. I have to stop now. I need my ears;)

tonyb · January 2008

You getting your db's at 1 meter or 3 ?

ben62670 · January 2008

tonyb wrote: »

You getting your db's at 1 meter or 3 ?

If I am a 1 meter, or if I am at 2 between the two speakers I get about the same.

engtaz · January 2008

You sonosub looks pretty small now.

engtaz

jakelm · January 2008

Are those speacial subsonic boxes at the top of the towers?:p

After a day of listening, is it sounding better? Starting to warm up?

ben62670 · January 2008

engtaz wrote: »

You sonosub looks pretty small now.

engtaz

It makes me feel so inadequate:o

jakelm wrote: »

Are those speacial subsonic boxes at the top of the towers?:p

After a day of listening, is it sounding better? Starting to warm up?

Yes! Transistor burn in has a tremendous effect I gained much more power, and the high end smoothed out a lot! I am thinking of changing all the transistors, and caps in my GFA-5800 also!

engtaz · January 2008

Let us know what caps your changing and what differences it makes.

Just want to say thank you to the mad scientist for the constant updates,
engtaz

jakelm · January 2008

Did the change effect the ohm stability?

Is the temp the same?

ben62670 · January 2008

jakelm wrote: »

Did the change effect the ohm stability?

Is the temp the same?

Stability is sweet. It does get hot, but never goes into thermal shut down. The temps reach 150f, well within spec for longevity, and would run cooler if DC offset was corrected. I must include the new caps, and transistors helped a lot. I was get a beta of about 70 on the old chips, and this batch I am getting 80. Thats a nice little gain;) Add to that my distortion lights are never flickering:)

jakelm · January 2008

Have you ever tested the efficiency of your towers?

2 channel; 3 amps 6 channels 2250watts

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