Hi ApD,
Don't use pull up resistors.
I do not recommend modifying the input circuit. This is not a design fault. If Bob intended to use pull up or down resistors, he would have installed them.
The engineer who approved these mods was Vic Richardson. I used to talk to him often. These changes are the ones to use, Vic has the ability to solve these problems properly, and he did. I've learned to respect his judgement over the years.
-Chris
Don't use pull up resistors.
I do not recommend modifying the input circuit. This is not a design fault. If Bob intended to use pull up or down resistors, he would have installed them.
The engineer who approved these mods was Vic Richardson. I used to talk to him often. These changes are the ones to use, Vic has the ability to solve these problems properly, and he did. I've learned to respect his judgement over the years.
-Chris
Pull-ups do no harm. They help sometimes.
Offtopic:
If these gyus are as good and thorough as you say, I wander where they were during the design phase of the amp - why did they let it out of the factory door in such a condition the first place... I wouldn't. 🙂
Offtopic:
If these gyus are as good and thorough as you say, I wander where they were during the design phase of the amp - why did they let it out of the factory door in such a condition the first place... I wouldn't. 🙂
Hi ApD,
There is evidence that forcing op amps into class A may not always help. In any event, you shouldn't give this a blanket recommendation. If you wanted to do this, a current source would be much more linear. Look at the Marantz 3600 / 3800 preamp for an example (uA749 or 739, can't remember).
If you want to see bad designers, there are many products that will fit the bill. A long list. Once you compare the designs you can appreciate the good ones. Look at the list of simple, stupid mistakes in basic circuits, then consider a system as complicated as, say a Carver amplifier. I'd say they have done a pretty good job.
I don't want to name names here, but I have seen many amps that cause fires due to poor design. Most are out of business - thank goodness!
-Chris
There is evidence that forcing op amps into class A may not always help. In any event, you shouldn't give this a blanket recommendation. If you wanted to do this, a current source would be much more linear. Look at the Marantz 3600 / 3800 preamp for an example (uA749 or 739, can't remember).
There is more than one engineer on staff, each are assigned a project. Cost cutting accountants force creativity against most engineer's best judgment. Service bulletins are the result. They may also make the odd error, but not often. Given that we don't belong to a perfect world, you can expect these things.
If you want to see bad designers, there are many products that will fit the bill. A long list. Once you compare the designs you can appreciate the good ones. Look at the list of simple, stupid mistakes in basic circuits, then consider a system as complicated as, say a Carver amplifier. I'd say they have done a pretty good job.
I don't want to name names here, but I have seen many amps that cause fires due to poor design. Most are out of business - thank goodness!
-Chris
Hi all,
The squeel was there even before i replaced the caps, it's a "feature" from carver, as my old pm-1200 had also, what i do now to remove the squeel is that turn dow the volumes on the amp,but now when i turn it off i hear the music still being played from my mixer going down and with distorsion, for the input board mods for the noise i still can't figure out what jumper i need to cut, they are not marked anywhere....
The squeel was there even before i replaced the caps, it's a "feature" from carver, as my old pm-1200 had also, what i do now to remove the squeel is that turn dow the volumes on the amp,but now when i turn it off i hear the music still being played from my mixer going down and with distorsion, for the input board mods for the noise i still can't figure out what jumper i need to cut, they are not marked anywhere....
Hi pjaneiro,
I haven't a clue what trace you are talking about cutting. There is no mention in any of my 1200 notes, or PM 1.5a notes.
May I see the document you are looking at?
Did you read the two service notes I posted? The number 2 document covers the squeel as it may exist in stock units, so it may apply to you directly.
-Chris
I haven't a clue what trace you are talking about cutting. There is no mention in any of my 1200 notes, or PM 1.5a notes.
May I see the document you are looking at?
Did you read the two service notes I posted? The number 2 document covers the squeel as it may exist in stock units, so it may apply to you directly.
-Chris
Hi Anatech, in the service manual i sent you, page 1 of 2 is page 81 in the pdf manual and page 2 of 2 is page 21 in the pdf doc, it's all explained there on how to remove the output noise, but there is no clear indication on wich jumper is wich..
Thanks...
Thanks...
Hi pjaneiro,
If possible could you mail me the manual you have?
That would be great.
Here is my address:
dome
at => @
advalvas.
be
Thanks,
Tarzan
If possible could you mail me the manual you have?
That would be great.
Here is my address:
dome
at => @
advalvas.
be
Thanks,
Tarzan
Hi pjaneiro,
That mod was for noise pickup from the mag coil. Kinda "tick tick tick" noise. You are running the signal via a twisted pair rather than the traces on the circuit board. The two jumper are simply the other end of the traces you are cutting. Follow the trace on the PCB.
You can do this if you want, I do not believe it will help you in the least unless you are also getting interference from the mag coil circuits. Nothing you have posted would lead me to believe this.
-Chris
That mod was for noise pickup from the mag coil. Kinda "tick tick tick" noise. You are running the signal via a twisted pair rather than the traces on the circuit board. The two jumper are simply the other end of the traces you are cutting. Follow the trace on the PCB.
You can do this if you want, I do not believe it will help you in the least unless you are also getting interference from the mag coil circuits. Nothing you have posted would lead me to believe this.
-Chris
the noise is more of a high pitch buzzing from the left channel my pm-1200 used to do it before i did the mod, ok i'll follow the traces and see where it leads me , thanks
Hi pjaneiro,
That will help the high pitched buzz. I think you'll find the mod fairly straight forward.
-Chris
That will help the high pitched buzz. I think you'll find the mod fairly straight forward.
-Chris
i have the service manual, but it's 10mb, i've tried to send to a few people but their email account bounced back, i would need a site where i could upload it
Hi pjaneiro,
Did you try the mod yet, or are you waiting for the weekend? It should take you 1/2 hour or less to do this.
-Chris
Did you try the mod yet, or are you waiting for the weekend? It should take you 1/2 hour or less to do this.
-Chris
pjaneiro ,
could you send it to me?
my mailbox unlimited, docfin @ gmail . com (remove spaces)
thanks in advance
John
could you send it to me?
my mailbox unlimited, docfin @ gmail . com (remove spaces)
thanks in advance
John
I should have some time tonight to try this one out, for the other mod abot the squeel, no go, i do not have the same boards, so i won't venture myself into that one, i was wondering if i could just use relays to cut the output stage to the amp ? that should work no ?, as i stated i only hear the squeel when my mixer is on with music still playing
Hi pjaneiro,
That will work of course, but defeats the normally quiet design and effectively protected Carver amp. You will need the really big ones. You may have trouble with contacts due to the high peak currents this amp will deliver.
Why not use a signal relay to short the input when you switch off?
-Chris
That will work of course, but defeats the normally quiet design and effectively protected Carver amp. You will need the really big ones. You may have trouble with contacts due to the high peak currents this amp will deliver.
Why not use a signal relay to short the input when you switch off?
-Chris
mod worked perfectly fout the high pitch buzzing, i noticed something , the ground post for my speakers has a wire soldered going to a 2 screw post connected to the chassis, but this wire has been cut, and the wire connecting the 2 screws are removed the amp works fine, but should i solder back the ground to the chassis ? and put reconnect that 2 screw post ?
Hi pjaneiro,
I think your are referring to to the barrier strip with two screws on the back of the amplifier. Chassis ground goes to one terminal, circuit ground to the other. There should be a shorting strip between the screws on the back that you can removeif you want to float the circuit ground.
It made no sense for anyone to remove those wires.
-Chris
I think your are referring to to the barrier strip with two screws on the back of the amplifier. Chassis ground goes to one terminal, circuit ground to the other. There should be a shorting strip between the screws on the back that you can removeif you want to float the circuit ground.
It made no sense for anyone to remove those wires.
-Chris
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