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Old 21st August 2005, 12:16 AM   #551
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Also Ed, Try running it with the inputs shorted, do you get hum then?
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Old 21st August 2005, 03:43 AM   #552
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Default Progress

I found that I had the output grounds swapped. Again, I assumed they would remain on their respective sides which was not the case. (Picture the fun I've had on Christmas' past when putting toys together at the 11th hour. Instructions? I don't need no freakin' instructions!.....How many times have I paid for that?....)
This is the reason the RCA body to ground measurement didn't check. Now I measure 1.2 ohms on both. This after putting fresh batteries in my DVOM.
I still get no reading for resistance between the RCA pin to body. I'll make some shorting jacks tomorrow and continue the search. In spite of the hum, which is less now, I can hear the quality of this amp will be worth the effort.
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Old 21st August 2005, 07:51 PM   #553
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Default Ask for guidance

I ask of all who have completed their amp:
How do you isolate or connect power ground and amp ground?

I currently have a lead from power ground to a lug on the bottom (aluminum) of my case. Is amp ground connected to or isolated from this lug?
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Old 21st August 2005, 08:22 PM   #554
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My input AC power ground is connected to the chassis. Nothing else. I may put some bypassing in later but for now, there is nothing connecting DC power output or amplifier signal ground to anything else. Only the fastons and the input connectors straight to their off-board connectors and the off-board connectors are isolated from the chassis. I hear no hum, or much of anything except the music.
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Old 21st August 2005, 08:43 PM   #555
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Default Re: Ask for guidance

Quote:
Originally posted by bg40403
I ask of all who have completed their amp:
How do you isolate or connect power ground and amp ground?

I currently have a lead from power ground to a lug on the bottom (aluminum) of my case. Is amp ground connected to or isolated from this lug?

Ed there is no good reason to connect you mains ground and your power ground. The main ground is just there for safety, in case the case somehow gets mains voltage to it.

I always just attach the mains ground to the chasis, but the power ground should be isolated to the power supply/circuit(in this case all on the same board).

There is absolutely no beneifit to connecting mains GND to anything in the circuit, in fact it can really only cause problems, as the circuit's GND is really a voltage reference, not a safety feature.

Once again the Mains ground is there to protect the user from mains voltage on the case. Nothing more.

Most of this I am stating for the noobs, not so much to you Ed.

The best way to keep them isolated is to use RCA jacks that have an insulator as well as the same type of binding posts. I would suspect your RCA connectors based on your symptoms.

Cheers!
Russ
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Old 21st August 2005, 09:51 PM   #556
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Default Don't do as I do, do as I say

It's a necessary phrase for raising children...

Let me share with you my experiences;

The amp is running fine, no hum.
I had a combination of faults
My RCA's were not isolated from the chassis. I made the holes larger so the "barrel" of the jack didn't come in contact with the case.
I removed the...ahem...strap from amp ground to case ground...noob?...that would be me...
I checked isolation of the speaker posts from the case.
When I plugged it in through the Marchand active x-over, the hum was still there. I removed the Marchand from the loop and the hum is gone. Thank God!
Seems I've had a ground problem I wasn't aware of in the Marchand. Guess which component I'll open up next? I suppose the reciever I was using before wasn't suseptible in the same way.

Thanks to all: Russ, hayenc and Panelhead for your responses in helping me get through this.

My pre-amp output runs 0-90. I had been listening around 65-70 with a 35w/ch amp. This amp rums fine (louder) set around 55. no gain problem. I'm just beginning the use of the amp now. That's Little Feat's "Last Record Album" playing in the background. You really ought to find a copy and give it a listen.
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Old 21st August 2005, 10:39 PM   #557
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Default Re: Don't do as I do, do as I say

Quote:
Originally posted by bg40403
That's Little Feat's "Last Record Album" playing in the background. You really ought to find a copy and give it a listen.
Will do!

Glad to hear its sounding right now. I have run into non-isolated RCA problem a couple of times.

Cheers!
Russ
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Old 22nd August 2005, 09:41 AM   #558
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Default my findings

I followed this thread with great interest and I was a bit sceptical at first. But at the same time excited about a new approach. I was getting tired of the "micro tweaking" (add a snubber and remove a cap here and there) of the chip amp and nobody really could give a fresh approach.

I myself am a JLH fan an I have my configuration build up as monoblocks. I also have tried all the "silly" tweaks and the good ones suggested on the web. The capacitance multiplier being outright ridiculous. But I am wondering here.

Over the weekend I quickly whipped up a Rev-A. Just to have good grounds for further comparisons and Mauro, you have done a BRILLIANT job with this design.

I can answer a couple of questions that has not been addressed.
1- putting an OPA627 into the equation does not improve it. It sounds the same.
2- you need a LM317 in order to run Rev-C, it uses pin 8 with you don't on other op-amps (it is a very good and cheap little op-amp that does a good job).

I have build mine with twin bridge rectifiers (just a habit I have when building amps) this make it easier to add another transformer at a later stage, and splitting the rails properly. This also brings the noise down by a large margin, and you do not get any cross talk

I do not have the speaker protection circuit in my system. (Being experimental)
Turn-on thumps. This is the strange thing. I have no turn-on thumps, just a small click. OK then I have to admit I do not have any DC protection. But this is only an experiment and I will be doing the Rev-C next. With the protection

Listening impressions
The first things that I found is that you have a bit more accentuation on the high mids and tops. Making it sound “forward” as explained by Russ in his evaluation. I did find however that the tonality is not as resolved or rather rounded as my JLH and the Bass is not as deep (it is however much better than a standard JLH). BUT having said that. The bass is extremely good. And the overall balance is much better that anything else I have heard. If you still wander how it compares to a chip amp with all the micro tweaking. It is A LOT better by a large margin. I believe that the REV-C will be the preferred version at the end of the day specially because the tonal balance will be in line of what it should be without the accent on the high mids and tops.

Suggestions.
Split the bridge rectifiers giving you two instead of the one per channel (this way you decouple the transformer from earth). And a higher voltage input cap, they do tend to sound a lot better that the small caps (why I do not know).

Mauro I have to congratulate you on a very good design I am impressed.
Russ, keep up the good work. You will have a Gem to offer the people here

Regards
Rudi
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Old 22nd August 2005, 10:21 AM   #559
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Default Re: my findings

I have build mine with twin bridge rectifiers (just a habit I have when building amps) this make it easier to add another transformer at a later stage, and splitting the rails properly. This also brings the noise down by a large margin, and you do not get any cross talk


I have always used dual rectifier bnridges for dual pail supplies. A frind who builds a lot more products than I do uses a single bridge and references ground. He says the single bridge scopes better. I have used both and cannot hear a difference.
I can see, where a dual bridge should have lower value switching spikes. Just twice as many. Mauro must prefer this method.




I do not have the speaker protection circuit in my system. (Being experimental)
Turn-on thumps. This is the strange thing. I have no turn-on thumps, just a small click. OK then I have to admit I do not have any DC protection. But this is only an experiment and I will be doing the Rev-C next. With the protection



I bumped up the on board filter capacitance for the circuit. There is a no turn on transient, but a small turn off pop sometimes. It seems heat related, worse after a hard workout.
I think if it was built using the stock value filter caps mine might be quiet on turn off too. Could not bring myself to use so little capacitance for an amplifer. Usually 150,000 ufd to 250,000 ufd per channel is about right.
It is a nice circuit. I might add it to some other amps I have laying around.
What value of dc on the output wil trigger it to open the relay? I guess 0.6 - 0.7 volts.


Agree 100% on the sonics. The RevA is not perfect. But is close. I suspect the Rev C will be a little better.
Many thanks to Mauro for sharing the design, and to Russ for making this happen.


George
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Old 22nd August 2005, 10:49 AM   #560
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Hi Panelhead.

You will make an excellent candidate for building a class A amp. With that much capacitance per channel you will get a truly remarkable power supply.

I think it was Mark Levinson who once said that anything under a farad is a waste of time.

Cheers
Rudi
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