Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 21st March 2008, 02:34 PM   #11
diyAudio Member
 
Join Date: Dec 2007
hi,

i'm actually away from the carver circuits at the moment.
the circuit djk shows is a theoretical model of a type of filter i call a 'snubber', it soakes up the spikes using the resistor, the inductor limits the rate of change of current (i'm a bit rusty, so someone correct me if i'm wrong).
to use this circuit in the amp, you would have to look at the filter /snubber that is already there and decide whether you wanted to change carver's cicuit (or maybe just change a few component values).
Its quite likely that the circuit in the carver is already very similar to this one - its just what you use when you have a triac with a large inductive load.

the problem you describe may just be the inherrent hum and noise in the carver design. (you didn't say how loud the buzz was in relation to the music).
It's almost impossible to design a compact amp without some electro magnetic pick-up from the power supply's transformer this is why some audiophile gear has an external power supply (of course, not practical in a high power amp).
the way the hum goes up when the volume control is away from either end of its travel suggests 3 possibilities to me. possibly interference pickup in the wire leading from the input card at the back, to the pot (carver use 3 wires twisted together rather than screened cables although the signal level is high enough for then to get away with this.
alternatively, there may be a poor groung connection between the pot terminal and the input circuit, thirdly, there may be an earth loop through the chassis.
as i said - i'm no-where near a carver at the moment so i can't see exactly how they're doing things.

problems like this are not easy to solve and its quite likely its just a design shortfall in the amp. (you should hear the PM2.0t - it has a 1kHz buzz ! ).

i hope this has been of some help - or at least interesting.
jonathan
  Reply With Quote
Old 22nd March 2008, 01:13 AM   #12
djk is offline djk
diyAudio Member
 
djk's Avatar
 
Join Date: Feb 2001
Location: USA
The GE filter was actually suggested for a light dimmer.

The light dimmer has the same basic problem as an audio amplifier, you don't always know how much current it will draw. With low-current loads the Q of a filter will peak, and can actually make the noise greater. This filter design works over a 10:1 current range.

For 120V AC line the capacitors must have a 200V minimum rating. I used a 16ga cup-core inductor with a very small air-gap. The resistor was a half-watt carbon film type.
__________________
Candidates for the Darwin Award should not read this author.
  Reply With Quote
Old 22nd March 2008, 02:49 AM   #13
diyAudio Member
 
Join Date: Dec 2007
hi djk,

did you replace the original snubber / filters in the carver, or did you add this ?
as i said, i havent got the circuit in front of me untill i get back to the workshop next weekend, but i'm curious as to how much it improved the amp.

jonathan
  Reply With Quote
Old 26th March 2008, 03:49 PM   #14
djk is offline djk
diyAudio Member
 
djk's Avatar
 
Join Date: Feb 2001
Location: USA
I removed the commercial Corcom filter in a couple of Carver M1.0t and replaced with this circuit.

It seemed to make it quieter at low volumes.
__________________
Candidates for the Darwin Award should not read this author.
  Reply With Quote
Old 26th March 2008, 06:18 PM   #15
diyAudio Member
 
Join Date: Dec 2007
ah - i'm not familiar with the pm1.0t

i have a few racks of pm1.5's and a single pm2.0t.
the 2.0t has a push-pull switchmode supply running at the stupidly chosen frequency of 1kHz ! lovely!

i cant remember how they do the filtering in the 1.5's - i'll investigate next week when i'm home.
j
  Reply With Quote
Old 30th March 2008, 06:44 PM   #16
diyAudio Member
 
Join Date: Dec 2007
i've got the circuit diags for the carver 1.5 here - i don't have an actual amp in front of me to double check - but i can see they've been pretty mean.

The AC line comes in and there is a 0.47uF (Class-X) across it. The Live terminal also has a 0.01uF (Class-Y) to earth with a 3.9M / 1/2 W bypassing it.

The live goes through the triac, and then through the transformer primary, and out to the neutral terminal completing the circuit.

the triac snubber was a 0.1uF(X) in series with an 18R / 1/2W (although there is an ammendment drawn on the sheet to say this should be a 51R (possibly for 240V) as the layouts came from the UK service agent.

No wonder it upsets everything !


As for the PM2.0t (with its awful switchmode PSU), we have slightly better filtering...
typically - my circuits for the 2.0 are with the 2.0, in the warehouse, but from memory live and neutral each had an open choke - about 10 turns of 1.2mm copper wire on a 12mm diameter, with a 9mm cube of ferrite glued in the centre.
this was then followed by the usual class x and class y capacitor filter that you would find in any SMPSU.
The 2.0t used a pair of obsolete darlington transistors MJ10025 20A/800V/250W to drive the primary in centre-tapped push-pull mode.
I have never found an equivalent for these, although i did manage to pick some up on ebay.
The snubber arrangement for the psu drivers is 'interesting'.... 2 x ceramic 11W resistors each in series with a class X cap ... all wrapped in a tube of cardboard and literally shoved in loose on some flexible wire.
don't think that would get a CE mark nowadays !

jonathan
  Reply With Quote
Old 19th June 2012, 08:56 PM   #17
srinath is offline srinath  United States
diyAudio Member
 
Join Date: Feb 2010
Default Inside the amp ?

Quote:
Originally Posted by djk View Post
A typical filter will not work properly with a Carver, try this:

Click the image to open in full size.

Hi,
I have a M1.5t with a big ground hum. Now id this circuit supposed to go inside the amp - I mean that Transformer in your circuit is the one in the amp, we dont add an external trafo right ?
Thanks.
Srinath.
  Reply With Quote
Old 19th June 2012, 09:28 PM   #18
diyAudio Member
 
Join Date: Dec 2007
Hi Srinath, The picture is detailing the snubber around the Triac, so the Triac and transformer are already in the circuit.
I don't have the circuit for the M1.5t, but the principle is the same for many of their amps (with the exception of the 2.0t which uses a conventional SMPS supply running at 1kHz).

You describe the sound as 'ground hum'.
we usually associate ground hum with incorrect earthing or tired filter caps.
the sound we're talking about on this thread is a sharp buzz caused by the triac's switching spikes... these can travel back down the power cable into mixers, crossovers etc.

It's worth getting a scope onto the DC power supply rails and checking them for symmetry with, and without load. The No. 1 fault i find in these amps is dried-out power supply caps (usually the 50V rails, not the 110V ones).
  Reply With Quote
Old 19th June 2012, 10:23 PM   #19
srinath is offline srinath  United States
diyAudio Member
 
Join Date: Feb 2010
Oh OK and I got 3.1v at the transformer input and almost 0 on the output side.
This is @ the transformer when it was playing from my cd player, basically not at idle.
Thanks.
Srinath.
  Reply With Quote
Old 20th June 2012, 01:30 PM   #20
srinath is offline srinath  United States
diyAudio Member
 
Join Date: Feb 2010
Now how can this amp make that much ground hum with that little voltage ? It is really loud, way more than what it can make IMHO if its getting nothing out of the transformer.
So when its working what voltage should I see out of the transformer ?
Thanks.
Srinath.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Amp for IB with low idle consume wingman Class D 5 23rd July 2009 12:53 PM
Carver PM-1.5 Amp buzz humm SoundQuest Solid State 3 24th June 2008 09:36 PM
Carver PSC-60 Preamp - Buzz. AltheaToldMe Digital Source 0 27th January 2008 08:46 PM
Melos triode and computer as source: BUZZ BUZZ BUZZ zigo3 Tubes / Valves 4 28th November 2007 02:11 AM
aleph2,3,5 idle dissipation ? kslim Pass Labs 6 3rd September 2004 04:29 AM


New To Site? Need Help?

All times are GMT. The time now is 11:33 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2