jheis Posted October 15, 2004 Share Posted October 15, 2004 I have a Carver TFM-45 Amp (375w) that works fine except that I get a rather loud POP or thump when I power down. I know that this can't be good for my speakers, so, since I'm running it through a Niles Audio speaker selector, I disconect the speakers before I turn off the amp. Any idea what is wrong with the Carver? It didn't do this for the first 6-8 years of its life. Any advice/comments would be appreciated. James Quote Link to comment Share on other sites More sharing options...
Griffinator Posted October 15, 2004 Share Posted October 15, 2004 That's probably a short between the power switch and the supply. Get it fixed post-haste, because every time you power down, you are damaging those speakers. I had this happening on a Gallien-Kreuger guitar amp once. It was not a fun ordeal. Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted October 15, 2004 Share Posted October 15, 2004 A pop across a power switch is common. I install snubber capacitors across the switches of my components, and these can be just easily found and inexpensive ceramic capacitors. Any electronics technician can do this for you, and requires two soldered joints. What would work for this is a .01uf HIGH VOLTAGE ceramic cap. Radio Shack used to carry this capacitor in something like a 3K volt rating, but I haven't seen them for awhile. They seem to be downsizing there parts selection in order to sell more plastic electronic toys and gadgets. The capacitor absorbs the spark that would otherwise travel down the system and out of the speakers. If you are hearing more of a heavy 'thump' on powering up or down, that can be related to some other things Quote Link to comment Share on other sites More sharing options...
djk Posted October 15, 2004 Share Posted October 15, 2004 The Carver does not have a power switch in the sense that you guys are thinking, don't mess with it (a triac is used in a phase control mode). Your filter caps are no longer new and are discharging at different rates, use your speaker switch (unless you want to spend big bucks). Quote Link to comment Share on other sites More sharing options...
RAPTORMAN Posted October 15, 2004 Share Posted October 15, 2004 Do you have a preamp?? If you do--this is the way I do mine: 1. I turn on the preamp first wait for about a minute. 2. Turn on the source cd player or TT or whatever. 3. Turn on the amp. 4. Wait for 5-10 minutes and enjoy the music.( 5-10 minutes because they are tube amps) To turn it off: 1. Turn off the amp 2. Turn off the source 3. Turn off the pre amp Quote Link to comment Share on other sites More sharing options...
D0N Posted October 15, 2004 Share Posted October 15, 2004 I had a phase linear pl400 that did that every time I powered down. Very loud! Some amps are known for that. It was the cause of a blown tweeter diaphragm in a cornwall. Be careful with that! Quote Link to comment Share on other sites More sharing options...
RIklipsch Posted October 15, 2004 Share Posted October 15, 2004 ---------------- On 10/15/2004 1:30:04 AM jheis wrote: I have a Carver TFM Amp (375w) that works fine except that I get a rather loud POP when I power down. I know that this can't be good for my speakers, so, since I'm runing it through a Niles Audio speaker selector, I disconect the speakers before I turn off the amp. Any idea what is wrong with the Carver? It didn't do this for the first 6-8 years of its life. Any advice/comments would be appreciated. James ---------------- James, The problem has nothing to do with the power switch. Modern amplifiers such as your Carver use a differential input amplifier, and OCL (output-capacitor-less) output stage, also known as DC Coupled. This eliminates an output coupling capacitor for improved sound. The differential input stage allows for 0VDC on the output stage. You have DC (direct current) voltage on one of your speaker channels. Using a DC VOM set to the millivolt range, measure the voltage of the affected channel from the speaker outputs. Refer to the instruction manual on how to adjust DC Offset (may also be called DC Balance). The manual will refer to a potentiometer, for example "VR-301". Remove the bonnet on the amplifier to access the driver board where the pot will be mounted. Follow the service manuals instructions. With a simple VOM, this is very simple. You want to adjust the output voltage so that it is 0, +/- 30 mV. Over the years, transistor characteristics drift, causing the DC Offset to be off. DC on the speaker outputs in excess of 30 mV can damage speakers, especially efficient speakers. Be sure there is no DC Offset voltage before you power up the Carver again. -R.Inman Quote Link to comment Share on other sites More sharing options...
jheis Posted October 15, 2004 Author Share Posted October 15, 2004 R. Inman Thanks for the advice. My instruction manual doesn't go into that kind of depth nor does it provide schematics. I don't have a service manuel. Are you talking about a DC voltage from an output terminal to ground or measured across the terminals? Obviously the amp whould have to be powered up for there to be any voltage and I assume the measurement would be done without any input. James Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted October 15, 2004 Share Posted October 15, 2004 James: Ok, I took some more time to read your post, and you did mention that this is kind of like the thump to which I referred in my response to this. I have no idea what kind of power switch the amp uses, and the capacitor 'cure' I mentioned is in fact more common on older equipment. My brain seems to work better with less modern things, for some reason -- probably because they are often more simple! But as Ryan says, there are adjustments that can be made to at least bring this noise down to a more tolerable level. Many SS amps will produce a similar effect when powering down, but at a level that won't damage delicate speaker voice coils. And this is in no way to say anything against what Ryan says, because he knows more about this than I, but if you are not familiar with working with electronic equipment, have someone else work on it for you who does. Touch the wrong thing, such as a charged high voltage power supply filter capacitor, and you will get a shock that you'll remember. It's not worth the risk -- IMO. Some techs who work with electronic equipment can be unfairly expensive (this is AUDIO afterall!), and you could possibly end up paying more for the repair than the amp costs -- although I have no idea about what amp it is, when it was built, etc. Best of luck, Erik Quote Link to comment Share on other sites More sharing options...
RIklipsch Posted October 15, 2004 Share Posted October 15, 2004 James, It would be pretty difficult to make this adjustment without a service manual. The best advice I could give you is to find an authorized Carver service center in your area to make the needed adjustments or repair work for you. And Erik is certainly correct about the potential shock hazard. With over 300W of output, you're looking at 85V+ positive and negative rails in this unit. If you had the service manual, it would be easy, but going in blind is never a good idea. Sorry I could not be of more help. -R.Inman Quote Link to comment Share on other sites More sharing options...
RIklipsch Posted October 15, 2004 Share Posted October 15, 2004 ---------------- On 10/15/2004 5:32:32 PM jheis wrote: R. Inman Thanks for the advice. My instruction manual doesn't go into that kind of depth nor does it provide schematics. I don't have a service manuel. Are you talking about a DC voltage from an output terminal to ground or measured across the terminals? Obviously the amp whould have to be powered up for there to be any voltage and I assume the measurement would be done without any input. James ---------------- Correct, James. The DC Voltage would be measured across the actual speaker terminals. You can safely make this measurement with no speaker load connected. Once you verify that this is indeed the problem, you may save yourself some money, being able to mention this problem to the repair tech. If you take the measurement and get over 30 mV on either channel, shut it off immediately. Generally, when a solid-state amplifier begins to make a loud THUMP when powered down, it is about to fail. The output transistors would be the first to fail, and they are rather costly for your high powered amplifier (probably Mototola MJ21194 or equal) -R.Inman Quote Link to comment Share on other sites More sharing options...
jheis Posted October 16, 2004 Author Share Posted October 16, 2004 R. Inman & Erik: Thanks again. I found a listing for Carver manuals - it may be old since Carver has been out of business for awhile, but I may be able to get a service manuel. In a past life, long, long, ago I had some training as a radar electronics tech in the Air Force (it didn't take - they kicked me off the flight line to an office job - I'm a lawyer now) so, while not a techie by any stretch of the imagination, I'm not totally clueless. I've got an adequate VOM and know not to test live circuits using the wet finger method, but I also know it's not smart to just dive in and start tweaking things. The Carver amp is dormant at the moment, but I've picked up two pair of Heresys to go with my Cornwalls and hate to have a 375 w/c paper weight just sitting there. I'd like to put it back in the game. Besides, to my ears, the Carver sounded pretty sweet - except for the THUMP when I turn it off. James Quote Link to comment Share on other sites More sharing options...
djk Posted October 16, 2004 Share Posted October 16, 2004 "The problem has nothing to do with the power switch." Glad we agree on something. "You have DC (direct current) voltage on one of your speaker channels." I doubt it. The amp only makes noise when being powered down. "Refer to the instruction manual on how to adjust DC Offset (may also be called DC Balance)." Carver amps do not have DC off-set controls. "Over the years, transistor characteristics drift, causing the DC Offset to be off." The diff pair in a Carver amplifier are monolithic (made on a common substrate) so they drift together, and are laser trimmed when fabricated. "DC on the speaker outputs in excess of 30 mV can damage speakers, especially efficient speakers." Music waveforms are highly asymetric, 12dB on piano can be seen on an o-scope. Most pro amps set the DC trip around 8V~10V for that reason. A Klipsh K33 woofer is rated for 40W DC, 30mV is only 0.0001125W (that's 112 micro watts at 8 ohms). "Be sure there is no DC Offset voltage before you power up the Carver again." And how is he to do this without turning it on? "you're looking at 85V+ positive and negative rails in this unit." Try ±125V at idle. If you get your fingers in the wrong spot you can get 250V across them. Like someone who was an authorized Carver dealer and service center previously said: "Your filter caps are no longer new and are discharging at different rates, use your speaker switch (unless you want to spend big bucks)." This is big bucks in a Carver amp because of the ±125V on the main caps, plus there are another pair at ±80V and another pair at ±40V and another pair at ±15V. Caps are like roaches, get 'em all or you're wasting your time. Quote Link to comment Share on other sites More sharing options...
InventiveAudio.com Posted October 19, 2004 Share Posted October 19, 2004 What is a speaker switch? Quote Link to comment Share on other sites More sharing options...
NOSValves Posted October 19, 2004 Share Posted October 19, 2004 Usually it turns the speakers on/off Quote Link to comment Share on other sites More sharing options...
rigma Posted October 19, 2004 Share Posted October 19, 2004 If I turn off my Crown amp via a switch on a power strip I get a loud thump. Using the amp switch, no thump. Question is could I add a capacitor across power cord to stop this as Erik mentioned about the switch? Quote Link to comment Share on other sites More sharing options...
RIklipsch Posted October 19, 2004 Share Posted October 19, 2004 ---------------- On 10/19/2004 8:14:41 AM rigma wrote: If I turn off my Crown amp via a switch on a power strip I get a loud thump. Using the amp switch, no thump. Question is could I add a capacitor across power cord to stop this as Erik mentioned about the switch? ---------------- Yes, you can. Use an 0.047 uF 1000V ceramic disc capacitor. The capacitor is placed in parallel with the switch contacts, and the idea is that the capacitor opposes any change in voltage. The capacitor will "supress" the momentary switch "bounce", or pop. R. Inman Quote Link to comment Share on other sites More sharing options...
RIklipsch Posted October 19, 2004 Share Posted October 19, 2004 ---------------- On 10/19/2004 6:08:44 AM InventiveAudio.com wrote: What is a speaker switch? ---------------- You fix vintage amplifiers and have never seen a speaker switch? What the heck do you work on? Quote Link to comment Share on other sites More sharing options...
NOSValves Posted October 19, 2004 Share Posted October 19, 2004 ---------------- On 10/19/2004 11:45:58 AM RI wrote: ---------------- On 10/19/2004 6:08:44 AM InventiveAudio.com wrote: What is a speaker switch? ---------------- You fix vintage amplifiers and have never seen a speaker switch? What the heck do you work on? ---------------- Yup but I'm the one that attacks my competition !!! Nice guy Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted October 20, 2004 Share Posted October 20, 2004 Yes, you can. Use an 0.047 uF 1000V ceramic disc capacitor. The capacitor is placed in parallel with the switch contacts, and the idea is that the capacitor opposes any change in voltage. The capacitor will "supress" the momentary switch "bounce", or pop. R. Inman ...not to insult anyone's intelligence, but please unplug the power strip before you install the capacitor across the switch. Depending on the type of preamp you have, if you have one, the same can be done there ,as well -- as well as across the switches of your amps, garbage disposals, fans, light sockets, electric tooth brush, Tivili Model 1, food processor, blender, and toaster. Using one on your fish tank filtration system will feed high frequency noise back into the house wiring, which will in turn be heard through your audio system -- and has been said to also grossly narrow the soundstage. (actually, please take note of this only up to and including the amp switch -- actually don't inlcude the amp switch/es. Stop after the preamp application, since the preamp should be the first in the turn-on sequence. Quote Link to comment Share on other sites More sharing options...
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