Lilkey DC problem. RSP 1068 clicks faintly when...

[gp4Jesus]

...changing surround decoding or sources while connected to one of my a Belles Series 1 amps.

What I'm really concerned about, when connected to my other Belles the left channel pops loudly and trys to suck the mids & woofers into the cabinet.

Dead silent connected to a Hafler xl-280.

how to fix?

[Glen B]

I think the faint clicking that you hear when you change decoding options or sources is very likely coming from relays employed in switching/signal routing. Perfectly normal.

You could have a DC offset issue somewhere. At first I though the Hafler amp may have a blocking cap at its input, and that's why you don't have a problem with it, but after doing some checking, the XL280 is direct coupled, so that's not it.

I suggest that you get the processor and Belles amp both checked for significant DC offset. If you have a digital multimeter (DMM), you can do this yourself. Set the DMM to the millivolt DC (mVDC) scale. With the units under test turned on and nothing connected to the inputs or outputs, place the meter test probes across the outputs and take a reading.

DC of a couple hundred mV or more will cause the popping and mid/woofer cone movement you are experiencing. Checking for DC (a symptom of a problem) is only a preliminary step. The cause of your issues will need to be diagnosed before we can talk solution.

[gp4Jesus]

Thanks for the reply and taking the time to be thorough-Hafler SILENT in spite of direct coupling; learned something new!

I guessed a DC issue when I saw (one channel's) drivers ONLY get sucked IN, hard, for just a moment, then return to rest. BTW The clicks are VERY faint on both channels of the other amp.

Also, some operations on my DVD player would do same even w/optical connection.

After I check the offset, if you can describe what to look for & where to look w/a DMM...

In search of Belles schematic, I started one thread (I'll pay) & posted replies to others on DIYAudio.com. If any one on this forum knows where I can get one...


"Mille Grazie" Italian for Thousand thanks, tony

[Glen B]

Also, some operations on my DVD player would do same even w/optical connection.

Like in the processor, faint clicks in the DVD player during some operations should be normal, the sound of relays performing switching.

After I check the offset, if you can describe what to look for & where to look w/a DMM...

As I said above, first you have to read the mVDC on the DMM and report the figures. I can't give you an answer until I know what levels of DC (if any) you're getting.

To check for DC in the processor channels, you will have to use a short bit of RCA cable with the insulation stripped off one end. Plug the jack into each processor output and connect the meter probes to the bare hot and cold wires on the other end. To check the amps, connect your probes to the positive and negative output posts. Again make sure nothing is connected to the inputs.

[gp4Jesus]

Like in the processor, faint clicks in the DVD player during some operations should be normal, the sound of relays performing switching.

Sorry for the ambiguity. The "DVD operational" clicks (or pops), amp dependent of couse, mentioned in my previous post, come from the amp/speakers.

I will report DC offset data in next post.

Again, "Mille Grazie" , tony

[gp4Jesus]

1.03V DC offset! (left channel....)

Glenn B:

Right channel measured 153ma on the 200m (200ma?) scale.

I thought I posted the all DC offset data for both amps w/my Blackberry over the weekend. Either way this confirms what you and I suspected. I'll take readings again after both amps have been powered up for 30 minutes*.
* if that matters

Now if I could obtain a schematic...

thnx tony

[Glen B]

You did mean 153mV not mA right ? 1.03V DC huh ? Try contacting David Belles at Power Modules, Inc. to see if he will provide you with a schematic. You may be able to reduce the DC by adjusting the offset trimpot, in the absence of a schematic. However, with the amount of DC you have and age of the amp, more than likely the components in the differential stage may need to be replaced, in which case, you WILL need the schematic. Another member had a similar problem with his Rotel amp. He was able to reduce his DC offset to an acceptable level. You will need to shoot for ±0mV-15mV.

http://www.htguide.com/forum/showthread.php4?p=507954#post507954

http://www.powermodules.com/power_modules/Contacts.html

[gp4Jesus]

Yes, I meant 153mV. Thanks for your help & the Belles/Power modules link.

BTW the other Belles w/the faint clicks (the Clicker!) both channels measured under 50mV.

Does it matter that the amps were on for less than a minute before I took readings?

Mille grazie, tony

[Glen B]

Yes, it matters that the amps were on less than a minute, at least the one measuring under 50mV. Some amps can have a moderately high DC offset that goes down as they warm up. The amp with the 1V+ offset, you know that's too high period. The second amp though, you may want to have warm up for at least 15 minutes and see what the offset is after that time.

Can you identify the DC trimpots ? You could try adjusting those to zero out the offset. Are both amps the same model ? Does the amp that is clicking have output relays ? 50mV DC should not be high enough to activate protection circuitry, although it is not impossible for the manufacturer to have set such a low threshold.

[gp4Jesus]

Glen B, pour yourself a tall one & get comfy. I hope all of my responses & questions are clear; none of my footnotes confuses anything. This reply comes from my Blackberry.
[QUOTE=Glen B] Yes it matters the amps were on less than a minute...
[/QUOTE=Glen B]
I'll power them* up when I get home-1 hour+. I should be alone tonight for 2+ hours allowing QUALITY** time for partial diassembly to get a good, long look & check the things you suggested.
* Haflers, too although their offsets in the single digits
** I have 8 kids
[QUOTE=Glen B]
Can you identify the DC trimpots ? Does "clicker" have output relays ?
[/QUOTE=Glen B]
Took a quick glance before leaving this AM. Didn't notice any pots* or relays** on the top*** board.
* assuming I see one & its NOT for bias
** 30 amp relays are stout-easy to see I'm sure
*** 2 boards layered vertically

Belles may have spent $ for quality multi-turn* pots*, unlike Hafler-explaining why I haven't noticed them (yet).
* TnT-audio's article on bias adjustment-author touches on cheap pots, their effects on DC offset, & pot replacement


What's your take on pot replacement to fix offset problem(s)?

Side note: these amps seem to have just an AC line fuse. The Haffies have fuses on the (finals) PS rails, speaker outputs, & AC line.

[QUOTE=Glen B]
You could try adjusting the DC trim pots to zero out the offset
[/QUOTE=Glen B]

When I attempt to tweek DC offset, what will tell me I'm twisting the correct pot? Can tweeking bias affect DC offset? Can tweeking DC offset affect bias? I refer you my TnT-audio coments above.

If the amps have DC trim pots, can I expect instant change while tweeking? Or is it like bias tweeking; "give the circuit time to stabilize after ajustment." Either way I'll connect my DMM to the outputs to watch the changes.

Somewhere in the midst of this I hope to tweek bias.
[QUOTE=Glen B]Are both amps the same model ?
[/QUOTE=Glen B] Yes. The "clicker" ser# 100 series; the "popper", #224. I mention this because the driver board layouts* & PS transformers** differ.
*quite a bit ** slightly

If I have time I will listen to Popper's other channel for clicks.
[QUOTE=Glen B]50mV DC should not be high enough to activate protection circuitry
[/QUOTE=Glen B]
I'll take new readings first thing, post them later tonight.

Yesterday I sent an email w/Popper's ser# to power modules requesting a schematic. Will follow-up by phone tomorow.

After receiving your reply & before I finished editing this, I received a reply from a diyaudio thread I started last week entitled "will pay for Belles 1 Series amp info & Schematic"

I will STILL call Power Modules tomorow If I don't see or hear anything by mid-day.


Thanks for your help,support,& guidence Glen, tony

[Glen B]

About 30 minutes warmup time should be more than enough. If the Hafler DC readings are below 25-30 mV, those are acceptable values. The XL-280 has only bias adjustment pot, no DC trimpot, relying only on close matching of the differential transistors to keep DC offset low. Let me know if you need a copy of the schematic.

If a pot is bad, it can problems adjusting and maintaining stable DC values. If a cheaper pot is in good condition, its a judgement call whether or not to replace it with something better.

We've already established the Haflers have no DC adjustment pot, so these comments are for the Belles units (if they have the pots). As you adjust a DC trimpot, the DC reading will change. Yes, like bias, give the amp time to stablize between adjustments. Bias and DC are independent, tweaking one will not affect the other. You will need to find out what the recommended bias values for the amps are before you can perform bias adjustments.

[gp4Jesus]

Glen: tonight's quality time was pre-empted by a date night at a just-opened italian resturant!

I did power up the amps. About 30 minutes later, took some readings* and a good look inside under bright lights: NO pots on top board in either amp.
Bottom appears have "swamp" (big, rectanglular, ceramic) resistors and little else.
*Clicker: 33 mV. & -74 mV
*Popper: 150 mV & 1.02 Volts
Yeah, both have issues.

Got a reply w/serial numbers to the diyaudio "schematic" post.

Used the Hafler stuff for comparison. I'll limit future discussion to Belles.

Will re-take readings* & another good before bed.
*will post later if different

Yours, tony

[Glen B]

Tony,
It is probably best to continue this discussion privately, since it is not Rotel related.

Glen

[gp4Jesus]

Spoke to Dave Belles today.

"Send them to me, I'll take look at them. Get them up to snuff" he said. " Schematics are our intellctual property. We don't hand them out."

"I'm willing to pay for it."

"Its our policy. Sorry."

W/a notebook handy & Popper powered up, I'm going to poke around some more w/a DMM before I completely give up.

Glen, Thanks for your patience & replies.

Merry Christmas, Felice Natale
Tony

Tony

[Glen B]

You may have no choice but to send them to Belles for service. I suspect the unit with high offset will very likely need parts replacement. This would be made more difficult without a schematic. I can understand not wanting to give out schematics for current products, but stuff that's a couple decades or more old ?
This is like how Classe used to shave off part numbers on transistors and op-amps, and leave them unidentified in their schematics. Now it turns out those "secret" parts are just regular old ones, commonly used by everyone else.

[gp4Jesus]

I can understand not wanting to give out schematics for current products, but stuff that's a couple decades or more old ?

About 20-25(+) years

[gp4Jesus]

#7 Today, 11:51 AM
gp4Jesus
New Member Join Date: Apr 2010
Posts: 13

Re: Likely DC problem. RSP 1068 clicks faintly when...

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I invite anyone interested in following my progress and provide input w/solving these problems, to click on the links below.

this is DC offset problem, one severe, w/2 Belles 1 power amps. Go to post #3 for more mind-blowing data!
http://www.diyaudio.com/forums/solid...schematic.html

In the next link you will find drawings of:
1. the artwork, post #16
2. circuit diagram-referred to as "My Drawing", post #20
3. very important: in post #24 currently the latest, several corrections, one critical, to My Drawing.
http://www.diyaudio.com/forums/solid...hematic-2.html

I feel very confident, with the knowledge & experience on these forums, WE will solve the offset problems!

PS: no adjustment pots DC offset or bias in these amps

Merry Christmas tony