FDP Forum / Hot Rod Deville Loud Hiss/Crackling/ 36 messages in thread.

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STR87



Panama

Nov 19th, 2017 11:28 PM        

Hi,<br /> I was recently playing and my HRD amp started making a loud hiss and crackling noise. Now it seems to appear as soon as i turn on the amp and flip the standby switch.<br /> * Changed the tubes and nothing.<br /> * When i plug into the power amp in, the noise is gone.<br /> * I checked all the plate resistors and they seem fine.<br /> * I've got voltages on pin 1 & 6 of every preamp, and pin 3 of the power tubes.<br /> * Screen resistors seem fine.<br /> * guitar sounds fine behind the noise. (no volume drop).<br /> <br /> Any ideas?? i'm going crazy trying to nail down the culprit!<br /> Thanks for the help



Peegoo

Contributing Member
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Enjoying

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Nov 20th, 2017 08:14 AM        

If it's the classic Fender "bacon frying" sound (and the tube sockets are tensioned and you have good preamp tubes in) it's probably the plate load resistors. <br /> <br /> Testing a resistor for Ohms spec will not reveal the defect that causes the noise. <br /> <br /> Replace 'em with 1-watt metal film type. Many amps now come equipped with carbon comps here (they're cheaper), but they also have a higher noise/failure rate.



SonicBlue



Sunbury-on-Thames

Nov 20th, 2017 08:15 AM        

Is the noise present on the Preamp Out socket?



Hammond101

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So. Cal. USA

Nov 20th, 2017 10:18 AM        

+1 on everything above.<br /> <br /> What happens if you put a jumper in the FX loop? Bad/dirty jacks here are sometimes overlooked. Does the noise go away when you plug in a guitar? You may also have failed solder joints at the input jack/board connections.<br /> <br /> You may have cracked solder connections where the tube socket pins meet the daughter board. Very common failure and hard too see. <br /> <br />



STR87



Panama

Nov 20th, 2017 11:50 AM        

I Turned the amp on today and got no noise, after 10min it came creeping back again. Sound's like and old radio looking for a station (the in between station static kind of with a little crackling). <br /> *Noise still in the preamp in, also when i jumper the fx loop<br /> *With the guitar plugged in the sound is still there louder than the guitar sound.<br /> * I checked again all the plate voltages and they seem normal (about a 37% drop across the 100k resistor). 389v to 244v.<br /> * Shook a little all the tube sockets while the amp was on with noise but didn't hear any changes. joints seem fine here.<br /> * did the same with the inputs and jacks and nothing.<br /> * I get noise on the drive also.<br /> * the eq seem to affect the noise (cutting treble or adding bass would accentuate this on the noise.<br /> <br /> Still thinking on changing the plate load resistors anyways to get them out of the equation!



STR87



Panama

Nov 20th, 2017 01:51 PM        

UPDATE:<br /> * The noise seems to go away completely after aprox. 10min for 2min then resumes back in.<br /> (waiting for the 82k and 100k resistors to arrive).



SonicBlue



Sunbury-on-Thames

Nov 20th, 2017 02:04 PM        

"* the eq seem to affect the noise (cutting treble or adding bass would accentuate this on the noise."<br /> <br /> This narrows it down quite a lot to the circuitry around V1.<br /> <br /> While you're waiting for the resistors to arrive try removing V1 and firing it up. Hopefully it will be lovely and quiet. If that's the case reflow all the joints on the valve base, replace V1 and try again.



STR87



Panama

Nov 20th, 2017 02:30 PM        

"Try removing V1 and firing it up."<br /> I just removed V1 and the noise is still there.<br /> *I did the same without V2 and no noise yet! wow i'm getting closer hopefully



Peegoo

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Nov 20th, 2017 03:37 PM        

It's on the V2!



STR87



Panama

Nov 20th, 2017 10:49 PM        

UPDATE:<br /> Still checking V2<br /> *Socket joints and grey ribbon look solid. I've been rocking the socket to hear any changes but nothing.<br /> *Plate voltage normal.<br /> *Did another tube swap but nothing.<br /> Any ideas to pin the problem down?



willie

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Too Near Atlanta GA

Amp Tech Emeritus
Nov 21st, 2017 08:19 AM        

I would be especially suspicious of dirty contacts on stereo jack J3 which does couple the output of the preamp stages to the phase inverter. Like has been aptly mentioned, these jacks (all of them) are prone to failure due to debris causing intermittent connections in the signal chain. I recommend as a precaution prior to digging into the "innards" that you attempt to clean the jacks with a lubricant free electronic contact cleaner...do not use one with a lubricant such as mineral oil in it. Then, after spraying the cleaner into the jack, plug and unplug a 1/4 inch plug into the jack a few times and see if this causes the symptom to go away. It's worth a shot. <br /> <br /> willie



SonicBlue



Sunbury-on-Thames

Nov 21st, 2017 10:18 AM        

If cleaning the jacks doesn't clear it, without the amp in front of me I'd plump for R11 being the culprit, the anode resistor for V1b.<br /> <br /> I'm going for this because it's still sort of in circuit with V1 removed and the fact the tone controls affect the noise. <br /> <br /> Remove V1 it's still noisy so fault is after V1. Remove V2 it's quiet so fault is before or in V2. Tone controls affect noise so it must occur in or before tone stack but after V1b. A crispy R11 is the most likely, capacitative coupling notwithstanding. High impedances play funny sometimes.



STR87



Panama

Nov 21st, 2017 03:23 PM        

UPDATE:<br /> Did clean all the inputs especially J3 with contact cleaner and a 1/4 plug, the noise is still there.<br /> * Rechecked R11, meter shows accurate resistance and dc readings. (how can i make sure that resistor is 100% fine).<br /> * I can dial out the noise turning off all the eq dials. Volume dial doesn't affect the hiss. (TONESTACK MOD - jumper across the mid dial lug).<br /> *Traced all components before V2 and rocked them a little to hear any audible differences and nothing.<br /> **this past weekend my friends studio room got flooded for a couple of days but NO water touched my amp thank g-d** <br /> <br /> Any other places to look for?<br />



willie

Contributing Member
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Too Near Atlanta GA

Amp Tech Emeritus
Nov 21st, 2017 04:10 PM        

Good job...needed to get that eliminated. Frying sounds can most certainly be the phase inverter plate load resistors which you have on order. Beyond that, it appears that you will have to start component checking which is facilitated by a cap meter, ESR meter, scope and audio sig gen as well as a good digital volt/ohmmeter. <br /> <br /> Diagnosing a problem is never easy over the internet beyond the usual fixes. In the shop, we could check a dozen or more likely issues in the span of a few minutes...meaning that nothing takes the place of having the amp in front of us on a well equipped bench. :) <br /> <br /> You could possibly have a snafu in your tone stack...regardless, it does sound like an intermittent issue, possibly electromechanical in nature (bad solder joint or similar). <br /> <br /> willie



STR87



Panama

Nov 21st, 2017 06:45 PM        

Should i be replacing the plate load resistors with 1/2W or 1W?<br /> I see voltages above 350v on those, schematic call's for 1/2W, would it make any sonic difference going with 1W?



willie

Contributing Member
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Too Near Atlanta GA

Amp Tech Emeritus
Nov 21st, 2017 08:38 PM        

No difference...we always used 1 and 2 watt resistors but largely because we ordered in large quantities and it saved us money. <br /> <br /> w



STR87



Panama

Nov 21st, 2017 10:22 PM        

Thanks W,<br /> I saw C60 a little chipped off, will change it. It's 220pf cap, any idea what is the voltage rating on that cap?<br /> I'll be opening the amp guts on TG to do some checking. will post results on my finds!



willie

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Too Near Atlanta GA

Amp Tech Emeritus
Nov 22nd, 2017 07:40 AM        

I'm not seeing any reference to a C60 cap in the tech manual we have on file for the HR Deville. <br /> <br /> w



STR87



Panama

Nov 22nd, 2017 09:36 AM        

Yes that's weird. I started looking and it's on the new Hot Rod Deville III revB schem!



STR87



Panama

Nov 22nd, 2017 09:38 AM        

Sorry it's C61



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