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what to look for in blown Vali 1 ?
what to look for in blown Vali 1 ?
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Old 27th August 2019, 07:28 AM   #1
freddi is offline freddi  United States
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what to look for in blown Vali 1 ?
Default what to look for in blown Vali 1 ?

my rarely used Vali 1 with very low hours has appeared to bit the dust. It gave out trying to drive some (terrible) 250 ohm Koss Pro 4AAA Titanium cans with clean percussion.

I will double check to make sure it wasn't a DAC failue. Symptoms = garble, very high audible IM and HD on both channels. There is no schematic available from Schiit and long out of warranty.

Is the "coaster" amp reasonably close to a Vali 1?

It's not the first time I've kilt a headphone amp as the headphone section of my Zhaolu DAC caught fire.

(my solid state luck is poor - XK280, Mostet12, Samson F1200, Carvin with few hours, Hafler Trans-Ana and more have croaked - and those not driven hard.)

Why might the Vali have failed with just a few minutes of tough play ? Who makes a simple transparent comnercial amp suitable for vintage and modern planar cans? (my Sopviet cans are perhaps 6dB less efficient than T20RP MK2 - I have a new Bravo V1 but leery whether it will prove reliable as reviews note problems)

;
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Old 27th August 2019, 12:50 PM   #2
sgrossklass is offline sgrossklass  Germany
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Given your kind of luck, I'm inclined to suggest a Lake People amp, maybe the G103-S or -P (one is unbalanced RCA input, the other XLR). Maximum gain isn't super high (+14 dB in both versions, despite consumer levels generally being lower than pro levels), and their consumer level amps have not always shipped with the jumpers set right, but there is nothing to suggest that these aren't tough as nails. Kind of unsurprisingly so, given that the power amp stage in this particular model employs a 20+20 W speaker power amp IC (LM1876), besides this was LP's original claim to fame anyway.

Do look for an official US (115 V) version - some box shifters will apparently happily sell you a European market version (more common and presumably slightly cheaper, given that LP are based in Germany, and that includes assembly BTW), and while changing transformer wiring from series to parallel primaries isn't rocket science per se, it would constitute a bit of a nuisance at least. It looks like Power Holdings Inc. is the official distributor in the US. Violectric

As for the Vali, both channels being out suggests a potential power supply problem. No idea what voltages are generated in this one. It being replaced by a revamped design less than two years after launch does suggest some issues.
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Old 27th August 2019, 02:14 PM   #3
freddi is offline freddi  United States
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what to look for in blown Vali 1 ?
Thank you very much for the thioughts. I believe you're onto something regarding the power supply as that could affect both channels. Its powered by an external 16vac transformer so assume that part is good and something maybe have broken down in filtereing (or a regulator0 (?) Perhaps I can find some comments as to what problems it had.

FWIW - I just ordered one of those so-called JLH1969 assembled amplifiers so hope that will fujnction for a while.. (would it be good to add a capacitor on its output?)

I have some vintage low impedance headphones which could use a stout amp (including an old lower-range Koss electrostat)

Last edited by freddi; 27th August 2019 at 02:16 PM.
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Old 28th August 2019, 08:33 AM   #4
Mark Tillotson is offline Mark Tillotson
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Quote:
Originally Posted by freddi View Post
(my solid state luck is poor - XK280, Mostet12, Samson F1200, Carvin with few hours, Hafler Trans-Ana and more have croaked - and those not driven hard.)
Is your mains polluted with spikes perhaps? I'd be a little suspicious...

Quote:
Why might the Vali have failed with just a few minutes of tough play ?
Such high impedance phones will mean its outputing higher voltages than the designer probably considered (32 ohms is more common). This might be contributory factor with these drivers.
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Old 28th August 2019, 03:28 PM   #5
sgrossklass is offline sgrossklass  Germany
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Quote:
Originally Posted by freddi View Post
FWIW - I just ordered one of those so-called JLH1969 assembled amplifiers so hope that will fujnction for a while.. (would it be good to add a capacitor on its output?)
Erm, a '69 JLH is a speaker amp, usually single supply, so with output caps already included. It is not the same as the JLH headphone amp, which while based on it, is a lower power, higher performance circuit, generally with split supplies and DC-coupled output. (Actually there even were two different JLH headphone amp circuits.)
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Old 31st August 2019, 11:01 PM   #6
freddi is offline freddi  United States
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what to look for in blown Vali 1 ?
the headphone amp with split supplies is the one coming - seller says DC offset runs 10mV - 60mV
-( I already have the 1969 circuit cap coupled single supply JLH design)
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Old 15th September 2019, 10:48 PM   #7
nigelwright7557 is offline nigelwright7557  United Kingdom
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If you have a very noisy mains it can sometimes kill amplifiers.
Nasty spikes get through and push transistors out of the SOA.
On one of early designs I skimped on decoupling and on unplugging my soldering iron the glitch blew up the output transistors.

Other than that keep away from cheap ebay or Chinese stuff.
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Old 16th September 2019, 09:27 AM   #8
xrk971 is offline xrk971  United States
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what to look for in blown Vali 1 ?
Given how many of your amps have died I wonder if your source might be the culprit. What is the source and how many volts is it capable of making? Perhaps you have a tube preamp driving these? Is it cap coupled and maybe missing a bleed resistor that allows maximum voltage to build up on output cap? You might look at adding some transzorb clamp diodes on the inputs until further notice.

Garbled sound sounds like damaged transistors. Check PSU walwart to see if still making 16vac.

I suspect you have a blown input stage on all of these amps.
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Old 16th September 2019, 12:39 PM   #9
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+1 ... I would also recommend to inspect your mains.
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