Damaged amp - advice please guys

Hi all. I'm after a bit of advice please, particularly from people with some electronics knowledge if possible.

Long story short... I bought a nearly new (expensive - 2.5k) headphone amp from a guy in the USA. I asked him to ship it to the maker of the amp to have the voltage changed to 240v (I'm in the UK). So, all went fine until the amp finally landed with me today and it's misbehaving. Basically, it's gain is WAY too high. I can only turn the volume knob a couple of millimetres before it's ear-splitting with my HE1000. I checked with the previous owner and he confirmed he had the knob at 9 o'clock with his HE1000, which sounds fine.

The amp maker and guy who did the voltage mod says it was fine when it left him. I'm an electronics dummy so don't know what to think, but it does seem pretty odd that the output is so high (clearly a fault, the amp maker guy agrees) after a voltage change. He hasn't said as much but basically he's claiming it must have been damaged in transit. Seems like quite the coincidental fault to me.

Could anyone with a bit of electronics knowledge comment on whether this is plausible or not please? I'm pretty gutted as this was meant to be my end game amp at last. Many thanks.

 

IMO the person you should talk to is the amp maker.
Ask him that if you should open the amp up and take pictures, and where you should pay special attention and take close-ups. It could be any problem but my guess would be loose sockets like opamp or tube. But then again you won't get much help from the forum, much less so without detail and pics.

 

Thanks. I guess I was after a steer on whether this kind of fault could be caused by the amp jostling around in transit. Sounds like it could from what you're saying. I am of course also in touch with the amp maker but he seems pretty solid on the side of "it ain't his fault".

 

Ok, another dumb question please . If a 120v amp (solid state) is plugged into 240v mains... is it possible that, rather than blowing something up, it'd just sound twice as loud?

 

It makes sense to me. The rail voltages in a solid state amp are related to the voltages coming from the transformer. If the incoming voltage is twice as high then the rail voltages should higher as well. If nothing blows up then you have an increased power output. I don't know if increased rail voltages affects gain but I wouldn't be surprised if it did.

 

By the way, is this a valve amp? If so then try using a different set of valves.

 

transformers have primaries that are specific to the country's established household AC mains voltage. many off-the-shelf transformers available in the US have dual primaries where the primaries can be wired for either 115V or 230V. presumably, your amp had dual primaries and the builder re-wired them for 230V. the resultant voltage on the secondaries of the transformer feeding the PS should be the same when powered by 230V assuming the builder used an auto/step-up transformer to bring the 115V mains to 230V. assuming this, all other voltages throughout the circuit should remain the same as well.

it's hard to diagnose without being able to open the amp up. i wouldn't recommend poking about unless you know what you're doing. you should bring the amp to a local repair shop with a schematic in hand.

 

Good luck getting the schematic. He probably considers that proprietary and
he'll need to reverse engineer the amp to get a schematic.

 

Thanks guys. It's a solid state amp (Wells Audio Enigma). The chap I've been dealing with at the builder's isn't a techie it seems. He's checking with his technical guy on Tuesday whether he actually did change the voltage. Incidentally, it still has a "120v" sticker on the back. I'd expect he'd have replaced it if the voltage change had actually been done. If this is the case, I feel very fortunate that I haven't destroyed anything by hooking it up to 240v !

 

Have you considered opening it up to take a look/pictures of the transformer? Normally the transformer windings are marked to indicate voltages/how they can be connected. Some transformers are quite easy to re-wire, others can only accept one voltage.

If the transformer has been wired for 240V operation, it would also be a good idea to check that the fuse was replaced from the 120V sized fuse to one that is half the rating. (Everything is in sized accordance with VA which is volts x amps. For example, a 240VA transformer would be fully loaded at 120V and 2A, or 240V and 1A.)

 

Have you tried to point a mic (your smartphone should be fine. Just use a SPL meter app) directly at the headphone at the level where you'd consider it "ear-splittingly loud"?

It could be that you listen at a volume level FAR lower than what the amp maker or the seller thought was the case.

Note that an amp's gain has nothing to do with however much voltage it's being supplied. Sure, more rail voltage would allow for more gain to be applied, but the gain is entirely set within the amplification section, and it is also independent from the power supply. A voltage change should not cause the gain to jump up at all unless something else was done to the amp.

Also if anything was damaged during transit, you would not have been able to turn it on at all.

 

A mismatched voltage on the primaries would have broken something.

Specs show a gain of a whopping 30dB.
That huge for any headphone.

What's the Vrms output of the source and is it adjustable?

 

Yeah, that's why I asked the OP what his listening level was.

30dB gain is really a LOT. I honestly can't stand HD600/HD800 on an amp with 12dB gain past 50% volume knob, and I listen nominally at around 80-85dB, so that should tell ya how much 30dB gain really is.

I think the high gain is just inherent to the amplifier.

And fishski13, Vrms output would depend on the input Vrms as well. Unless you're asking for max Vrms...? Then in which case, the specs should tell you.

 

I mean Vrms output from the source/DAC. Since it appears that the amplifier has no switchable gain, dropping the input voltage from the source will drop voltage output at the amplifier output.

Pedal, do you have XLR input/output and is this a balanced topology? It appears that the XLRs are there for convenience and that this is not a balanced topology.

 

With a gain of 30dB I am not surprised that you get high volume with barely any turn of the volume. I have an amp that has a gain of 12 dB which I consider to be quite high.

For an amp that outputs 50 watts into 8 ohms I am surprised it doesn't have any speaker terminals.

 

Wow lots of info thanks guys. So, despite being an electronics dummy I have a lot of experience with headphone gear over the past decade or so (have organised national meets etc). I've listened to the big brother of this amp, the Headtrip, and it's been fine with my headphones volume-wise. I tend to listen regularly at 75 to 80+ dB (edit - actually I'm going to check this, I use a sound meter to measure an 80dB signal at headphones when reviewing stuff, but my daily listening level may be higher). There's definitely something wrong with this thing as, whilst yes it's a powerful amp, it's basically unusable with headphones that were fine with it before the "voltage change" work was done.

My source is a Metrum Hex, although I've tried a DiDiT DAC212 and Pulse X Infinity and all seem to provide the same voltage.... and it's also the same whether I use balanced or SE inputs on the Enigma.

I'm hoping to avoid having to use something like a Rothwell Attenuator, which would bring the line level input voltage down by - 10dB, but it is always an option... as is a passive volume control or a preamp with variable output. Unfortunately, the Metrum (my main dac) doesn't have a variable output, nor does the Yggdrasil I've had on loan and am considering buying. Anyway I'd be concerned that the amp isn't performing at its best in this state of uber loudness.

Sigh. Thanks for the continued input guys. I opened it up the other day to see if anything obvious was wrong but didn't check the transformer closely to see if it's easy to adjust. Will take a closer look. Thanks.

 

Incidentally, poor pictures but I took these the other day...

https://goo.gl/photos/r1v3pHt2uWXAPyqU7

https://goo.gl/photos/aLPVUCu6P7CzfV3K7

 

I've made this pic and sent it to Wells Audio to show how bad the issue is...

https://goo.gl/photos/yz8JP8XErytLupsT7

 

Generally, correct.

Often, not always.

Not necessarily. A feedback resistor coming loose could cause a huge gain increase. However, here it does seem that the amp just has too much gain.

That's preposterous. Most sources put out 2V or so. 2V into 300R Sennheisers is 13mW which is something like 110dB. 30dB of gain is about 32x amplification. So to listen at 80dB with a 2V source, you need to attenuate 60dB, which means you need 1/1000 of the original signal.

 

Thanks for the info. Is it generally possible to reduce the gain on an amplifier without drastically affecting the configuration or sound quality?