This mess...

[Chuck H]

I'm on a thread right now with a sheer novice.

http://music-electronics-forum.com/t29556/

His amp has a parasitic oscillation from what I can tell (see pic). What can I tell this guy? The layout on this amp is an atrocity. I'm sure he paid good money for an amp from a respected manufacturer. This is really disheartening. How can VHT sell this thing to vendors with a straight face and sleep at night?

[teemuk]

Indeed....

a) AXL is hardly a "respected manufacturer". More like an importer of run-of-the-mill cheap Chinese OEM.

b) The Special 6's do not have parasitic oscillation as a "stock" feature.

c) The layout is still better than what I've seen in many, many $$$ "boutique" amps out there. In fact, it's way less atrocious than those of vintage Fender amps.


Now, THIS is disheartening. And these amps cost way more than a cheapie Chinese VHT.

[Chuck H]

I have to concede that those look awful. I especially like the make shift board potting!?!

But notice that in most cases the input is away from the output and the preamp leads aren't layed on top of the OT. Though I can't abide such ugly work as your pics, it's the actual locations and routing that make the VHT a candidate. Regardless of it's otherwise tidy execution. I actually DO think that a parasitic oscillation is probably common on many of that particular model.

The outputs, volume and tone controls are all in the same place, the OT secondary leads are long and routed under the preamp board. The OT is on the input side of the chassis, the very lobg lead bundle from the controls is routed over the OT and somewhat parallel to the OT secondary leads and all the filter grounds are daisy chained. There may be other offenses that I missed or can't see. The amp is stock and oscillating! Only unknowing, unsuspecting players who don't do a thorough test at purchase or soon thereafter are buying these, factory useless, amps.

I can understand that there are small builders making some crap and selling it to a few people. But when your a company the size of VHT isn't there some higher authority you must answer to that polices the relative "goodness" of what is presented to the public? I know it's not like a defective automobile or melamine in the baby food. Because there's very little risk of health. But when a company reaches a certain size they should, at least, not be allowed to sell a product that doesn't actually work as that product. An amp that is so functionally unsound as to not be useful as an amp is a scam and a lie. And that should be illegal.

[diagrammatiks]

there's nothing wrong with having the ot where it is.

the special 6 is a fine amp.

I've seen a lot worse..

as teemuk said those amps are way better then 90 percent of the vintage fenders, which were real atrocities.

[Chuck H]

there's nothing wrong with having the ot where it is.

Except that they run the secondaries into the chassis there and as a result, directly under the preamp circuitry. And that because of the OT's location they have the preamp control lead bundle pushed down on top of it. I know Soldono and others have located the PT on the input side of the chassis. But it was done much more gracefully than this.

the special 6 is a fine amp.

I'll agree to disagree on this.

as teemuk said those amps are way better then 90 percent of the vintage fenders, which were real atrocities.

The late model SF's were awful. But it was more of a lead dress issue than a fundamental layout and grounding issue. I guess I'm just seeing this from a different angle.

[soundguruman]

I think I would advise him to file a complaint or a lawsuit.
demand a full refund, it's an abortion.
DO NOT work on this amp. YOU could be held responsible for future failures or injuries.
YOU do not want to be associated with it in any capacity.
Run Away.

PS warn others

[Chuck H]

Wow! Don't hold back though. Tell us how you really feel. Lawsuit? It's just a $350 amp. And $100 of that is for the speaker. I think the normal return/complaint MO will be fine. But I agree that it's an over rated, poorly designed amp.

FWIW I did a little google-ing and it seems that there are many complaints about these amps that read very much like oscillation related issues. Maybe they don't all do it. But on threads where it was addressed there were a lot of responses like "Mine doesn't do it. But I never turn it up that loud." And in the thread I attached the OP didn't have a problem until he turned it up. I think we'll see a lot more trouble with this. I'd bet that an unacceptible and disproportionate number of these amps suffer layout related oscillation problems when turned up.

[diagrammatiks]

Except that they run the secondaries into the chassis there and as a result, directly under the preamp circuitry. And that because of the OT's location they have the preamp control lead bundle pushed down on top of it. I know Soldono and others have located the PT on the input side of the chassis. But it was done much more gracefully than this.



I'll agree to disagree on this.



The late model SF's were awful. But it was more of a lead dress issue than a fundamental layout and grounding issue. I guess I'm just seeing this from a different angle.

It's been a while since I had a unit to review but I don't remember it being much worse then any other amp in that price range.
the board itself looks alright.

I do see what you mean though. All of those leads would definitely benefit from some shortening and rerouting.

[Chuck H]

Yeah. It's not a real high gainer so I think some re routing and isolating the preamp filter grounds would fix the issues I've read about. I guess they make a higher gain version of that amp. The "Ultra"? or something. I'll bet it's layed out, or at least routed more carefully.

Still not sure what to sayto the novice though. He won't want to go in with an iron and the amps not worth paying a tech to experiment on it.