Ampeg SVT410HE Cab - A whole lot of hiss

[coffee_king]

Hey all
Im getting a load of hiss coming from my Ampeg SVT410HE Cab (Its about 20 years old now)
Its especially noisy when coming through the PA (Via DI), but can be dialed up and down with the High Frequency Horn Level Control on the rear of the cab.
The problem being that if I turn the HFHLC all the way down I of course loose all the high levels that are a good part of my sound.

Any ideas?
Thanks in advance.

[Bill Fitzmaurice]

Cabs don't hiss. Amps do. That's where you should be considering a change.

[dmccombe7]

Agree - has to be an amp issue if its hiss.
You'll robably find it reduces if turning treble off which is much same as turning horn off
What kind of amp are you using and can you get a loan of another amp to confirm.

Dave

[coffee_king]

Your definitely right here. Although the horn control on the back of the cab does increase the hiss its the amp thats the fault.
Its an Ashdown 500ABM (One of the first ones)

I had it running last night without the cab going straight into my desk via the DI and the hiss gets louder when adjusting the INPUT dial.
Adjusting the OUTPUT dial does not change the amount of hiss.

Thoughts?

[dmccombe7]

shouldn't run an amp without a speaker load. Can damage the output transistors or power stage unless one of the new lightweight amps.

Dave

[Dad3353]

[quote name='dmccombe7' timestamp='1431117123' post='2768047']
shouldn't run an amp without a speaker load. Can damage the output transistors or power stage unless one of the new lightweight amps.

Dave
[/quote]

This is not a universal truth. Valve amps with o/p transformers need a cab connected, but most, if not all, solid-state amps are OK without. There may be some, rare, exceptions I'm unaware of, of course.

[dmccombe7]

I wasn't aware of that and was always told to never run a power amp without a load transistor or valve but it could have been from the old valve amp days ?
I've always connected my cabs before powering up any amp.
Dave

[Dad3353]

[quote name='dmccombe7' timestamp='1431202810' post='2768827']
I wasn't aware of that...
[/quote]

Change nothing, you're doing things the 'safe' way, ss or valve. If one may run an ss amp without a cab, I would recommend against plugging a cab into an amp already under power. Not good for the cab nor the amp, plus the risk of maybe suddenly applying full-out signal at max volume..! Not good; not good at all.
Some folks use their ss amp at home with no cab connected, listening through headphones, so it can be a useful feature. A studio may want a post eq DI from an amp, too, without the 'fuss' of connecting a cab.

[Bill Fitzmaurice]

[quote name='Dad3353' timestamp='1431117538' post='2768051']
This is not a universal truth. Valve amps with o/p transformers need a cab connected, but most, if not all, solid-state amps are OK without. There may be[b] some, rare, exceptions[/b] I'm unaware of, of course.
[/quote]Those exceptions would be transformer coupled first generation SS amps from the 1960s. They, like tubes, always have current flowing into the transformer primary, so a speaker load or a short circuit of the transformer secondary is required. With direct coupled SS if there's no speaker no current flows through the output devices and there's no problem.

[discreet]

[quote name='dmccombe7' timestamp='1431202810' post='2768827']
I've always connected my cabs before powering up any amp.
[/quote]
[quote name='Dad3353' timestamp='1431203934' post='2768832']
Change nothing, you're doing things the 'safe' way.
[/quote]