• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Line-out on tubes

Hi, again speaking of this preamp:
Guitar Preamplifier Schematic - All Tube - KBapps.com

Will the output be a line-level one as we know them today in the sold state world? I mean, can I hook it to my home stereo, computer audio card (line-in), etc. without being afraid of blowing my house in a thousand pieces? Or is the output of a tube preamp something different than that?

Thank you all in advance!


P.S. I'm learning a lot about tubes lately... such an exciting new (old) world!
 
One thing to be careful of is turn on and turn off. Tube stuff can generate rather alarming transients because of the high voltages in the circuit. Some solid state equipment may not be happy about those pulses, and if your amp is on when the preamp is turned on and off, the speakers will definitely be unhappy. So make sure you have turn-on/turn-off order well-memorized and you may want to put some sort of over-voltage limiter across the input of your power amp..
 

korey

Member
2008-03-04 2:00 pm
It prevent DC, but does not prevent "pops"...

Usually, it does! Any kind of pop you hear when powering up a tube preamp after the solid state amp is already powered up, usually comes from the preamps power switch contacts.

Aside from the power switch, you should hear no pops or thumps from a tubed preamp as the power supply is not in the audio path. It takes about 25-30 seconds before the power starts to flow.

But, rule of thumb, is to always power up the preamp (tube or solid state) first, followed by the amplifier, and the reverse when shutting down!
 
Last edited:

Arnulf

Member
2009-02-02 9:41 am
Usually, it does! Any kind of pop you hear when powering up a tube preamp after the solid state amp is already powered up, usually comes from the preamps power switch contacts.

Aside from the power switch, you should hear no pops or thumps from a tubed preamp as the power supply is not in the audio path. It takes about 25-30 seconds before the power starts to flow.

And what happens at the output end of output coupling capacitor when HT is applied ?
 

M Gregg

Disabled Account
2010-06-28 11:04 pm
UK
Hi,

As stated by "SY".
As stated by "Arnulf".

If you power up or switch off a tube amp with a SS amp connected and powered, the power on and off thumps can be very loud. DC blocking is not the problem it is the change across the output cap "charge transient" as stated by Arnulf. If you ignore this you may get away with it, however one day you may find your speaker cone hanging out of the amp!
Power out from preamp delay and output off then power off is a good safety measure.

Regards
M. Gregg
 

korey

Member
2008-03-04 2:00 pm
Nothing! Why should it? Never does anything on my equipment in my lab!

Been building electronics and amps for over 40 years and still haven't come across voltage transients as some people have described here!

The original poster has nothing to worry about!
 
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M Gregg

Disabled Account
2010-06-28 11:04 pm
UK
Nothing! Why should it? Never does anything on my equipment in my lab!

Been building electronics and amps for over 40 years and still haven't come across voltage transients as some people have described here!

The original poster has nothing to worry about!

I guess you build in transient protection MOV, caps, etc? Some equipment does not (Cost cutting)!

Regards
M. Gregg
 

korey

Member
2008-03-04 2:00 pm
I'm old school! Don't like the new solid state rectification devices, although some people do.

I have yet to come across this problem with older tube equipment, preamps or amplifiers.

It is however, more prevalant in todays sophisticated IC OP AMPS and newer equipment.
 

M Gregg

Disabled Account
2010-06-28 11:04 pm
UK
Korey,

Another thing I noticed is that if the output is from an output Tx, then as you say the tubes warm up and then you get output. However when the output is cap then you get sudden HT the charge of the cap can create a transient.

At power off the back EMF from the secondary does the same thing "in reverse".

Kind regards
M. Gregg
 

M Gregg

Disabled Account
2010-06-28 11:04 pm
UK
The output is on the cathode side so I agree that the HT is not in direct contact with the output cap. The path "may" come through the tone control section via bass, mid, treble caps via HT.

However agreed the resistors in the cathode will limit the effect!

Regards
M. Gregg
 

Arnulf

Member
2009-02-02 9:41 am
Nothing! Why should it? Never does anything on my equipment in my lab!

Been building electronics and amps for over 40 years and still haven't come across voltage transients as some people have described here!

The original poster has nothing to worry about!

I'd say this is a pretty realistic scenario:
- solid state rectifier in the PSU
- B+ in 200+V range
- coupling capacitor in the single digit uF range
- high load impedance (100K-1M) attached to the output

This will result in multiple [even up to dozens of] volts across the output of the preamp. Many amplifiers will not be very comfortable with that and as for speakers, this should indeed result in a significant "thump".