Whats' the max allowable / reasonable ripple in SE amp?

[AmadeusMozart]

Tried to find an answer in some of the books but got nowehere. So perhaps some of the guru's can (want to) help out here?

We have from Duncan's pages the wonderfull PSU designer software.

With the software it is easy to "go overboard" and try to desing a PSU with nanoVolts ripple but for a normal SE (EL34 / KT66 / 6L6) what is a figure to aim for and what is "good enough"? SHould the B+ have less than 1V ripple or is it more or is it less?

Thanks a lot, AM.

[Ty_Bower]

It depends on the sensitivity of your speakers, and your preferred listening levels.

[AmadeusMozart]

Originally Posted by Ty_Bower

It depends on the sensitivity of your speakers, and your preferred listening levels.

near field listening, background music while working on computer. speakers are approx 92db/1 meter/1 watt

[DualTriode]

Hello,
You want a book check out Morgan Jones’ book, Building Tube Amplifiers. Morgan goes into finite detail regarding ripple voltage. If you want to see ready to use technology read Tubelab.com’s power supply information for his Simple SE amplifier; buy his PCB. The part values are called out on the BOM. Use the recommended extra choke and motor start capacitor.
In my opinion if I can hear hum or buzz it is not High-Fi.
For small output watts I prefer regulated power supplies, check out TubeCad.com. John has some nice kits that make thing fast and easy.
BTW it is not just hum that is important for a SET power supply. By the time the power supply includes capacitors, resistors and chokes the power supply has impedance in the tens of ohms. The power supply impedance is in series with the load and consumes power that otherwise would go into the load, adds to the output impeadnce. Also this series impedance is not constant with frequency. Put it another way the power supply will color the sound.
DT
All just for fun!

[bob91343]

Well it also depends on how sensitive the amplifier is to power supply ripple. An amplifier with large amounts of feedback is much less sensitive to ripple than a simple no-feedback model.

Having said that, in my memory it seems I have seen 'normal' ripple of about 2%. So 350V would mean 7V of ripple.

So the answer to the original question is, it depends. I will stand by that.

[AmadeusMozart]

Thanks for the thumbs up on the Jones' book, I'll look into that. I want to stay away from solid state parts, they seem to have a history of quickly becoming obsolete.

The plate in a pentode is not too sensitive to the voltage variation but the g2 is and indeed it is important to know the configuration (global feedback, no feedback or Schade feedback) and the way g2 is being fed.

edit: are you referring to Jones' book "Valve amplifiers" with the theory or the book "Building tube amplifiers" which deals with the physical construction and testing the amp? Thanks

AM

[chrish]

Originally Posted by AmadeusMozart

I want to stay away from solid state parts, they seem to have a history of quickly becoming obsolete.

I can still get parts for my 20 year old Adcom 555 if I need them.

If you don't want to use solid state for the fun of it or some technical reason, fine, but because it might become obsolete? Even if the 317 regulator becomes obsolete there will be a replacement that will do as good or better job. Even MJ has no objection to sand in this application.

[Yvesm]

Originally Posted by AmadeusMozart

. . .
The plate in a pentode is not too sensitive to the voltage variation but the g2 is and indeed it is important to know the configuration (global feedback, no feedback or Schade feedback) and the way g2 is being fed.

AM

Indeed !

Look at the power stage as three elements in serie:
- The (more or less noisy) PSU.
- The primary (Zp) of the output transformer
- The internal resistance (so called Rp) of the tube.

The PSU noise that appears at the OPT primary (and that will be transmitted to the LoudSPeaker) will divide itself by (Rp + Zp) / Zp. The larger this value, the lower the noise in the LSP.
That's why pentodes having high Rp are "less sensitive" to PSU noise than triodes.

But, applying some amount of feed back results in a reduction of the effective Rp. This is routinely done to improve the damping factor.

So, the first question should be "wich damping factor will make my LSP happy".
The second one should be "wich noise level may I accept" expressed as a ratio with "normal listening level".
(Not less than 50 dB, that represents a 1/100000 power ratio -about 1/300 voltage ratio- , or also 10µW for 1 W "normal listening level" !)
In a pratical 8 ohm LSP, this gives roughly 2.8 V for 1 W and less than (2.8 / 300) around 9 millivolts of residual noise (not easy to trace even with a good o'scope !).

The answers will give the necessary internal output impedance (the reflected effective Rp) to reach, and will allow to compute the allowable PSU residual noise from the above formula.

Yves.

[AmadeusMozart]

Originally Posted by chrish

I can still get parts for my 20 year old Adcom 555 if I need them.

If you don't want to use solid state for the fun of it or some technical reason, fine, but because it might become obsolete? Even if the 317 regulator becomes obsolete there will be a replacement that will do as good or better job. Even MJ has no objection to sand in this application.

I know of a 10K US transceiver that 3 years after its introduction had unobtainable parts: the RF output finals were no longer available and there was no easy substitution without having to do extensive work. Basically if you blew the output power transistors then the rig was good for the rubbish tip as far as transmitting was concerned. Other issues are often with LCD control screens that more often than not are unobtainable after a couple of years.

For the Simple SE amp from tubelab.com one cannot find in our country the CCS mosfet and it is very hard to obtain it even worldwide. Some of the places won't ship outside their country, others charge ridiculous amounts when shipping and others just send fakes and not even the originals.

AM

[aardvarkash10]

not quite true AM - the 10M45 has been done as a group buy to NZ and I'd be interested if anyone was doing another one!

Having said that, there is plenty of scope to use VERY common sand devices to build shunt regulators and the like to tame ripple. MJE340/350 series BJTs come to mind...