My DIY SVT bass amp

[powerdimer]

wow, thats really awesome, i'd love to know how to do that stuff. god just didn't gift me with the electronic knowledge

I don't think he did that with anyone.

 

[spankdaplank]

subscribed.

 

[beans-on-toast]

I don't think he did that with anyone.

What about Thomas Edison and Uncle Fester?

 

[gurensan]

Perhaps, but I have already built a 100w bass amp and I have found that the filament hum is easily controlled with a hum balance pot and the place you need the absolute cleanest DC (besides the B+ is the Bias supply.

If it's well-enough filtered and regulated (LM317 or equiv) it's all good.

 

[BassmanPaul]

If it's well-enough filtered and regulated (LM317 or equiv) it's all good.

That regulator has no chance of stabilizing the heater supply of a 100W amp.

With a maximum out of 37V it's no use for the bias supply either. You'd need something like a TL783 to do the job. I do use a regulator IC in my designs, can't remember the part# at the moment, bUT you have to consider the heat generated within an average tube amp's chassis. It can't rise above the part's upper temperature limit.

 

[redhed]

You are THE man!!

 

[beans-on-toast]

If you look at high end tube pre-amps, they usually have DC heater supplies to help keep the noise floor as low as possible. So the amp is quieter. You need to have ripple in a power amp B+ supply. Without it, the amp is sterile sounding, lacking in dynamics.

 

[T-Bird]

Hi.

You need to have ripple in a power amp B+ supply. Without it, the amp is sterile sounding, lacking in dynamics.

Care to elaborate a bit farther?

Regards
Sam

 

[beans-on-toast]

Remember, to keep this in context, we are talking about an amp with character such as an SVT, not a PA amp. My comment was more along the line as to what helps make a tube amp sound good.

Tube amps perform in a non linear way. Part of that comes from how the power supply performs. In designing a B+ power supply, I find that it is important to find the right balance with the amount of ripple and sag. Too much ripple and you can hear it hum. I find that an amp with too much filtering looses the dynamics that make it have a great tube sound. It looses what many would call a musical sound. So getting the sag and ripple in the power supply just right is what helps make a tube based musical instrument amp sound good.

Scientific instruments amps (not musical instrument amps) tend to be highly regulated with DC supplies and they sound horrible when used for musical instrument applications. I think that they would build them that way if they sounded better.

You might find this of interest. They explain some of what I am trying to convey.

 

[Oobly]

....

You might find this of interest. They explain some of what I am trying to convey.

Very interesting article! I "overdid" the supply for my DIY preamp, and I do think it sounds a little sterile. It's got a sag resistor, but also a multistage ripple filter, all for a pair of preamp tubes which aren't drawing much current. The heater supply is DC, 2x1n4007s with snubbers, 3x10mF caps and a pair of 2.2ohm resistors. The caps get pretty hot, so I have to change the design a bit.

For version two I am going with a much simpler PSU, keeping the sag resistor, but less filtering and playing with an AC heater supply with a smallish negative bias, and it's almost ready for testing. It's nice to see that some other people's experiences match my "guesstimation" of how to improve the tone. If there is heater supply hum, I may go back to DC heater supply, possibly SMPS.

Another thing to keep in mind is that a tube rectifier has different characteristics to a silicon one, but for something as powerful as an SVT, it's not so easy to use tube regulators. They certainly affect the "sag", but perhaps some characteristics of the ripple, too.

 

[T-Bird]

Hi.

You might find this of interest. They explain some of what I am trying to convey.

Thanks for the clarification and the link.

An interesting read.

However, tube and SS rectification and PS filtering are obviously two totally different animals, and if we leave the few selected skinny string amps of different vintages out, there's not many examples left of tube rectified tube amps.
Not many 100W+ bass MI amps that I know of anyway.

That's BTW one of my pet peevees along the PTP vs. turret/eyelet board construction.
Full tube amps IMO (and I'm not alone on that ) aren't quite full tube if the rectification is done with semiconductors.
The marketing talk blinded sheep can ramble all day long about the signal path being "full tube", I ain't buying any of that.


On none of my very few tube rectified tube amps have I ever felt the need to convert 'em to SS rec., or vice versa, so until I have some personal experience I have to believe that the ripple has indeed some positive influence on the amps distortion characteristics.
I don't believe that to be so though .

Regards
Sam

 

[beans-on-toast]

Full tube amps IMO (and I'm not alone on that ) aren't quite full tube if the rectification is done with semiconductors.

That is true Sam. Sag in a solid state power supply can also occur in the transformer as well as the caps in some amps if they never get a chance to fully recharge because of a heavy demand caused by intense playing. So even though an amp has a solid state rectifier, it can have sag. Not necessarily though as it depends on how it is designed and used. But ripple is a component that tube amps all share and my experience tells me that the amount of it does affect how the amp performs. So that article makes sense to me.

I think that many manufacturers believe that if the signal path is all tube, that constitutes an all tube amp. Then again some will call it a tube amp even if there a single tube in the pre-amp. It comes down to marketing.


David