how to make tube amp sound layback and mellow?

[jj2]

how can I change my preamp and amp to sound more layback and mellow ? tube , ps or caps ?
preamp 12b4 linstage.
amp sun audio 2A3.
Thanks for any help.
John

 

[spock]

tube rolling would seem to be the first preference; providing you have a supply of difffernt tubes to try.

 

[ashok]

Maybe a gentle HF roll off starting quite early?

 

[mach1]

Vitamin Q or Russian K40Y paper in oil coupling caps (ebay).

 

[hagtech]

Forget the rolloff. Rebias the preamp tube. Run it at much lower current! Then you will get the warmth and mellowness all at once. You have to run the tube where it distorts the most.

jh

 

[ashok]

I've no idea how the distorted sound by re-biasing would be to the ear.

However the suggestion of changing coupling caps might be a very good idea. Some caps can soften up the sound .

Maybe you should try all suggestions because its your ear that wants a particular type of sound. Easiest will be to try the re-bias suggestion as it only needs resistor juggling. Caps might require an expensive purchase!
Cheers.

 

[Elso Kwak]

Increase feedback!

 

[arnoldc]

Increase feedback!

huh?!

Rebias the preamp tube. Run it at much lower current! Then you will get the warmth and mellowness all at once. You have to run the tube where it distorts the most.

Based on experience, I would tend to agree with Jim here. I've been playing with a Western Electric tube, biased it to what should be the linear region. It sounded good but some people complained about being analytical. I dropped down the voltage and a little bit current and they liked it more.

My 12B4 preamp is also biased lower when compared to the rest of the gang (see 12B4 linestage thread). Mine is at 17mA and 180V only.

If you're using Sovtek 2A3, you may also want to look for RCA which will improve the mids.

Another thing is that the SV-2A3 is using a 750R cathode resistor. I find that it sounds a bit shouty at that current. I use 880R resistors which are good for my taste.

 

[cogsncogs]

Here too.
Lowering the current through the tube will give you a more 'toob' sound, if my head is screwed on right more 2nd harmonics. Don't know about till distortion is max tho...
Running with low B+ will work also (along with lower bias) but lower max output. You will need to find the 'sweet spot' to your ears.
Tube rolling? nah. If that route try a different tube circuit altogether. May be a little off topic btw but one experiment I've tried to get a 1950's sound (used w/ a NAD SS pwr amp) was a 6BQ7 both sections in //, 80V B+, 47k or 33k (dunno) plate load, 470 or 390 cathode resistor, 500k volume control, ?k grid stop, 12AU7 and/or 6BQ7 cathode follower w/22k load resistor. It gave a very old 1950's rolled off sounding pre. Most likely due to the 500k volume control and low (80V) B+.
I've found that using a B+ of 80V and below with tubes such as 12xx and 6DJ8, 6Bxx gives a very pleasing to the ear sound, tho maybe less lively.

Oh hi Arnold! I think Elso Kwak is talking about the increasing the value of the cathode resistor, less current. I would increase the value of the anode resistor also for a 'warmer' sound.

Cheers
Wayne

 

[ashok]

Since we are touching biasing , can we dwell a bit on the "shouty" problem

This topic continues to interest me. If you listen to many amps you will probably find that some patches of difficult vocals can appear to be " shouty " . How much the effect is depends on the amp and keeping everything else unchanged I have found the difference between amps quite remarkable . However in the rest of the music the differences between amps seem to be very hard to find.

So would vocals with sections that tend to " shout" in some systems be a method of determining how good the amp / system is ........all else being similar ?
The difference can be quite subtle sometimes but certainly audible. This problem is probably level dependent also.

Any thoughts?

 

[arnoldc]

Oh hi Arnold! I think Elso Kwak is talking about the increasing the value of the cathode resistor, less current.

Hi Wayne, I sure he's talking about something I don't know. But I said the same thing (increasing cathode)

 

[lndm]

Re: Since we are touching biasing , can we dwell a bit on the "shouty" problem

So would vocals with sections that tend to " shout" in some systems be a method of determining how good the amp / system is

Any thoughts?

This could be anything but reminds me of the dramas associated with electrolytics in the power supply, or the signal path for that matter, if it is actually the amp and not the speakers.

 

[rdf]

I've found with many tubes two things happen with reduced plate current: 2nd harmonic goes up, higher harmonics go down. The second's another potential explanation for the 'mellower' sound of light biasing.

 

[Dave Cigna]

I don't claim to understand exactly what it is about some amps that make them sound more laid back, but I don't think 'laid back' is the opposite of 'bright' or 'clean.' Consequently, I don't think that rolling off the high end or deliberatly trying to make the amp mushy is likely to get you the sound you're looking for.

Having said that, experimenting with different bias point on the 12B4 might get you closer to what you want, but try higher bias as well as lower.

I do agree that different coupling caps at the 2A3 grid can make a big difference. Tube rolling too, but that's a craps shoot unless you have a large collection of tubes to try. If you did then you would have tried them already.

Changes to the ps ... not familiar with the Sun Audio, but replacing electrolytics with motor run oil caps can help get a smoother more natural sound that can be more relaxing to listen to.

 

[Geek]

I'll second the IMO, best piece of advice given so far, add/increase feedback, NFB, not cathode resistors. It's the simplest to do and if it has the desired effect, great

 

[jj2]

I have try bais, higher voltage & bypass cap.

I don't claim to understand exactly what it is about some amps that make them sound more laid back, but I don't think 'laid back' is the opposite of 'bright' or 'clean.' Consequently, I don't think that rolling off the high end or deliberatly trying to make the amp mushy is likely to get you the sound you're looking for.

Having said that, experimenting with different bias point on the 12B4 might get you closer to what you want, but try higher bias as well as lower.

I do agree that different coupling caps at the 2A3 grid can make a big difference. Tube rolling too, but that's a craps shoot unless you have a large collection of tubes to try. If you did then you would have tried them already.

Changes to the ps ... not familiar with the Sun Audio, but replacing electrolytics with motor run oil caps can help get a smoother more natural sound that can be more relaxing to listen to.

You are right bright is the word with the 12b4.
it is a brett 12b4 linstage.
I have try changing the the bais form 15ma to 19ma to 25 ma.
change the from 265v to 300 v
change bypass cap to black gate.
try 3 other SET amp, they all sound bright.
can it be the out cap ? .22 beewax.
Thansk again for all the help.
John

 

[Dave Cigna]

Re: I have try bais, higher voltage & bypass cap.

You are right bright is the word with the 12b4.
[...]
try 3 other SET amp, they all sound bright.

Do you mean that you tried 3 other amps with your linestage and they all sounded bright? If so, that narrows down the problem quite a bit doncha think?

Have you tried skipping the line stage? A passive volume control might make you happier.

Brett's 12B4 linestage is a good example of a circuit that is so simple that pretty much every component will contribute to the overall sound. The output cap will definitely make a difference, though I don't remember anyone calling the beeswax bright. Are you using a cathode bypass cap? If so, try removing it entirely. Even the plate resistor will have a noticeable impact on the sound.

I'll stick with my recommendation of replacing any electrolytics in the ps with oil caps.


The output cap in the Brett linestage will definately make a difference, though I don't remember anyone calling the beeswax bright. For kicks you could remove the cathode bypass cap.

edit: it occurs to me that that some 12B4's are pretty microphonic. A fussy tube mounted on a thin aluminum chassis could result in some unpleasant resonances

 

[Nafty]

Mellow

Hello.
I do agree with Jim.
On the other hand, I dont like feedback circuitery and less, to increase it for some reason. Yes, it may give an less analytic type of sound but...I didn't like what I got. Feedback yes, if only local. Thats more or less my opinion.
Best regards to you all.
Nafty

 

[jj2]

Re: Re: I have try bais, higher voltage & bypass cap.

1) Do you mean that you tried 3 other amps with your linestage and they all sounded bright? If so, that narrows down the problem quite a bit doncha think?

yes it was the 12b4 preamp

2) Have you tried skipping the line stage? A passive volume control might make you happier.

yes I know ,I have a NOH TVC which sound better but I want to make this work

3) Brett's 12B4 linestage is a good example of a circuit that is so simple that pretty much every component will contribute to the overall sound. The output cap will definitely make a difference, though I don't remember anyone calling the beeswax bright. Are you using a cathode bypass cap? If so, try removing it entirely. Even the plate resistor will have a noticeable impact on the sound.I'll stick with my recommendation of replacing any electrolytics in the ps with oil caps.

I have change the beewax to a 3.3uf cap which sound much better, but still want to improve the sound.
will try the oil cap later.


4) The output cap in the Brett linestage will definately make a difference, though I don't remember anyone calling the beeswax bright. For kicks you could remove the cathode bypass cap.

the beewax was not bright by itself , I think my problem was using a .22uf cap that did not let the bass out.

I will like to know what parts other people used to build their 12b4 pre.

Thanks John

 

[dimitri]

Forget the rolloff. Rebias the preamp tube. Run it at much lower current! Then you will get the warmth and mellowness all at once. You have to run the tube where it distorts the most.

Jim, thanks for spreading "the cat's" ideas here