replacing the volume control in a Traynor YBA-3A super

[pbman1953]

Here's the map for the YBA-3A Super, the 250 watt version of the YBA 3 series. The issue is that , on the volume dial, the amp doesn't really kick into gear until 7. After calling Traynor, and talking to an old tech that was still there from the old days, the value chosen was kind of on purpose. Do you remember that "amp on 10" mentality, that was it.

http://www.freeinfosociety.com/electronics/schematics/audio/traynor_customspecial_yba3a.pdf

I could easily leave it, but I'd rather have a more conventional volume control.

Any suggestions on what the replacement would be? Or leave it?

Thanks

[sluckey]

I don't see anything special about that volume control. It's a 1M audio taper pot just like thousands of other volume pots in tube amps. I'd leave it alone.

You could replace it with a 1M linear pot and the amp would get louder at lower numbers. However, I bet you would prefer the audio taper once you can compare.

[pbman1953]

I understand what your point is, but can you think of any reason why the amp doesn't get going until 7?. Because from there it's straight up hill hard and fast


All my other amps, like my Sunn 2k and even the other Traynor YBA-3 , gradual

[jjasilli]

Guitar amps tend to work best with the vol control on "6", or at "1:00 or 2:00 o'clock".  Your amp is in the ballpark.

If you want less sweep of the vol control, you'll need more gain.  The input circuit and 1st stage seem designed for very low gain. Some suggestions.

*  the 68K input resistors are in front of the grid leak resistor, thus forming a voltage divider which decreases the input signal.  Try shorting one or both of those resistors.  If you get radio noise put a grid stop resistor of 10K - 68K on the tube's G1 (signal) pin on the far side from the input jacks.  Then you'll have the benefit, if needed, of an input resistor without voltage division.

*  increase that grid leak resistor from 470K to 1M.

*  Increase the value of the 1st stage cathode resistor to 1.5K - 3.3K. 

*  Decrease the value of that bypass cap to 1 - 4.7uF (but not if your using the amp for bass guitar).

Not sure of the point though.  The amp will get louder at a lower vol control setting, rendering the rest of the dial useless.  I guess this a a long-winded way of saying I agree with sluckey.

[pbman1953]

Not sure if I'll change much but just to  clearify the dial.  When I say it doesn't get going till 7,  7 is like 3 o'clock not 1 or 2. But most nights I'm on 8 which is 5 to 6 o clock

[sluckey]

Well, put in a linear pot. It'll get going as soon as you touch the knob.

[pbman1953]

Will go that route first

Thanks

[jjasilli]

Well, put in a linear pot. It'll get going as soon as you touch the knob.

OK, so sluckey & I don't fully agree.     A linear pot will get you to higher volume sooner on the dial.  But often its sweep is so rapid that it is uncontrollable:  like maybe 2 is too loud, but 1.8 is too low; and the rest of the dial is useless (think Fender Hot Rod Deluxe).  Still it might work on your amp.

[pbman1953]

Whoa, clash of the titans 

I just got the 1m meg linear , so I'll give it a try and report back

Thanks

[pbman1953]

So far Slucky's in the lead. I just changed it . So instead of having a minimal climb to an extreme it now has 3 to almost 3-4 stages of escalation.

At 2 it's a sensing and slight feelable low level playing volume. At half way it would compete with a set of drums but light duty music. At 7-8 it rocks and at 10 it doubles.

So the explanation of being uselss on the upper range doesn't come into play in this situation

Thanks Guys!!

[jjasilli]

 

[sluckey]

OK, so sluckey & I don't fully agree.

Hey, I disagree with me too!

I think the audio taper pot is the best choice.

[HotBluePlates]

You could say the linear taper rate of volume change would be "too fast" on the low numbers and "too slow" on the upper numbers. This might be bad for some people.

But if you do not need an equal volume change per equal rotation angle at all settings, a linear volume pot could be a useful trick.

[pbman1953]

For this amp I can see the argument for an audio taper if it was going to be used in a low level need plus high level. Being that this amp is such a high power, it will never be used in that situation. I have other amps for that, at much lower wattage.

Looking at the audio graph, the audio taper in this amp is more like the rotation at 80 with a voltage at 10-20. Then it spikes

[PRR]

> I don't see anything special about that volume control.

It's heavily loaded. There's NFB around the stage after it. If that were infinite, the pot wiper is loaded in R6 68K. Which is very-small for a 1Meg pot. The NFB is far from infinite, but V2 is worked oddly (22K plate resistor??) and I'm not inclined to work out the numbers. I do think the wiper "sees" 80K-200K or so, which is heavy sag on a 1Meg pot.

And V1b could drive a lower value.

Let's make pot-makers rich. Get 250K Lin, 250K, Aud, 100K Lin, 100K Aud. The ones you don't like can be used in other repairs or builds.

Change of pot may imply change of C3 "Treble Boost" cap, if you use it. Smaller pot wants larger C3, though because R6 loading is semi-fixed it won't be perfect proportion. Treb-boost is player-preference anyway, make the cap-makers rich too, buy an assortment.

OR... very NON-appropriate mod: Make R29 470r lower, 220r or 100r. Take it low enuff, "10" should be like 23. The cops will have to e-mail your arrest warrant because the sound blows their patrol car away from you. Well, it's still just 250+ Watts, but it will be Real Easy to get every last watt in there.