New Ampeg PF20-T - very low Transformer Output volume.

[Zbysek]

Another weird things is that the transformer on the right hand side makes a high pitched sound, which when I grab it stops.

That might indicate a defect...

 

[brianrost]

Whining transformers are pretty common. Not ideal, but not a sign that it's going south soon.

Addendum to my earlier post: I assumed that the transformer out was a 1/4" connection. It's a balanced XLR, run it into the mike input on your audio interface and you should get plenty of gain.

 

[Wasnex]

There is definitely some confusion on the terminology.

The Transformer Line Out is not transformer driver. It takes a tap off the output transformer and feeds a solid state op amp that drives the output. FYI, The little triangle symbol means amplifier.

The manuals says:

17. PREAMP OUT: This signal may be used to feed an external power amplifier, mixing console, interface or house PA system.The lift/gnd switch [18] is available to reduce any noise that may occur.

19. TRANSFORMER BAL OUT: This signal may be used to feed an external power amplifier, mixing console, interface or house PA system.​

The language is pretty much identical for both outputs. The fact that it says both outputs can be used to drive a power amp suggest that the level is "line level" as indicated in the naming convention. Signal strength will vary by signal path and how the amp is adjusted.

It does seem to be fairly widely reported that the Transformer Line Out produces a lower level than the Balanced Line Out. The way the tone controls are set will have a significant impact on this. Weak tubes in V1 and V2 could also be a contributing factor.

Keep in mind that 12AX7s have two triodes. V1a is before the Bass and Treble controls. V1b is before the Mid control and Master. V2a is between the Master and Pre/Post switch and feeds the Balanced Line Out circuit . V2b is driven by V2a and feeds the output tubes, which feed the Transformer Balanced Line out. Consider the consequences if one of the triodes is very weak. For example what happens if V2a is weak?

Also if you have subbed in a lower gain tube for one of the 12AX7s, that would be another contributing factor.

 

[agedhorse]

It's common for such an output to be mic level, by design.

I think some assumptions being made about what the output should be are simply incorrect.

 

[DirtDog]

You bought a new unit and they sent you a used one? That alone, I'd be sending it back so the seller for a full refund.

 

[JKos]

@TEMAS ,
Are you plugging the Transformer Line Out into a mic pre (or at least mic input) as intended?

 

[JeezyMcNuggles]

Thanks. Interesting to know, but I still can't imagine it being this much. Setting the dials to 10 O'clock is 30db lower than the DI. Setting all the dials to full is 20db lower than the DI.

I would love that feature, because the DI out on my v4b drives any sound board with my channel gain all the way off and my master at about 9 oclock. It's really hard to get a clean DI signal off of it and still be loud enough out my cab.

 

[Wasnex]

It's common for such an output to be mic level, by design.

I think some assumptions being made about what the output should be are simply incorrect.

The manual should not say the outputs are suitable to push a power amp if the signals are mic level.

 

[pie_man_25]

You bought a new unit and they sent you a used one? That alone, I'd be sending it back so the seller for a full refund.

This. That transaction is not off to a good start. Though tbh the amp could still be working as intended.

 

[agedhorse]

The manual should not say the outputs are suitable to push a power amp if the signals are mic level.

Agreed, though IIRC Ampeg had some power amps that had a higher sensitivity.

 

[Deleted member 165050]

I just ran a quick test on my PF-50t...

-10dB 1kHz signal into the amp standard input
All front controls set to 12 o'clock
No speaker load

Taking transformer balanced line out to my industry standard measuring device (an app on an iPad ) I trim gain and volume to show 30dB.

Then taking the output from pre-amp out my meter goes up to 36dB, showing an apparent difference of 6dB with my admittedly amateur setup. But then I repeated at 40dB transformer and preamp shows 50dB, 50dB transformer and preamp shows 63dB. I'm sure someone can work out what that means Unfortunately can't go lower than 30dB due to the noise floor on this setup.

Transformer balanced output is quoted as line level, however there are two definitions of line level:

-10dB for consumer units
+4dB for professional equipment

I would guess Ampeg opted for the lower level, assuming a lot of use would be for DAWs.

 

[Xavierbass]

Besides the lower output, using the transformer output, I found the gain turns the sound noisy at low levels. Do I need to replace the power tubes?

 

[JKos]

-10dB for consumer units
+4dB for professional equipment

To be correct, it is -10 dBv and +4 dBu. The difference between -10 dBv and +4 dBu is not 14 dB. It's actually 11.79 dB in AC voltage difference.
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[JimmyM]

I have a PF-50T and it's designed to have a pretty big difference in output between the two outputs. Do you not have any control over your input volume once it goes into your interface? You might want to raise that if you can.

 

[JimmyM]

Besides the lower output, using the transformer output, I found the gain turns the sound noisy at low levels. Do I need to replace the power tubes?

Adding gain does add noise once you start getting into its dirtier tones. It's to be expected to some degree. Does that mean you don't need a new tube or two? No. But it doesn't mean you do, either.

 

[Xavierbass]

Adding gain does add noise once you start getting into its dirtier tones. It's to be expected to some degree. Does that mean you don't need a new tube or two? No. But it doesn't mean you do, either.

Hi Jimmy, I expected to see you here!
Of corse I want noise at some point, but it start to distort at 7 o'clock :/ so it doesn't allow me to get a clean tone.

 

[JimmyM]

Hi Jimmy, I expected to see you here!
Of corse I want noise at some point, but it start to distort at 7 o'clock :/ so it doesn't allow me to get a clean tone.

I'd be more tempted to replace a preamp tube than the power tubes, then. Do you have a spare 12ax7 laying around? I'd swap out V1 with it and see what happens.

 

[Xavierbass]

Thank you Jimmy, I'll try that!

 

[agedhorse]

To be correct, it is -10 dBv and +4 dBu. The difference between -10 dBv and +4 dBu is not 14 dB. It's actually 11.79 dB in AC voltage difference.
[This invalid link has been removed]

When comparing dBu and dBv, these days they are essentially the same due to the load impedances being >10k and not 600 ohms.

 

[Turok1928]

I have a PF-50T and it's designed to have a pretty big difference in output between the two outputs. Do you not have any control over your input volume once it goes into your interface? You might want to raise that if you can.

Hey, so JimmyM, if I understand, pf-50t does have weak Transformed balanced output line? Something like my ex SVT3-pro for which sound engineers always complained about weak signal? Or does it have something aprox. the same level as SVT7-pro?