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

[TEMAS]

Hi there. Hoping someone that owns this unit can share their experiences so that I can compare. I just received a 'brand new' Ampeg PF20T and am getting an extremely low signal, especially from the Transformer output.

I've tried several basses and several cables. The highest output that my RME soundcard registers from the DI output (pre EQ) is about -12db. This is when hitting the bass low E string as hard as I can with the instrument volume fully up. I guess this might be right.

But when I switch to the transformer output, the highest I can register is about -32db and that's playing as hard as I can with the gain and volume dials on the amp set to full. I can hear the drive but its just really quiet. As I ease up to get a clean sound (at around 10 oclock on gain and volume) my RME registers about -40db.

Surely one would expect the transformer output to go louder than the DI output? Or at least be similar when playing clean. I have no bass speaker cab here to test that output. I put it through a guitar cab and there is a signal, but can't test properly.

The unit had obviously been used before, as the package was open and there were greasy fingerprints all over it. It was about £50 cheaper than the other stores, but it said new and I expected to at least get a working unit.

Anyway, any advise welcome.

 

[Zbysek]

Generally, the trasformer output on PF-20T provides lower signal than the preamp output...

 

[TEMAS]

Generally, the trasformer output on PF-20T provides lower signal than the preamp output...

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.

 

[Zbysek]

See post No. 75 in the following thread:

Ampeg PF-20T to (power) amp

 

[Zbysek]

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.

My undesrtanding is that the difference between line level and mic level can be even greater

Line level, instrument level, mic level explained

 

[brianrost]

Surely one would expect the transformer output to go louder than the DI output?

The transformer line out on a tube amp normally uses a resistor to lower the voltage from what the speaker sees to a voltage compatible with line level inputs on mixers and power amps. The designer has to consider the maximum voltage that the amp can produce at the transformer tap when choosing the resistor value. If you experimented with diming the amp you'd get more signal

The standard for "consumer" gear line outputs is -10dBV (0.316 volts), usually RCA or 1/4" connections, so the -12 you see at the DI output sounds about right. "Professional" gear line level is +4dBU (1.23 volts), usually balanced XLR connections.

If you're only getting -32 dB out of the transformer, try the mike level input on your interface. Those are typically 20 to 30 dB hotter. You probably need an adapter, 1/4" to XLR, unbalanced is OK.

 

[TEMAS]

Replying to Zbysek...

Yes exactly. DI signals are usually lower than the line signal. Usually one feeds a DI signal into a mic preamp. My PF20-T is the opposite. The line output is much lower than the DI.

 

[TEMAS]

If you're only getting -32 dB out of the transformer, try the mike level input on your interface. Those are typically 20 to 30 dB hotter. You probably need an adapter, 1/4" to XLR, unbalanced is OK.

Thanks. This really shouldn't be necessary. But yes, I could plug it into a channel of my Shadow Hills GAMA 8 mic preamp. The TX output is an XLR socket not TRS, so I presume this is balanced not unbalanced.

 

[Zbysek]

Replying to Zbysek...

Yes exactly. DI signals are usually lower than the line signal. Usually one feeds a DI signal into a mic preamp. My PF20-T is the opposite. The line output is much lower than the DI.

I think there is some confusion in terminology. I was speaking about "line level signal" and "mic level signal".

Btw.: what makes you think that the "transformer out" is "line output" and the "preamp out" is "DI"?

 

[TEMAS]

Just thinking.... maybe they have put an unbalanced line output on an XLR socket? That would be stupid, but possible. Nothing in the manual about this.

 

[TEMAS]

Btw.: what makes you think that the "transformer out" is "line output" and the "preamp out" is "DI"?

The TX output is labelled 'Transformer Balanced Line Output.' The DI output as I called it is labelled 'Preamp Output.' But I don't know what signal type it is. The manual is shocking.

 

[TEMAS]

I've uploaded two files. In both cases the Gain and Volume knobs were at full power, EQ knobs were at 12 o'clock.

 

[Zbysek]

The TX output is labelled 'Transformer Balanced Line Output.' The DI output as I called it is labelled 'Preamp Output.' But I don't know what signal type it is. The manual is shocking.

I see. The labels might be misleading to some extent...

Let's make a step back. You were concerned by the fact that the transformer output signal is lower than the preamp output signal. As I stated earlier, other units (mine, fiscelles') work the same in this respect. So, your unit is probably not defective.

The question remains whether the output is too low for your intended use. I have not heard any increased noise floor in your sound samples. Are you able to increase the sensitivity/gain on your soundcard/mixing console? If yes, than there should be no problem...

 

[Mushroo]

Here's my experience with my PF20T:

The loudest signal is the Preamp Out with the switch set to Pre-EQ, and I use the Line input on my mixer.

The quietest signal is the Transformer Balanced Out, and I use the Mic input on my mixer.

They are two different outs for two different purposes, so it's intuitive enough to me, that they would be different levels. I wouldn't expect them to be equal. The question to ask yourself is, do you want to use your PF20T with a preamp or as a preamp?

 

[Zbysek]

They are two different outs for two different purposes, so it's intuitive enough to me, that they would be different levels. I wouldn't expect them to be equal. The question to ask yourself is, do you want to use your PF20T with a preamp or as a preamp?

Yes.

Let me add that I am using:

• the transformer output to feed recording/mixing console
• the preamp output to feed additional (power) amp (daisy chaining)

 

[Mushroo]

Oh yeah, one other comment about the PF20T is that it doesn't have a -15db input "pad" like its bigger cousin the PF50T. So if you have a passive or quiet bass, you might want to experiment with putting a Boost (up to +15db) before the amp.

 

[Zbysek]

Oh yeah, one other comment about the PF20T is that it doesn't have a -15db input "pad" like its bigger cousin the PF50T. So if you have a passive or quiet bass, you might want to experiment with putting a Boost (up to +15db) before the amp.

+1

 

[TEMAS]

Ok thanks for the input. I'd be interested to know if your difference between the outputs is as significant as my results, which as you can hear are extremely dramatic. I'm finding I have to add so much extra gain to my TX output that it becomes so noisy that its unusable.

I have now found the proper manual on the internet (mine came with the quick start guide only). But it says nothing about the outputs being different, only that they are both balanced line outputs. I don't understand why they would make one about 24db quieter the other.

It would definitely make sense though that if a tube or transformer was defective the result would be that the TX output would be lower.

 

[Zbysek]

I'd be interested to know if your difference between the outputs is as significant as my results,

It is, I think (based on listening to your sound samples).

I have now found the proper manual on the internet (mine came with the quick start guide only). But it says nothing about the outputs being different, only that they are both balanced line outputs.

Yes, the manual is silent on the difference between the outputs.

I don't understand why they would make one about 24db quieter the other.

One possible explanation is that the transformer output is designed for feeding mixing consoles (usually equipped with mic level inputs)...whilst the preamp output is designed to feed power amplifiers (usually equipped with line level inputs)​

 

[TEMAS]

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