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Post subject: Output transformer FYI
Posted: Sun Jun 16, 2019 10:47 am
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I bought a direct drop-in output transformer made by Allen Amps for the Princeton. I had a great tech install it. However, the amp developed digital distortion with the clean sounds when the volume was moderate to high. I had the stock transformer reinstalled and the problem went away.


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Post subject: Re: Output transformer FYI
Posted: Tue Jun 18, 2019 2:28 am
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Look a issue with the Allen Output transformer itself, a defective one. Not because is no a Fender IMO.

Any good push pull 6V6 output transformer must work.


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Post subject: Re: Output transformer FYI
Posted: Tue Jun 18, 2019 2:53 am
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stratele52 wrote:
Look a issue with the Allen Output transformer itself, a defective one. Not because is no a Fender IMO.

Any good push pull 6V6 output transformer must work.


I think it will remain a mystery unless I get a Princeton Reverb and swap its transformer with this one. My guess is if it was defective, it would fail in a more significant way than enhancing digital artifacts.


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Post subject: Re: Output transformer FYI
Posted: Tue Jun 18, 2019 3:31 am
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medblues wrote:
stratele52 wrote:
Look a issue with the Allen Output transformer itself, a defective one. Not because is no a Fender IMO.

Any good push pull 6V6 output transformer must work.


I think it will remain a mystery unless I get a Princeton Reverb and swap its transformer with this one. My guess is if it was defective, it would fail in a more significant way than enhancing digital artifacts.


Not IMO.
A output transformer is not a a rocket science.
What do you do with this Allen ? Return back to the seller ? Where do you buy it ? E-Bay or ....


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Post subject: Re: Output transformer FYI
Posted: Tue Jun 18, 2019 9:28 am
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The aftermarket transformers are not the same as factory units. I wouldn't be surprised by the digital effect.
The Allen OT uses a larger iron core than the stock unit. This raises the inductance of the primary windings.
Over at DIY audio forum, a commenter explained," Oversized transformers will have excess leakage inductance and stray capacitance. This will affect the amplifiers stability with deep GNFB, cause phase shift at higher frequencies and as a result, higher THD and intermodulation distortion at higher frequencies, at 10 - 20Khz."
This means that, yes, the transformer can cause high frequency instabilities at high power because its too big.
While it just looks like a hunk of iron, the OT is the result of deep design considerations that are completely unseen. But core size is not. Guitar amps run small cores that saturate at low frequencies. This limits bass and adds interesting distortions to the low midrange of your guitar.

HiFi OTs run large cores to get full power to the bottom of the bass.
The difference here is that HiFi is predigested music that has has unwanted bass already removed.

The right size core is important and the lower the inductance, the better.
For a summery illustration of an output transformer, suppose you're in a pool of water that represents the core, with two floatiing toys on top for windings. The game is to push down on one floaty and make the other one rock in the same motion. If the pool is a kids inflatable, its easy to make a splashing effect to make the other one dance. The short and long period waves impart a significant amount of energy to the free floaty.
Now make your pool a full-sized in-ground swim fest. Pushing on one floaty doesn't get the action into the free floaty. The short period waves dissipate over distance due to leakage inductance and capacitance. The long period waves dominate so bass response is prevalent.
For home players, this may be fine and add to your solo pallette, but the bass harmonics rob power from the midrange and the clarity is reduced. For gig players, the bass muddies up the midrange tone of the guitar and creates harmonic conflicts with the bass player.
Fender tried out large cores with high power and high inductance OTs for a while. These silverfaces were not considered sucesses and Fender went back to low inductance transformers. The inductance stores energy and takes time to release it. Sonically, it sounds like a wet blanket over the speaker.


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Post subject: Re: Output transformer FYI
Posted: Tue Jun 18, 2019 10:17 am
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Tim you are a king,

I wish to know where OP bought this Allen transformer.


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Post subject: Re: Output transformer FYI
Posted: Tue Jun 18, 2019 12:49 pm
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TimsAudio wrote:
The aftermarket transformers are not the same as factory units. I wouldn't be surprised by the digital effect.
The Allen OT uses a larger iron core than the stock unit. This raises the inductance of the primary windings.
Over at DIY audio forum, a commenter explained," Oversized transformers will have excess leakage inductance and stray capacitance. This will affect the amplifiers stability with deep GNFB, cause phase shift at higher frequencies and as a result, higher THD and intermodulation distortion at higher frequencies, at 10 - 20Khz."
This means that, yes, the transformer can cause high frequency instabilities at high power because its too big.
While it just looks like a hunk of iron, the OT is the result of deep design considerations that are completely unseen. But core size is not. Guitar amps run small cores that saturate at low frequencies. This limits bass and adds interesting distortions to the low midrange of your guitar.

HiFi OTs run large cores to get full power to the bottom of the bass.
The difference here is that HiFi is predigested music that has has unwanted bass already removed.

The right size core is important and the lower the inductance, the better.
For a summery illustration of an output transformer, suppose you're in a pool of water that represents the core, with two floatiing toys on top for windings. The game is to push down on one floaty and make the other one rock in the same motion. If the pool is a kids inflatable, its easy to make a splashing effect to make the other one dance. The short and long period waves impart a significant amount of energy to the free floaty.
Now make your pool a full-sized in-ground swim fest. Pushing on one floaty doesn't get the action into the free floaty. The short period waves dissipate over distance due to leakage inductance and capacitance. The long period waves dominate so bass response is prevalent.
For home players, this may be fine and add to your solo pallette, but the bass harmonics rob power from the midrange and the clarity is reduced. For gig players, the bass muddies up the midrange tone of the guitar and creates harmonic conflicts with the bass player.
Fender tried out large cores with high power and high inductance OTs for a while. These silverfaces were not considered sucesses and Fender went back to low inductance transformers. The inductance stores energy and takes time to release it. Sonically, it sounds like a wet blanket over the speaker.


Tim's description fits my experience to a T (pun intended). Thanks. My post was intended to save other potential modders of X2 some time and headache (and $$).

I purchased it from Billmaudio. David Allen and Bill M (RIP) co-developed this output transformer to be used in Blues Junior, Pro Junior, Princeton etc.

http://billmaudio.com/wp/?page_id=545


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Post subject: Re: Output transformer FYI
Posted: Tue Jun 18, 2019 12:56 pm
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Thank you for the answer,.

I read on your link ;

"This brilliant new output transformer, co-developed with Allen Amps’ David Allen, is a breakthrough for the Blues Junior, Pro Junior, Princeton Reverb Reissue, and Super Champ XD. "

:shock:


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Post subject: Re: Output transformer FYI
Posted: Tue Jun 18, 2019 1:29 pm
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stratele52 wrote:
Thank you for the answer,.

I read on your link ;

"This brilliant new output transformer, co-developed with Allen Amps’ David Allen, is a breakthrough for the Blues Junior, Pro Junior, Princeton Reverb Reissue, and Super Champ XD. "

:shock:


True. That's why I wanted to try it on the X2 but the experiment failed.


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Post subject: Re: Output transformer FYI
Posted: Tue Jun 18, 2019 2:00 pm
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medblues wrote:
stratele52 wrote:
Thank you for the answer,.

I read on your link ;

"This brilliant new output transformer, co-developed with Allen Amps’ David Allen, is a breakthrough for the Blues Junior, Pro Junior, Princeton Reverb Reissue, and Super Champ XD. "



:shock:


True. That's why I wanted to try it on the X2 but the experiment failed.


Thank you for the answer.

I will write to Billmaudio to tell him it is wrong for the X2


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Post subject: Re: Output transformer FYI
Posted: Mon Jun 24, 2019 8:44 am
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TimsAudio wrote:
The aftermarket transformers are not the same as factory units. I wouldn't be surprised by the digital effect.
The Allen OT uses a larger iron core than the stock unit. This raises the inductance of the primary windings.
Over at DIY audio forum, a commenter explained," Oversized transformers will have excess leakage inductance and stray capacitance. This will affect the amplifiers stability with deep GNFB, cause phase shift at higher frequencies and as a result, higher THD and intermodulation distortion at higher frequencies, at 10 - 20Khz."
This means that, yes, the transformer can cause high frequency instabilities at high power because its too big.
While it just looks like a hunk of iron, the OT is the result of deep design considerations that are completely unseen. But core size is not. Guitar amps run small cores that saturate at low frequencies. This limits bass and adds interesting distortions to the low midrange of your guitar.

HiFi OTs run large cores to get full power to the bottom of the bass.
The difference here is that HiFi is predigested music that has has unwanted bass already removed.

The right size core is important and the lower the inductance, the better.
For a summery illustration of an output transformer, suppose you're in a pool of water that represents the core, with two floatiing toys on top for windings. The game is to push down on one floaty and make the other one rock in the same motion. If the pool is a kids inflatable, its easy to make a splashing effect to make the other one dance. The short and long period waves impart a significant amount of energy to the free floaty.
Now make your pool a full-sized in-ground swim fest. Pushing on one floaty doesn't get the action into the free floaty. The short period waves dissipate over distance due to leakage inductance and capacitance. The long period waves dominate so bass response is prevalent.
For home players, this may be fine and add to your solo pallette, but the bass harmonics rob power from the midrange and the clarity is reduced. For gig players, the bass muddies up the midrange tone of the guitar and creates harmonic conflicts with the bass player.
Fender tried out large cores with high power and high inductance OTs for a while. These silverfaces were not considered sucesses and Fender went back to low inductance transformers. The inductance stores energy and takes time to release it. Sonically, it sounds like a wet blanket over the speaker.

Thanks for all the info, Tim!

What can you share about the the Super Champ X2's "noisy side"?
I notice the SCX2 is much fussier about A/C power than, say, a Hot Rod Deluxe.
If I don't plug my SC X2 into a good grounded circuit, it can get quite noisy.
The HRD is much more forgiving.

I suspect 2 things are at play here:

1a.) The amp contains a DSP chip.
1b.) The DSP chip's circuit is not as quiet as it could be.

2.) The filter caps are not as good as they could be.

Both understandable considering the low price for the amp.

Care to share any thoughts on it?

Thanks!


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Post subject: Re: Output transformer FYI
Posted: Mon Jun 24, 2019 9:14 am
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johne1 wrote:
TimsAudio wrote:
The aftermarket transformers are not the same as factory units. I wouldn't be surprised by the digital effect.
The Allen OT uses a larger iron core than the stock unit. This raises the inductance of the primary windings.
Over at DIY audio forum, a commenter explained," Oversized transformers will have excess leakage inductance and stray capacitance. This will affect the amplifiers stability with deep GNFB, cause phase shift at higher frequencies and as a result, higher THD and intermodulation distortion at higher frequencies, at 10 - 20Khz."
This means that, yes, the transformer can cause high frequency instabilities at high power because its too big.
While it just looks like a hunk of iron, the OT is the result of deep design considerations that are completely unseen. But core size is not. Guitar amps run small cores that saturate at low frequencies. This limits bass and adds interesting distortions to the low midrange of your guitar.

HiFi OTs run large cores to get full power to the bottom of the bass.
The difference here is that HiFi is predigested music that has has unwanted bass already removed.

The right size core is important and the lower the inductance, the better.
For a summery illustration of an output transformer, suppose you're in a pool of water that represents the core, with two floatiing toys on top for windings. The game is to push down on one floaty and make the other one rock in the same motion. If the pool is a kids inflatable, its easy to make a splashing effect to make the other one dance. The short and long period waves impart a significant amount of energy to the free floaty.
Now make your pool a full-sized in-ground swim fest. Pushing on one floaty doesn't get the action into the free floaty. The short period waves dissipate over distance due to leakage inductance and capacitance. The long period waves dominate so bass response is prevalent.
For home players, this may be fine and add to your solo pallette, but the bass harmonics rob power from the midrange and the clarity is reduced. For gig players, the bass muddies up the midrange tone of the guitar and creates harmonic conflicts with the bass player.
Fender tried out large cores with high power and high inductance OTs for a while. These silverfaces were not considered sucesses and Fender went back to low inductance transformers. The inductance stores energy and takes time to release it. Sonically, it sounds like a wet blanket over the speaker.

Thanks for all the info, Tim!

What can you share about the the Super Champ X2's "noisy side"?
I notice the SCX2 is much fussier about A/C power than, say, a Hot Rod Deluxe.
If I don't plug my SC X2 into a good grounded circuit, it can get quite noisy.
The HRD is much more forgiving.

I suspect 2 things are at play here:

1a.) The amp contains a DSP chip.
1b.) The DSP chip's circuit is not as quiet as it could be.

2.) The filter caps are not as good as they could be.

Both understandable considering the low price for the amp.

Care to share any thoughts on it?

Thanks!


I have a power conditioner in my studio but also a lot of EMI noise sources. My X2 head has a very low noise floor compared to many of my other amps.


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Post subject: Re: Output transformer FYI
Posted: Tue Jun 25, 2019 10:17 am
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If it doesn't like certain AC enviroments, it might be improved by clipping on some ferrite cores around the AC cord and speaker wires.
If the EMI is coming in over the input cable, you can build a noise cancelling cable. Get a good TRS cable and cut the ends off. Connect TS connectors to the cable. Connect the extra wire to ground on the amp end and connect the other end to nothing. Insulate it. Mark the ends. The extra wire picks up hum and EMI just like the signal wire. It is then injected 180 degrees out of phase into the ground circuit to cancel noise.

Internally, the difference in noise could be in the rectifier choice. Now, I don't have one to inspect, but the 1N400X diodes speced for the amp have switching noise that accompanies them.
The HRDX also specs 1N400X, but actually uses 1N540X schottky diodes that have lower switching noise. If they do use the 1N400X, it will be noisier.

The DSP chip does add noise as well. If you look on an oscilloscope at the clean signal going into and the noisy signal coming out of a dsp, you'd be surprised it sounds as good as it does.


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Post subject: Re: Output transformer FYI
Posted: Wed Jun 26, 2019 7:12 am
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TimsAudio wrote:
The DSP chip does add noise as well. If you look on an oscilloscope at the clean signal going into and the noisy signal coming out of a dsp, you'd be surprised it sounds as good as it does.

Digital/audio - it's been a challenge from the beginning. It's like oil and water. Some day they'll get it right (if we don't all get taken out by an asteroid first).


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