How much difference do output transformers do?

[Robert****]

I don't know much about output transformers. Can someone educate me a bit?

I have read an output transformer takes the signal from the tubes and transforms them into impedances and power suitable for your speakers. Seems like that wouldn't affect the tone much, but many people say the do.

So how much does an output transformer affect the amp's overall sound?

How do I know if an amp has a good one or not?

And what is a rectifier and what does it do?

[duhvoodooman***]

Calling Tunghaichuan....calling Tunghaichuan! Come in, Tung....

[tunghaichuan***]

Robert,

You are correct. An OT is basically an impedance matching device. Tubes are high voltage, high impedance, low current devices. Speakers are low voltage, low impedance, high current devices. The OT bridges the tubes and the spearker(s) to produce sound.

An OT is made of two coils of wire, the primary winding which connects to the tubes and the secondary winding which connects to the speaker. These coils surround a ferrous core. The core is made up of individual laminations that are physically separated by lacquer.

The OT has an effect on tone due to its composition. The composition of the wire and the gauge have an effect as do the composition of the laminations. Also the primary impedance will have an effect on tone. A particular set of tubes wants to "see" a particular primary impedance. For example amps using a pair of 6V6 tubes in push pull can use from 6K-8K for the primary. Not that the OT does not have an impedance of its own. Rather the speaker (connected to the secondary) reflects back the primary impedance to the tubes. For example if an OT has a impedance ratio of 1000:1, that means an 8 ohm speaker will reflect back an 8K impedance on the primary. If you plug a 4 ohm speaker into the same circuit, you get 4K reflected back to the primary. That is why it is important to match the proper speaker to the proper tap.

Some OTs are made for hifi use, they will produce the entire frequency range from 20hz to 20khz. These types typically do not saturate as this is bad from a hifi perspective. Guitar amp OTs are generally not "hifi" and will not produce such a wide band response. Some of them are more prone to saturation, others not so much. The classic example of saturation are Marshall amplifiers, particularly the plexis and metal panel models. The OTs in the aforementioned saturate when pushed hard and create the classic Marshall sound. Fender, OTOH, has OTs that are less prone to saturation. That's why Fenders never sound like Marshalls when cranked.

"Good" for an OT is very subjective. Some of the best makers of OTs are: Hammond, Heyboer, Mercury Magnetics, Schumacher, Triad, and a few others I'm forgetting. Generally, most of the OTs made in Canada, Europe, and the USA are pretty good. Those made in Asian countries aren't as good. Again, it comes down to the materials used in construction.

A rectifier is a device that changes AC to pulsing DC. The filter caps then smooth this out so that the tubes can use this filtered DC. Originally rectifiers were vacuum tubes. These had advantages and disadvantages. Then solid state rectifiers were invented. They are much more efficient, but also have advantages and disadvantages.

HTH,

tung

I don't know much about output transformers. Can someone educate me a bit?

I have read an output transformer takes the signal from the tubes and transforms them into impedances and power suitable for your speakers. Seems like that wouldn't affect the tone much, but many people say the do.

So how much does an output transformer affect the amp's overall sound?

How do I know if an amp has a good one or not?

And what is a rectifier and what does it do?

[duhvoodooman***]

See, I told ya Tung would have the straight poop! :

I can definitely vouch for the impact of a good quality/well-matched OT on the amp's tone. When I swapped out the stock OT from my Epi Valve Jr. with a Hammond 125ESE, it made a very noticeable tonal improvement, particularly in the bottom-end output. There's more bass now and it's punchier and better defined. Of all the many mods I did to my Valve Jr., this one had the single biggest benefit for the amp's tone. The Hammond OT was not only much better quality and rated for higher max. wattage (15W), but was also a better match to the VJr's EL84 output tube--another important factor, as Tung points out. When I upgraded a second VJr--the one Strummy bought from me--I used the 10W 125DSE model instead (still 2x the VJr's 5W rating), and it sounded just as good. Check out the difference in size and construction between the 125DSE and the stock OT:

[tunghaichuan***]

To add to what DVM said:

The Hammond 125ESE is about 4X the size of the stock VJ OT. The Hammond is made better than the stock VJ OT using better materials. Since the VJ is a single ended amp, the OT is made slightly different than a push pull OT to prevent core saturation. Physical size is also important: the larger the OT, the better the bass response.

tung

See, I told ya Tung would have the straight poop! :

I can definitely vouch for the impact of a good quality/well-matched OT on the amp's tone. When I swapped out the stock OT from my Epi Valve Jr. with a Hammond 125ESE, it made a very noticeable tonal improvement, particularly in the bottom-end output. There's more bass now and it's punchier and better defined. Of all the many mods I did to my Valve Jr., this one had the single biggest benefit for the amps tone. The Hammond OT was not only much better quality and rated for higher max. wattage (15W), but was also a better match to the VJr's EL84 output tube--another important factor, as Tung points out. When I upgraded a second VJr--the one Strummy bought--I used the 10W 125DSE instead (still 2x the VJr's 5W rating), and it sounded just as good.

[Robert****]

So what's this "saturation", more specifically? Does it mean the signal get distorted in some way on their way to the speaker, and this is why it may sound "better"?

[tunghaichuan***]

This explains it pretty well:

http://www.opamp-electronics.com/tut...on_2_09_11.htm

At this point, it starts to get way over my head.

tung

So what's this "saturation", more specifically? Does it mean the signal get distorted in some way on their way to the speaker, and this is why it may sound "better"?

[Robert****]

It's already over mine....

[duhvoodooman***]

So what's this "saturation", more specifically? Does it mean the signal get distorted in some way on their way to the speaker, and this is why it may sound "better"?

It's just one element of the overall distortion that guitarists know and (mostly) love. You have preamp distortion, output tube distortion, OT distortion, speaker distortion, and prolly a few more I've overlooked. And that's before you add a couple of good pedals!

[jim p]

Has any one measured the primary inductance of the stock Epi valve jr. output transformer? I used a signal generator and checked the old VJ I have and got approx 44 Hennery which is way high for such a little transformer. When I checked the stock Crate V5 the same way I got 8 Hennery which makes sense. I have a couple of Edcor transformers on order for the Epi amps I have. When I get them I was going to measure them to see what I get for there primary inductance.
On the low frequency response side the primary inductance is suppose to be in parallel with the reflected impedance and the plate impedance so higher primary impedance equals better low frequency response. The Hi-Fi transformers you can buy are 11 pounds on average with 48 hennery with 5k plate impedance so should be 3db down at 16Hz.(3db down when inductive reactance equals the reflected load in parallel with plate impedance) A guitar output transformer is probably 8 Hennery so if you are 5k reflected impedance you would be 3 db down at approx 100Hz.

On the old Valve Jr transformer I think it maybe that it does not have a gap in its core which it should being a single ended output transformer. That would explain the high inductance for its size but the core will saturate from DC current and distort the output.

[tjcurtin1]

Robert, are you sorry you asked yet? :

[Robert****]

Robert, are you sorry you asked yet? :

Not really, maybe one day this thread will lead to something I can understand. Or maybe not. :

[kia2094]

Has any one measured the primary inductance of the stock Epi valve jr. output transformer? I used a signal generator and checked the old VJ I have and got approx 44 Hennery which is way high for such a little transformer. When I checked the stock Crate V5 the same way I got 8 Hennery which makes sense. I have a couple of Edcor transformers on order for the Epi amps I have. When I get them I was going to measure them to see what I get for there primary inductance.
On the low frequency response side the primary inductance is suppose to be in parallel with the reflected impedance and the plate impedance so higher primary impedance equals better low frequency response. The Hi-Fi transformers you can buy are 11 pounds on average with 48 hennery with 5k plate impedance so should be 3db down at 16Hz.(3db down when inductive reactance equals the reflected load in parallel with plate impedance) A guitar output transformer is probably 8 Hennery so if you are 5k reflected impedance you would be 3 db down at approx 100Hz.

On the old Valve Jr transformer I think it maybe that it does not have a gap in its core which it should being a single ended output transformer. That would explain the high inductance for its size but the core will saturate from DC current and distort the output.

Little off the topics here but you raised a good point. But why did you calculated the low frequency inductance base on -3dB? I mean would the design for down -1dB sound better or its no necessary for guitar amps?

Reason for asking is I'm buying a plexi 100w OT , its inductance is base on -3dB (1930 ohm impedence , 82 lower frequency with 3.75 H inductance)

Thank you in advance

[marnold***]

Little off the topics here but you raised a good point. But why did you calculated the low frequency inductance base on -3dB? I mean would the design for down -1dB sound better or its no necessary for guitar amps?

Reason for asking is I'm buying a plexi 100w OT , its inductance is base on -3dB (1930 ohm impedence , 82 lower frequency with 3.75 H inductance)

Thank you in advance

I can't answer your question, but the post was made seven years ago and Jim P hasn't been on here since the end of 2011 so . . . Maybe DVM or someone else might have an answer for you.