Chinese Neve LO1166 Clone - Golden Age Pre-73 Output transformer

[Whoops]

Hi,
a friend replaced the Chinese transformers in his Golden Age Pre-73 units for Carnhill transformers, and gave me the Chinese ones.
The Golden Age Pre-73 is an affordable Neve 1290 mic preamp clone, same circuit, but uses cheap and chinese parts.

Replacing the stock transformers for current production Carnhill seems to be a popular modification being made so I took the opportunity to go into CJ mode and dissect and unwind the Chinese provided output transformer and see how close or far from the real thing are these transformers.
Is there a reason to change them? Did Golden Age cheaped out on the transformer or are they fine?
Let's see

The original transformer used in Neve preamps modules is the Marinair LO1166, it's a gapped transformer,
Carnhill does reproduction LO1166 transformers with the models VTB9049 (standard board size) and VTB1148 (narrower board to fit 1U rack)
I had an original Marinair LO116 and also a Carnhill VTB1148 so I was able to do some measurments to compare, like DC resistance, Inductance and Frequency response.

Here is the Chinese transformer:






The Gap is made with a piece of plastic and not Kraft paper like the Marinair.
CJ states the LO1166 gap is 0.003 inch Kraft paper, that's 0.076mm, this transformer uses a 0.03mm plastic ribbon gap.
So Gap size is smaller than the LO1166

 

[Whoops]

Here is the Bobbin:





Unwinding and counting turns:

 

[Whoops]

So here are the specs of this transformer compared to the Marinair LO1166.
DC resistance and inductance are my own measurements but all the other LO1166 transformer info came from CJ's LO1166 un-winding document shared in this forum.



Winding structure is also different than the Marinair LO1166.
While the Marinair has a more complex winding structure with a split secondary an a reverse wound primary, this Chinese transformer has a straight winding pattern, Secondary to Primary, just 4 sections. It seems to me also that the Primaries Pins were labeled in a way that this transformer will have an output with the Polarity Inverted/reversed.

 

[Whoops]

I measured the Frequency response using REW of the Chinese transformer, Marinair LO1166 and the Carnhill VTB1148.

Chinese transformer without RC network




Chinese transformer with RC network



Marinair and Carnhill both with network:

 

[Whoops]

Conclusions:

It seems Golden Age or the transformer manufacturer really tried to make a cheap and simple version of the L01166, and cut costs wherever they could.
Thinner wire was used for both primaries and secondaries, the gap is smaller, they wound less turns in both primaries and secondaries, no insulation was used between sections. Also they skipped on the winding structure not widing the split secondary neither doing the reverse wound primary, so not the same winding structure as the LO1166.
The costs were even reduced down to the varnish, the transformer was not dipped and impregnated in varnish, it seems that only the outside was just lightly brushed with a thin varnish layer.

They used less Lams also , but the Lams are actually thicker than the LO1166 so the core has the same size in the end. Even though the core is the same size I don't know if using less lams, 36 instead of 54, will not have some effect in performance. It's something for a transformer expert to tell us as I don't know the implications of that.

At least the lamination are the same size and the LO1166, they're Imperial Ei75, but I cannot attest the quality of the Metal used of the lamination, I don't know if they're M6 Steel or a cheaper alloy. But looking and handling them they look good and seem to have the expected weight.

So the transformer is not a replica of the LO1166, it's cheaply made and fails in most of the LO1166 construction specs.
In practical terms, I don't know how those differences would affect performance, if they're marginal and neglectable even though is cheaply made or it they’re detrimental.
Maybe someone can chime in.
But what I can say is that changing these transformers in the Golden Age Pre-73 for some better ones makes sense, so it's understandable that people are doing that.

The only thing I don't know is how faithful or not are the Carnhill VTB9049 and VTB1148 to the original Marinair LO1166, and people replace the Chinese tranformers with Carnhill.
Would be great to unwind a Carnhill one.

Well, hope this was entertaining

 

[tony hunt]

Thank you for your detailed report.

I would like to ask the forum about the impact of thinner lamination thickness, as on the Marinair.

A buyer of some of my old equipment, said that he has specifically looking for transformers with thin laminations. For him it was a tell-tale sign of quality. Does that translate to something audible?

 

[Whoops]

I would like to ask the forum about the impact of thinner lamination thickness, as on the Marinair.

A buyer of some of my old equipment, said that he has specifically looking for transformers with thin laminations. For him it was a tell-tale sign of quality. Does that translate to something audible?

I also don't know that, but with thinner laminations you get more individual lams for a given core size like what happens with the Marinair when compared to the Chinese transformer, I don't know enough about transformers to know what that details but I guess there's something to gain from having laminations otherwise we would just use a solid block of metal instead of laminations, specially in this case where the transformer is gapped and all E lams are on one side and I lams on the other side.

It would be great if some of the transformer experts in this forum chime in and give us some clues

 

[Tubetec]

I believe the lams help prevent losses due to eddy currents , the thinner the lams the less loss , Im not sure how this plays out in terms of the sound though.

 

[iampoor1]

Great work. Thank you for the teardown. Been interested in how this transformer compared since I first heard these preamps!

 

[Whoops]

Great work. Thank you for the teardown. Been interested in how this transformer compared since I first heard these preamps!

Unfortunately I didn’t have time to do some proper sound tests, with more time I could have used my 1290 preamp and do some recordings with the Chinese transformer fitted (I have the Chinese input transformer also) versus the original Marinair transformers and also the Carnhill.
Would love to know also if the Carnhill transformers respect the Marinair winding structure or not.

but now it’s not possible since I already unwound it.

I will use the laminations and bobbin to Wind a UA-5002 output transformer as it uses the same size laminations and I need it for an UA 1108 DIY preamp

 

[SIXTYNINER]

From test images seems the Marinair one , have more deep in bottom ......
(...which would result in a more rounded and enveloping bass ? )

very different from Carnhill ,
that seem to have worst performance ,
(... unbelievable surprise ...)

cheers

Ps:
Probably the Carnhill made for AMS Neve production
are more near to the Marinair ?

 

[moamps]

I measured the Frequency response using REW of the Chinese transformer, Marinair LO1166 and the Carnhill VTB1148.

Could you describe in more detail the measuring setup you used to measure the frequency response of the transformers? Did you measure the frequency characteristics and inductances at the same DC current bias?
Thank you.

 

[Whoops]

Could you describe in more detail the measuring setup you used to measure the frequency response of the transformers?

A very simple and basic setup, Sweep from REW sent though soundcard unbalanced Line output to transformer primary, transformer secondary to soundcard balanced Line input to REW.

 

[moamps]

A very simple and basic setup, Sweep from REW sent though soundcard unbalanced Line output to transformer primary, transformer secondary to soundcard balanced Line input to REW.

These transformers are designed for conditions where they are driven by a source with very low output impedance and with DC bias current. Also the output most likely needs to be terminated with a 600 ohm load to get the correct result. So it seems to me that your measurement results are wrong and not relevant (especially the bumps on LF and HF). You need to measure and compare them in real and identical working conditions, in BA283AV or similar circuits.

 

[Whoops]

If I had more time I would definitely do a frequency response with the circuit conditions,
but I didn't and now I will not do it anyway since the transformer is already un-winded.

Most important above all is all the relevant information that is in this thread, and even better is that it is for free and will be useful for someone interested in this topic.
The frequency response graphs were just a small part of plenty of collected info and at least all the transformers were tested with the same exact conditions, even if not optimal.

Being free info anyone can discard whatever they want and concentrate on all the other relevant info.

 

[3nity]

What I know for sure it's the input transformers on those GAP preamps are really bad...OEPs are far better

 

[Aleguitarpro]

Thanks for your work here.
About this Chinese clones and GAP (from my experience ) changing input transformer with carnhill impacted more than output. I tested them during updating.

I know it's off topic but you quoted ua-5002 since they use same ei75 laminations.
I'm searching for winding scheme for them.. does anybody have?
Thanks in advance

 

[samplebias2]

Great write up! The cool thing about these super cheap units is guys like you figure out what components can be upgraded to a much more quality part, greatly increasing the sound; without having to build something from scratch.

 

[Whoops]

Great write up! The cool thing about these super cheap units is guys like you figure out what components can be upgraded to a much more quality part, greatly increasing the sound; without having to build something from scratch.

The GAP Pre73 costs arount 300€, I have to be honest, personally I would definitely prefer to build a Neve mic pre from scratch than to buy a GAP and try to improve it.
I can build a 1290 (mic pre of the 1073 circuit) from much less than 300€, and I can use a quality pcb, choose all the electronic components myself and just use high quality components.
Thats my personal choice.

I just did this thread because I was given the transformers and had no use for them, so why not unwinding them and try to understand how much did the chinese manufacturer cheaped out in making this and how close or far they were to real thing.
Reality is they cheaped out a lot and it can serve as an example to other people of what to expect from a chinese clone transformer.

Saying this I don't know if changing the chinese transformer will improve the sound or not, I never tried it . So although the Carnhill transformer should be better built I don't know if the practical impact in sound is marginal or not.

 

[Whoops]

I know it's off topic but you quoted ua-5002 since they use same ei75 laminations.
I'm searching for winding scheme for them.. does anybody have?
Thanks in advance

you can find it here:
https://www.delatsch.com/product/ua-5002-output-transformer-winding-datasheet-pdf/