stay at home type 69 project

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lestatdog

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dogears said:
I don't know what OEP input you want.
It looks like the OEP A262A3E works as a 1:10 . Available in us for $13, worth a try.
The Sowter and Lundahl seem to be harder to get and expensive in US,  for me anyway.

Thanks.
 

ruffrecords

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lestatdog said:
It looks like the OEP A262A3E works as a 1:10 . Available in us for $13, worth a try.
The Sowter and Lundahl seem to be harder to get and expensive in US,  for me anyway.

Thanks.

I would go for the A187A15C . It comes in a screened can which is essential for a mic input transformer and it has the required 1:10 ratio. It is about half the price of the equivalents made by the big names.

Cheers

Ian
 

lestatdog

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ruffrecords said:
I would go for the A187A15C . It comes in a screened can which is essential for a mic input transformer and it has the required 1:10 ratio. It is about half the price of the equivalents made by the big names.

Cheers

Ian

This 1 looks great but I can only find it at america. RS. $50 plus ship. Newark does not stock this one.

There's 1 on ebay $97!

How is it the best transformer price I get in US is Carnhills from AML? I can get the VTB input transformers for $50. But is anyone shipping to us right now?
I talked to Volker in Germany said he had now reasonable way to ship even circuit boards.
 

Rocinante

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You are going to need to get the inductors from AML so that might be something to keep in mind. The Cinemags shouldn't be unreasonable. Probably around $75 I would guess. I have a few of the wired I am going to try. I have seen the Jensen's on EBay occasionally. I am all about saving a buck but having a nice input xfmr is going to matter. I went as far as using NOS caps and polystyrene where it was used in the original along with Wima.  The inductors aren't cheap either but you are building a great eq so are worth it.
 

Whoops

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lestatdog said:
It looks like the OEP A262A3E works as a 1:10 . Available in us for $13, worth a try.

Isn't he A262A3E, Turn ratio is 1+1 : 6.45+6.45? So more like 1:12.9

Anyway OEP transformers are cheap because they are not that good, problems with ringing, small headroom at the low end with translates in higher distortion at the low end, and limited frequency response above 10khz and under 100hz.

Sowter, Cinemag, Jensen are much better alternatives for this project.
Better would even be a Ed Anderson Clone of the Lustraphone M10 transformer
 

dogears

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You’re gonna spend a couple of hundred bucks on switches and inductors. Saving $40 on the input transformers seems penny wise and pound foolish to me.
 

Whoops

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dogears said:
You’re gonna spend a couple of hundred bucks on switches and inductors. Saving $40 on the input transformers seems penny wise and pound foolish to me.

Yes, it really makes no sense trying to save money on such an important thing as the input transformer
 

lestatdog

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Whoops said:
Yes, it really makes no sense trying to save money on such an important thing as the input transformer

Words of wisdom, for me it looks like this might be project for later when money starts coming in and normal shipping resumes.

Anyone making PCBs?
 

Whoops

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lestatdog said:
Anyone making PCBs?

Dogears was kind enough to design and provide gerbers.
Nowadays it's not that expensive for any of us to send the files to a factory and make the boards for cheap, even in small quantities
 

RuudNL

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Maybe it is my misunderstanding, but when SW1.4 is closed, the phantom power on 'LO' is connected to ground.
This means 48/6.8 = 7.06 mA * 48 = 338 mW wasted energy dissipated in RP1, without any reason.
Or am I seeing things wrong?
 

dogears

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RuudNL said:
Maybe it is my misunderstanding, but when SW1.4 is closed, the phantom power on 'LO' is connected to ground.
This means 48/6.8 = 7.06 mA * 48 = 338 mW wasted energy dissipated in RP1, without any reason.
Or am I seeing things wrong?

Yikes! Absolutely correct!

That's a three position switch, with high, -20 dB using center tap, and low with a pad formed by R52 and R51 - but yes, totally forgot to isolate it from phantom.

But I think the actual power is less - If we look at both the DC paths to ground, you end up with 6.8k in parallel with a the high string - 6.8k + 10k+4.7k, which comes out to ~5.1k load. Actual current through the 200 ohm resistor is about 9 mA, for a power of  16 mW. I'm less worried about RP1 than the risk of boogering up upstream gear.

Anyone got a suggestion here? The peril of sharing a line and mic level input..
 

ruffrecords

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Whoops said:
Anyway OEP transformers are cheap because they are not that good, problems with ringing, small headroom at the low end with translates in higher distortion at the low end, and limited frequency response above 10khz and under 100hz.

Sowter, Cinemag, Jensen are much better alternatives for this project.
Better would even be a Ed Anderson Clone of the Lustraphone M10 transformer
I think that is a little unfair. OEP do make some very cheap not particularly good transformers but they do make some very affordable pretty good ones too. Recently I have compared a £80 Sowter output transformer with its £40  OEP equivalent and the OEP measures better.

Cheers

Ian
 

Whoops

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ruffrecords said:
I think that is a little unfair. OEP do make some very cheap not particularly good transformers but they do make some very affordable pretty good ones too. Recently I have compared a £80 Sowter output transformer with its £40  OEP equivalent and the OEP measures better.

Cheers

Ian

Hi Ian,
thank you so much for correcting me, I was not aware of good OEP tx, the ones I used in the past were in the £20 range, and I used them for particular or economical applications. Not that I don't like their sound sometimes, I actually like it in some scenarios because the ones I used were more "lo-fi".

But thank you so much for letting us know they have also parts with good quality, although for an higher price than the cheaper models we're used to.
What models do you recomend?

Thank you
 

ruffrecords

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Whoops said:
Hi Ian,
thank you so much for correcting me, I was not aware of good OEP tx, the ones I used in the past were in the £20 range, and I used them for particular or economical applications. Not that I don't like their sound sometimes, I actually like it in some scenarios because the ones I used were more "lo-fi".

But thank you so much for letting us know they have also parts with good quality, although for an higher price than the cheaper models we're used to.
What models do you recomend?

Thank you

Most transformers are capable of good performance from 100Hz upwards with flat response and low distortion at operating levels. For me, the response and distortion below 100Hz are what separates a good transformer from a bad. My general criteria is <1% THD at 20Hz at the maximum operating level is satisfactory.

I think I may have posted this before but just in case, see attached file.

Note that the £40 OEP K30A06C nearly made the grade. I asked OEP if they could make a version using an M6 core and they sent me a sample. I am pleased to report its low end performance is noticeably better than the original and it is likley to become my preferred output transformer.

Cheers

Ian
 

Attachments

  • OEP Transformer Tests.pdf
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Strat96

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dogears said:
You know, that came from the buffer that was supposedly added to Lenny Kravits desk by Dave Amels...shared by Winston here:

https://groupdiy.com/index.php?topic=1222.msg930095#msg930095

He did mention a heatsink is required, but I can't see why you'd need 100 mA for this job. 20R  / 30 mA should be plenty I'd think. 18 dBu peak into 600 ohms...?

Ah he was driving a 1:2. Without the transformer we shouldn't need nearly as much.

That is interesting about David Amels. I have read many times the 15C1/2128 shouldn't drive a transformer, however my console has transformers across have of the outputs of the 15C1. They aren't stock (at least I don't think) and they are by WSW. One of the things I am trying to do now is figure out the sound difference and performance difference with and without these transformers.

Speaking of this mod, originally when I looked at your schematic I was wondering where was the 10K resistor that is supposed to be shunt across the output of the 15C1/2128 card. But after looking into the mod for the hi/low out, I see that it replaces that part of the output.
 

ruffrecords

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Strat96 said:
That is interesting about David Amels. I have read many times the 15C1/2128 shouldn't drive a transformer, however my console has transformers across have of the outputs of the 15C1. They aren't stock (at least I don't think) and they are by WSW. One of the things I am trying to do now is figure out the sound difference and performance difference with and without these transformers.

The 15C1 is the simple single ended three transistor stage. Its final stage runs at about 6mA. Its output impedance may be quite low due to the negative feedback used but its output drive capability is set by the final stage current. The power supply voltage (24V nominal) defines the maximum signal level it can output at about +18dBu.

There is no reason why you cannot add a transformer to this stage provided you only load it lightly. Feeding one or maybe two 10K bridging loads should be fine but it would not successfully drive a 600 ohm load.

I worked at Neve in the 70s where every input and output was transformer balanced and all outputs could drive +26dBu into a 600 ohm load. Helios did things differently, most likely to reduce costs, so they used unbalanced inputs for line inputs and inserts  and probably drove transformers from outputs not designed to drive 600 ohm loads. Nothing wrong with that as long as you are aware of the limitations.

Cheers

Ian
 

Whoops

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ruffrecords said:
Note that the £40 OEP K30A06C nearly made the grade. I asked OEP if they could make a version using an M6 core and they sent me a sample. I am pleased to report its low end performance is noticeably better than the original and it is likley to become my preferred output transformer.

Thank you so much for the  the pdf and information.

So the K30A06C in the tests is a Nickel core and it performs really well but now you have a version of the K30A06C with steel core that even performs better?

I searched to understand the subject and found a nice Nickel VS M6 thread:

https://groupdiy.com/index.php?topic=13562.msg156941#msg156941
 

ruffrecords

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Whoops said:
Thank you so much for the  the pdf and information.

So the K30A06C in the tests is a Nickel core and it performs really well but now you have a version of the K30A06C with steel core that even performs better?

I searched to understand the subject and found a nice Nickel VS M6 thread:

https://groupdiy.com/index.php?action=post;quote=949192;topic=74779.20;last_msg=949496

For some reason the link does not work properly for me.

I am not sure the K30 transformer is 100% nickel - many input transformers may be 100% but in output transformer it is often 50%.

Anyway, the basic differences between nickel and M6 are in the distortion they create and the maximum flux they can handle. The maximum flux is dependent on the input level and the frequency. Since flux is inversely proportional; to frequency, at highish frequencies you never get near maximum flux so there is not danger of saturation and distortion remains low. In this region, nickel generally beats M6 for distortion.

Since flux is inversely proportional to frequency, as you go down below 100Hz, the flux level begins to rise even if the signal is kept constant. So if you keep going down in frequency you will eventually reach a point where the core saturates and you get lots of distortion. For a given size of core, M6 saturates at a much higher flux then Nickel so its distortion rises much more slowly than Nickel as you approach 20Hz. Geberally M6 beats nickel every time below about 50Hz.

So changing the K30 core from nickel to M6 gives much better low frequency distortion at the expense of a little more mid band distortion.

Cheers

Ian
 

Whoops

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ruffrecords said:
For some reason the link does not work properly for me.

I posted the wrong link, here it goes:

https://groupdiy.com/index.php?topic=13562.msg156941#msg156941
 

ruffrecords

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Whoops said:
I posted the wrong link, here it goes:

https://groupdiy.com/index.php?topic=13562.msg156941#msg156941

That makes a lot more sense. The Edcor guy basically hit the nail on the head with regard to output transformers.

Cheers

Ian
 

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