How much high level exists below 40Hz?

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maybe sub-contract this out to Tubetec since he is across the pond,

yes need to test in circuit and listen,

low ratio transformers tend to have extended response, this one has a nice Bessel rolloff (no peaks)

i will do a blueprint tonight,
 
CJ said:
well we only had a  1/2" x 5/8" instead of 3/4" bobbin, so we are good for 15 Hz instead of 10, but that's why we over design JIC, 15 aint bad, 10  hz starts to suck current,  you could add more turns to get to 10 Hz but DCR creeps up with #33 wire,

10 v-ac/.00538 amps ac = 1859 ohms reactance at 15  hz ,

1859/ (2 pi x 15 hz) = 1859 /  94.2 = 19.73 Henries pri ind.

DCR came out to 30 ohms,  so this coil/core will work and fit in the rack, ask Sowter how much to wind.
  we used 750 turns instead of 730 to make up a bit for the 1/8" missing from the core with the 5/8" bobbin,

so wind  375T #32  1/2 pri ----375 T #36  sec -----375 T #32 1/2 pri  on 5/8" stack of 50 EI .

max permeability at 15 Hz = 12,000  , not bad for .014" gr or. silicon steel

we will try this tomorrow and see what the freq response does at the hi end,
Click to expand...

By a fortunate dose of serendipity, this could be just about perfect. Looking at the Edcor equivalence of this bobbin is seems its smaller dimension is 1.1 inches (28mm) which should just about squeeze into the module.

I have a  question. You start with 10V ac on the primary. This should really be the max secondary voltage so the primary voltage will be 6dB higher. I don't know how much of a difference this makes. Maybe I am asking the impossible.

Cheers

Ian
 
I made a couple of attempts at 10,000 turns over the last few days on the hand winder , finally tonight I made it past the 10,000 mark , I got a tip from the Latvian winder at work ,that was to use string between the former and the paper on the inside of the coil .
I pre wound the former with string and black motor paper ( with the shiney side to the former) once I was done I simply tied the four strings and it slipped off easily . I then bound the coil with stuff used on motors , problem was I forgot I had added a spacer , so my lovely 10,000 turn coil doesnt fit , but I think I can extract the spacer so I might be ok yet . pics to follow
 

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The coil ends are passed out through silicone/fibre tubeing and be soldered to  tags on the transformer frame , I think I'll use the bolt tightened  strap instead of the metal cable tie I was supplied with ,it looks a lot nicer and also allows the gap to be modified easily enough later.

So 10,200 turns of .08mm or 40 awg got me 60-200 + Hy depending on gap  and only hand preasure to pushing the cores together  ,dc resistance 3.7kohms ,four coils  will  drop  a little more than the 10k resistor it will replace .
 

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use smaller wire and double the turns to use 20 v-rms on the primary, increased DCR will not hurt much, plenty of freq response, so what if we come down to 200 K Hz, in fact that might be a good thing,

we will wind a new coil and see how it works,

 
CJ said:
use smaller wire and double the turns to use 20 v-rms on the primary, increased DCR will not hurt much, plenty of freq response, so what if we come down to 200 K Hz, in fact that might be a good thing,

we will wind a new coil and see how it works,
Click to expand...

Excellent news. Can you explain in simple terms why doubling the turns allows twice the input voltage?

Cheers

Ian
 
with frequency and core size held constant, then the formula simplifies to

Flux = Voltage/Turns

we just got done testing the new coil and it does 20 Hz at 19.5 volts

1600 turns #36 and 800 turns of #36 because we were in a hurry.

DCR is pri 155 and sec 90,

inductance:

48 H at 10 Hz    16.5 volts  (core is saturated)
98 H at 15 Hz  19.5  volts  (slightly saturated)
106 H at 20 Hz 19.5 volts no saturation
78 H at 30 Hz
86 H at 40 Hz

coil simply wound pri-sec

response starts to fall off at 40 K because we had it loaded with 680 ohms, the sec DCR is what is doing this,  there is a lot of bobbin left for bigger sec wire, so dcr could go down quite a bit extending hi freq response when loaded at 600.

unloaded the peak is at 120 K Hz and sloping down from there.

 
Hi CJ,

I have found a local transformer manufacturer prepared to build this for me. I got a prototype from them  today and put it through its paces. It performs very well. Test report attached.

Cheers

Ian
 

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Looks pretty good.  I suppose none of the Jensen offerings meet the size criteria, they certainly have some that should meet spec.  Probably much more expensive. 
 
EmRR said:
Looks pretty good.  I suppose none of the Jensen offerings meet the size criteria, they certainly have some that should meet spec.  Probably much more expensive.
Click to expand...
Size is the issue. I have looked at all the usual suspects. Very few have anything small enough and those that do tend to have nickel alloy cores which severely limits their low frequency high level distortion. I have also been looking at the Neve 35mm module output transformers. It looks as though they have longer than average laminations which means the can use a taller bobbin and get more turns or the same turns with larger gauge wire. That will probably be what I want to try next although this prototype comes so close to a VTB2291 performance I am not sure it is worth it.

Cheers

Ian
 
ruffrecords said:
My bad, these old fingers don't type so well any more. Should have been EI42.
Click to expand...
OK, that makes sense. I've used thousands of them in various guises; It's the standard core size that matches the typical audio requirement of +20dBu at 20Hz into 600 ohms.
 
abbey road d enfer said:
OK, that makes sense. I've used thousands of them in various guises; It's the standard core size that matches the typical audio requirement of +20dBu at 20Hz into 600 ohms.
Click to expand...

That is good to know because a) +20dBu into 600 ohms is what I want and b) the manufacturer was smart enough to pick it.

Cheers

Ian
 
ruffrecords said:
That is good to know because a) +20dBu into 600 ohms is what I want
Click to expand...
That is sensible. Targetting +24dBu, for an illusive 20dB headroom just means the xfmr must be at least 1.6 times bulkier.

b) the manufacturer was smart enough to pick it.
Click to expand...
It tends to show he knows a thing or two about audio. ;)
 
I contacted an English company before about a transformer very similar to a neve 1073 style output , I gave them the winding specs and they said they could wind them for about 20 pounds each ,its competitive with Carnhill ,but I could choose what I wanted exactly . I'll dig up the name in case its worth a try for your stuff Ian .


Calculation for the inner and outer winding wire is 0.16mm and the two
centre winding 0.355mm.

Price approximately £18.00 each ex works.


Kind Regards

Sue Jagatia (Director)

Repanco Bartlett Ltd
Unit 2 Challenge Business Park
Challenge Close
Coventry
CV1 5JG

Tel: +44 (0)2476 665666
Fax: +44 (0)2476 662820
www.repancobartlett.co.uk

Company No 2017843
VAT REG No 418 8202 55

those guys might be worth a try , they have been doing audio transformers since the 70's at least
 
Thanks for the link TubeTec. I remember Repanco from when I was a lad interested in wireless. I had no idea they were into audio transformers. Got a quote from the local company today which is very much in the same ball park. But I will also give Repanco a go. Always good to have a second source.

Cheers

Ian
 

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