Troodent Output Transformer
« on: December 29, 2018, 01:07:43 AM »
Newbie here trying to figure this thing out.

Is there a US equivalent to the Carnhill CA-18-VTB1148?
http://www.audiomaintenance.com/downloads/carnhill_design_guide.pdf

 Or better yet, is there a Sowter equivalent, as I read somewhere the originals were Sowter, so why not try to keep it original? And I couldnt really find anything on the Sowter page that was similar.

I found these Jensen JT-11-FLCF that seem like they would work, but really I dont know if Im missing something.
https://www.parts-express.com/pedocs/specs/246-0105--jensen-jt-11-flcf-premium-line-output-transformer-data-sheet.pdf

And I couldnt really find anything on the Sowter page that was similar.

Id just order the Carnhill's but im having trouble with their checkout page and Id rather not wait for them to ship across the pond. Ill post schematics so you know what im working with.


abbey road d enfer

Re: Troodent Output Transformer
« Reply #1 on: December 29, 2018, 03:36:59 AM »
Newbie here trying to figure this thing out.

Is there a US equivalent to the Carnhill CA-18-VTB1148?
http://www.audiomaintenance.com/downloads/carnhill_design_guide.pdf

 Or better yet, is there a Sowter equivalent, as I read somewhere the originals were Sowter, so why not try to keep it original? And I couldnt really find anything on the Sowter page that was similar.

I found these Jensen JT-11-FLCF that seem like they would work, but really I dont know if Im missing something.
https://www.parts-express.com/pedocs/specs/246-0105--jensen-jt-11-flcf-premium-line-output-transformer-data-sheet.pdf

And I couldnt really find anything on the Sowter page that was similar.

Id just order the Carnhill's but im having trouble with their checkout page and Id rather not wait for them to ship across the pond. Ill post schematics so you know what im working with.
The Carnhill is a gapped transformer, specifically designed to withstand DC current in its windings. It makes the transformer bigger and more expensive. The Jensen is not designed for that.
However, the schemo shows there is an output capacitor, that isolates DC, so an un-gapped transformer would work there. The value of said capacitor seems on the low side IMO.
Sowter types 4652 and 8403 seem adequate to me.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

Re: Troodent Output Transformer
« Reply #2 on: December 30, 2018, 06:30:27 PM »
What capacitor value would you recommend for it instead? I d rather not deal with a gapped transformer, especially if theres a output capacitor in the path.

abbey road d enfer

Re: Troodent Output Transformer
« Reply #3 on: December 31, 2018, 03:11:58 AM »
What capacitor value would you recommend for it instead? I d rather not deal with a gapped transformer, especially if theres a output capacitor in the path.
The "ideal" value of the cap depands on several factors:
LF response, which depends on the transformer's inductance; there are two factors here;

One is the actual cut-off frequency, but a more important factor is the LF hump caused by the resonance between the cap and the inductance. This hump happens above the -3dB point and its amplitude depends on how the circuit is damped. Typically, if the output is bridged (i.e. seeing a rather high impedance), which is the case in a modern studio environment, the hump can be rather high, sometimes 10-12dB. It results in amplifying all sorts of unwelcome noises, altering headroom and creating intermodulation distortion. The basic cure is to make the capacitor much higher in value than strictly needed for a typical 20Hz -3dB point. Making it about 2-3 Hz rejects the hump in a region where the rest of the circuit makes it impervious.

The other factor is distortion in electrolytic caps. It has been shown that this characteristic distortion depends directly on the AC voltage across the capacitor. If the capacitor was calculated for -3dB response, the voltage across it would be equal to the voltage across the transformer's primary at the cut-off frequency; that would be way too much. Again, setting the -3dB point at 2-3 Hz ensures the capacitor does not see too much voltage.

I would use a 470uF/25V for a start. In vintage equipment, designers were restricted by the bulk of high-value electrolytics, but today we have a better choice. A current 470uF is not bigger, even often smaller than a 100uF in the early 70's.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

CJ

Re: Troodent Output Transformer
« Reply #4 on: December 31, 2018, 04:01:13 AM »
you could probably use the API 2503 transformer for that circuit,

maybe use a 1000 uf cap at low volts, get an audio grade like Panasonic FM or Nichy green can,

If I can't fix it, I can fix it so nobody else can!
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abbey road d enfer

Re: Troodent Output Transformer
« Reply #5 on: December 31, 2018, 05:23:26 AM »
you could probably use the API 2503 transformer for that circuit,

maybe use a 1000 uf cap at low volts, get an audio grade like Panasonic FM or Nichy green can,
The output stage is single rail, so the output sits at about 12V. For safety, the cap should be rated at 25V.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.


 

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