Hi,
I am planning to build a passive pre amplifier. The design I am having in my mind is the one with a potentiometer and 2 transformers. I am planning to use an ALPS 100K log potentiometer. But, I am not so sure on the transformer configuration. Can some one contribute/suggest ?
Regards,
Bins
I am planning to build a passive pre amplifier. The design I am having in my mind is the one with a potentiometer and 2 transformers. I am planning to use an ALPS 100K log potentiometer. But, I am not so sure on the transformer configuration. Can some one contribute/suggest ?
Regards,
Bins
Hi,
Please suggest me a suitable transformer that can be used for the passive pre-amp that I am designing. The input will be provided from a DAC/CD player.
My power amplifier has the following ratings:
* Input impedance (unbalanced): 10 K Ohms
* Input sensitivity: 100 mV to 775 mV.
Best regards,
Bins.
Please suggest me a suitable transformer that can be used for the passive pre-amp that I am designing. The input will be provided from a DAC/CD player.
My power amplifier has the following ratings:
* Input impedance (unbalanced): 10 K Ohms
* Input sensitivity: 100 mV to 775 mV.
Best regards,
Bins.
Hi Bins,
I'm wondering why you want to use a pot with transformers. Why not use tapped transformers by themselves?
John
I'm wondering why you want to use a pot with transformers. Why not use tapped transformers by themselves?
John
Hi John,
I am not sure on how to design that. Can you give me a circuit/model that I can look at ?
Best regards,
Bins.
I am not sure on how to design that. Can you give me a circuit/model that I can look at ?
Best regards,
Bins.
A passive preamplifier ... okay, but idea from the start, but lets see where this goes...
A 100k log pot as a volume the volume control. So far so good. The input impedance of your "line attenuator" is about 100k. The output impedance is 0-25k. If the interconnects are kept really short, your amplifier, with an input impedance of 100k, will be a decent match.
Now, for some reason you want to use output transformers. You can use them as step-up transformers or step-down transformers. Funnily enough, neither configuration makes any sense.
If you need more gain (step up) it would be more efficient to turn up the volume control. (The output impedance increases either way.)
If you need lower output impedance (step down) it would be more efficient to turn down the volume control! (The output signal level decreases either way.)
You could use the transformers as 1:1 isolation units, converting the signal to balanced for the output. That gives you some immunity from ground loops and noise, but you won't find any that have input impedances much above 10k, so it's a really lousy idea to run them directly from the 100k volume pot, your frequency response tanks and, to add insult to injury, varies with the volume position. And you still can't drive any reasonable length of interconnect!
To paraphrase Steve Jobs, passive line stages are a a bag of hurt.
The only way to do it properly would be to drill a hole in your amplifier faceplate and retrofit in the volume control. Then build a passive line selector box.
Amplifiers should be driven by competently designed active line stages. The end.
A 100k log pot as a volume the volume control. So far so good. The input impedance of your "line attenuator" is about 100k. The output impedance is 0-25k. If the interconnects are kept really short, your amplifier, with an input impedance of 100k, will be a decent match.
Now, for some reason you want to use output transformers. You can use them as step-up transformers or step-down transformers. Funnily enough, neither configuration makes any sense.
If you need more gain (step up) it would be more efficient to turn up the volume control. (The output impedance increases either way.)
If you need lower output impedance (step down) it would be more efficient to turn down the volume control! (The output signal level decreases either way.)
You could use the transformers as 1:1 isolation units, converting the signal to balanced for the output. That gives you some immunity from ground loops and noise, but you won't find any that have input impedances much above 10k, so it's a really lousy idea to run them directly from the 100k volume pot, your frequency response tanks and, to add insult to injury, varies with the volume position. And you still can't drive any reasonable length of interconnect!
To paraphrase Steve Jobs, passive line stages are a a bag of hurt.
The only way to do it properly would be to drill a hole in your amplifier faceplate and retrofit in the volume control. Then build a passive line selector box.
Amplifiers should be driven by competently designed active line stages. The end.
Very bad idea !
Trust me on that , been there done that = a lot of crap !
But if you consider : 1 transformer and then the Alps 100k it is ok .
Done also that ! Good configuration .
You must to know when to much is tooo much .
Or as suggested by fellows just one transformer with a lot of taps and a good switch and discard the Alps .
Last edited:
The end is the new beginning....
Hi,
The original idea to develop a passive preamplifier using transformers has been called off in favor of George's light speed attenuator.....
Best regards,
Bins.
Hi,
The original idea to develop a passive preamplifier using transformers has been called off in favor of George's light speed attenuator.....
Best regards,
Bins.
Now you have gone another direction, the Jensen isomax transformers seem well received, especially following a CD player.
Audio Transformer Overview
Auto transformer for attenuators:
Silverrock (commercial preamp from Audio Consulting)
http://www.audio-consulting.ch/?Products:Preamlifier:Silver_Rock_TVC
http://web.archive.org/web/20071028...dio.de/produkte/passive_+tvc/tvc_passive.html
http://web.archive.org/web/*/http://www.rma-audio.de/produkte/passive_ tvc/tvc_passive.html
Stevens & Billington Limited Audio Transformers
Stevens & Billington Limited Audio Transformers
Stevens & Billington Limited Audio transformers TX-102
inside in finished commercial preamp
Your Page Title
SOWTER
SOWTER AUDIO TRANSFORMERS
http://web.archive.org/web/*/http://www.sowter.co.uk/attens.htm
Various informations about auto transformer for volume control
symasym5 - Phono - Restauration und Selbstbau - Analog-Forum go to post from 15. April 2007, 13:53
Euro Stevens and Billington TX102 Group Purchase - diyAudio
All kind of audio transformers:
http://www.cinemag.biz/
http://www.jensen-transformers.com/db.html
Palmer | PLI03
Lundahl Transformers, audio transformer and tube amplifier transformer manufacturer
PLITRON - audio transformers - toroidal transformers - toroids - output transformers - current transformers - power transformers - medical isolation transformers - power toroids
Output transformer
JAMES transformer from the factory in TAIWAN (single ended power amps)
http://www.bella-audioparts.com/transformer.htm
http://www.tubeaudiokits.com/PARTS/Transformers.htm
James Audio Output Transformers
Glockenklang (matching impedance)
uno
GLOCKENKLANG OUTPUT TRANSFORMER 600 W.COVER
Auto transformer for attenuators:
Silverrock (commercial preamp from Audio Consulting)
http://www.audio-consulting.ch/?Products:Preamlifier:Silver_Rock_TVC
http://web.archive.org/web/20071028...dio.de/produkte/passive_+tvc/tvc_passive.html
http://web.archive.org/web/*/http://www.rma-audio.de/produkte/passive_ tvc/tvc_passive.html
Stevens & Billington Limited Audio Transformers
Stevens & Billington Limited Audio Transformers
Stevens & Billington Limited Audio transformers TX-102
inside in finished commercial preamp
Your Page Title
SOWTER
SOWTER AUDIO TRANSFORMERS
http://web.archive.org/web/*/http://www.sowter.co.uk/attens.htm
Various informations about auto transformer for volume control
symasym5 - Phono - Restauration und Selbstbau - Analog-Forum go to post from 15. April 2007, 13:53
Euro Stevens and Billington TX102 Group Purchase - diyAudio
All kind of audio transformers:
http://www.cinemag.biz/
http://www.jensen-transformers.com/db.html
Palmer | PLI03
Lundahl Transformers, audio transformer and tube amplifier transformer manufacturer
PLITRON - audio transformers - toroidal transformers - toroids - output transformers - current transformers - power transformers - medical isolation transformers - power toroids
Output transformer
JAMES transformer from the factory in TAIWAN (single ended power amps)
http://www.bella-audioparts.com/transformer.htm
http://www.tubeaudiokits.com/PARTS/Transformers.htm
James Audio Output Transformers
Glockenklang (matching impedance)
uno
GLOCKENKLANG OUTPUT TRANSFORMER 600 W.COVER
Last edited:
Hi,
Does anyone have the schematics for a passive magnetic preamplifier like the one described on the site: StereoKnight Silverstone Magnetic Passive Preamplifier ? (This is the one that I had in my mind earlier, but with 2 transformers instead of 4)
Best regards,
Bins.
Does anyone have the schematics for a passive magnetic preamplifier like the one described on the site: StereoKnight Silverstone Magnetic Passive Preamplifier ? (This is the one that I had in my mind earlier, but with 2 transformers instead of 4)
Best regards,
Bins.
Hi,
There is one that I drew some time in the last millenium. It was meant for an Amplifier that never happened, a 1000 MilliWatt Amplifier using the WE/TJ 205D and WE/TJ 102D Triodes, no electrolytic capacitors and no coupling capacitors and destined strictly to drive the Lowther equipped Audiovector enclosures.
Sadly the gentleman I was working on this project passed on before it ever went past the paper stage. He is sadly missed (not for bankrolling crazy projects, but for his generous, humble and helpful spirit).
Having been later passed to S&B it is one of the first to have been drawn I believe and has formed the basis of the Diyhifisupply Django Kit, the original Bent Noh and the Music First Passive Magnetic Preamp (and indirectly likely also the one you note). At one point in time it was "wallpaper" on the Music First Audio Site.
It is still one of my most favourite ways for a preamplifier.
Ciao T
There is one that I drew some time in the last millenium. It was meant for an Amplifier that never happened, a 1000 MilliWatt Amplifier using the WE/TJ 205D and WE/TJ 102D Triodes, no electrolytic capacitors and no coupling capacitors and destined strictly to drive the Lowther equipped Audiovector enclosures.
Sadly the gentleman I was working on this project passed on before it ever went past the paper stage. He is sadly missed (not for bankrolling crazy projects, but for his generous, humble and helpful spirit).
Having been later passed to S&B it is one of the first to have been drawn I believe and has formed the basis of the Diyhifisupply Django Kit, the original Bent Noh and the Music First Passive Magnetic Preamp (and indirectly likely also the one you note). At one point in time it was "wallpaper" on the Music First Audio Site.
It is still one of my most favourite ways for a preamplifier.
Ciao T
Attachments
Hello,
Is there any specific ratio to be followed while winding the transformers ? Are the primary and secondary in 1:1 ratio so that what comes in the input is passed on as such to the output without any changes ?
Best regards,
Bins.
Is there any specific ratio to be followed while winding the transformers ? Are the primary and secondary in 1:1 ratio so that what comes in the input is passed on as such to the output without any changes ?
Best regards,
Bins.
Hi,
As you can see, the transformer has a large number of secondary taps, each outputs 2db lower level then the prior one. Equally, the primary is split into two sections that can be connected in series or parallel.
Designing such a transformer is quite non-trivial, so you may wish to purchase a suitable ready made transformers, such as the silk or promethius items:
Silk Transformers TVC/AVC List
Promitheus Audio Transformer Page
Ciao T
As you can see, the transformer has a large number of secondary taps, each outputs 2db lower level then the prior one. Equally, the primary is split into two sections that can be connected in series or parallel.
Designing such a transformer is quite non-trivial, so you may wish to purchase a suitable ready made transformers, such as the silk or promethius items:
Silk Transformers TVC/AVC List
Promitheus Audio Transformer Page
Ciao T
Hi Thorsten,
1. What should be modified in the input section if I need only a single source input (Can I connect them directly to the transformer so that I can avoid the input selection stage) ?
2. What is the need of a split primary - Is that for the gain selection ? Can you tell me the correct need for the series/parallel modes ?
Best regards,
Bins.
1. What should be modified in the input section if I need only a single source input (Can I connect them directly to the transformer so that I can avoid the input selection stage) ?
2. What is the need of a split primary - Is that for the gain selection ? Can you tell me the correct need for the series/parallel modes ?
Best regards,
Bins.
Hi,
In principle yes.
All the transformer volume controls that derive from my original work with first Sowter and later S&B have split primaries so they can provide 6dB "passive gain". Of course, this could be omitted and made in just one ratio.
Ciao T
In principle yes.
All the transformer volume controls that derive from my original work with first Sowter and later S&B have split primaries so they can provide 6dB "passive gain". Of course, this could be omitted and made in just one ratio.
Ciao T
Hi Thorsten,
OK, Clear. What modification should be done on the secondary section of the transformer if I need to use an audio pot instead of the stepped attenuator ?
Best regards,
Bins.
OK, Clear. What modification should be done on the secondary section of the transformer if I need to use an audio pot instead of the stepped attenuator ?
Best regards,
Bins.
Hi,
Non at all.
In fact, if you use a pot you might as well not bother adding the transformer.
The whole TVC thing was put together to get away from using resistive dividers as volume control.
Ciao T
Non at all.
In fact, if you use a pot you might as well not bother adding the transformer.
The whole TVC thing was put together to get away from using resistive dividers as volume control.
Ciao T
Hello Thorsten,
OK, Got the idea. The transformer is having several secondary taps and each one provides a particular level increasing in 2 dB steps. We will be using a rotary switch/control for selecting the required level/step. What I had in my mind was to use a 1:1 ratio transformer for impedance matching and use a conventional audio pot for adjusting the transformer secondary output/level (Input -> Source -> Transformer -> Pot -> Output)
1. How is the source and power amp impedance matching done ? Is that based on the primary and secondary impedance ratings of the transformer employed ?
Best regards,
Bins.
OK, Got the idea. The transformer is having several secondary taps and each one provides a particular level increasing in 2 dB steps. We will be using a rotary switch/control for selecting the required level/step. What I had in my mind was to use a 1:1 ratio transformer for impedance matching and use a conventional audio pot for adjusting the transformer secondary output/level (Input -> Source -> Transformer -> Pot -> Output)
1. How is the source and power amp impedance matching done ? Is that based on the primary and secondary impedance ratings of the transformer employed ?
Best regards,
Bins.
Hi,
A 1:1 transformer simply keeps impedances the same.
To understand how TVC's work, please consult the following:
Stevens & Billington Limited Audio transformers TX-102
Ciao T
A 1:1 transformer simply keeps impedances the same.
To understand how TVC's work, please consult the following:
Stevens & Billington Limited Audio transformers TX-102
Ciao T
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