Transformer Volume Control

Sandor · 3rd August 2008, 09:12 PM

I have found a transformer for volume control with the following specs:
primary 1200 ohm center tapped, secondary 10 Kohm with 23 taps.
The manufacturer suggests to put a 50 ohm series resistor on input.
Using center tap on input provides a 6dB gain.

It seems to me that input impedance is too low to provide a good match with the source. Do you agree? Or that input impedance is typical for that kind of component?

Best regards.

Paul

oshifis · 4th August 2008, 02:20 PM

I am just guessing:

Are these impedance values measured at 1kHz or at DC? Or do they come from the data sheet? Are the taps logarithmically arranged? Do you have any further info from the manufacturer (at least the type or part number)?

Sandor · 4th August 2008, 02:58 PM

Values given by the manufacturer refer to impedance (frequency not known) and not to DC resistance. No further information. I have found the transformer on ebay, item #110217168156.

oshifis · 4th August 2008, 04:31 PM

Hm, it looks interesting. Probably it has the flattest or widest frequency response if the primary is driven by 600/1200 ohms and the secondary is loaded with 10k. That fits for studio environment, I think. Altough the schematics shows a 30-50R source and 50-100k load, which is more suitable for home DIY use. You will need also a good quality 24-pole rotary switch.

Sandor · 4th August 2008, 09:42 PM

Thank you for you answer.
Don't you think that input impedance is way too low for use in a preamplifier? not to mention the fact that it should have a voltage gain of about 16...
The use that comes to my mind is as a step-up xformer in a resistor-based I-V converter for current output DACs, such as TDA1541A. Naive idea?
Best regards.

Paul

ondesx · 18th August 2008, 07:40 AM

May we know more on this Tranny ? Manufacturer, refs, specs, availability, price, etc.

TIA.

ondesx · 23rd September 2008, 11:55 AM

I think there is some misunderstanding with the provided data. There is no sense to speak of the input or output impedance of a tranny, since it "reflects" to the input the impedance of the load and to the output the impedance of the source weighted by the square of the number of turns !

A more interesting data would be the inductance, the attenuation curve and the voltage input before saturation at 20 Hz !

I'll ask the vendor these infos before buying any...

I designed several TVC with gear from different countries (England, Thailand, USA...) most of them are trannies but the present one which is an autoformer !

I'm still looking for a very good price/quality ratio for such devices since the previous trannies remain expensive...

ondesx · 1st October 2008, 09:51 PM

The vendor doesn't answer to any question... May we trust with this guy ? Humm...

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Poor man's transformer volume control?	Bill F.	Tubes / Valves	59	11th April 2012 10:45 AM
transformer volume control (TVC)	louie 3	Solid State	22	4th October 2009 02:41 PM
Transformer volume control questions.	gsd	Tubes / Valves	18	4th March 2009 02:33 PM
FS: Bent Audio TX102 MKIII Transformer Volume Control	Firebottle	Swap Meet	2	26th January 2005 11:32 PM
Transformer-based volume control	wboyd	Analogue Source	4	18th August 2004 04:57 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

3rd August 2008, 09:12 PM	#1
Sandor diyAudio Member Join Date: Mar 2004 Location: Milan	Transformer Volume Control I have found a transformer for volume control with the following specs: primary 1200 ohm center tapped, secondary 10 Kohm with 23 taps. The manufacturer suggests to put a 50 ohm series resistor on input. Using center tap on input provides a 6dB gain. It seems to me that input impedance is too low to provide a good match with the source. Do you agree? Or that input impedance is typical for that kind of component? Best regards. Paul

4th August 2008, 02:20 PM	#2
oshifis diyAudio Member Join Date: Mar 2004 Location: Budapest, Hungary	I am just guessing: Are these impedance values measured at 1kHz or at DC? Or do they come from the data sheet? Are the taps logarithmically arranged? Do you have any further info from the manufacturer (at least the type or part number)?

4th August 2008, 02:58 PM	#3
Sandor diyAudio Member Join Date: Mar 2004 Location: Milan	Values given by the manufacturer refer to impedance (frequency not known) and not to DC resistance. No further information. I have found the transformer on ebay, item #110217168156.

4th August 2008, 04:31 PM	#4
oshifis diyAudio Member Join Date: Mar 2004 Location: Budapest, Hungary	Hm, it looks interesting. Probably it has the flattest or widest frequency response if the primary is driven by 600/1200 ohms and the secondary is loaded with 10k. That fits for studio environment, I think. Altough the schematics shows a 30-50R source and 50-100k load, which is more suitable for home DIY use. You will need also a good quality 24-pole rotary switch.

4th August 2008, 09:42 PM	#5
Sandor diyAudio Member Join Date: Mar 2004 Location: Milan	Thank you for you answer. Don't you think that input impedance is way too low for use in a preamplifier? not to mention the fact that it should have a voltage gain of about 16... The use that comes to my mind is as a step-up xformer in a resistor-based I-V converter for current output DACs, such as TDA1541A. Naive idea? Best regards. Paul

18th August 2008, 07:40 AM	#6
ondesx diyAudio Member Join Date: Apr 2008	May we know more on this Tranny ? Manufacturer, refs, specs, availability, price, etc. TIA.

23rd September 2008, 11:55 AM	#7
ondesx diyAudio Member Join Date: Apr 2008	I think there is some misunderstanding with the provided data. There is no sense to speak of the input or output impedance of a tranny, since it "reflects" to the input the impedance of the load and to the output the impedance of the source weighted by the square of the number of turns ! A more interesting data would be the inductance, the attenuation curve and the voltage input before saturation at 20 Hz ! I'll ask the vendor these infos before buying any... I designed several TVC with gear from different countries (England, Thailand, USA...) most of them are trannies but the present one which is an autoformer ! I'm still looking for a very good price/quality ratio for such devices since the previous trannies remain expensive...

1st October 2008, 09:51 PM	#8
ondesx diyAudio Member Join Date: Apr 2008	The vendor doesn't answer to any question... May we trust with this guy ? Humm...

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)