9335 transformer volume control TVC Attenuator transformer

Attenuator transformers used in conjunction with a multi position switch provide a high performance volume control function.  Sowter proprietary winding technique ensures 100 kHz bandwidth at all switch positions.  The transformer action of these attenuators ensures the loading circuit sees a low driving impedance regardless of the switch position.  This ensures the maximum bandwidth potential and minimum distortion of the whole circuit can be realised at all gain settings.   As the attenuation is related to the number of turns at the winding tap, the attenuation is exactly matched between stereo channels.  A range of transformers is available for different total attenuation and step size.  The Mumetal core ensures very low Total Harmonic Distortion.  High input impedance to minimise loading on the driving circuit.  Mumetal can to ensure minimal hum pick-up.  Colour coded leads.  The transformers provide good dc isolation and can be used in balanced or unbalanced circuits.  

Type 9395 is the same as type 9335 except taps are provided on the primary.  These will provide a gain of 0 dB, +6 dB and +12 dB. Suitable for driving from 2k ohms or less source when +6 dB tap is used and 600 ohms or less when +12 dB tap is used.  The overall bandwidth is is reduced when these taps are used. Typically +/- 3 dB from 10 to 50 kHz for either primary tap. The performance when the 0 dB connection is used is identical to 9335.

Types 1035 and 9985 have 5 x 0.5 dB primary taps which can be used for a stereo balance control providing up to +/- 2 dB difference between channels. 1035 has balance taps which include a maximum of 6 dB gain.  The balance control can be wired so that with a single two wafer switch and two attenuators gain can be added in 0.5 dB steps to the left or right channel. See schematic.

Types 9150 and 9155  have been redesigned to bring the performance to be comparable with the other types. They can be used separately or in cascade for a coarse and fine control.

These transformers should be driven from a source impedance as low as possible but will work well with a source up to 10k ohms.  Where necessary a blocking capacitor should be used to ensure no dc is applied to either winding. The secondary load can be any value the higher the better.  A Zobel network is not required on types 9335 to 9339 to damp high frequency resonances which are non-existent. These transformers provide isolation and may be used for balanced to unbalanced conversion or vice versa. It is recommended to use a separate transformer in a high noise environment or if long cables are to be used.  If a ratio change, high common mode rejection is required or dc in either winding is required we will be happy to recommend a suitable transformer to be used in concert with 9335.  Depending on the circuit configuration this may be possible with minimal loss of performance.

We recommend switches from Shallco.  The suggested type number is 214-FB-26 for 26 position attenuators and type number 123-DB-9 for the balance control.  Shallco prices are in US Dollars and may be ordered using a credit card.

Our French Distributor MADOTEC can supply Shallco rotary switches up to 48 positions ( 26 is enough for any attenuator from the 93xx range ). Prices are on the MADOTEC webpage.  We recommend "non-shorting"  (break before make) switches.

SPECIFICATIONS for types 9335 to 9339
+20 dBu 50 Hz
0.03 % typical
PHASE SHIFT AT 20 kHz Less than 1.0 degree
(Midband secondary open circuit)
Better than 30k ohms
6 db at 10 KHz
CAN DIMENSIONS 45mm dia x 52.5mm high.
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world wide
TYPE Nominal impedance Maximum input level at 20 Hz Max attenuation Steps Gain taps Balance taps Inductance Ratio DC resistance (pry or sec)  Mumetal can size
Quote/Buy 9335 10k +20 dBu
(7.74 Volts)


50 dB 2 dB     85 H 1:1 310 ohms i
Quote/Buy 1035 10k 50 dB 2 dB +6 dB 5 x 0.5 dB
Quote/Buy 9395 10k 50 dB 2 dB +6/12 dB  
Quote/Buy 9985 10k 50 dB 2 dB   5 x 0.5 dB
Quote/Buy 9336 10k 42 dB 3 dB    
Quote/Buy 9337 10k 28 dB 2 dB  
Quote/Buy 9338 10k 6 dB 0.5 dB            
Quote/Buy 9339 10k 24 dB 1 db            
Quote/Buy 9150 10k +17 dBu
(5.5 Volts)
40 dB 10 dB     120 H 1:1   e
Quote/Buy 9155 10k 10 dB 2 dB     120 H 1:1   e
Transformer volume control schematic
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Start White/Orange Clear sleeve 0 dB Blue/Yellow Clear sleeve
-2 dB Yellow Greensleeve
-4 dB White
-6 dB Green
-8 dB Brown
-10 dB Violet
-12 dB Pink
-14 dB Blue
-16 dB Orange Orangesleeve
-18 dB Black
-20 dB Yellow
-22 dB White
-24 dB Green
-26 dB Brown
-28 dB Violet
-30 dB Pink
-32 dB Blue
-34 dB Orange Redsleeve
-36 dB Black
-38 dB Yellow
-40 dB White
-42 dB Green
-44 dB Brown
-46 dB Violet
-48 dB Pink
-50 dB Blue
Finish Red Clear sleeve Common Grey Clear sleeve