Here is another preamp that is using the amazing 01A tube. It has a very pleasant sound that will not fatigue your senses even when played for long hours.

This is an  DHT preamplifier/ line stage using the tungsten filament Cunningham CX-301A tube.  I has one stage and is built with separate enclosure power supply.

The power supply unit uses Hammond 270BX for main HV in a CLC configuration -47uF(Obbligato Film-Oil)-15H(75mA)-47uF(Obbligato Film-Oil). HV is supplied with a low ripple which is perfectly adequate considering that SSHV will add at least 60-80dB PSSR bringing the ripple at extremely low levels ( I could not measure with my equipment).  The raw power supply for the filament bias are using Hammond167L12, 1N5822 and 10mF-2x1ohms-10mF-0.1uF-220pF. PSU is supplying all voltages (HV and LV) through a 7 wire umbilical cord, which is permanently attached on the main preamp side and can be disconnected on the PSU side. However, it is not recommended to run the PSU without load because of the risk of damaging the preamp when reconnect the umbilical cord.

The main preamp uses one stage CX-301A in filament bias, DC input and transformer coupled output. It uses the Lundahl LL2745/PP that is working great for 3-6mA single ended. The main preamp enclosure incorporates the SSHV and two Coleman filament regulators. The 01A is filament biased at 7V on 30 ohms at 230mA.  The secondary of the LL2745 is using either Alt Q (2.8:1)or Alt R (5.6:1) providing two fixed gain alternatives. A 6 pole two position rotary switch is facilitating this function. The preamp is provided with volume control. I installed individual stepped attenuator by Gold Point ( a very good price quality solution).

Specifications

The following measurements are only to give you a sense  of the approximate performance. I used a computer software and interface and this comes with some artifacts and noise that are not present when the amp is connected in a audio path. One, if owns high quality audio analyzer, can take more precise measurements

• Gain : Alt R: 3-4dB(x1.5) and Alt Q: 9-10dB(x3)
• Input impedance: 80kohms, unbalanced
• Output impedance measured comparing output on Z load (523K and 300pF) and (10k and 300pF)

Alt R: 437 ohms

Alt Q: 1750 ohms

• Power consumption: about 50W

“Shiny Eyes” 01A Line stage Measurements

• LL2745 Alt R  6:1       
• FR 20Hz @ -1dB, 20kHz @-1.5dB,  12Hz-27.5 kHz @ -3dB

• THD at 2.9V output (1.92Vrms input) Gain 3.58dB, 2nd @ -75.5dB bellow fundamental, 3rd @ -73dB

• LL2745 Alt Q 8:1       
• THD at 5.83V output (1.92Vrms input) Gain 9.65dB, 2nd @ -73.3 dB bellow fundamental, 3rd @ -72.7dB

• FR 17Hz @ -1dB, 42kHz @+1 dB,  one dip at 11kHz @-1.6 dB

Recommended Operating Mode: Alt R or 3dB gain position. Reason: the 3 dB gain has a very good frequency response and low output impedance, consequently providing the best sound. The 9dB gain option was provide in case there is not enough gain in the audio chain and there is no other alternate option.

More pictures:

This is an all DHT preamplifier/ line stage.  I has one stage and is built with separate enclosure power supply. This a very flexible solutions preamp. One can choose from:

• 01A or 26 type tube
• line output transformer or capacitor coupled output
• two level of gain on transformer output

The power supply unit uses Hammond 270Ex for main HV in a quasi choke input 0.68uF(MKP)-20H(100mA)-47uF(Obbligato Film-Oil)-20H(100mA)-47uF(Obbligato Film-Oil).

Here is the PSUD2 result:

in reality the rectifier used was 6BY5GA so the above results are slightly different. HV is supplied with a low ripple which is perfectly adequate considering that SSHV will add at least 80dB PSSR bringing the ripple at extremely low levels ( I could not measure with my equipment).  The raw power supply for the filament bias are using Hammond167L12, 1N5822 and 10mF-2×0.33ohms-10mF-0.1uF-220pF. PSU is supplying all voltages (HV and LV) through a 7 wire screened umbilical cord, which is permanently attached on the main preamp side and can be unplugged on the PSU side.

The two raw filament supplies are placed in the PSU enclosure and are providing the following :
– PSU raw filament supply for 26: biased at 900mA. Output 15V, ..no more than 10.3V supplied after Coleman that is 9V on 10ohms

Same PSU when switched to 01A ( biased at 230mA), will provide at least 12.5V after Coleman or 7.1 V on 30 ohms bias resistorThe main preamp incorporates the two SSHVs and four Coleman filament regulators ( one pair for 01A and one pair for 26). In order to switch between 01A and 26 tubes, there are 2 sets of DTDP high quality Carling switches. Three of the poles are used to switch between the Coleman regulators ( each channel has one Coleman filament regulator for the 01A @ 230mA and one Coleman filament regulator for the 26 @ 900mA) and the fourth pole is switching the bias resistors placed between one of the filament pins and signal ground ( a permanently connected 30 ohms Mills MRA12 is used to bias the 01A and when switching to the 26 tube there are 2 more 20 ohms Mills MRA12 added in parallel to the 30 ohms( equivalent bias resistor for the 26 will consequently be 7.5 ohms)).

The other feature of this preamp was to switch between transformer output and capacitor coupled output. An additional DPDT Carling switch will do the job. One section (pole) of the switch will be connected to the anode of the tube and connect the anode to either the primary of the line output transformer (LL2745) or the Gyrator ( Ale Moglia’s Gen 2 ).  The secondary of the LL2745 is using either Alt Q (2.8:1)or Alt R (5.6:1) providing two fixed gain alternatives. A 6 pole two position rotary switch is facilitating this function. There are two sets of RCA Neutrik jacks, and in order to use either transformer or capacitor outputs one needs to physically move the interconnection cables to the appropriate jack.

The preamp is provided with volume control. I installed a stereo stepped attenuator by Gold Point ( a very good price quality solution).

Specifications

The following measurements are only to give you a sense  of the approximate performance. I used a computer software and interface and this comes with some artifacts and noise that are not present when the amp is connected in a audio path. One, if owns high quality audio analyzer, can take more precise measurements

• Gain when transformer output T out) : Alt R: 3-4dB(x1.5) and Alt Q: 9-10dB(x3)
• Gain when capacitor output (C out): 18-20dB(x8)
• Input impedance: 80kohms, unbalanced
• Power consumption: max 85VA

“Shiny Eyes” switchable 01A-26  Line stage Measurements

• 26 type vacuum tube
• Transformer output
• LL2745 Alt R  6:1   

• THD at 3.03V output (1.92Vrms input) Gain 3.58dB, 2nd @ -66dB bellow fundamental, 3rd @ -68dB
• 

• FR 14Hz @ -1.5dB, 21kHz @-1.5dB,  8Hz-29 kHz @ -3dB

• LL2745 Alt Q 8:1       

• THD at 5.93V output (1.92Vrms input) Gain 9.8dB, 2nd @ -66.3 dB bellow fundamental, 3rd @ -67.4 dB

• FR 6Hz @ -1dB, 37kHz @+1 dB,  one dip at 11kHz @-1.35 dB

• Gyrator load and capacitor coupled output
• THD at 16.83V output (1.92Vrms input) Gain 18.8dB, 2nd @ -66.3 dB bellow fundamental, 3rd @ -67.4 dB

• FR 12Hz – 41kHz @-0.25 dB

1. CX-301A type vacuum tube

• Transformer output
• LL2745 Alt R  6:1     
• THD at 3.1V output (1.92Vrms input) Gain 4.16dB, 2nd @ -66dB bellow fundamental, 3rd @ -68dB

• FR 20Hz @ -0.7 dB, 20kHz @-1.7dB,  7Hz-25.5 kHz @ -3dB

• LL2745 Alt Q 8:1       
• THD at 6.2V output (1.92Vrms input) Gain 10dB, 2nd @ -66 dB bellow fundamental, 3rd @ -69 dB

• FR 6Hz @ -1dB, 37kHz @+1 dB,  one dip at 11kHz @-1.35 dB

• Gyrator load and capacitor coupled output
• THD at 17.6V output (1.92Vrms input) Gain 19.2dB, 2nd @ -66.1 dB bellow fundamental, 3rd @ -98 dB

• FR 8Hz – 43kHz @-0.5 dB

• Output impedance measurements

And here are some more pictures: