Sunday, May 2, 2021

Mimic - Custom, chip based MM RIAA phono preamp

 

















Yet another chip (OPA2134) based phono stage. Most parts were on hand and in this build I used Russian PIO 4uf (snubbed) caps on the output. Metal film resistors here where in other builds I have used carbon. Other caps are a mix of MKT - for accuracy - and Polyester. Once more there is no PCB but a very small piece of vero-board. Differential PS in on board and two 9V batteries power the unit. Silver plated hookup wire (wire wrap) and WBT silver based solder is used. With quality batteries 50 hours of play can be expected. 

The metal enclosure is deadened in the lid and under the bottom with bituminized heavy Al. This adds weight to an otherwise light metal (Al and steel) enclosure and also dampens any resonances. There is  an earthing point and an external battery test point. The overall sound is very neural and dynamics are outstanding. The preamp is dead quiet with good gain. Simple and over-achieving.

Sunday, March 7, 2021

Altec/FaitalPro and Ploycone woofer speakers

 











Initially I was asked to make an amp to work with some speakers. It turned out I made a whole system for the customer;- tube preamp, 300/500W SS amp, Xover and speakers. Boxes were supplied along with woofers (polycones) I recommended. Boxes are 170ltr, Dacron lined. The woofers are 95db efficient and the Faital compression drivers 109. I had to pad down the horns (Altec 511B) 14db. Xover at 1100hz and 3rd order on the horns and 2nd on the woofer. Owner to paint boxes.

The sound is a little forward but pleasantly so and the woofers are flat to 30Hz. Fs for this inexpensive efficient woofer is 25Hz. Bass is tight but with the speakers closer to the wall bass will lift a bit and sound even fuller. Very transparent sound driven by the Holton based amp. 

Sunday, February 28, 2021

"La Ruse" - Gold Lion ECC83 SRPP preamp in a plastic jiffy box

 












"La Ruse" as the name suggest is hiding something. Its under the paint work and similar to "Illusion", its chassis is a plastic jiffy box. This time spray with Ocean Blue hammertone. Mach that with a large gold knob, looks the part. The tubes I've had for years and are Genelex Gold Lions ECC83 gold pin (similar to 12AX7) which have high gain. About time I finally put these premium tubes to work.

All resistors are 1/4W carbon. I like carbon because it appears to produce great musical flow and combined with the high gain tubes produces a big bold sound. No cost cutting with the attenuator which is my favorite Alps Blue velvet and it is on the output. With the pot on the output you are not throwing away precious raw signal by attenuating the input then trying to amplify what remains producing more noise. 

Once more Russian Military paper-in-oil caps are on the output, they always sound good. There are two inputs selected by the small switch at the front. The external PS produces 12V regulated and 250VHT electronically smoothed. All hookup wire in the audio path is silver plated fine copper wire. There is no PCB. Wiring is a combination of  component-2-component and point-2-point. The preamp is dead quiet. La Ruse not only looks good but sounds great and very grounded. 

Friday, February 5, 2021

"Noir" - SRPP Psvane 12AU7 TII preamp

 












A new preamp all completed in record time. Should be I've probably made eight like this. Sounds detailed, laid back and smooth with the Psvane 12AU7 TIIs. Worked at first on.

 

Voltages are;

HT = 247V

bias = 2.44V

current = 5mA.

 

I'm using a Radi0kit external PS kit. Regulated 12V and electronically smoothed HT. Turn it up and it’s dead quiet no hum, buzz, crackle, snap or pop. Looks and sound extremely good. 
 

Alps pot on the output, Russian PIO output caps and SRPP topology. Metal film resistors. Wood cheeks have been finished with a finishing oil. They really have lifted.  Epoxy enamel paint on top of etching primer.


Thursday, January 28, 2021

"fiih-300" - Holton based 300W power amp



 



Once again a powerful 300W Holton based power amp using the upgraded 200W modules. These have the more powerful dual die power FETs installed to allow the modules to produce 300W into 8 ohms and 500 into 4. 80,000uf of 100V filter caps all snubbed and an RFI/EMI power filter.

An over size heatsink is used but still runs up to over 50C. Tranni is 500VAC but will be more than enough to drive the hardest loads to high volume. Once more excellent Holton bass depth and control. Clear, transparent mids. Allover an excellent sounding amp. 

Friday, January 15, 2021

“Sortilege” - enhanced Class D power amp

 



















Another 180W Class D amp based on the hifimediy T4 module. This time the input caps have been upgraded to Mundorf EVO oils and an additional 22,000uf of Mundorf MLytic audio grade capacitance has been added to the PS. Total caps with onboard Nichicon is 32,000uf. The filter caps are snubbed. Enclosure is attractive two tone, earthed and fused. A RFI/EMI power filter has been added and a ferrite choke on the power cord to block RFI. A 500VA tranni does the grunt work and the onboard Motorola ultrafast/soft recovery diodes for the rectifying. 

The amp sounds excellent, clean, clear and fast with optimum bass control. For the extra work replacing the input caps and adding the better filter cap the sound quality has improved. Other amp builders who have heard it agreed and its new own is very pleased. So am I.