Lesha's HiFi Projects

DISCLAIMER: I am not responsible for any damage caused by using the information below. Use it at your own risk. Please remember that there are lethal voltages inside audio equipment while it is turned on and after that. Please do not try to make things described below if you do not have enough skills to deal with high voltages or if you do not understand something in the schematics. Though all of these things were successfully implemented by me (unless explicitly specified) I could make a mistake plotting the schematics.

MY JOLIDA 302A MODS

Here are modifications I've made to my Jolida 302A amp (excluding obvious ones: feedback removal, triode mode, etc) almost completely redoing it. They can be used to some extent with Jolida 202 and Jolida 502 and may be other amps. I leave the decision if they are applicable to your amp to you.
The tubes I use now in my amp are: Svetlana EL34s, Voskhod and Mullard 12AU7s.

Class A output stage and replacement preamp/driver - This one uses 12AU7 SE in preamp and (6N6P, probably can be replaced with 5687 or ) tube in driver. Requires 8 Ohm speakers.
Planned: a single parallel SE transformer coupled stage replacing both preamp and driver.

MY PARALLEL TDA1541 NON-OVERSAMPLING DAC
(Please note that the DAC doesn't use a computer PS, it just uses a convenient computer PS steel box :)

My DAC is DIY non-oversampling one using parallel Philips TDA1541 DAC chips with passive I/V conversion including first order LPF and 6S15P/45P / tube output stage.

The DAC details are on a separate page

A QUICK AND EASY OTL SE PHONE AMP

This phone amp took me only a couple of hours to build. The amp uses one

tube per channel. The output impedance is slightly below 300 Ohm so it works well only with 600 or 300 Ohm phones. The amp gain is around 1 at 300 Ohm load.

Schematic The

's are operating at 108V/35mA. Since they are very linear tubes unlike the other regulator triodes the operating point can be changed in a wide range. The power supply uses separate RC filtering for each channel. The RC time constant of the power supply is much higher than the time constant of output coupling cap * load resistance, this prevents power on/off transitions from damaging the phones. Higher coupling cap values are not recommended. A 10-15V bidirectional transient voltage suppressor diodes can be connected in parallel with R5 and R11 for extra safety in case of a tube failure but they add distrotions at high frequencies. Each one of R3, R9 is two 2W 4.3k resistors in parallel.