This modified integrated amp is inspired by the RAM 301 (Response Audio RAM 301 Integrated - An Amplifier Review on TNT-Audio [English]) and is in a different class from the stock unit altogether. I'm selling it because my current speakers are <86dB in sensitivity so I've been using an amp that's ten times more powerful the last few years.
Despite being over a decade old, the design of the amp is almost timeless - a basic 12AX7 circuit + Gainclone. The stock unit, with inexpensive components, is already very musical:
Jolida JD 301 Integrated Hybrid Amplifier Integrated Amplifiers reviews - Audioreview.com
Jolida JD-1301 Amplifiers reviews - Audioreview.com
Here is the list of changes I made:
- Coupling Capacitor replaced with Auricap in signal path; Jantzen caps bypassing power supplies
- SIgnal path resistors changed to Texas Component Naked Bulk Foil Resistors, Dale RN metal film at other select places.
- Larger value Panasonic FC low ESR capacitors (Elna Silmic was in the circuit for a while but I found it to be not as good for this purpose) supplies the power amp and feedback coupling.
- Stealth Soft Recovery rectifying bridges for both preamp and power amp cirucits (This made a big difference in reducing grain and glare)
- Improved star grounding in the power amp circuit for better background blackness
- Left-Right balance pot removed (the pictures shows a hole that lets you see the Auricaps instead) to shorten signal path; ALPS blue velvet pot replaced the stock volume pot.
- Hook-up wires remain stock for the most part except for a little bit of Neotech OCC wires. I experimented with some high-quality pure silver wires but decided that the stock copper strands sound more balanced at the end.
- After trying a large number of new and NOS 12AX7/5751 tubes, I have settled with Shuguang Natural Sound 12AX7 and Jan Phillips Cryo'ed 5751, both pairs included in the sale. The tubes provide a different level of details compared to basic ones like the Electro-Harmonix in RAM 301
- Equally important as tube rolling is tube vibration control. In one of the photos you can see a little bit of the wonderful Herbie's Lab Ultrasonic tube dampers around the 12AX7.
- The chassis feet were removed as I use three springs from Michael Green Audio for vibration control; I can include the springs for free if needed. Transformer feet are unscrewed and damped with putty instead after much experimentation.
- The original power cord is shortened with an Oyaide style plug that can be plugged directly into a power conditioner or an after-market cord. The power LED is removed (the tube glow can tell you if the unit is on) and the fuse is bypassed (this is a low power amp after all) with a DIY fuse made with speaker wires that can be switched back to any standard small fuse if necessary.
The modifications above made significant differences to the level of transparency, detail, and grain-free fluidity. If my speakers were just 2 dB more efficient, I'd have kept the unit. It's not that it can't played loud with my 85-86db speakers; the sound when pushed hard gets a tad soft / less defined with orchestral climaxes and big piano chords, all the while remaining very musical.
Conditions of the unit is fair, due to a lot of handling during the modification, so a lot of markings have faded, but from a distance it's a very discreet little black box with orange glow on top. I've also repurposed the auxillary input to be a line level output, so three line-level inputs remain.
Despite being over a decade old, the design of the amp is almost timeless - a basic 12AX7 circuit + Gainclone. The stock unit, with inexpensive components, is already very musical:
Jolida JD 301 Integrated Hybrid Amplifier Integrated Amplifiers reviews - Audioreview.com
Jolida JD-1301 Amplifiers reviews - Audioreview.com
Here is the list of changes I made:
- Coupling Capacitor replaced with Auricap in signal path; Jantzen caps bypassing power supplies
- SIgnal path resistors changed to Texas Component Naked Bulk Foil Resistors, Dale RN metal film at other select places.
- Larger value Panasonic FC low ESR capacitors (Elna Silmic was in the circuit for a while but I found it to be not as good for this purpose) supplies the power amp and feedback coupling.
- Stealth Soft Recovery rectifying bridges for both preamp and power amp cirucits (This made a big difference in reducing grain and glare)
- Improved star grounding in the power amp circuit for better background blackness
- Left-Right balance pot removed (the pictures shows a hole that lets you see the Auricaps instead) to shorten signal path; ALPS blue velvet pot replaced the stock volume pot.
- Hook-up wires remain stock for the most part except for a little bit of Neotech OCC wires. I experimented with some high-quality pure silver wires but decided that the stock copper strands sound more balanced at the end.
- After trying a large number of new and NOS 12AX7/5751 tubes, I have settled with Shuguang Natural Sound 12AX7 and Jan Phillips Cryo'ed 5751, both pairs included in the sale. The tubes provide a different level of details compared to basic ones like the Electro-Harmonix in RAM 301
- Equally important as tube rolling is tube vibration control. In one of the photos you can see a little bit of the wonderful Herbie's Lab Ultrasonic tube dampers around the 12AX7.
- The chassis feet were removed as I use three springs from Michael Green Audio for vibration control; I can include the springs for free if needed. Transformer feet are unscrewed and damped with putty instead after much experimentation.
- The original power cord is shortened with an Oyaide style plug that can be plugged directly into a power conditioner or an after-market cord. The power LED is removed (the tube glow can tell you if the unit is on) and the fuse is bypassed (this is a low power amp after all) with a DIY fuse made with speaker wires that can be switched back to any standard small fuse if necessary.
The modifications above made significant differences to the level of transparency, detail, and grain-free fluidity. If my speakers were just 2 dB more efficient, I'd have kept the unit. It's not that it can't played loud with my 85-86db speakers; the sound when pushed hard gets a tad soft / less defined with orchestral climaxes and big piano chords, all the while remaining very musical.
Conditions of the unit is fair, due to a lot of handling during the modification, so a lot of markings have faded, but from a distance it's a very discreet little black box with orange glow on top. I've also repurposed the auxillary input to be a line level output, so three line-level inputs remain.