Finally my DIY tube amp project gets kick-started

[drlowmu]

Hari,
During the past few years, the stability of the power has improved a lot.

Still Voltages in India do tend to fluctuate even beyond their rated value.

Your equipment seems to be on the brink with even the rated variation in the Mains Supply Voltage.

A regulated supply will probably not be acceptable from an audiophile point of view.... then maybe it would be prudent for you to build in an Over voltage Power cut out with a relay ?

Just a thought.....

I designed Hari's DC SE KT88 amp co on a 230 VDC design center. At even a high 245 VAC Line, his 6FQ7 input tube is dissipating 1.0 Watt of its 4 Watt rating, or 25% onservativelyf maximum. The KT88 at that line voltage is dissipating just 13.9 Watts of its 42 Watt rating, or 33% of it's maximum rating.

What did fail was a 402 Ohm series 5 Watt supply resistor, ( while dissipating 0.8 Watts ) from the Covid-aftermath Indian high line. It was sometimes B+ voltaged 55 VDC over its rated maximum, at Hari's home.. I have since changed such resistors in all new am builds, to be rated, not at 500 VDC maximum, but rather maximum voltage-rated comfortably at 1250 VDC. ( 50 Watt rated ARCOL HS series ). It is a wirewound pulse-duty resistor.

 

[IndianEars]

I designed Hari's DC SE KT88 amp co on a 230 VDC design center. At even a high 245 VAC Line, his 6FQ7 input tube is dissipating 1.0 Watt of its 4 Watt rating, or 25% onservativelyf maximum. The KT88 at that line voltage is dissipating just 13.9 Watts of its 42 Watt rating, or 33% of it's maximum rating.

What did fail was a 402 Ohm series 5 Watt supply resistor, ( while dissipating 0.8 Watts ) from the Covid-aftermath Indian high line. It was sometimes B+ voltaged 55 VDC over its rated maximum, at Hari's home.. I have since changed such resistors in all new am builds, to be rated, not at 500 VDC maximum, but rather maximum voltage-rated comfortably at 1250 VDC. ( 50 Watt rated ARCOL HS series ). It is a wirewound pulse-duty resistor.

Excellent, Conservative Design, drlowmu.

A 'Trick' that I often use where there is High voltage across resistors, (to prevent Voltage Breakdown) is to use 2 series resistors.... effectively providing double the Voltage Breakdown rating & Much higher Power dissipation margin.

 

[Sanjeev Kumar]

Hariji, since I am new to forum and technically not very sound, may I dare to ask you a question that are evaluation boards supplied by well renowned companies like https://www.mouser.in/ are reliable, robust and good enough to produce clean sound like a DIY HIFI. I was particularly checking

REFAUDIOAMA12070TOBO1 by Infineon Technologies​

https://www.mouser.in/ProductDetail/Infineon-Technologies/REFAUDIOAMA12070TOBO1?qs=%2Fha2pyFaduhAPAdmoEqvp7xJbbB22ly84PpDlDzN9TYWPHXTZEubOExj6t1YElDp

Thanks

 

[Hari Iyer]

Hariji, since I am new to forum and technically not very sound, may I dare to ask you a question that are evaluation boards supplied by well renowned companies like https://www.mouser.in/ are reliable, robust and good enough to produce clean sound like a DIY HIFI. I was particularly checking

REFAUDIOAMA12070TOBO1 by Infineon Technologies​

https://www.mouser.in/ProductDetail/Infineon-Technologies/REFAUDIOAMA12070TOBO1?qs=%2Fha2pyFaduhAPAdmoEqvp7xJbbB22ly84PpDlDzN9TYWPHXTZEubOExj6t1YElDp

Thanks

Infenion is my Automotive customers direct supplier and I deal with them daily for chip shortage project that I am currently working on. But that's related to supply chain issues and not technology.

The measured result of this evaluation board looks quite impressive. Can't say the same how they would sound. If you can figure out the source section of this board then no harm in purchasing and testing this device. It certainly is not a plug and play device and will require careful mating with the input device as that part is digital.

If you know what you are doing, please go ahead. Price is ok and won't break your bank. Definitely not sound like a tube amplifier as tubes have much higher distortion than these puny devices.

 

[Hari Iyer]

After 2+ years of being an happy soul of using these monoblocks, I finally am giving final touches to the finish of this amplifier. Started with the top plate - and changing the laminated plywood to a 1mm MS sheet. Powder coating is pending

 

[Hari Iyer]

After 2 years of starting this project, the amplifier is finally getting completed with a logo and a MS top metal powder coated plate. The CAD drawing was done by FM @sadik and executed by an engineering firm at Pune (Any FM looking for building any kind of Chassis should consider this. You can PM me for details if required). Here are some final images to feast your eyes,



The logo is of my mentor/guru who has designed and provided atleast 80% of the components for me to assemble the amplifier with all detailed schematics, inputs etc. I have to admit i could not follow all his advise 100% and in some cases have deviated from the original. But i have realized my mistake and have taken corrective action in almost 50% of my mis-adventures. The amplifier logo fully deserves to be called a "Jeff Medwin" amplifier.











Thanks for looking.

 

[drlowmu]

We are viewing above, a monaural amplifier. Two exist at Hari's for stereo playback.

Tubes we see : two 5U4GB rectifiers, an obscured 6FQ7 and a KT88.

Also visible, one Softone RW-20 ( R-Core type ) Output Transformer, vertical at rear / center.

Thank you ! for this super - nice mention Hari.

Jeff

 

[LLiu]

After 2 years of starting this project, the amplifier is finally getting completed with a logo and a MS top metal powder coated plate. The CAD drawing was done by FM @sadik and executed by an engineering firm at Pune (Any FM looking for building any kind of Chassis should consider this. You can PM me for details if required). Here are some final images to feast your eyes,


View attachment 73786
The logo is of my mentor/guru who has designed and provided atleast 80% of the components for me to assemble the amplifier with all detailed schematics, inputs etc. I have to admit i could not follow all his advise 100% and in some cases have deviated from the original. But i have realized my mistake and have taken corrective action in almost 50% of my mis-adventures. The amplifier logo fully deserves to be called a "Jeff Medwin" amplifier.

View attachment 73787

View attachment 73788

View attachment 73789

View attachment 73790

View attachment 73791

Thanks for looking.

Congrats Hari, we are the lucky ones who appreciate and enjoy the unconventional designs and execution by Jeff, happy listening!

 

[arj]

Also visible, one Softone RW-20 ( R-Core type ) Output Transformer, vertical at rear / center.

Jeff, whats your view on Softone components ? I had interacted with Shoichio san many eyars ago and ended up buying the his CDM Pro2 CD transport which is such an excellent , well engineered product.

 

[drlowmu]

I have looked and re-looked at the schematics. I have never been compelled to buy anything, other than RW-20s.

I both like and dislike what I see on their Softone schematics. Where they use silicon rectification, I would always want tube rectification, little if any solid state devices, and much better treatment of Ra and Rk resistors, and better coupling caps where used in their circuits. LOL, I looked seriously just last week for an hour at their phono EQ !!

Their R-Core RW-20 Output Transformer is VERY nice for the money. $120.00 USD plus shipping. It is built on a 50 VA R-Core, so it has weak low end extension, but it's midrange and top end, in my amps, is just lovely and engaging to hear. Speedy music delivery also ! An RW-20 is fine where most of the music lies, so we live with it for now.

Yes, I agree, their engineering is NOT shoddy. I like them. I typically want " more " than what they offer, for my own use.

Jeff

 

[IndianEars]

Do you still have the CDM Pro2 transport ?

Are they still available from Softone?

 

[Kannan]

Do you still have the CDM Pro2 transport ?

Are they still available from Softone?

check Jay's Audio CDPs, They employ the CDM pro2.

 

[arj]

Do you still have the CDM Pro2 transport ?

Are they still available from Softone?

I still have it. I think CDMPro by itself is hard to come by so they have stopped it. I believe there are newer mechanisms being made and Jays audio and North star design still make them amongst others.

I would guess the Esoteric mechanism is still No 1 followed by the CDM Pro based transports.

 

[IndianEars]

check Jay's Audio CDPs, They employ the CDM pro2.

Kanna,
I believe the Jay's CDT employs the CDM-4 mech.....

 

[arj]

Their premium version has the CDM Pro2LF if i remember right.

 

[drlowmu]

An addendum and correction to my post #131 above, regarding the Softone RW-20 SE Output transformer's "weak" low end. I was WRONG !!!

We have re-tested ( fully broken-in / 800+ hours ) RW-20s on several different state-of-the-art direct coupled SE monoblock amps, over the last week or two. The conclusion was the RW-20 beat out in fidelity, every SE output transformer we know of.

Previously, our LSES amps used only a 50 uF FILM cap, feeding the Final's tube B+. We have increased that "C2" 50 uF amount, by adding our favorite performing 15 uF WIMA cap across the existing 50 uF cap, ( 65 uF total now ). There is NO problem on the RW-20's low end anymore .

Speaker used was a state of the art MLTL, about 11 cubic feet internal volume, and the lovely new GPA 604 16 inch Duplex / point source driver.

The RW-20's tested audible performance, and speed, has now ( finally and rightfully ) EARNED it's way, as THE SE output XFR of our first choice, into every new amp we build, going forward.

This is highly important audio information, shared, only - on HFV.

Jeff

Softone RW-20 Single-Ended Audio Output Transformer