The much-awaited moment finally arrived. After yesterday’s driver tests, I did a lot of work this morning to assemble cables and test the output stage. What I clearly know now is that I won’t be needing any heating this winter! What on earth was on my mind when I decided to build this amp? God only knows…
Here are some pictures of the first tests in the workshop and then when I hooked it up to my system downstairs in the sitting room:
I did a quick measurement of the output THD without burning in the 4-65a or the amp. The operating point is not optimised but clearly shows a nice picture. First of all, the amp is absolutely quiet. The Rod Coleman regulators plus the extensive filtering on all supplies (LCLC and CLCLC) make this the quietest amp I’ve ever made! The distortion is higher than predicted. With the valves at 100mA/540V and with a non-inductive resistor load of 10Ω, the THD is about 2.7% for nearly 6W of pure class A power. Only 4% of the harmonic content is H3 and with a nice H2 component. The footprint of an SE amp is clearly on this amp.
Hooked it downstairs and after a lot of wiring I finally got to play some good records on this amp. I used my 26 DHT preamp. First record to be played was “a love supreme” (John Coltrane). Here are my impressions so far:
- I’m surprised with the bass. It is powerful and not something I was used to in a single ended amp
- Definitely needs some burn-in time. The amp improved after 1 hour of use
- It’s loud! You can get 10W easily in class A2. Very loud for my room!
- The tone is warm and very sweet. you get the sound of the DHT clearly
- Dynamics are its forte. This amp responds very well to them
Some more pictures:
Now is time for proper listening after so much work. A real accomplishment and I’m feeling very proud. The amp fits within my cabinet so wife is happy 🙂
Amazing accomplishment Ale. I love the pictures, there is almost no need for words…it is such a good feeling to see that someone who share the same interests is successful.
Hope that your heating bill will go down a lot
You be walkin’ the walk with this build my friend. As Radu Tarta stated in his coment above, “Amazing accomplishment, Ale.” I wholeheartedly second his words. Truly amazing. You have stumbled across (created?) an arcane audio niche with your blog/builds. Or is it more like a trench in the ocean’s floor? Regardless – it’s amazing. -Edward
Congratulations mate! Can’t wait to hear it!
Just between us you should probably see a doctor about this though… 😉
I don’t dare think what the next amp will look like……….
Probably going back to basics and a simple SE one! On a second thought, I think my wife will kill me if I come with a new amp at this stage…
Hullo Ale.
Well, the Ultimate Breadboard eh? Nice to see the 4/65s and glad to hear that it sounds good. Well done and regards
Paul
Thanks Paul! I’m yet to try the 814s but need to modify the filament supplies…
Cheers
Ale
Love it ! Looks like you’re getting a nice bit of colour in the anodes . Get another piece of thoriated glass up front . 3C24 comes to mind 🙂
Yes, a lot of heat. Thanks for the tips on the 4-65a!
3C24 is another filament beast. Would be nice, how would you bias given filament requirements. Cathode bias?
Cheers
Ale
2 x red LED at >6mA does the trick 🙂 Just need to get a bit of colour in the anode . I’ve done filament bias but it’s a bit tricky to get the fil supply quiet enough (I used chokes) . Large 1 ohm fil bias resistor required which will run very hot 🙁 Makes a very good driver for PX4 but slightly low gain . Microphonic but then again , aren’t all the decent sounding drivers like this ?
🙂
Here we go then. Need to get sorted the raw dc supply but would be worth trying. I have a pair of them I think.
I may get the 814s in replacing the 4-65a first…
Anyway, enjoying the sound of this amp now after all the work. Just playing “loaded” from velvet underground now 🙂
Cheers
Ale
Hi Ale,
Could you post your 4-65A amp in detail ? I have one pair of 4-125A, so building amp with these tubes will do in future.
Tks n regards,
QA.
Hi there, search the blog well as it is already posted in detail. Cheers.