great I have a couple of dead Hackeramps I can't be bothered to fix so can re-use case etc
So Good... I built it twice!
- Thread starter S-Man
- Start date
This is the link to the build information that I used for this amp, it measures very well. There's some useful set-up tips and BoM at the end with recommended component types. It translates surprisingly well from Russian to English with Google translate:
https://cxem.net/sound/amps/amp240.php
https://cxem.net/sound/amps/amp240.php
martin clark
pinko bodger
Given the 'T' output stage, I rather suspect the optimal caps for such use will be rather smaller than 1uF as marked in first link: there simply isn't so much effective base-capacitance charge, that needs shifting...
(haven't gone through the schematic with the calculator in hand for first-apprehension yet tho..)
(haven't gone through the schematic with the calculator in hand for first-apprehension yet tho..)
S-Man
StrivingON
I'm not sure how the value of these caps would be calculated. In my little mind they allow a low impedance HF path for the PNP driver to pull the charge from the base of the NPN output device and vice versa and the value doesn't matter much. Prof Leach stated that they are not needed because this happens anyway via R29 & 30.
I will be fitting 0.68u since that what I have to hand. The first boards have the official 1u (Panasonic polypropylene).
I will be fitting 0.68u since that what I have to hand. The first boards have the official 1u (Panasonic polypropylene).
Agent_Cooper79
pfm Member
A question for the technically minded here:
How high voltage would be acceptable to feed this circuit given a loudspeaker load that is reasonably benign, ca 6 Ohm speaker (no racy impedance shifts etc.)?
I am on the lookout for a DIY-project with really good audio properties, phase margins, stability etc. that is able to provide amplification without clipping. I am not planning on punishing the amp. Just looking for some voltage headroom.
All the best, Magnus
How high voltage would be acceptable to feed this circuit given a loudspeaker load that is reasonably benign, ca 6 Ohm speaker (no racy impedance shifts etc.)?
I am on the lookout for a DIY-project with really good audio properties, phase margins, stability etc. that is able to provide amplification without clipping. I am not planning on punishing the amp. Just looking for some voltage headroom.
All the best, Magnus
In the page I linked to above the "designer" is using +/-42V rails which I think is a sensible maximum for it, as built.
With that said the only DIY chassis I have available has +/-50V rails so I'm going with that initially (I've uprated the necessary capacitors from the specified 50V to 63V) but with the plan to fit an additional pair of paralleled output transistors to give more reliability (and current drive) once I've got it up an running,
S-Man
StrivingON
Just having a good blast and it seems that my second pair of OM2.7s are not that great 
.
I fitted the speedup caps and maybe it made a small difference, possibly a smidge less forward sounding. However after a while I just couldn't seem to find any tunes that I wanted to hear. The sound seemed a bit constricted and the stereo image seemed a bit ping-pong.
So I put my Leach amp back in the system... normal service was resumed. All of a sudden I wanted to listen and the tracks in the playlist kept piling up.
At this point I was wondering if the OM2.7 was all a big mistake. So with some trepidation I put the first build back in the system. Needn't have worried... bloody superb!
There are a lot of differences between the two builds. I had assumed that because the 1st set are sharing a PS the amp was PS agnostic. The 2nd set are dual mono, but not using my preferred transformers. There are plenty of variables to eliminate but I think getting the PS right is vital, just like any other amp.
.I fitted the speedup caps and maybe it made a small difference, possibly a smidge less forward sounding. However after a while I just couldn't seem to find any tunes that I wanted to hear. The sound seemed a bit constricted and the stereo image seemed a bit ping-pong.
So I put my Leach amp back in the system... normal service was resumed. All of a sudden I wanted to listen and the tracks in the playlist kept piling up.
At this point I was wondering if the OM2.7 was all a big mistake. So with some trepidation I put the first build back in the system. Needn't have worried... bloody superb!
There are a lot of differences between the two builds. I had assumed that because the 1st set are sharing a PS the amp was PS agnostic. The 2nd set are dual mono, but not using my preferred transformers. There are plenty of variables to eliminate but I think getting the PS right is vital, just like any other amp.
And so it begins...
Sure, but doesn't S-Man's OM 2.7 experience illustrate that it isn't just amp X versus Y.
So much depends on the whole build (and indeed the system) and the details therein.
Personally I am really keen to hear what exactly made the sound difference between the two OM2.7 builds.
So much depends on the whole build (and indeed the system) and the details therein.
Personally I am really keen to hear what exactly made the sound difference between the two OM2.7 builds.
Agent_Cooper79
pfm Member
Thanks a lot for this OldSkool! Please share your build later, I am very curious on how you will implement the dual outputs.
Also, best of luck to you S-Man! I very much appreciate your honest sharing of the findings albeit good or bad.
Br. Magnus
A little update after I got my pair running this weekend...
For information my build is dual mono using a pair of Canterbury windings 400VA trafos with 35V AC outputs (50V DC) into a pair of Hackercap 6's and then the OM2.7s.
These boards certainly have promise, very clean and open sound across the audio range with very little colouration and everything sounding tonally correct. Voices are particularly good, but likewise trumpets, sax ,guitar and piano sound realistic without any grain or edge. There's excellent low level detail and although its a bit of a cliché but I've heard new things on tracks that I thought I knew well, particularly in the mid and bass regions. Bass is very well damped and detailed with good texture and sounds very unflappable particularly on dense and busy tracks. Timing is also excellent and the sound is very fluid, at least as good if not better than the NCC builds I've had before in this respect.
But (and there always seems to be a but) the overall presentation is definitely a bit forward in the upper mids and a bit lean in the bass, making some recordings a bit uncomfortable a listen.
With these boards I'm guessing the large local decoupling caps will have a significant influence on the sound , perhaps more so than the main PSU smoothing caps. I've used 470uF Elna Silmics for the output stage and 220uF Panasonic FCs for the input stage currently. I do have some 470uF Panasonics in "stock" so will try these out for the output stage next to see if that evens things out a bit, I'm hoping their lower ESR may increase bass response.
The only other downside of these boards is that the tight layout makes it difficult to experiment with different parts, especially as 63V electrolytics are mostly much larger diameter than the specified 50V versions. Similarly the main feedback cap has very little room for something bigger.
Will keep you posted on how things progress but it seems these are fundamentally decent and worth a go.
For information my build is dual mono using a pair of Canterbury windings 400VA trafos with 35V AC outputs (50V DC) into a pair of Hackercap 6's and then the OM2.7s.
These boards certainly have promise, very clean and open sound across the audio range with very little colouration and everything sounding tonally correct. Voices are particularly good, but likewise trumpets, sax ,guitar and piano sound realistic without any grain or edge. There's excellent low level detail and although its a bit of a cliché but I've heard new things on tracks that I thought I knew well, particularly in the mid and bass regions. Bass is very well damped and detailed with good texture and sounds very unflappable particularly on dense and busy tracks. Timing is also excellent and the sound is very fluid, at least as good if not better than the NCC builds I've had before in this respect.
But (and there always seems to be a but) the overall presentation is definitely a bit forward in the upper mids and a bit lean in the bass, making some recordings a bit uncomfortable a listen.
With these boards I'm guessing the large local decoupling caps will have a significant influence on the sound , perhaps more so than the main PSU smoothing caps. I've used 470uF Elna Silmics for the output stage and 220uF Panasonic FCs for the input stage currently. I do have some 470uF Panasonics in "stock" so will try these out for the output stage next to see if that evens things out a bit, I'm hoping their lower ESR may increase bass response.
The only other downside of these boards is that the tight layout makes it difficult to experiment with different parts, especially as 63V electrolytics are mostly much larger diameter than the specified 50V versions. Similarly the main feedback cap has very little room for something bigger.
Will keep you posted on how things progress but it seems these are fundamentally decent and worth a go.
S-Man
StrivingON
That is pretty much exactly what I thought when I first built the OM2.7 (the 1st set). Clean and tight but maybe just bit too forward in the upper mids.
I kept swapping between the OM and the Leach and really wanted the mellower sound of the Leach with the detail and control of the OM. I'm not sure how long I've had the OM now, but it resides in the system 80% of the time. FWIW the Leach gets about 15% air time and my mosfet amps 5%.
My 2nd OMs seem to have mellowed out a bit. They are still not as good as the 1st set, and I intend to find out why. But, although I don't want to believe in burn-in, I do think they are sounding better.
I kept swapping between the OM and the Leach and really wanted the mellower sound of the Leach with the detail and control of the OM. I'm not sure how long I've had the OM now, but it resides in the system 80% of the time. FWIW the Leach gets about 15% air time and my mosfet amps 5%.
My 2nd OMs seem to have mellowed out a bit. They are still not as good as the 1st set, and I intend to find out why. But, although I don't want to believe in burn-in, I do think they are sounding better
.
a.palfreyman
pfm Member
I reckon it's FB cap forming. When I built a high gain low noise amp (for measuring etc) this used very low FB resistors: 1k5 and 4R7 for the high gain with low noise so you need a lot of capacitance to get a low corner F.
I initially had erratic results and a higher than expected lower F cut off. When I got the caps I was going to fit, I formed them at a few volts prior to fitment and run them with a small DC bias. These then operated as expected so it could be a small leakage current in the FB cap as this affects bottom end the most and will take quite some time to form in circuit with low dc bias.
I initially had erratic results and a higher than expected lower F cut off. When I got the caps I was going to fit, I formed them at a few volts prior to fitment and run them with a small DC bias. These then operated as expected so it could be a small leakage current in the FB cap as this affects bottom end the most and will take quite some time to form in circuit with low dc bias.
S-Man
StrivingON
Zombie
pfm Member
It's mentioned in that link above. Somebody's opinion.