Is it okay to run the heaters at ground potential? The datasheet is recommending 100V maximum between Cathode and heater.
That's good to know. I thought it would run much higher with 250V on the plates. I'll add resistors on my revised boards along with the extra caps then. Thanks.
Hi Guys,
A little bummed because I just typed three paragraphs only to hit Ctrl-A by mistake and erased the whole thing. I shall start again.
I got a chance to sit down and do some listening. I hooked up this amp to my A/B system and do some comparisons. I started with the Honey Badger, then Symasym, DX Super A and Peeceebee. Each of these amps sound more Hi-fi than this amp. Compared to those this amp sounds subdued. Less detail, a little looser bass, a little more pronounced mids. I thought I would like this amp more on jazz but that didn't turn out to be the case. Little details like the sound of the bass players fingers on the strings and the sax players breath on the reed were kind of missing. I actually preferred this amp on electric blues and female voices. The pronounced mids and tempered highs seemed to enhance those things. Rock drums are a little easier sounding with this amp. The snare is less harsh and wetter sounding that on some of the other amps. This reminded me a biit of the SKA GB150 so I hooked that up and low and behold, I found its match. These two amps could be brothers. Very, very similar sound stage. So I would say, if someone is a SKA fan they will like this amp a lot.
Now I will qualify this review with saying that the tubes may have a big influence on the sound and I have installed NOS Sylvania tubes. Other brands may give a different tonal quality. YMMV
Blessings, Terry
A little bummed because I just typed three paragraphs only to hit Ctrl-A by mistake and erased the whole thing. I shall start again.
I got a chance to sit down and do some listening. I hooked up this amp to my A/B system and do some comparisons. I started with the Honey Badger, then Symasym, DX Super A and Peeceebee. Each of these amps sound more Hi-fi than this amp. Compared to those this amp sounds subdued. Less detail, a little looser bass, a little more pronounced mids. I thought I would like this amp more on jazz but that didn't turn out to be the case. Little details like the sound of the bass players fingers on the strings and the sax players breath on the reed were kind of missing. I actually preferred this amp on electric blues and female voices. The pronounced mids and tempered highs seemed to enhance those things. Rock drums are a little easier sounding with this amp. The snare is less harsh and wetter sounding that on some of the other amps. This reminded me a biit of the SKA GB150 so I hooked that up and low and behold, I found its match. These two amps could be brothers. Very, very similar sound stage. So I would say, if someone is a SKA fan they will like this amp a lot.
Now I will qualify this review with saying that the tubes may have a big influence on the sound and I have installed NOS Sylvania tubes. Other brands may give a different tonal quality. YMMV
Blessings, Terry
How does it compare to your TubSoMo? From your description that sounds like my first impression.
I try to get them hooked up side by side and see. I'll have to clear off a little more space on the bench. 😀
I have experienced the same tonality with NO NFB amps too. You must pay attention to lot of things with NO NFB amp - intristic linearity of the parts, quality of passive parts, PSU etc. NFB implemented correctly just make amplifier better.
I keep wondering if I'm choosing the wrong types of capacitors. Is this possibly where some of the fidelity is lost?
Try changing some parts and you will propably hear it.
I am not saying that this amplfiier design is bad, just in my experience NO NFB is hard to make it right.
As I do not want to hijack or spam with this thread, PM me and I will sent you schematic of another hybrid amplifier with NFB if you are interested.
I am not saying that this amplfiier design is bad, just in my experience NO NFB is hard to make it right.
As I do not want to hijack or spam with this thread, PM me and I will sent you schematic of another hybrid amplifier with NFB if you are interested.
Hi Terry, interesting comparison. Did you try it with Slewmaster-based HexFET output section - that was the best combination during my tests. Since there is no global NFB loop, reducing distortion, different OPS sections sound pretty different.
Cheers,
Valery
Actually, these two sound rather different to me.
TubSuMo is an ultra-low distortion, this one is, let say - ultra-high 🙂
THD is sort of 0.0008% and 0.4% respectively in the same conditions (2W output power @ 8R, 20KHz).
Hi Valery,
I didn't try the hexfet ops yet but I will. I spent the afternoon trying to fix my Tubsumo so I could compare them. My wife walked in while I was setting it up and I forgot to plug in the nfb. Blew the cap multiplier transistors in both ops and something else in one of the ips. I still haven't figured it out. Gave up for the night. I doubt these two will sound similar. My memory of the Tubsumo was that it was very detailed. That doesn't describe this amp so far. Like I said, this amp is closest to my SKA.
I didn't try the hexfet ops yet but I will. I spent the afternoon trying to fix my Tubsumo so I could compare them. My wife walked in while I was setting it up and I forgot to plug in the nfb. Blew the cap multiplier transistors in both ops and something else in one of the ips. I still haven't figured it out. Gave up for the night. I doubt these two will sound similar. My memory of the Tubsumo was that it was very detailed. That doesn't describe this amp so far. Like I said, this amp is closest to my SKA.
Valery, can you give any recommendations on capacitor composition? I know to use ceramics for decoupling. I've just been picking film caps for in the audio signal. Could polyester be dulling the sound?
My TubSoMo seemed like they were running through a low pass filter.
My TubSoMo seemed like they were running through a low pass filter.
Same as with yogurts - "not all of them are equally healthy" 🙂
This is a good question. Capacitor distortion very much depends on the material used.
Based on my knowledge and experience, the best caps are metal film ones (polystyrene, polypropylene, teflon). I use them wherever I can. Mica is very good, but expensive, limited availability in my area and bulky cases (although "true audiophiles" like those big red barrels a lot 😉).
For the low values, like HF compensation, you normally would not find any of those, as you need really low values (1-th or 10-th pF) - in this case I use multi-layer ceramics. Ceramics are not good if higher values are used in the signal path - they suffer from noticeable non-linearity.
Cheers,
Valery
This is a good question. Capacitor distortion very much depends on the material used.
Based on my knowledge and experience, the best caps are metal film ones (polystyrene, polypropylene, teflon). I use them wherever I can. Mica is very good, but expensive, limited availability in my area and bulky cases (although "true audiophiles" like those big red barrels a lot 😉).
For the low values, like HF compensation, you normally would not find any of those, as you need really low values (1-th or 10-th pF) - in this case I use multi-layer ceramics. Ceramics are not good if higher values are used in the signal path - they suffer from noticeable non-linearity.
Cheers,
Valery
I've reread a few sections of one of Slone's books. He recommended not using Polyester. I think I read a paper by Richard Marsh saying the same. I think that is what I may have used for C1 although I used the same input caps in CFA-CFPx2. China should be back to work next week. I'll order some more boards and be more selective what I use for passives and see if there's an audible difference. Maybe my input fets will have arrived by then too.
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Here is a reprint of a good material by Walter G. Jung and Richard Marsh:
>PICKING CAPACITORS<
My harmonics spectrum measurements don't show any problems with polyester ones...
>PICKING CAPACITORS<
My harmonics spectrum measurements don't show any problems with polyester ones...
I didn't see any signal change at higher frequency when I had the amp on the scope either but I can definitely hear one.😀 My scope isn't a very good quality unit though.
That was the paper I was thinking of as well.
That was the paper I was thinking of as well.
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