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Solid State Talk all about solid state amplification.

The AMNESIS amp: a good amplifier, like a gentleman, has no memory.
The AMNESIS amp: a good amplifier, like a gentleman, has no memory.
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Old 13th February 2019, 11:58 AM   #491
Symon is offline Symon  United Kingdom
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Unfortunately I missed the obvious problem with MPSA18, it's NPN and the input devices Q3 & Q5 are PNP. and there is no PNP equivalent to MPSA18 that I can find, I've looked before.

Regads,
Symon
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Old 14th February 2019, 10:49 AM   #492
maxlorenz is offline maxlorenz  Chile
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Thanks, dear Symon,

Fortunately, the amp is still very stable. It is a nice transistor indeed. It can be used at input but as the NPN for the CFP. Simulations did not outperformed the previous, though. Besides, Hans and JOSI1 have given enough recommendations about different options there to be occupied for a long time...

You see, it is astonishing how the flavor of the sound can change with a tinny mod.

Burning-in is still going on for the MPSA18. I am not sold on it yet. I can advance that it sounds indeed more delicate, detailed, refined and articulated than the BD139 in that position, but I miss some of the raw power sensation and bass of the former, which sounds a bit primitive by comparison. The sound is too tight for my taste at the moment...

It only sees 22mW of dissipative stress.
BTW, I tried 2N2222 and 2N2907 on the Sziklai bootstrapped output, since the input transistors see around 10mW of stress there, thinking that they will be excellent. Well, the simulations are awful, reminding me that the Sziklai output is more a balance act than the rest of the output options...

Cheers,
M.

PS: isn't this the best hobby ever???
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Old 14th February 2019, 03:04 PM   #493
Symon is offline Symon  United Kingdom
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Hi Max,
I know what you mean about small chnages agffecting character of the sound.
I spent a lot of time modifying a CD player, and was interesting how the sound
changed with even components not obviously in signal path.

I'm not surprised MPAS18 and BD139 sound different they have very
different characteristics. I would have thought something like BC337
would be more appropreate in this position. It is more of a driver than MPSA18
but faster and more gain than BD139. But only listening will show how it sounds.

Happy listening

- Symon
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Old Yesterday, 10:35 AM   #494
maxlorenz is offline maxlorenz  Chile
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Quote:
Originally Posted by Symon View Post
Hi Max,
I know what you mean about small chnages agffecting character of the sound.
I spent a lot of time modifying a CD player, and was interesting how the sound
changed with even components not obviously in signal path.

I'm not surprised MPAS18 and BD139 sound different they have very
different characteristics. I would have thought something like BC337
would be more appropreate in this position. It is more of a driver than MPSA18
but faster and more gain than BD139. But only listening will show how it sounds.

Happy listening

- Symon
Yesterday I had another Van der Graaf Generator marathon and I am happy to say that the dynamics and bass are coming back. Understand, I am not saying that this tinny unit needs a lot of heavy action to burn-in: it is the case that when doing quick and dirty mods I sometimes overdo my soldering and heavy lumps of new metal end up on the signal track...

Interesting comment about BC337. I am sure there are lot of possibilities for this critical VAS position, so it is recommended to put there connector pins to allow easy swapping of different units to evaluate sonic presentation differences. One can find then a sound balance that better match one's taste.
MPSA18 has Cbc of 1,5pF and Ceb of 5,6pF, typical, as per datasheet.

Another aspect to evaluate is average working temp (not instant T change of the junctions) as, per convenience, I had the BD139 attached to the heatsink from the 2SC4793 cascode which does all the heavy work, sharing its T behavior. So the BD139 was warmer than needed...could this influence sound balance? I guess the answer could be positive. It should be easy to perform an ear test...

Cheers,
M.
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Old Yesterday, 11:11 AM   #495
JRZoid is online now JRZoid
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Filter IT. I hate Solid State...Low voltage has hardly no Power or Energy....They Require LOTS of Capacitance and for Smoothing/Ripple Rejection.

A couple 6800uf's do not Sound good at all lol. I will Replace with Audio Grade 10,000uf.
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Old Yesterday, 04:54 PM   #496
maxlorenz is offline maxlorenz  Chile
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Quote:
Originally Posted by JRZoid View Post
Filter IT. I hate Solid State...Low voltage has hardly no Power or Energy....They Require LOTS of Capacitance and for Smoothing/Ripple Rejection.

A couple 6800uf's do not Sound good at all lol. I will Replace with Audio Grade 10,000uf.
Thanks for the post JRZoid, but I do not know why you are here if you hate SS, with all due respect...
For the record, we are exploring strategies to avoid or reduce LTMD, and hope this will aproach SS to Tubes, while keeping the advantages of SS over Tubes.

Cheers,
M.
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Old Yesterday, 05:32 PM   #497
ostripper is online now ostripper  United States
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Even 4700uf is good( sounds good ? subjective) if it is bypassing 70KHZ rectification.


That would be SMPS. I'm permanently out of the big trafo 100,000uf
"fetish". No more " boat anchor" SS power amps.


OS
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Old Yesterday, 05:42 PM   #498
Hans Polak is offline Hans Polak  Netherlands
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Dear Max,

I don’t doubt for even a second your impression that changing the VAS transistor changed the sound perception.
However I find it hard to understand how one single transistor could have this noticeable effect.
Therefore my question: do you still have an old transistor radio.
This is a perfect tool to detect HF oscillations in the Mhz region without invading or loading the amp and if not excludes that HF is changing the perceived sound.

Hans

Last edited by Hans Polak; Yesterday at 05:45 PM.
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Old Today, 12:15 AM   #499
maxlorenz is offline maxlorenz  Chile
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Quote:
Originally Posted by Hans Polak View Post
Dear Max,

I don’t doubt for even a second your impression that changing the VAS transistor changed the sound perception.
However I find it hard to understand how one single transistor could have this noticeable effect.
Therefore my question: do you still have an old transistor radio.
This is a perfect tool to detect HF oscillations in the Mhz region without invading or loading the amp and if not excludes that HF is changing the perceived sound.

Hans
Yes. You are most probably rigth. I already thought about this possibility and dear Symon commented about it also. This amp has still the SMPS supply which has those bursts of oscillation that surelly are a too big test for any amp, and probably I have bursts of oscillation that I am not catching on the scope and that is the reason why there is perception of unbalanced sound to the mid-highs. I did not had the time to transplant the linear PS that I have spare.
But I am officially on vacation for two hours now so I will revert to the last version for now and then when the linear supply is installed I will try again.

The other amp, the red PCB, has a linear supply ("charge-transfer supply"), without noises and I will try the mod there, which shall be faster to do.

Quote:
Ostripper wrote:
Even 4700uf is good( sounds good ? subjective) if it is bypassing 70KHZ rectification.

That would be SMPS. I'm permanently out of the big trafo 100,000uf
"fetish". No more " boat anchor" SS power amps.

OS
My good SMPS (not the present one) sounds nice with added capacitance.
Usually 10.000uF per side. On this one I used 20.000. Perhaps that caused the malfunction...
Anyway for 35W you don't need more...

Cheers,
M.
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