I think that (apart distortion bandwidth and slewrate ) the main thing witch make the difference between preamps is their ability to drive very low impedance loads, something like 10 ohms.. Of course, power dissipation is not a concern.
So it would be a very good idea to make a preamp from a headphone SSA.
Well, the lazy dogs will not forget they are many current feed back video operational integrated circuits witch can do it very well too.
How about lowering the supply rail. Then the cascoded VAS can be avoided and the more complementary bipolar can be used for the output stage (I don't think IRF610 with 20mA bias or even higher is suitable for preamp). EDIT: AND Salas type regulator will be more suitable for it too. The otput stage will look like the attached circuit (or you can "modify" the attached circuit with SSA frontend, doesn't matter)
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About SSA Preamp
I don't think that preamp has more benefit than drawback. DCB1 buffer is enough for me, but some MOSFET amps seem to need preamp. I think a SSA preamp will be suitable for SSA crescendo. The topology between the preamp and amp is also similar. I found that when the topology is similar between preamp and amp, the sound tends to be good.
I'm reluctant to build the SSA Crescendo because the supply rail is 70V minimal. I don't want to use a big trafo that I usually use for PA amp. I already consider using dual transformer, but what I have on hand are 2x30V=60V (below recommended value) or 2x42V=84V (too big even after regulation).
If I know how to modify the SSA Crescendo for 55-60V, I will sure build the preamp and the SSA Crescendo.
I don't think that preamp has more benefit than drawback. DCB1 buffer is enough for me, but some MOSFET amps seem to need preamp. I think a SSA preamp will be suitable for SSA crescendo. The topology between the preamp and amp is also similar. I found that when the topology is similar between preamp and amp, the sound tends to be good.
I'm reluctant to build the SSA Crescendo because the supply rail is 70V minimal. I don't want to use a big trafo that I usually use for PA amp. I already consider using dual transformer, but what I have on hand are 2x30V=60V (below recommended value) or 2x42V=84V (too big even after regulation).
If I know how to modify the SSA Crescendo for 55-60V, I will sure build the preamp and the SSA Crescendo.
SSA Basic - Balanced - VAS + OPS - Mosfet ?,
LC, Please have a look at this sch, if eventually this should work, and if the termal stability would be an issue?
Thank You,
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SSA Basic - Balanced - VAS + OPS - Mosfet ?,
LC, Please have a look at this sch, if eventually this should work, and if the termal stability would be an issue?
Thank You,
Nice try, but this sch won't work at all. Corrections:
- omitt R17, R18, completely!
- T9, T10 must be at least 100V trannies like 2SA970/2SC2240, BC's would fail in the moment, VAS bias current max. 7 mA because of power dissipation on these BJT's
- you have complete mess around T13, T14, connected like this you'll have smoking hazard in a split second
- so you want to drive outputs to the rail potential, correct output sch in attachment
- thermal stability won't be an issue as long as T11 is BD441 bolted to the main heatsink (needed to compensate positive tempco of IRF's)
Hope all this helps, regards, Andrej
P.S. OMG R10, R11 are not connected to the SSA bridge, only to LED !!!
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Please don't worry, I'll do all needed parts value calculations for lower rails potential, no problem.
I am on waiting NJL4281 since NJL4302 are arrived as NJL3281/NJL1302. I have 4x 22.000µF/40V, 2 toroids 300Va 2x25V, and some nice rubish heatsink that mesure l:150 x h:195 x d:27mm i think that wil be enough for one chanel ( 2 output transistor).Ooooo yeah Marc, cannot wait to hear the news from you, the board is just awesome. Please continue in a high gear mode, regards
Marc
Hi Marc
Drivers will be hot at operating conditions in either case. Faster getting there with more constant thermal conditions for the whole amp and the drivers themselves would be if they will have their own heatsink. Power dissipation is app. 1W per driver so you have to find suitable on board heatsink to hold the temperature of the drivers below 75°C in a closed amplifier case at max. musical loading programme.
Drivers will be hot at operating conditions in either case. Faster getting there with more constant thermal conditions for the whole amp and the drivers themselves would be if they will have their own heatsink. Power dissipation is app. 1W per driver so you have to find suitable on board heatsink to hold the temperature of the drivers below 75°C in a closed amplifier case at max. musical loading programme.
LC, if we admit t° in case is around 40°C i will need a heatsink with Rth = (75-40)/1W= 35°c/W per driver
I am rigth?
MArc
SSA - Bal. Lat-Mos
LC,
Thank You for the Sharp Eye Inspection, and all suggestions,
In a very early morning hours, tired eyes tend to sleep and errors appeared quickly. I did all the sugg. changes and hopefully now is the SCH correct, my I ask You is there any better currently obtainable Lat-Fets to successfully replace IRF 960-9610 fets to get same tempco as the OPs?
I upl. corrected SCH.
@ Jaj,
Please explain a bit more what do You mean by that and how to come closer to the rail Op. and not to raise OP DC40V Rails.
I have already all the PSU hardware for this particularly setup avail. and will try to replace the stock Amp. boards with these SSA-Bal. Mos.
Thank You, &
LC,
Thank You for the Sharp Eye Inspection, and all suggestions,
In a very early morning hours, tired eyes tend to sleep and errors appeared quickly. I did all the sugg. changes and hopefully now is the SCH correct, my I ask You is there any better currently obtainable Lat-Fets to successfully replace IRF 960-9610 fets to get same tempco as the OPs?
I upl. corrected SCH.
@ Jaj,
Please explain a bit more what do You mean by that and how to come closer to the rail Op. and not to raise OP DC40V Rails.
I have already all the PSU hardware for this particularly setup avail. and will try to replace the stock Amp. boards with these SSA-Bal. Mos.
Thank You, &
Attachments
@ Jaj,
Please explain a bit more what do You mean by that and how to come closer to the rail Op. and not to raise OP DC40V Rails.
I have already all the PSU hardware for this particularly setup avail. and will try to replace the stock Amp. boards with these SSA-Bal. Mos.
Thank You, &
I think you haven't fixed the output stage in your attachment.
No, I cannot help you with the technicality as I don't understand electronics (tho I guess you cannot do much). I'm just a builder (build-discard-build-discard-and so forth). And I'm pretty sure that the output topology suggested by LC will not give you a good sound.
I guess you want a higher wattage than the lateral circuit recently suggested/posted by Lazy Cat, which is very nice. How much power do you want btw? I know that low voltage transformer usually is low power also. But I think even if the voltage is low (40V) if you use a big power (current capability) transformer, 40V is fine (you just need to watch out the speaker impedance)
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