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Old 12th February 2013, 01:13 PM   #1
tim614 is offline tim614  United States
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Default What's going on?

First off, I'm new in this game.
I've built several amps using existing designs mostly SE, from el84 to kt88.
Recently I try my hand at PP, so I built a pair of PP kt120 triode strap with IT phase splitter and 6n6p as driver, the amps are bias at 80ma per tube.

I recently acquired a pair of drd 300b, my first DHT. The drd have a fresh pair of
Tj mesh plate 300b.

My preamps is a monarchy nm24 also with fresh tubes, my cdp is a nad 515bee.

And my speakers are a pair of yamaha ns1000.


I've been listening to both amps 300b & the PP and one thing I notice the 300b sounded much deeper in the bass, it goes much lower than the PP, it does everything better than the PP.

So. Am I experiencing the magical of DHT?
Or there's a flaw in my PP?
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Old 12th February 2013, 01:19 PM   #2
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Most probably a flaw in your circuit which leads to poor low frequency behavior.
If you want professional advice, post your circuit, a list of parts you used with all its parameters (obviously your OPTs) and even better some frequency sweeps and other measurements.

Quote:
So. Am I experiencing the magical of DHT?
No
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Old 12th February 2013, 03:07 PM   #3
DF96 is offline DF96  England
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Bass is not determined by the valves but by the circuit (e.g. feedback, cathode decoupling) and components (e.g. OPT primary inductance). A weak circuit can give more bass at the speaker bass resonance.
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Old 12th February 2013, 04:28 PM   #4
kevinkr is offline kevinkr  United States
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Fill in the details on both the PP amp and the 300B amplifier, for example a PP amplifier without feedback may actually have a higher source impedance - i.e. poorer damping factor than the SE amp, with feedback the situation would of course be reversed.

FWIW I have designed and built a lot of PP and SE amplifiers over the years and for personal use I prefer a well designed SE amplifier to a comparably well designed PP amplifier.

It may also be down to the way the NS-1000 interacts with the output stage of any given amplifier. (Relating to source impedance, distortion spectra and LF/HF extension IMVLE.)
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Old 12th February 2013, 09:41 PM   #5
tim614 is offline tim614  United States
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Thanks!
I will try to post a schematic and more details.
I guessing its a synergy thing, but I'm learning.
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Old 12th February 2013, 11:54 PM   #6
tim614 is offline tim614  United States
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Click the image to open in full size.here the shematic for the PP, 6n6p for driver tube with 2 red led for bias.
Attached Images
File Type: jpg pp kt88-IT.jpg (608.2 KB, 96 views)
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Last edited by tim614; 12th February 2013 at 11:56 PM.
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Old 13th February 2013, 02:46 AM   #7
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There's a fad to float output transformers' secondaries from ground, but it's dangerous and irresponsible. Just my opinion, but firmly held.

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Old 13th February 2013, 03:48 AM   #8
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Please explain to the OP why it is dangerous and irresponsible. It helps to know the "why".

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Old 13th February 2013, 11:44 AM   #9
DF96 is offline DF96  England
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If the transformer insulation breaks you could have a speaker cable attached to the high voltage rail.

What are the screen feed diodes supposed to do? Under normal conditions they will do nothing, being forward biased. If screen current tries to become negative (possible under certain circumstances) then the triode-connection suddenly gets disconnected which will cause distortion on peaks. Am I missing something, or is this just part of the modern fad for inserting diodes everywhere?
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Old 13th February 2013, 12:24 PM   #10
tim614 is offline tim614  United States
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my secondary is grounded. and no diode in the triode strap.
sorry that i didn't state that clearly.
i use the schematic as reference but leave out what i though was unnecessary, i did use the lundahl IT but for OPTX i use hammon.

the amps didnt sound bad at all, just that when compare to the 300b, with everything
else the same cdp, pre, speakers, same song (hotel california). i notice that the 300b were more detail sounding especially in the lower note. if you're familiar with the song, the begining of that song there are 3 bass notes the third note were clearly different from the first two when play through the 300b, but when play through the pp all three bass note sounded almost the same.
i dont like posting stuff like this but its bothering me, so i have to get it out there. i hope this is just a synergy thing, i will try to switch thing around to see if its because the pre is better match with the 300b by taking out the pre and put in a passive.
thanks again guys! i will try to do a signal sweep to see whats going on also.
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