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PostPosted: 24 Jul 2018, 19:04 
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Joined: 03 Feb 2018, 00:47
Posts: 41
Location: Brisbane, Australia
I found this statement over on another site (whathifi.com).
Truly flat speakers can sound a bit mid-range-heavy, bass-light and 'dark' to many people, until they get used to the sound.
Could this be what I am hearing? I am new to high end audio equipment. I do hear the very clear audio that sounds like I am there, voices and instruments sound like they are coming from somewhere other than the speakers.

Source is an iPhone by the way, which I gather are a fairly good DAC.

Thanks,
Glenn.


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PostPosted: 24 Jul 2018, 21:41 
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Location: Arizona, USA
HI, I could not locate your speakers on the web to see actually what they are able to do. Most speaker specs are optimistic and the bottom end spec at 65 is not all that low. Full range speakers normally spec at 30 HZ or lower. In all probability yours start to roll off around 100 so by 65 they are 3 db or more down in response. Depending on the truthfulness o f the maker it could be even further down. 88db/w is average for book shelf ones. The amps...depending on the build and various components used are flat to below 20 HZ. I have a pair of EL34 ones on my bench right now and they show flat to about 11HZ (and out past 25KHZ). They use the 0.22 caps. 0.33 are not really any better and the chance exists that you might amplify sub sonic noise is greater. Something to check if the amp seems to have too much top end and not enough bass (and perhaps doesn't sound just right) is to verify that the phase of the negative feedback is correct. Temporarily disconnect it on one amp and see if the volume goes up or down. When disconnected it should go up. Not a whole lot as there is only a minimal amount of it. If it goes down then the phase of the output is backwards. This design uses the output transformers to invert the signal. If it is backwards there are a few ways to fix it. Change which of the output tubes gets the signal from the driver stage is often the easiest. Alternatively swap the anode and screen wires from one tube to the other.

Nearly everyone I know of and those that have commented on the amps (both the diy and commercial versions) clearly indicate that they are not bass shy. Depending on how much of a purist you might be there is no reason that some "tone" control can't be used. Just note that when you boost a range...it means the amp must supply more power to those sounds and eventually you could get past the amount it can deliver and get distortion.

An iPhone is an ok source, but there may be an impedance mismatch at the junction between it and the amp. The iPhone may not be able to correctly drive the 100K ohm input impedance of the amps. I don't have one to test that, but my Fiio and Sony players do fine as does my laptop. I have not tried my S7 on one though.

Good listening
Bruce

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PostPosted: 24 Jul 2018, 22:43 
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Location: Brisbane, Australia
Thanks Bruce. First up, I have to admit that I grew up through the Disco era. Thumping bass may have distorted my musical appreciation... ;) I suspect that it is a mix of this and my less than stellar speakers. Their site seems to have gone, and there are rumblings about them being dodgy. I have also been told that these speakers might need "running in" before they give out their best bass, and I may need to sit them on proper stands to propagate the bass properly.

Bass aside, the sound out of this unit is amazing.


My feedback was definitely wrong, volume increased when connected. Having read through the whole forum several times, I fully expected the feedback reversal (wasn't disappointed). I reversed the anode and UL connections to the output tubes to fix it.
As a helpful note to future builders, if you connect to the tubes on the schematic with the windings as drawn on the Edcor schematic, it is reversed. Swap the transformer vertically to make it right. ie swap the brown/white brown pair with the blue/white blue pair.

Oh, I used 0.33uF caps because they were readily available.


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PostPosted: 25 Jul 2018, 06:29 
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Joined: 01 Apr 2017, 19:56
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Just to corroborate with Bruce, I have a pair of Lando LX190 tower speakers (30Hz - 20kHz / 92db) and the Oddwatt (KT88) pushes them with a lot of bass!


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PostPosted: 25 Jul 2018, 19:12 
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Location: Brisbane, Australia
Thanks Guys.
I have learned a few things. The speakers apparently need breaking in. They need to be punished initially to soften up the cone surrounds. The main problem I have learned is that I have to listen at low levels as my workshop is not soundproof. At low levels bass is "underemphasised". Harking back a few years, devices had a "loudness" control which I guess was to combat this problem. I just need to give my Wife and neighbours earplugs... :)

So there is nothing wrong with my amplifier build, and of course we know there is nothing wrong with Bruce's design.

For the benefit of other potential builders:
I am in Australia (240V mains). Power transformer is XPWR117. Valves (Tubes to most of you Guys) are JJ EL34's. DC6V on driver heaters (7806 regulated), AC on outputs all heater supplied from the power transformer. Currents balance between 62-64mA per tube. I have only 63 volts lift on the heaters, need to tweak that up a tad I guess.
At cold power up, 520 VDC on the first filter cap. After 15 seconds (max) it drops to 495-ish. I will replace the first cap with a 100uF 550V one from Element 14 to avoid the need for the timer circuit.
After 1 hour runnning, the power transformer is barely warm, the output transformers are all but cold.
The LM317's are running at 37 deg. C, noticeably warm.
My sense is that I would be able to run KT88's in this amp, but might need extra heatsinks on the 317's.

I want to personally thank Bruce for his design and making himself available to help. As my Grandfather would have said... "Your blood is worth bottling".. :)
Capacitor details:
http://au.element14.com/epcos/b43541a7107m000/cap-alu-elec-100uf-550v-snap-in/dp/2750281


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PostPosted: 25 Jul 2018, 20:17 
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Location: Arizona, USA
Hi, You should be able to use the KT88s without any issues. The LM317 can run a lot hotter than that. Exactly how hot would it get with KT88s is hard to tell, but my experience has been that the voltage across it is lower with KT88s than KT77s. So while the current is greater (about 180 ma vs 125 ma) the actual increase in heating is not as much as you would initially expect. One thing that is helpful...if you didn't already do this is to use heat sink compound between the LM317 and the heat sink.

520 volts is about what I would expect on cold start up without a delay. A higher rated cap is definitely in order.

Good listening
Bruce

EDIT: BTW, I'm using a bi-amp set up for my main system right now and both sets of amps are using KT77s at 465 volts B+. One pair of the amps is the original ones from 2008 that has been updated to current specs.
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PostPosted: 25 Jul 2018, 21:09 
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Location: Brisbane, Australia
One question. I am adding a 100uF 550V cap as the first filter. The physical can in there needs to stay as it is a dual 100uF which also serves as the next cap inline. So I have three choices:
1. Don't use the extra 100uF.
2. Put the 550V, then resistor (value TBA) to the next 100uF, then resistor to the final B+ 100uF (so a chain of 3 caps instead of two)
3. Put the 550V one in there, then the parallel 100 ohm resistors, and parallel the 100uF caps as 220uF for the B+ instead of 100uF.

Any guidance on which would be better?


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PostPosted: 25 Jul 2018, 23:32 
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Joined: 03 Feb 2018, 00:47
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Location: Brisbane, Australia
Who needs a fire when you have 4 Class A Tube amps running... :)


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PostPosted: 26 Jul 2018, 05:43 
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Joined: 07 Jan 2018, 07:13
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Hi Bruce,

Just curious, Is that 4th tube on your Oddblocks a thermal delay tube?

Thanks


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PostPosted: 26 Jul 2018, 08:56 
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Location: Arizona, USA
Hi, Questions...I would put the extra 100uf section in parallel with the second or third filter. Either will give a bit more filtering and in position two a bit lower impedance in the B+ circuit for the output tubes.

4 class A amps....You should have seen it when I had a pair of the KT120s and a pair of the KT88s. A house warming situation. :hot: EDIT: you notice that they are in front of the fireplace :D

Yes the 4th "tube" is a thermal delay tube like in the original design and the amps from 2008. It is an Amperex 6NO30. 6 volt heater and 30 second delay. I bought a few back then for $5 each. Now they are in the $30 and up range. It switches 12 VDC for the B+ relay. Simple durable and reliable. In the timing area they hold the 30 second delay time quite well. The originals (now 10 years and 1000s of operations later) are within about 2 seconds of each other. Other delay tubes can be used and you can set the relay for NO or NC depending on it the tube is NO or NC. My preference from a safety viewpoint is a NO tube and NO relay. If something fails it would nearly always fail in an inactive state and thus there would be no high voltage on the caps to zap you when you discover there is something wrong. With the NO/NO combination if the 6 volt or 12 volt supplies fail or there is a dead delay tube there will be no B+. A relay that failed closed is still possible, but rather unlikely.


Good listening
Bruce

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