New Eiclone

[Shannon Parks]

Yes, the feedback was connected and it was connected properly. It also had the same behavior without the feedback connected. As I mentioned above, I tried reversing the primary halves and it oscillated right away so they were correct to start with. I connected them in accordance with the polarity as shown on Ned's drawings. So all is well there.

Hi Ed,

What outputs are you using again? Also, the 12AU7 won't work well unless you did the CCS mod, as the DC coupling bias will be too low for the LTP. That's one neat trick with the CCS and AC coupling! Yellow_Light_Colorz_PDT_06

All sounds good. I'll see what I can come up with over the next few days with my stock Ike. Using a stock Rev A board and chassis wiring straight out of the Rev B manual I got 1mV of noise last night, FWIW. I'll see if I can't standardize the hookups for a better success rate of noise performance.

Shannon

[WA4SWJ]

Hi Shannon,

I'm using Uncle Ned's Dynaco equivalents. I bought 3 of his Dynaco power transformer/output/choke packages. They are beautiful transformers.

I finished the second eiclone last night and started testing it. I double checked everything and it performed exactly as the first one. Hum with the input shorted and feedback disconnected. Volume control dependent hum (severe as the control is advanced) happened along with minor oscillation with the feedback disconnected with the input terminal jumper removed. I have the input wires shielded with the ground connected only to the board ground at one end.

Connecting the feedback quieted it down some (lower gain) but the volume control dependent hum did not go away. I strapped the board ground (pin 4 on the TB) to chassis ground and it quieted down and eliminated the volume control dependent hum completely, but it still has idling hum of about 6mV into an 8 ohm speaker. I did not ground the CT of the 6.3V winding on this one, but grounding the board to the chassis had the same effect in eliminating all the garbage noise. The hum level of 6mV is slightly higher than the first amp I built. So, it is behaving exactly like the first one I built even with a completely different layout. It does sound great though. It is functioning correctly and the audio is really good when the "signal to hum" ratio is higher with movie playing or a CD.

I did notice that as I was lowering the bias voltage from the initial -50V setting the hum got louder as the tube idling current increased to the setpoint of 55mA. Of course the operating point of the tubes was changing as I adjusted the bias. One thing I think I'm going to try is to disconnect the coupling caps to the EL34's to see if the hum is in the output stage or if it's further upstream in the signal path. Sure wish I had a 'scope! I was also wondering if the bias filtering caps are sufficient, but since you're not having these troubles they're probably OK. That 'scope would again be nice.

Again, both amps sound great and don't get me wrong - I'm not complaining. I just think they both hum too much with no signal. It's noticeable across the room. Also as in the earlier posts, my ST-35 is silent. It is working wonderfully. I am truly impressed with how it sounds. I have JJ Tesla tubes in it along with Ned's ST-35 transformers. They also are beautifully made and are performing very, very well.

I'll send some pictures tonight of the new layout to see what you think. You'll be able to see those great looking transformers too. I didn't have time to take pictures last night. More later. Looking forward to the results of whatever it is you're doing with your eiclones.

Best Regards,

[Shannon Parks]

Hi Ed,

Been having some real fun going back to my 'original' Ike! The 6B4s and CCS mods were a distraction. Anyhow, I'm close to a break-through of sorts. My stock Ike had only .8mV @ 31dB gain. I was very happy with this. It dropped to .4mV @ 25dB gain with the 2K/1000pF change. All this was on the test bench. The open loop is 46dB gain and I think there is plenty of margin for stability with the extra NFB.

Anyhow, when I hooked it up to my home stereo, the buzzz was there until I removed the safety ground. Then it was dead silent. I was able to operate Ashok's amp silently with the safety ground, so there is a grounding tweak I need to discover. BTW, all this was done with a Rev A board and I'll take my Rev B amp 'to stock' tonight. Need stereo! Yellow_Light_Colorz_PDT_01

Shannon

[WA4SWJ]

Shannon,

I posted more pictures on my webshots page (see the initial posts in this thread for the URL). The new pictures are mostly of the second eiclone I just finished. I tried to get some close-up shots of the interior. Note that I grounded the ground lead from the line cord to the back of the chassis and then connected pin 4 of the TB to the same point. This took out all the noise but the hum is still there.

A suggestion - Ned's (and I'm sure others) transformers have a bias tap on the high voltage seconday. Of course some resistor values might need to be changed. It would be nice to have a point where it could be connected to the TB instead of soldering it to the board. I didn't do that - I used your tap via capacitor to pick off bias voltage.

Let me know if you can't get to the pictures. Can't wait to hear about the results of your testing.

Regards,

[Shannon Parks]

Hi Ed,

OK, so I have two stock Ike monoblocks - one is a Rev A and one is a Rev B. The main difference is that the Rev B has isolated mounting holes. Both were wired up according to the logical diagram in the Rev B manual.

The Rev A tested with .8mV noise - primarily a 120Hz component. This dropped to .45mV when changing the feedback resistor to 2k//1000pF (the 560pF cap is left in there, so 1560pF total). In my stereo setup, though, there was a noisy hum. By disconnecting the safety ground, the amp went totally silent.

The Rev B tested with 4.5mV noise - primarily a 120Hz component. Sound familiar? This dropped to 2.8mV when changing the feedback resistor to 2k//1000pF. But in my stereo setup, the amp was also totally silent with 101dB/w/m speakers. Excellent! I got lost listening to some Poco at that point.

While I still had the Rev B amp on the test bench before the Poco distraction, I was able to drop the noise down to 1mV by disconnecting the input ground at J1-2 and moving it to J4-3 - the same ground as the output ground reference. Ed, you can try this test with just a jumper for expected results. I will try this test in my stereo on the Rev A, to see if I can get the safety ground reconnected.

Shannon

[WA4SWJ]

Shannon,

OK - I'll try that. I have to go out of town this weekend so the earliest I can try it will be Monday night.

Am I correct in assuming you're recommending a change in the feedback network? If so, I'll order some parts.

Hope you got a chance to look at my pictures.

After I finish the third eiclone and get them all "de-hummed" I'm going to build an amp with some 832's in it. Just ordered a chassis (Wellbourne Labs) so this will be my first "good looking" amp (I hope!). It will be a few weeks though but I'll post pictures once it's done. I already have the tubes, socket and Hammond transformers for that one as well as most of the parts.

Have a great weekend and thanks!

[Shannon Parks]

Am I correct in assuming you're recommending a change in the feedback network? If so, I'll order some parts.

Hi Ed,

Go ahead and get some 2k resistors and 1000pF caps. I twisted them together and mounted them at R8 and left C7 alone. Though this isn't related to the hum problem you have, I like this mod for many reasons. Plus the gain will more closely match your ST35.

I'm pretty confident that your hum issue is a grounding scheme fix. Though I can't recreate it in my stereo setup, I did see the 4.5mV on my bench. I'll see what my Rev A test reveals.

Shannon

[JochenH]

Hi,

i also had a serious hum problem with my Ikes Rev. B and everything i tried with different connections of signal ground / chassis / mains ground didn't help.

Then i tried this mod

While I still had the Rev B amp on the test bench before the Poco distraction, I was able to drop the noise down to 1mV by disconnecting the input ground at J1-2 and moving it to J4-3 - the same ground as the output ground reference. Ed, you can try this test with just a jumper for expected results. I will try this test in my stereo on the Rev A, to see if I can get the safety ground reconnected.

and the hum went away totally.

I isolated the J1-2 from the ground plane on the PCB by cutting the two stubs which connected the pad and put a small wire from the pin to J4-3. So i can use J1 as the input terminal.
This again shows that the old star ground rule is still alive Yellow_Light_Colorz_PDT_09

Everything else is as stated in the manual, i don't use the heater CT and the rectification is solid state.

Now i'm totally satisfied with the amp! I'm using the new TungSol's 6550 and the 12AX7 / 6SN7 are from electro-harmonix.

Jochen

[Shannon Parks]

Hi,

i also had a serious hum problem with my Ikes Rev. B and everything i tried with different connections of signal ground / chassis / mains ground didn't help.

Then i tried this mod

While I still had the Rev B amp on the test bench before the Poco distraction, I was able to drop the noise down to 1mV by disconnecting the input ground at J1-2 and moving it to J4-3 - the same ground as the output ground reference. Ed, you can try this test with just a jumper for expected results. I will try this test in my stereo on the Rev A, to see if I can get the safety ground reconnected.

and the hum went away totally.

Excellent!! Thank's for confirming this, Jochen. What happens on my bench wasn't being recreated in my stereo setup - my apologies. Yellow_Light_Colorz_PDT_05 I have learned quite a bit about noise troubleshooting, though. Interestingly, moving J1-2 to J4-4 or J4-5 did not have the same improvement as J1-2 to J4-3. So much for PCB ground planes or 'buss bar' type grounding. Long live star ground.

BTW, for earlier Rev A users this mod doesn't do anything as it doesn't have this issue (yeah, I played with the ground planes bewteen revs). Removing the safety ground should fix any noise issues, otherwise you need to get isolated standoffs to use the safety ground.

Shannon

[WA4SWJ]

Jochen and Shannon,.

Thanks for the suggestion Jochen! I broke the traces to J1-2 and connected it the ground point on the main TB pin 3 with a small wire. The amp is now significantly quieter. But I still have to ground the center tap of the filament winding to eliminate hum. It has to be grounded to the chassis. If I ground the CT to pin 3, the hum is bad. Otherwise it is as I said, significantly quieter. An ungrounded CT generates even more hum. So, the jumper is on the board and the CT is grounded to one of the power transformer mounting screws.

I have not tried the feedback network change yet because I don't have the parts, but I'll try that in a few days.

Thanks for the info!

[erichayes]

Hi All,

Good grounding is good grounding, regardless of the method (star, bus or plane) employed. And yes, it can be a gold plated supercharged pain in the ass to achieve good grounding.

Shannon, your remark about the superiority of a star ground method over plane and bus methods prompted me to drag my 50/50 watt almost-clone prototype of the HF-89 onto the bench for some spec.ing. This is a point-to-point version with minor component changes (primarily in the FB loop) using iron of my design and a choke-input filter network. A 10 ga. silver plated copper ground bus is utilized, with the chassis grounding point at the power entry module. The test equipment used were Tektronix SG-505 signal generator, AA-501 distortion analyzer, SC-503 dual channel 10 meg 'scope, and a DC-504A freq. counter (to keep the '505 honest). The residual noise floor of the test setup was 0.2mV.

Absolute values for noise floor were as follows:

Left chan: .902 mV, Right chan: 1.78 mV

With High Pass Filter engaged:

Left chan: .212 mV, Right chan: .238 mV

Relative S/N+N Ratio referred to 1 watt

Left chan: -70 dB Right chan: -62.8 dB

HPF in LC -83.1 dB RC -81.4 dB

Relative S/N+N ratio at .5% THD:

LC: -87 dB RC: --80.4 dB

HPF in LC -99.6 dB RC -98.3 dB

The distortion at one watt was .0089% on the left channel and .023% on the right. I think the distortion/hum discrepancies are due to a squirrely 6SN7 in the right channel.

My point is that bus bar grounds are every bit as good as star grounds, if they're implemented correctly (and, in my opinion, a damned sight better). Ground planes, on the other hand, create capacitave disasters. You might get rid of hum with a GP, but you're going to screw up all the other parameters of an amp that separate the good ones from the mediocre.

[Shannon Parks]

Good grounding is good grounding, regardless of the method (star, bus or plane) employed. And yes, it can be a gold plated supercharged pain in the ass to achieve good grounding.

Amen.

Shannon, your remark about the superiority of a star ground method over plane and bus methods...

I think anything can be done right. I didn't mean to sound dogmatic. In fact, my Rev A Ike dual-sided ground plane still measures lower noise at .4mV noise and the early ST35 boards test well, too. It was born out of working in an RF lab where ground planes (and lots of vias) are essential. My ignorance at that time was bliss. But then throw in a safety ground and we have a much tougher task.

I will admit to being lost in the ways of trouble-shooting the bus bar ground. For example, Thermion's new preamp has 6mV noise - all sub-400Hz. I am convinced it is in the grounding scheme via the power supply. The bus bar is maybe 6 inches of 16GA copper. Both channels are identical. I tried DC on the filaments, too, with no change. It is two 6SN7s in a common cathode circuit with CCS. Any pointers?

BTW, where's the 3dB point of your high pass filter? I'm assuming that you are just looking at the noise floor of your test setup at that point (which you had noted was .2mV)?

Shannon

[erichayes]

Hi All,

Shannon, the measured -3dB point on the '501's HPF is 392~ ... not too shabby for a spec'd 400~ hinge point.

Bud Wyatt showed up on my doorstep on Sunday after an 8+ month dissapearance, and we've been playing Ham radio games for the last couple of days. Hey Eds: 32 miles line of sight on '6.52 @ 700mW, full quieting. I have found radio Satia.

Anyway, we talked at length about grounding techniques as we were installing a 2 meter antenna on my roof, and I'll distill the conversation for future publication on the forum.

FWIW, I hit the double nickel at the beginning of the year, and Bud's a handful of years senior to me. We both admitted that, after today's antenna rigging and tranceiver testing, we felt like a couple of twelve year olds playing with our first radios that we'd breadboarded. I won't elaborate here, but amateur radio is as much fun as DIY audio...it's just a little different.

73

[EWBrown]

Friend of mine is thinking of building up his pair of boards to use 6BG6s, 6384s or 6889s (the latter two are some unique Bendix "Red Bank" tubes made for use in 1950s era guided missiles). These tubes all have different pinouts than do EL84 / 6L6GC / 6550 / KT88, etc, so using chassis mounted tube sockets wired to the PCB output tubes' locations is necessary. Power and OPT will be salvaged MK III iron.

My own approach was far more "traditional" except in that I assembled the Rev A boards with everything except the terminal strips on top, and then mounted the board on top of the chassis on short standoffs. The C354 choke and all tranny-to-board wiring is under the chassos. They do look a little strange, but work very well, no hummmmm problems, and next step is to replace the Svet 6550Cs with EH KT88s and push the bias up to 65-70 mA per tube.

/ed B in NH

[WA4SWJ]

Everyone,

I finally finished all 3 of my eiclone amps and they are working great. Thanks to all the suggestions I was able to get the great majority of hum out of them and they are sounding fabulous. I have uploaded a picture to Webshots (link info is earlier in this thread) of all of them working in the setup I have (along with an ST-35 I built) to watch movies home theater style. I am enjoying the amps immensely. Although there are better ways to do this with all the new solid state amps and so on (and I have those in Arizona), I wanted to build these myself and enjoy them. So, I'm done with the effort for now. I'll just be listening and enjoying.

Thanks for all the suggestions for hum reduction and improvements. I still need to do Shannon's feedback change but I'll have to order some parts. Once I do that tweak I'll be truly done. Maybe some more will come along.

Now I have an Eico ST-70 I'm going to work on and after that I'm going to build a stereo amp using 832A power tubes for my office. Again, just for fun.

But I have to tell you, these amps sound great. I am hearing things in the movies I watch that I wasn't hearing before so these are wonderful amps.

Good luck to everyone and I hope you're having as much fun as I am.

Regards,