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A Very Compact Hybrid Amp - Page 83

post #1231 of 2203
5/10/09 at 2:01pm
Quote:
Originally Posted by adamus View Post
If i built the kit with a 12au7, I may have never questioned it.... its very quiet, maybe just a hint of white noise. 6n1p is a different matter.
x2 -- either that or just been spoiled with the SOHA II
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post #1232 of 2203
5/10/09 at 2:07pm
Quote:
Originally Posted by runeight View Post
Somehow we missed this issue during prototyping.
I know in my case, I didn't notice it until the first time I tried a 6n1p. Now I realize it was probably there all along, but not very obvious or bothersome running 12au7's, as Adamus noted...

Quote:
Originally Posted by runeight View Post
It does appear that the hum/buzz is related to the draw from the heater supply. This kind of makes sense since the ability of the first filter cap to handle the ripple goes down as the current draw goes up.

The only way to tell the difference would be to make C3H much large and see if that reduces the hum problem.
I'd be willing to try this... How big can C3H be?
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post #1233 of 2203
5/10/09 at 2:17pm
As big as you can get it as a test (470uF-1000uF), if you've got it on hand. I would think something around 120uF might work, but try big first. I would also look at C1H and C2H. If you've got them, try 220uF (for those going after the 1A version) after C3H though.
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post #1234 of 2203
5/10/09 at 2:18pm
Quote:
Originally Posted by runeight View Post
Thus you would expect that if this were radiation the right would have a bigger problem than the left.
None of this will probably help:

I never noticed the noise during prototyping. Nor did any of the rest of th eproto team I think. I have always heard some white noise in both channels at full volume with no inpuut - it's a tube amp!

It seems to be tube and current dependent - my 6H30 is the loudest. HOWEVER, I didn't seem to notice it before.

To fuel the confusion - what noise I can hear is more prevalent in the right channel. (Is that Runeight syaing @*&#%@$%%*! )

I also replaced C3H with 220uF - seems to reduce noise at 6V. EDIT - missed the C3H suggestion, I can make it even bigger...

No one has actually done CFCubed's suggested battery heater supply. I may try this in the afternoon, gotta see what's in the battery drawer.

Adamus - did I miss what value you changed L1H to?
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post #1235 of 2203
5/10/09 at 2:25pm
Quote:
Originally Posted by wiatrob View Post
I never noticed the noise during prototyping. Nor did any of the rest of th eproto team I think. I have always heard some white noise in both channels at full volume with no inpuut - it's a tube amp!
I've never noticed it on mine using my high sensitivity low-Z headphones (D2000) on the 2 that I have built. I have, however, never tried IEMs with this.

For those hearing the hum, what are your output resistor values? I've got 100.
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post #1236 of 2203
5/10/09 at 2:31pm
Quote:
Originally Posted by wiatrob View Post
I also replaced C3H with 220uF - seems to reduce noise at 6V. EDIT - missed the C3H suggestion, I can make it even bigger...
Try different values and report back.

If you've got a scope it would help. If not, a DMM should be able to pick up the ripple to a certain degree. If it is 40mV or so, you'll see it.

If you check it on the input to the reg, it'll be larger, and you can view the impact on the input vs output ripple. For high heater versions, you'll want larger C1H and C2H as well. 100uF isn't enough. I'm going to go with 220uF for 1A, according to the datasheet.
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post #1237 of 2203
5/10/09 at 2:31pm
Thread Starter 
No, I wasn't thinking of builder error, but I was wondering if we can find a way to compare the amps that are quiet with the ones that have noise to see if we can discern any differences.

These might be caps, enclosure, wiring, or other component choices.

If we can find something then we can alert everyone to what might be a build issue. If we can't find any real difference between noisy amps and quiet ones then this implies that it is external factors of some kind.

If you all would be willing to answer a few questions, perhaps we can get a sample of data.

1. Is your amp quiet or noisy
2. What enclosure are you using
3. What coupling caps are you using
4. Where have you located the off board components and their wiring
5. Is your pot grounded
6. Have you done anything else unique to your build
7. What headphones

Edit: Added Q number 7

Thanks
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post #1238 of 2203
5/10/09 at 2:39pm
I'll start

1) noisey with most tubes apart from 12au7 and 5693
2) small hammond
3)bom, 1uf box
4) power and heater switch at the rear, pot and mini jacks at the front. RK09 pot.
5) tried both, no difference
6) no.
7)HD650's (little noise), Cx300 (IEM) louder noise.
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post #1239 of 2203
5/10/09 at 3:00pm
Quote:
Originally Posted by runeight View Post
1. Is your amp quiet or noisy
2. What enclosure are you using
3. What coupling caps are you using
4. Where have you located the off board components and their wiring
5. Is your pot grounded
6. Have you done anything else unique to your build
7. What headphones
1) quiet
2) Context Engineering 3008 and Hammond 1455K1601
3) Context Engineering - AVX caps. Hammond - Wima
4) Board is mounted in the upper slots. Large caps (taller than tube socket) underneath. Power and heater switches underneath and to the rear. Fuse, underneath between power and heater switches. All wiring is underneath. Wiring (if looking at Ric Lee's diagram) input is upper right, Output is lower left. Wiring runs along the upper wall, bends at the face plate to the pot.

LED on the front panel, on diagram, bottom left.

Proto, heater reg and 24V reg underneath.
Production, heater reg and 24V reg on top.

5) Yes
6) Proto has output resistors on the jack instead of in the servo loop.
7) tested with Denon D2000, Beyer DT440, Beyer DT990.

Tubes used.

6N1P
6N6P
12AU7 and variants
6922 and variants
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post #1240 of 2203
5/10/09 at 3:12pm
Two builds with the longer case: One proto one production

1) No
2) Large hammond
3) BOM
4)
->production one with mini jacks has i/ps and o/ps in the front along with the pot.
-> proto one has RCA jacks at the back and a full size neutril on the headphone out up front along with the pot.

->power and heater switch for both at the rear.
5) Yes, on both
6) No.
7) Fostex T50RP, Yamaha Hp2 orthos


Tubes used were, 6DJ8, 6N1P, 12BH7, 5963.

My other production build went to smeggy and his is in a plastic case and is not reporting any noise in his as well.
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post #1241 of 2203
5/10/09 at 3:15pm
I don't have the scope with me, but I do have a good meter. I'll look for ripple changes before I go changing things willy-nilly.

I'll get to the questionnaire in a moment - BUT:

The 6H30 is the loudest - but it is DEAD silent with my 150R orthos (YH-3s). Blacker than Black...All the 6 volt tubes are.

EDIT: I used the proto build at work mostly with the YH-3s early on in the proto phase...
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post #1242 of 2203
5/10/09 at 3:34pm
Quote:
Originally Posted by runeight View Post
1. Is your amp quiet or noisy
2. What enclosure are you using
3. What coupling caps are you using
4. Where have you located the off board components and their wiring
5. Is your pot grounded
6. Have you done anything else unique to your build
7. What headphones
For the Proto:

1. Slight noise (more with 6V tubes, EDIT: Unnoticeable with some 12V {5963, 5814WA, clear top} - very low with 12BH7)
2. Hammond 1202 Wooden Ends
3. 100V Wimas
4. Standard front placement of jacks and BoM pot. Wires gathered with zip tie 1" between board and panel. Shielded wire from input to pot.
5: yes and no, grounding doesn't affect hum
6: switching inductors changed to 1A rating. Slight decrease in noise from stock. Cap mods in progress.
7: Output resistors 56R

Phones:
Senn PX100
Senn HD650
Grado RS-1
Yama YH-3 (amp is silent with ALL tubes with these phones)
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post #1243 of 2203
5/10/09 at 4:09pm
Quote:
Originally Posted by runeight View Post
If you all would be willing to answer a few questions, perhaps we can get a sample of data.
1. Is your amp quiet or noisy
2. What enclosure are you using
3. What coupling caps are you using
4. Where have you located the off board components and their wiring
5. Is your pot grounded
6. Have you done anything else unique to your build
7. What headphones
1. 12AU7, quiet with a very faint hum (unnoticeable), with 6N1P noise/hum level is increased.
2. nekid right now
3. sprucecanyon bom (i.e. 100% stock)
4. air wired everywhere (uncased), no effect moving wires around
5. yes, hookup wire to SG
6. unshielded wires, soldered to bottom instead of top of pcb
7. mdr-xb700, beyer dt880
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post #1244 of 2203
5/10/09 at 4:20pm
Quote:
Originally Posted by holland View Post
Try different values and report back.

If you've got a scope it would help. If not, a DMM should be able to pick up the ripple to a certain degree. If it is 40mV or so, you'll see it.

with the 220u, I get 5.5mV at pin 2 of the lm2595 at 6.3V setting

However, should there be AC on the OUTPUT of the switching reg (measured from SG)? I'm measuring ~12 and 14VAC (6.3/12.6V Heater) on pin 1 of the 2595...
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post #1245 of 2203
5/10/09 at 4:29pm
that could be a dmm error. Mine does that when measuring ac with highish dc.
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