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SOHA II Builders Thread - Page 15

post #211 of 1686
Thread Starter 
So, would this mean that the hiss is dependent on the impedance of the heaphones and not their sensitivity? That is, high Z sensitive heaphones have less hiss than low Z not-so-sensitive headphones?

If so, then the hiss would have to be buffer related somehow.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #212 of 1686
The hiss is equal on both sides. I did let the amp warm up some time, noise goes down a bit, but still there.

I'm not sure what you mean by feeding regulated HV into cap multiplier, the reg is after the cap multiplier.

I also had a little bit of hiss when I was using the older 60V PSU, can't recall exactly if it was better/worse, I only tested with KSC75.

I'm not positive, but I don't think it's exactly related to impedance.

My 60Ohm KSC75 has SPL of 101 dB and I can just ever so slightly hear a hiss, 32 Ohm Grado RS-1 is 98dB and I can hear it very lightly but 25 Ohm Denon D5000 with SPL of 106dB it's very noticeable.
post #213 of 1686
Quote:
Originally Posted by runeight View Post
So, would this mean that the hiss is dependent on the impedance of the heaphones and not their sensitivity? That is, high Z sensitive heaphones have less hiss than low Z not-so-sensitive headphones?
I don't believe so. The 16 ohm IEMs would almost certainly have higher sensitivity than the 32 ohm headphones, wouldn't they?
post #214 of 1686
Quote:
Originally Posted by FallenAngel View Post
I'm not positive, but I don't think it's exactly related to impedance.
A little bit of probably irrelevant apples v oranges......

With my Mini Max, ATH-ESW9 (32ohm, 103dB/mW), SuperFi 5 Pro (16ohm, 119dB/mW) and output resistors including 0, 10, 22 and 33ohm, the SuperFi are noisier with 33ohm than the ATH-ESW9 are with 0ohm. That says to me that sensitivity is more important to noise than output impedance.

Also, the noise drops to virtually zero in all cases if the tubes are removed. The buffer is dead silent.
post #215 of 1686
Quote:
Originally Posted by runeight View Post
So, would this mean that the hiss is dependent on the impedance of the heaphones and not their sensitivity? That is, high Z sensitive heaphones have less hiss than low Z not-so-sensitive headphones?

If so, then the hiss would have to be buffer related somehow.
I'll have to double check, but my IEMs have the hiss really loud and I believe it's sensitivity is around 120dB (crossroads mylarone x3). I have some other IEMs I can try.

I know I tested it with my other headphones, and heard a slight hiss with the K81DJ (32 ohm, 115dB/mW) and ATH-ANC7 (260ohm, 109dB) and DT-660 (32 ohm, 96dB). I have tested, but can't recall how loud it was with my M-Audio Q40 (64 ohm, 116dB/mW). I don't hear it with my DT-990, HD650, and K240 Sextett.

The sensitivity ratings don't list the reference points for all the headphones, so it's hard to say if it's dB/V or dB/mW. Anyhow, it does seem to be more closely related to sensitivity, as the ATH-ANC7 is up there in impedance as well as sensitivity.

I think it's in agreement with FA.

Tubes removed, I hear no hiss. It definitely is something in the VAS stage, but where exactly it's hard to say. I did try turning down to 55V and it was quieter, and turned it back up to 95V and it was noticeably noiser. The regulator is worse at noise rejection in the higher voltages. So, it could still be the HV.

I have pics of my reg I can upload in a few days.
post #216 of 1686
Quote:
Originally Posted by FallenAngel View Post

I'm not sure what you mean by feeding regulated HV into cap multiplier, the reg is after the cap multiplier...
The capacitance multiplier is the circuit around Q1P and Q2P, yellow marked on the left of the schematic, after the HV-regulator.
The red marked circuit on the right of the schematic, before the HV-regulator is the voltage multiplier to multiply the secundaire transformer voltage to a higher desired level.


post #217 of 1686
Quote:
Originally Posted by Ferrari View Post
The capacitance multiplier is the circuit around Q1P and Q2P, yellow marked on the left of the schematic, after the HV-regulator.
The red marked circuit on the right of the schematic, before the HV-regulator is the voltage multiplier to multify the secundaire transformer voltage to a higher desired level.
Ah, in that case, yes, I am feeding regulated HV to the capacitance multiplier.
post #218 of 1686
Don't like people posting silly suggestions & hope this isn't one

Although perhaps not audible, I turn off all fluorescents near my amps when I scope/test them... I've cheap fluorescent lighting over my bench that hums & can show up on the scope (esp. for unboxed builds).

BTW I'm on my 3rd build of essentially this HV mult/filter (albeit, less TL783 & feeding std SOHA frontends) and have had no problems. Edit: Using 25 ohm D2000s or 250 ohm DT880s.
post #219 of 1686
Thread Starter 
OK. So Holland's info would say that the hiss is at a constant level but that more sensitive phones make it more audible. And, further, that it increases with increasing regulating voltage. Which would definitely point to the regulator.

I have built the HV ps with the regulator and plugged it onto the proto board exactly as it is on the current boards. I dont' know, offhand, the sensitivity of my headphones, but I did listen for any increase in noise with the HV supply and I didn't hear any. Could just be my headphones are not sensitive enough, or possibly, that some of the regs are noisier than others??

Does anyone else with the new HV supply have this hiss issue?
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #220 of 1686
Quote:
Originally Posted by runeight View Post

Does anyone else with the new HV supply have this hiss issue?
Let me take a listen again now that I have a few more sets of cans to listen with. I do remember having more noise with my test headphones (cheap apple earbuds, melted testing the MCubed!) but silence with my 650s

per cfcubed's comment - I took the amp over to a friends house and nearly soiled myself at the amount of noise coming out of it, until he pointed out the amp was on the same circuit as a flaky neon transformer. I imagine a 'scope would quickly show that noise...

However, both holland and Fallen Angel have had quite a few builds across their benches, so I would think their baseline for judging noise was established there...
post #221 of 1686
yeah, most of my amps are quiet. the tube ones tend to be a bit noisier (soha 2 is my 2nd tube after ssmh) but the ssmh has a crappy power section. all my ss amps are dead quiet.

i'll have to get this on my scope, but my scope is so damned big i hate pulling it out of the closet and i don't have time till the new year.
post #222 of 1686
My balanced SOHA II is in the making and I have intensively listening to it in both SE and balanced mode this evening. Due to the recent posts here regarding the hiss issue, I have paid more attention to the possible audible hiss, but it’s definitely not on this amp in progress. The ground noise (without input signal) is lower than that from a MH Max, and approximately the same as from my M³, for example.

Balanced mode: Marantz SA-11S1 => SOHA II (balanced mode) => HD650
SE mode: Marantz CD63-KI => SOHA II (SE mode) => HD600 / AKG K701 / AKG K240 / Philips SBC HP1000

I don’t remember the sensitivities of all these headphones but the impedance of these headphones is ranging from 32Ω to 600Ω.

I will ask my GF to bring her SOHA II home from the office next week to give it a close listen.
That amp is deviated a bit from the stock BOM (120V B+ voltage, current mirror with MPSA92, and some other changes…), but basically it’s a SOHA II.
(To be followed).
post #223 of 1686
do you have IEMs? I don't hear it on my 650 and K240. I have the SBC HP1000 as well, I'll pull it out and give it a listen this weekend. I haven't tried it with the SOHA 2 yet.

SBC HP1000 is 32ohm, 106dB.
post #224 of 1686
I get a very distracting hiss from my SOHA II as well if I plug in cheap IEMs (Creative EP-630, if I recall the model correctly). However, it's silent with both the AKG K-601s and MB Quart QP-280. I also get a slight hiss (inaudible with any actual audio present) if I use the SOHA II as a pre-amplifier for a speaker amplifier.

In all cases, the hiss is independent of the volume control, so I figure it would be solved by padding the output signal from the pre-amp outs and the 3.5mm miniplug output (I have that as an alternative on my amp, with the switched 1/4" jack turning it off when in use). In both cases this would also give a more useful range of volume control… I'm just not sure yet what would be the best way to achieve this.
post #225 of 1686
I got a chance to listen away from the noise of computers and heaters (winter is here in the Rockies!) tubes in, iPod source/no source (phones pressed to head):

HD650's - (Imp. 300, Sensitivity 103dB @1 mV) No noticeable hiss with or without source at full volume

Yh-3's - (Imp. 125, Sensitivity 97dB @1 mV) No noticeable hiss with or without source at full volume

325i's - (Imp. 32, Sensitivity 98dB @1 mV) Noticeable hiss with volume >75% with no source ( Without pressing the phones and thereby covering the grills - hiss isn't audible until volume hits ~85%)

So while it does appear to be there - I'd never subject my ears to that level with music with those 'cans
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