Phase Alignment The Best Thing

[PeterSt]

May be I will send you PA.

Send me one too please. But what is it ?

[CoenP]

Very interesting finding for your single-ended tube amp. I thought that the DC issue is usually not a problem for all tube amps since they have output transformers. I am not sure if my KT 88 tube amp has coupling capacitor at the input but with output transformer, I have low DC output reading as if PA is not engaged.

So you highly recommend to add coupling caps at the input. Can you explain how? May be I will send you PA.

Thanks a lot.
Praphan

Hi Praphan,

My Amp = 80% diy so I can insert anything at a moments' notice when I like to. Commercial gear with PCB and so on may be more challenging.

My amp is two stages, coupled with a capacitor. Any DC on the output is caused by the feedback circuit from the output terminals to the cathode of the input tube (which has a positive voltage across it). Probably your amp has such an arrangement too, so don't be surprised to find some dc there.

The first tube does about 60X of gain so 33 mV translates into something like a 2 Volt difference at the anode. Nothing special, tube and resistor variation cause bigger differences. But the impact of the input cap is dramatic, this is imho not related to the shifted operating point but to some sideeffect of DC on the wire (yet unknown to me).

Inserting a cap is simple. I used a Black Gate NX 4,7uF I had lingering around and soldered it between the cinch/RCA input plugs and the wire to the input(resistor) of the first tube. You may open the amp (everything diconnected!!!) and find those wires and follow them to the input tubes. You may encounter a big cap or not. If not it makes sense to enter such a cap between the RCA and the first tube (any place will work provided that the cap is in series with the signal).

PA on with minus engaged puts everything in its right place.

regards, Coen

[praphan]

You may open the amp (everything diconnected!!!) and find those wires and follow them to the input tubes. You may encounter a big cap or not. If not it makes sense to enter such a cap between the RCA and the first tube (any place will work provided that the cap is in series with the signal).

Hi Coen,

Thanks for your prompt response. McIntosh has 3 year warranty policy and I am just at the end of second year. Modification will effectively void the warranty. Flipping this monster around is not a one man job. Each monoblock weights 52 kg.

I will write to Mc tech support and ask for circuit diagram to check if MC2301 has an input coupling cap.

Thanks so much for your help.
Praphan

[CoenP]

Hi Praphan,

Good plan. With the circuit diagram (service manual may allready be on the internet) you can see if there are allready any capacitors in the signal path before the input tube.

No need to open your amp to void warranty or wait for another year . Another idea is to solder the grounds of a male RCA to a female RCA to eachother and connect the hot pins with the capacitor. You can plug this homebrew adapter into your amp and your interlink into the female end.
If you are balanced, you can do the same but then you will need two capacitors per channel.

regards, Coen

[praphan]

Hi Praphan,

 You can plug this homebrew adapter into your amp and your interlink into the female end.
If you are balanced, you can do the same but then you will need two capacitors per channel.

regards, Coen

Hi Coen,

I use balanced XLR interconnect. If I see no cap in the input signal path, I will definitely come back to you for more elaborated help again on the homemade adapter.

Thanks again
Regards,
Praphan

[Jud]

Hey Jud,

What was not successful:

- (1) Buffer at 4096, SFS of 2.

- (2) Attempts without OS minimized (is setting the OS to minimize part of the PA instructions I managed to overlook?).  If attempting without OS minimized, I would get the dialog about turning off services, and it never went away.

- (3) Also didn't get it to work using the N22 as an integrated amp (around 20wpc, as opposed to the PSE's 100wpc), but actually I don't think this was critical.

Ad 2.
PA works without Minimized just the same. Or at Attended. It is not related to anything. It needs Activation though (is this a secret ? I think so).
The (apparent) fact that your Waiting for Services to shutdown never goes away without Minimized is not related to anything and is just a separate problem (if you think it is worth while, please open a separate topic for it). Notice though that it can *easily* take 4 minutes outside of Minimized.

Ah.  Well then I could simply have been impatient, because I did not wait anything like 4 minutes.  *Maybe* a minute or two at most.  But from what you say below, I don't want to listen to PA without the OS minimized anyway.

Ad 3.
Do you mean that the 22W amp needs too much XXHE output so PA can't engage ?

Sorry, I wasn't clear enough.  I don't think changing from the 22W amp to the 100W amp had anything to do with it.  When testing with the 22W amp originally, I thought it must be muting the output, because although the XXHE UI showed everything correctly for PA, I heard no sound.  That's why I thought of trying the 100W amp, and using the N22 as a preamp. 

But now I think it may have been incorrect buffer settings.  4096 didn't work with the 22W *or* 100W amp, 512 worked with the 100W amp.  I don't want to fuss around with wires again to try the 22W amp with a buffer of 512, but my guess is that it would work.

What was successful:

- Keeping everything as close as possible to my former settings in KS Special Mode, i.e., buffer of 512, SFS=430.

Aha. Now *that* is great information. Hahaha.

Btw, during the development my focus wasn't on Special Mode at all (which I myself also can't test), but I can imagine strange things to happen at Stop. Don't you receive unavoidable ticks there ? If so, try Adaptive and see whether that changes things (leave all other settings be). And if it does, let me know please.

No ticks at all with Special Mode.  With Adaptive Mode and PA engaged, no ticks, but if I halt playback by clicking the Stop button *in the middle of a song*, occasionally I get a fairly good thump, not a tick.  Nothing on a level to endanger the speakers, but, errm, interesting.

- Having the OS minimized.

I know you didn't tell this for the reasons I have in mind myself, so here are my reasons to agree :

Like the NOS1 needs Minimized generally because otherwise the baddies of the OS are emphasized (at least that is how I perceive it), PA needs Minimized just the same. Eh, somehow. So, the other day I had a session of a couple of hours with Normal OS and PA, and I don't think I even have been so annoyed about the sound. Not sure whether it was PA doing that, but at least it was the first time I listened to that combination. Ouch.

Peter

[CoenP]

Hi Praphan,

Found the manual. Your Mc2301 has 10uF input caps on the balanced inputs. So no need go soldering!

Regards, Coen

P.s. if you want a copy, pm me your mailaddress

[praphan]

Hi Coen,

I don't know how you find it. But truly appreciated your help. I will pm you.

Thanks so much.
Praphan

[Robert]

God I just tried it without checkin DC and what an improvement in sound. If you have GOOD well made gear this should not be a problem DC that is.

No plops, clicks or what ever just music.
 

[Jud]

God I just tried it without checkin DC and what an improvement in sound. If you have GOOD well made gear this should not be a problem DC that is.

No plops, clicks or what ever just music.
 

Would you consider Spectral well made gear?

Some extremely well made gear has response to DC as a design/sound quality choice.  Take Peter's advice and do *not* try this without checking DC first.  You want to take a chance on frying thousands of dollars worth of equipment/speakers because you wouldn't buy a $30-$40 multimeter?  I can hardly think of a better recipe for feeling sick and stupid if you take a chance and you're wrong.

[praphan]

I concur with Jud. It is a cheap insurance to check and eliminate this unwanted DC.

I wrote to McIntosh tech support and they told me not to feed signal with DC in their tube amps despite coupling caps up front in the signal path. Yes this is a preemptive advise since they have no idea if their customers really know what they are doing.

Regards,
Praphan

[Scroobius]

I have to agree as far as DC offset is concerned it is not at all a question of whether the kit is good quality or not it is a question of whether it is direct coupled or not. NOS1 is great quality (the best?) and it is direct coupled. If your amp is direct coupled then you can expect problems. The vast majority of amps will not be direct coupled so for most it will not be a problem at all. But as Peter points out if in doubt it is a simple matter to get the volt meter out.
P

[Robert]

The dangers of drinking and Hi-Fi, certainly was stupid to attempt this without checking DC first. I most certainly would have been devastated if I had created needless destruction.

I would call Spectral gear very good in fact most if not all on these forums have very good equipment.

I suffer foot in mouth disease!!!!