Another MET1 on the forum - NO problems

The PV-1 to now...
Mr_BT
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Re: Another MET1 on the forum - problems

Post by Mr_BT »

The bad:

After 12h MET1 died on me with loud pop, reduced, distorted sound and within a couple seconds dead. Resulted in blown fuse at mains and after replacing fuse the internal fuse F1 also blown. Some brief troubleshooting lead me to shorted small 0.15uF cap on SW channel. Why on SW only? weird....However, after removing faulty cap, getting back old PS caps in their places and replacing fuse got enough courage to turn the unit on. Pushed the power button and heard faint sound of static jumping all over caps (not sure if it's normal, however preamp was left overnight and all caps got discharged and maybe that's how it is when they charge itself at power on??). No fuse blown! Hurray!
Time to hook it up to source and amps. Can hear sound but there also is this terrible loud lower-mid frequency HUM....sounds like one or more filter caps went bananas???. The HUM is present on every channel.

Here it's my theory of how it happened:
I was burning-in the preamp with only two L and R tubes in (some discarded previously GEs). All other sockets were empty. When I checked voltage across output caps, the ones without tubes in were close to 400V DC!!! The ones with tubes in
(LR channel) were 150V DC. Now, the 4uF caps are 400V rated but small 0.15uF are only 200V. One small 0.15uF decided to gave up finally under 400V and shorted.......
jeffreybehr
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Re: Another MET1 on the forum - problems

Post by jeffreybehr »

Did you see my PM about the schematic diagram?

Also check, as best you are able, that the MOSFET output buffers...Qs 15 - 20...are or are not shorted. It never occurred to me that someone would operate his preamp without tubes in the sockets.
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Mr_BT
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Re: Another MET1 on the forum - problems

Post by Mr_BT »

When I check my messages it says:

"This message has been removed by its author before it was delivered.
by jeffreybehr » Sat Jun 15, 2013 8:11 pm "
PM from you is unaccassible for whatever reason.
Could you resend it to btylutki(at)gmaildotcom
jeffreybehr
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Re: Another MET1 on the forum - problems

Post by jeffreybehr »

E-mailed a moment ago.
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Mr_BT
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Re: Another MET1 on the forum - problems

Post by Mr_BT »

All channel are now operating fine. All mosfets seems to be fine (the best I could do without desoldering) . How the hell do I get rid off this loud HUM? It has got to be voltage leakage on one of PS caps.

There is my favourite saying: "if you want to play, prepare to pay". It was from my motorcycle days but it also applies here perfectly. :)

P.S. I'd imagine a couple of scenarios in which user is not having all tubes in....anyways, in my opinion these small 0.15uF should also be rated 400v simply to make design smart enough to save dumb user (not pointing fingers :) ) from making fatal mistake.
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Re: Another MET1 on the forum - problems

Post by Mr_BT »

All caps seems to be fine.
Q12 from HV supply definitely busted. Q11 not sure but will replace just in case.

Parts ordered!
Mr_BT
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Re: Another MET1 on the forum - problems

Post by Mr_BT »

Preamp is up and running!!! Well....at least it has been running fine for 30min. Don't want to jinx it but it looks like it will be ok. Went through all the components on pcb and found no fault elsewhere except the two mosfets in HV circuit and shorted cap mentioned above. Lesson learnt! Tubes always in, unless I'll go ahead and change all the 200 rated caps for more "idiot proof" rated. Hey, you never know.

At this point I reverted all mods to original state. Will let the MET1 run for some time and than I'll start with output caps following the golden rule of: "one mod at a time". If the first mod turns to be fine than I'll change caps in power supply.

Will I sound boring saying again: "Thank You Jeffrey!!!!!" . Almost all of my posts have "Thank You" included :)
Without you providing schematics it would be very difficult for me to troubleshoot.
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Re: Another MET1 on the forum - problems

Post by jeffreybehr »

Mr_BT wrote:Preamp is up and running!!! Well....at least it has been running fine for 30min. Don't want to jinx it but it looks like it will be ok. Went through all the components on pcb and found no fault elsewhere except the two mosfets in HV circuit and shorted cap mentioned above. Lesson learnt! Tubes always in, unless I'll go ahead and change all the 200 rated caps for more "idiot proof" rated. Hey, you never know.

At this point I reverted all mods to original state. Will let the MET1 run for some time and than I'll start with output caps following the golden rule of: "one mod at a time". If the first mod turns to be fine than I'll change caps in power supply.

Will I sound boring saying again: "Thank You Jeffrey!!!!!" . Almost all of my posts have "Thank You" included :)
Without you providing schematics it would be very difficult for me to troubleshoot.
GREAT news, and you're very welcome.
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Re: Another MET1 on the forum - problems

Post by Mr_BT »

Here it is, what I believe to be almost final version. It has been running problems free for a couple of months already. Almost final version, because I plan on removing bypass SCP after I'm sure they are broken-in completely (500h) and see if I need them or not.
Also, I replaced original 0.15uF 200V bypass caps with SC 600V rated (just in case :) )

I probably have to outline a benefits of this whole operation and to do so I'll have to switch cables to use channels with old capacitors but I'm simply too lazy :)

In the mean time, driven by "upgrading capacitors madness" also upgraded my Martin Logan crossovers with SC Gen 1 and this also gave very positive results.

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jeffreybehr
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Re: Another MET1 on the forum - problems

Post by jeffreybehr »

Mr_BT wrote:Here it is, what I believe to be almost final version. It has been running problems free for a couple of months already. Almost final version, because I plan on removing bypass SCP after I'm sure they are broken-in completely (500h) and see if I need them or not.
Also, I replaced original 0.15uF 200V bypass caps with SC 600V rated (just in case :) )

I probably have to outline a benefits of this whole operation and to do so I'll have to switch cables to use channels with old capacitors but I'm simply too lazy :)

In the mean time, driven by "upgrading capacitors madness" also upgraded my Martin Logan crossovers with SC Gen 1 and this also gave very positive results.
B, looks great; I'm happy that it's running well. Any feeling so far on sonic qualities?
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Mr_BT
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Re: Another MET1 on the forum - problems

Post by Mr_BT »

Difference is so obvious that I didn't even have to go through extensive listening sessions to come up with following observations:

Before (with new PS caps in place and small bypass 0.15uF Sonicap):
- shy on bass/lower extension weak,
- satisfactory instruments separation/clarity, although sometimes congested,
- balanced somewhat cooler,
- imaging NOT pin point precision
- 3d stage mostly speaker-speaker
- lack of "sparkles" at top end

After:
-"puts meat on bones"
- vocals precise, clearer
- improved separation between instruments
- slightly wormer
- pin point imaging
- 3d stage clearly goes deeper and wider
- both upper and lower registers extended

It's just my quick and somewhat loose list of observations of sonic qualities.

All in all, worth the hassle. :D :D
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another tubes tryout

Post by Mr_BT »

This time Sylvania Gold. Long story short: 3 out of 5 hissing/noisy. Two tubes are fine, however sonic signature is quite different from original Mullards. I'd name it brighter and less-flat_freq-balanced than M8080. That's, of course, considering nature of my system and my personal preferences. I see how Gold Sylvanias would nicely supplement darker-balanced system. Differences between two brands of tubes are very delicate.

Another observation regarding "Jeffrey's mod" is that tubes change delivers obvious, audible sound character difference to the listener (me).

At last, BYPASS SCP 0.33uF REMOVED. It turned, the bypass caps were making sound heavier, darker less liquid. Removing them freed some space in the air.


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jeffreybehr
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Re: another tubes tryout

Post by jeffreybehr »

Mr_BT wrote:
At last, BYPASS SCP 0.33uF REMOVED. It turned, the bypass caps were making sound heavier, darker less liquid. Removing them freed some space in the air.
BT, did you have 0.33uF SoniCap Platinums on all-3 front-channel output couplers? Pls let us know exactly what coupling caps you're now using.

If those 0.33uF Platinums are surplus, pls e-mail me at jeffreybehr(at)cox(dot)net if you'd like to sell them.
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Re: Another MET1 on the forum - NO problems

Post by Mr_BT »

Jeffrey,
Yes, I did have 0.33uF SCPs on all front channels. It turned out, Mundorf Silver/Oil 2.2uF alone, without bypass, suited my taste better.
The 0.33uF SCPs I removed are currently employed in my phono preamp with great success :D .
Last edited by Mr_BT on Sat Nov 09, 2013 10:06 pm, edited 1 time in total.
jeffreybehr
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Re: Another MET1 on the forum - NO problems

Post by jeffreybehr »

Mr_BT wrote:Jeffrey,...The 0.33uF SCPs I removed are currently employed in my phono preamp with great success :D .
Great; thx for responding.
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Re: Another MET1 on the forum - NO problems

Post by Mr_BT »

Anybody knows what's INPUT IMPEDANCE of the MET1? Some time ago emailed CJ with this question and never heard back from them.
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Re: Another MET1 on the forum - NO problems

Post by jeffreybehr »

Mr_BT wrote:Anybody knows what's INPUT IMPEDANCE of the MET1?
My first reaction was to think 'look in the manual', but then I looked in mine, and that spec isn't included. I measured mine--13K-Ohms.

BTW the preamp must be turned on and an input selected for that input jack to be connected to its load resistor. If the preamp is turned off or an input not selected, that input jack is open.
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Re: Another MET1 on the forum - NO problems

Post by Mr_BT »

Thanks Jeffrey for the info.
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Re: Another MET1 on the forum - NO problems

Post by Mr_BT »

Another set of "worry free" tubes. Mullard Master Series 10M - 6c4. It probably won't get any better than this. No microphonics and dead quiet. Very neutral sounding.
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Re: Another MET1 on the forum - NO problems

Post by Malcolm02 »

Mr_BT wrote:Another set of "worry free" tubes. Mullard Master Series 10M - 6c4. It probably won't get any better than this. No microphonics and dead quiet. Very neutral sounding.
Would you mind saying where you got them from and how much you paid? Which ones have been the best overall in your experience?

I have had me MET1 for just over a year now with stock tubes. I had one replaced under warranty because of noise, and since then at least a couple more have been at least intermittently noisy. Apart from that I'm loving the unit.

Malcolm
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