Audio analogue enigma preamp issue

[perette]

hello everybody

I had the chance to find at the waste an Audio Analogue Enigma (V1) dropped there by its previous owner.

when I've started to investigate why someone get rid of a 1500$ unit I've found that the main power fuse was blown. I replaced it and miracle the monster started.

then I've tested it and the headphone output was working correctly.
the problem appears when I've connected speakers. the left channel is lower than the right one.

What I've done and seen so far.
- no bubbled/ damaged components inside
- voltages out of the power are OK
- by inverting the preamp to amp cable, the problem was clearly on the preamp board.

further investigation has shown that two resistors (10 ohms) (see pictures) have heated (color code is hard to read) and the wire between them seems to be brown (sames on the other side of the board).

I need your help to try to understand if the sound problem comes from this heating issue, the fuse problem (don't know why it was out) or any other idea. the lamp seems to be OK. I can only notice that there are two red spots inside it when it runs (normal) but one seems to be a bit less bright than the other one.

I've taken some pictures of the all system open and the region i suspect.

Reviving this nice piece of HIFI could be a good job. thanks for your input

JM

[stj]

Re: Audio analogue enigma preamp issue

chick if the part on the heatsink or the diode in front of it are shorted.

[perette]

Re: Audio analogue enigma preamp issue

HI stj

I'll test this and post you the outcome.

thanks for this quick reply

JM

[budm]

Re: Audio analogue enigma preamp issue

That is the power supply section, you need to get the P/N of those two devices close to those two resistors which are mounted on the heatsinks, it looks like they use the resistors (connected in series) to drop the Voltage from the main power supply to feed Q5? which looks like it is used as Linear regulstor, not a good way using resistors due to wasted power.
Sine the power supply is common to both channel, I doubt that it is the cause of having low sound level in just one channel.
So this unit has one tube for pre-amp?
Can we also see the pictures of the whole unit, the front panel, rear panel? Your pictures are cutout.

' I can only notice that there are two red spots inside it when it runs (normal) but one seems to be a bit less bright than the other one.'
I do not understand as to what you mean 'Red spots).

[stj]

Re: Audio analogue enigma preamp issue

i'm not sure it's a good idea to run a valve on it's side, from a thermal standpoint!

[R_J]

Re: Audio analogue enigma preamp issue

I have never seen an issue with mounting valves sideways, tv mfgr. for one, did it all the time.

[budm]

Re: Audio analogue enigma preamp issue

Never seen any problem, seen them a lot in 1-RU equipment, just like light bulbs mounting.

[stj]

Re: Audio analogue enigma preamp issue

i would be concerned about the guts slowly dropping and potentially shorting like on the last of the narrow-neck crt's!

[CapLeaker]

Re: Audio analogue enigma preamp issue

Inject a signal into both channels, then start tracing with the oscilloscope. Compare one channel to the other one. Stage per stage.

[perette]

Re: Audio analogue enigma preamp issue

hello everybody

Thanks for your input and i'll try to do my best to provide more detaileld infos on that case.

for Budm : I'll take pictures of all parts more in detail (preamp board and front /back panel), this evening (I'm in France)
The two red spots (sorry, poor English) are the two red heat points inside the lamp (that's why you'll see a window on the front panel, to see it glowing)

I'll also test what STJ proposed. (surely this evening too).

Hi CapLeaker, I'll have to find a working oscilloscope to do some tests.

just forget to mention : I've tested the two resistor and they seems to be ok as the connection between them.

I'll keep you posted.

best regards

JM

[rhomanski]

Re: Audio analogue enigma preamp issue

Bottleheads love to watch them tubes glow.

[budm]

Re: Audio analogue enigma preamp issue

They use one Vacuum tube so they can claim warm sounding tube when the rest of the circuits are solid-state.

[stj]

Re: Audio analogue enigma preamp issue

Bottleheads love to watch them tubes glow.

put some dead / random tubes or capsules from a vending machine in an amp, hide a neon lamp under each of them,
then put it on ebay then!!!!

[perette]

Re: Audio analogue enigma preamp issue

Hello

So I've tested both diode and they seem to be ok.

I've also verify and corrected any soldering that was looking questionable especially in the lamp board.

If I follow your comments (not on the concept which is what it is....) if there is a output pow difference between channels it can c from the audio analogic part or the lamp itself.

How can I check this ?.
It seems that there are some voltage control points to investigate.

I ll keep y posted.

FYI, picture of the two components close to the two resistors


Best regards

Jm