As my CCS currents are safe, I'm tempted to fit a multiturn pot across each R5 and leave it there. I've got some good quality Bournes pots lying around somewhere.
How sensitive are inputs ?
I think I know the answer to this as I post it.
The Impasse is nearing completion, I think the heater supplies should be re-routed between the PSU and the Impasse to distance them from the audio input and output sockets.
I think I know the answer to this as I post it.
The Impasse is nearing completion, I think the heater supplies should be re-routed between the PSU and the Impasse to distance them from the audio input and output sockets.
Finished
The Impasse is finally finished - I've still got to cut a few holes in the lid to let the valves fit but that's easy enough.
You'll notice that I stayed with my original plan and have added 2 x 5K multi-turn pots to the CCS stages. Both currents were slightly below the recommended 8mA so even if the pots fail, nothing catastrophic will happen to the circuit.
Shame I can't listen to it yet, I need to modify the power amp to balanced input to fully appreciate it.
Anyone else building the Impasse, don't bother with the suggested transformer, even SY, the designer states that it was just a cheapy. That might be true in the USA but it cost me a fortune to get one in the UK and then I had to add the second 240/115V transformer so that I could use it.
The Impasse is finally finished - I've still got to cut a few holes in the lid to let the valves fit but that's easy enough.
You'll notice that I stayed with my original plan and have added 2 x 5K multi-turn pots to the CCS stages. Both currents were slightly below the recommended 8mA so even if the pots fail, nothing catastrophic will happen to the circuit.
Shame I can't listen to it yet, I need to modify the power amp to balanced input to fully appreciate it.
Anyone else building the Impasse, don't bother with the suggested transformer, even SY, the designer states that it was just a cheapy. That might be true in the USA but it cost me a fortune to get one in the UK and then I had to add the second 240/115V transformer so that I could use it.
Attachments
You can listne to it - make a cable that is XLR to RCA - the details of the connection is in the article - all of which can be found here - Index of /Preamplifiers/ImPASSe
CRAZY, but the additional transformer is making a hell of a hum, so I've just ordered a custom transformer for the build (£150), cheaper than what I paid to import the original. Anyone wanting the original transformer let me know, it no longer has its end cheeks.
I finally got to connecting up the Impasse.
FAIL
Only one channel is working. Everything is lighting up OK and no magic smoke but one channel is dead. Tried RxR both valves but they are OK.
I'll have to get the 'scope out and see what is happening. My guess is a fractured joint under one of the valve sockets.
FAIL
Only one channel is working. Everything is lighting up OK and no magic smoke but one channel is dead. Tried RxR both valves but they are OK.
I'll have to get the 'scope out and see what is happening. My guess is a fractured joint under one of the valve sockets.
Silly Bunt comes to mind
Well, it didn't take me long to find my mistake.
I'd managed to get HOT and GND crossed over on one of the inputs.
Now, I'm not a great favourite of the F5 but it is sounding quite nice with the Impasse. It's as though the Impasse is knocking off the harsh edges of the F5 and producing a more pleasant Aleph type sound that I am used to.
Well, it didn't take me long to find my mistake.
I'd managed to get HOT and GND crossed over on one of the inputs.
Now, I'm not a great favourite of the F5 but it is sounding quite nice with the Impasse. It's as though the Impasse is knocking off the harsh edges of the F5 and producing a more pleasant Aleph type sound that I am used to.
Glad you got it sorted out. Swapping leads unintentionally is my specialty- I fried the power supply of a new phono preamp last week by swapping plus and minus in the heater supply. At least yours didn't smoke!
Hi Sy,
After an hours use I've got to listen to the background noise. The Impasse does seem to "HISS" a lot. It's not intolerable but it is way above the noise of any op-amp pre-amp that I have tried.
In use it's going to be the pre-amp for my mid amp in a tri-amp set up.
After an hours use I've got to listen to the background noise. The Impasse does seem to "HISS" a lot. It's not intolerable but it is way above the noise of any op-amp pre-amp that I have tried.
In use it's going to be the pre-amp for my mid amp in a tri-amp set up.
This graph was done with the Impasse out of its chassis, 2.83 Vout,
An externally hosted image should be here but it was not working when we last tested it.
That's a bit extreme!😀 At that point, I wouldn't worry.
I think that's his test tone.
I've still got to swap out the Mains Transformer. After spending over £250 on importing the Allied 6K3VG. it's being let down by a cheapie 240-110V transformer.
I've now got a custom made 240V transformer to replace the pair of them.
I've now got a custom made 240V transformer to replace the pair of them.