Dennis Had Inspire Amps

[pechelman]

Originally Posted by FloridaBoy

The tube that worked best in my PSE is a Silvertone labeled 5Y3G with ribbed plates.

thanks! I've got one of those on its way. Supposedly a 100/99% high testing matched sides. Also a couple extra.

I tried pulling the preamp off the shelf as far away from anything else as i could get it. Swapped back to a GE 5Y3, moved cables around, tried covering tubes with a metal container to see if maybe it was rfi/emi, all with no change. Will try again with the new 5Y3G's when they arrive. Also am now picking up 120hz buzz in addition to the 60hz hum on the spectral analyzer app.

[FloridaBoy]

Originally Posted by pechelman

thanks! I've got one of those on its way. Supposedly a 100/99% high testing matched sides. Also a couple extra.

I tried pulling the preamp off the shelf as far away from anything else as i could get it. Swapped back to a GE 5Y3, moved cables around, tried covering tubes with a metal container to see if maybe it was rfi/emi, all with no change. Will try again with the new 5Y3G's when they arrive. Also am now picking up 120hz buzz in addition to the 60hz hum on the spectral analyzer app.

Good luck. Are you using shielded interconnects? I once lived in an area where the electric grid was the source of a lot of grunge.

[oldominion]

Originally Posted by pechelman

thanks! I've got one of those on its way. Supposedly a 100/99% high testing matched sides. Also a couple extra.

I tried pulling the preamp off the shelf as far away from anything else as i could get it. Swapped back to a GE 5Y3, moved cables around, tried covering tubes with a metal container to see if maybe it was rfi/emi, all with no change. Will try again with the new 5Y3G's when they arrive. Also am now picking up 120hz buzz in addition to the 60hz hum on the spectral analyzer app.

Not to be too obvious about it, but if you're picking up 120hz might that indicate a power supply cap going south? Might should be looked at...

[pechelman]

Originally Posted by FloridaBoy

Good luck. Are you using shielded interconnects? I once lived in an area where the electric grid was the source of a lot of grunge.

yea, using mogami 2549 cables. same cables are being used throughout my system but ive isolated the source of hum to the preamp.

Originally Posted by oldominion

Not to be too obvious about it, but if you're picking up 120hz might that indicate a power supply cap going south? Might should be looked at...

planning to pop the cover off this weekend to have a look for anything obvious, still havent heard back from dennis, but he did make this brand new for me 8/2019. Anything is possible with respect to the caps, but would imagine they're still fine. Will do the obvious visual checks. The 120hz does point to something with the power supply/rectification. I'm semi-hopeful the new tube(s) fix the issue.

Really appreciate all the help all. Hopefully I can report back soon with results.

[Comzee]

@pechelman I forgot to mention, the hum could be a grounding topology issue. Dennis's amps (at least the two I own) seems to have a peculiar grounding scheme, that interacts very negatively with one of my audio chains (creating LOUD hissing hum).

I fixed it by bridging the ground between my dac and the amp. Just soldered two alligator clips to a 12awg wire. Then clipped that from the DAC ground to AMP ground and it removed the hum. (or if you use TT, clip it to the phono pre)

Cheers

[pechelman]

was poking around inside the preamp tonight and noticed that grounding scheme you're talking about; essentially everything is being daisy chained all over the chassis, e.g. The transformer connects to the rectifier which connects to the filter cap which connects to the pot which connects to the drivers to the buffer to the outputs rather than having all of those connect to one single point which most people talk about trying to do with star grounding. I suppose the thought is the chassis is one big giant star in itself but it does seem to increase the chance of creating a ground loop somewhere.

I noted one 6SN7 base and the main power switch that had no continuity to ground. Having just finished building my own amp, part of me wants to try to fix all of this but I wish Dennis would reply to my reaching out to him first. Also even if I did want to fix some of these things there's a lot of potting/epoxy? that would make it pretty difficult for me to do anything on some components like the power switch, wires, and other components.

In the meantime I might try your trick of trying to ground the preamp chassis to the dac body.

[straitwire]

I spoke with Dennis a few minutes ago.
He wanted to make a few issues about chassis grounding very clear.
All the Inspire chassis's are aluminum (NON FERROUS METAL).
The aluminum (NON MAGNETIC) metal has much greater conductivity.
Ground loops are easily created with steel chassis's.
Now if one were to remove the ground wire runs in an Inspire amp or preamplifier and lift the terminal strips they would notice that the powder coat has been removed so that all the mechanical terminal strip ground connections are common to the aluminum chassis.
As an extra precaution Dennis ties all these points together at a common point that is in the greatest interest of electrical stability.
For instance in the Inspire amplifiers the actual extra main wire grounding scheme starts where the output tube grid leak resistors terminate.
Once again for stability.
Do not alter or remove the Inspire grounding scheme ..... this is also part of the sonic merits as well.

On a personal note I have a variety of Inspire design preamps, and they are all quiet with a matching Inspire amplifier.
Keep in mind ... Dennis is a proponent of AC filaments ... with an Inspire amplifier this is great.
If one were to use with a high sensitivity amplifier there may be a slight bit of hum.
The LP-3.1 measures -78 to -81 db noise and hum.
This would be picked up by a highly sensitive solid state amp or highly sensitive tube amp.
Another note ... sonically I do not know of a better sounding preamplifier...straitwire...

[pechelman]

Originally Posted by Comzee

@pechelman I forgot to mention, the hum could be a grounding topology issue. Dennis's amps (at least the two I own) seems to have a peculiar grounding scheme, that interacts very negatively with one of my audio chains (creating LOUD hissing hum).

I fixed it by bridging the ground between my dac and the amp. Just soldered two alligator clips to a 12awg wire. Then clipped that from the DAC ground to AMP ground and it removed the hum. (or if you use TT, clip it to the phono pre)

Cheers

I just tried to add a grounding wire from the preamp body to dac body and to the inspire power amp. No difference. Everything was already grounded to one another through the signal wires, though the preamp to dac had the highest resistance in the chain of about .6ohm.

Originally Posted by straitwire

I spoke with Dennis a few minutes ago.
He wanted to make a few issues about chassis grounding very clear.
All the Inspire chassis's are aluminum (NON FERROUS METAL).
The aluminum (NON MAGNETIC) metal has much greater conductivity.
Ground loops are easily created with steel chassis's.
Now if one were to remove the ground wire runs in an Inspire amp or preamplifier and lift the terminal strips they would notice that the powder coat has been removed so that all the mechanical terminal strip ground connections are common to the aluminum chassis.
As an extra precaution Dennis ties all these points together at a common point that is in the greatest interest of electrical stability.
For instance in the Inspire amplifiers the actual extra main wire grounding scheme starts where the output tube grid leak resistors terminate.
Once again for stability.
Do not alter or remove the Inspire grounding scheme ..... this is also part of the sonic merits as well.

On a personal note I have a variety of Inspire design preamps, and they are all quiet with a matching Inspire amplifier.
Keep in mind ... Dennis is a proponent of AC filaments ... with an Inspire amplifier this is great.
If one were to use with a high sensitivity amplifier there may be a slight bit of hum.
This would be picked up by a highly sensitive solid state amp or highly sensitive tube amp.
Another note ... sonically I do not know of a better sounding preamplifier...straitwire...

Thanks, straitwire.
I've not modified anything other than moving the hot AC run from the IEC to the switch a little away from the 5Y3 filament runs from the transformer an inch or so. Made no difference.

With the 45 firebottle and lp3,1 ultra preamp hum/buzz is audible from my regular listening position during quieter tracks (classical, jazz, leonard cohen, john prine, etc) and during pauses. It was at a level I could live with given how nice it sounds otherwise. With the amp I just finished that has 20dB of gain & 20wpc, it's even more audible at my regular listening position and even in another room to where I can hear it during some louder rock songs. I have 98db speakers, so not the ~87-89db proac's I believe he listens with at home. The amp I built is quieter than the Inspire 45 when I remove the preamp from either chain. On the 45 I hear a little bit of transformer buzz that is only audible an inch away from the speaker.

You noted stability for grounding, and I'm wondering if there is an issue with stability here since I did have brand new electroharmonix 6SN7 tubes that caused an incredibly loud feedback hum as they powered on. Could there be something funny going on with my amp? It doesnt seem to match your description of being quiet with its matching inspire amp. I sent Dennis an email a few days ago now with no response. Perhaps you could mention this to him? He also has my phone number. My user name matches my email address and includes my actual name.

-Phil

[bearcity]

Originally Posted by Comzee

@pechelman I forgot to mention, the hum could be a grounding topology issue. Dennis's amps (at least the two I own) seems to have a peculiar grounding scheme, that interacts very negatively with one of my audio chains (creating LOUD hissing hum).

I fixed it by bridging the ground between my dac and the amp. Just soldered two alligator clips to a 12awg wire. Then clipped that from the DAC ground to AMP ground and it removed the hum. (or if you use TT, clip it to the phono pre)

Cheers

Straitwire covered this specifically but I thought I might add on in a more general reflection. As I have spoken to Dennis over the years I can tell you that nothing about his Inspire gear is slipshod, or unintentional in any way. He truly has been designing and building amps for 60+ years. His understanding of electrons and electronics is quite remarkable. I would likely guess that there are only a handful of people world wide in his class. Usually, when I ask a question the answer goes way over my head, but one thing I am sure of, every detail of his designs are completely thought out, from chassis layout to, yes, grounding. Though it may seem he is not following best practices at times, I can tell you that it is intentional and from a level of understanding that goes way beyond some ‘rule of thumb’. Sadly, knowledge like his cannot be just transferred and when he is gone much will go with him. I am greatly appreciative of Staitwire and Analog Addict, and any of Dennis’ other protégés over the years, for doing what they can to understand and further the craft as best they can. I can tell you all hear though, we are all mere novices in the presence of a true master.

[FloridaBoy]

Originally Posted by pechelman

I just tried to add a grounding wire from the preamp body to dac body and to the inspire power amp. No difference. Everything was already grounded to one another through the signal wires, though the preamp to dac had the highest resistance in the chain of about .6ohm.



Thanks, straitwire.
I've not modified anything other than moving the hot AC run from the IEC to the switch a little away from the 5Y3 filament runs from the transformer an inch or so. Made no difference.

With the 45 firebottle and lp3,1 ultra preamp hum/buzz is audible from my regular listening position during quieter tracks (classical, jazz, leonard cohen, john prine, etc) and during pauses. It was at a level I could live with given how nice it sounds otherwise. With the amp I just finished that has 20dB of gain & 20wpc, it's even more audible at my regular listening position and even in another room to where I can hear it during some louder rock songs. I have 98db speakers, so not the ~87-89db proac's I believe he listens with at home. The amp I built is quieter than the Inspire 45 when I remove the preamp from either chain. On the 45 I hear a little bit of transformer buzz that is only audible an inch away from the speaker.

You noted stability for grounding, and I'm wondering if there is an issue with stability here since I did have brand new electroharmonix 6SN7 tubes that caused an incredibly loud feedback hum as they powered on. Could there be something funny going on with my amp? It doesnt seem to match your description of being quiet with its matching inspire amp. I sent Dennis an email a few days ago now with no response. Perhaps you could mention this to him? He also has my phone number. My user name matches my email address and includes my actual name.

-Phil

Which 45 tubes are you using?