Here's a problem for you TT gurus to solve! (I'm stumped!)

[Full Range]

Your two components are not friendly with each other 

Probably an magnetics to electronics mismatch between the 2   

[VanArn]

Perhaps there is some  cross talk or loopback, happening between the output of one phono  pre-amp into  the other unit. Sometimes the sections of a double pole ,double throw switch ( if that is the device used to select between the individual phonos) are too close together to  prevent  low level signals passing from one to the other. Shielded  switch sections, relays, muting and  distance between elements are the usual cures. This ,unfortunately, is  more complicated to do than a simple toggle or rotary switch set up.   A push button switch bank is better in this role but they are not  easy to obtain. I would also suggest muting the inputs to the pre-amps should be considered  although it can be difficult to avoid switching thumps when a changeover is made.

[Wimbo]

Something is exciting the Unitrac's Bearing. Hence why I said to move the offending Preamp. Have you done this yet?

[aussievintage]

11 hours ago, andyr said:

 

Very interesting suggestion.    The most likely one, yet! 

 

I will have to think more about what you said.  Maybe the Bugle has a rolled-off bottom end which 'solves' a feedback problem which the Unitrac arm has, in David's environment?  Which I don't have in my environment with the same arm and cart ... and a later version of the Muse?

 

Andy

 

 

Yes, that is what I was thinking.   I know that changing one component, in my case, the power amp, suddenly caused low frequency feedback/oscillation on one of my turntables.

[andyr]

16 minutes ago, aussievintage said:

 

Yes, that is what I was thinking.   I know that changing one component, in my case, the power amp, suddenly caused low frequency feedback/oscillation on one of my turntables.

 

 

To confirm your theory, David is going to do some listening, comparing the bass that he hears when one cart is on the LP vs. when the other one is (obviously, using the preamp's source selector switch to swap between the two).

 

I'm hoping he will be able to confirm that he hears lower bass from the Muse combo.

 

If this experiment is not conclusive, I'll bring my sig-gen and CRO over to David's place and measure the output from 50 to 20hz, for each phono stage.  I'm pretty sure the Muse is only marginally down at 20hz but I never measured the Bugle.

 

26 minutes ago, VanArn said:

Perhaps there is some  cross talk or loopback, happening between the output of one phono  pre-amp into  the other unit. Sometimes the sections of a double pole ,double throw switch ( if that is the device used to select between the individual phonos) are too close together to  prevent  low level signals passing from one to the other. Shielded  switch sections, relays, muting and  distance between elements are the usual cures. This ,unfortunately, is  more complicated to do than a simple toggle or rotary switch set up.   A push button switch bank is better in this role but they are not  easy to obtain. I would also suggest muting the inputs to the pre-amps should be considered  although it can be difficult to avoid switching thumps when a changeover is made.

 

But the problem didn't occur when the Stanton was mounted in David's OL-1 arm - only when the Stanton was mounted on his new Unitrac arm ... so I'm thinking the source selector switch in the preamp is OK, in terms of your suggestion.

 

25 minutes ago, Wimbo said:

Something is exciting the Unitrac's Bearing.

 

Yes, that is the most likely occurrence. 

 

33 minutes ago, Wimbo said:

Hence why I said to move the offending Preamp. Have you done this yet?

 

I don't understand how the physical location of the preamp would be affecting the arm?  As I said before, with all the equipment in exactly the same location, this sonic problem didn't occur when the Stanton was mounted in an OL-1 arm.

 

 

Regards,

Andy

[aussievintage]

2 minutes ago, andyr said:

 

To confirm your theory, David is going to do some listening, comparing the bass that he hears when one cart is on the LP vs. when the other one is (obviously, using the preamp's source selector switch to swap between the two).

 

I'm hoping he will be able to confirm that he hears lower bass from the Muse combo.

 

If this experiment is not conclusive, I'll bring my sig-gen and CRO over to David's place and measure the output from 50 to 20hz, for each phono stage.  I'm pretty sure the Muse is only marginally down at 20hz but I never measured the Bugle.

 

 

 

Yes, it may not be audible, except as the modulation/warbling you describe. 

[djb]

I have completed the listening tests as instructed. 

 

Test a lbums Eagles HotelCalifornia and Joan Armatrading show some emotion.

 

 

The Magnepan tone arm with Stanton  WOS CS 100 mm cart is connected to the (modified) Hagerman  Bugle phono stage and sounds flat ordinary with little bass.

 

The SME 12" with Grado Reference Master HOMC is connected to the Muse and sounds alive bright and delivers appropriate bass.

So after Easter the tech will operate.

We assume the Bugle has a low bass roll off incorporated deliberately which will need to be removed.

 

Thanks to you all for the advice.

not often that @andyr is stumped 

Edited April 11, 2017 by djb

[drdarkfish]

Ive heard its possible ( although very rare) to have a tuned circuit... this would be caused  by the cart, cable and pre in combo with one another. Are you able to switch out the cable? Perhaps try longer/shorter.

 

If this was the case it would explain why the 'all else being equal' variables didnt give a hint as to the cause.

[andyr]

1 hour ago, drdarkfish said:

Ive heard its possible ( although very rare) to have a tuned circuit... this would be caused  by the cart, cable and pre in combo with one another. Are you able to switch out the cable? Perhaps try longer/shorter.

 

If this was the case it would explain why the 'all else being equal' variables didnt give a hint as to the cause.

 

 

Good point Drd ... but, unfortunately, the Magnepan Unitrac (which dates from the late 70s) uses a peculiar (non-DIN) connector at the base of the tonearm.  So it's not just a simple matter of swapping to another phono cable.

 

I think - given @djb's above test - that aussievintage nailed it when he suggested that the 'echoey' effect we were hearing was the result of acoustic feedback acting on the Magnepan Unitrac's UP bearing.  (Given the same cart on an OL-1 arm didn't exhibit this behaviour.)  The Hagerman Bugle must have a 'rumble filter' to roll off extreme LFs - so you don't hear this echoey effect (but there is - as a result - no low bass  ).  IMO, such a rumble filter is essential if you have a TT which has rumble ... but not desirable for those that don't.  Unless you experience the problem which David has!  I will check out the extreme LF response of the Bugle in due course, to confirm whether or not it has implemented a LF roll-off.

 

Now, David - one option is certainly to have me modify the Muse, to implement a 20hz roll-off.  But I suggest this is not a good idea - as it reduces the SQ of the Muse!  IMO a better alternative is to keep the carts plugged into the phono stages they are current plugged into.  Or take the Unitrac out and put your OL-1 arm back in.

 

And a better option, I suggest, is to get Peter to do an REW frequency sweep and see if some PEQs on the miniDSPs can remove the problematic frequency which is causing the feedback to the UP arm.

 

 

Regards,

Andy

[djb]

1 Agree we don't touch your great Muse design 

2 Echoey effect seems to have disappeared 

3 Tomorrow I will test this further at higher volumes

4 remove rumble filter ...if it has one

5 I know ppl say Jim Hagerman is a good communicator we could email him prior to Easter for his input re rumble filter

6 @gone fishing will have done just that @gonefishing999 out after marlin 

7 You'd think he'd drop in a flat head or two  wouldn't you?

8 more chance of getting a fish out of 1 or the big 3 @Marc @Luc @evil c

 

ill give him a ring

 

[djb]

9 Oops I don't think we were able to earth the unitrack arm 

[Luc]

 

All yours @djb

[ThirdDrawerDown]

@andyr @djb solved?

[andyr]

53 minutes ago, ThirdDrawerDown said:

@andyr @djb solved?

 

Well, Murray, 'solved' in the sense that @djb no longer hears the echoey noise when he plays the Unitrac/Stanton combo through his Hagerman Bugle (rather than his Muse phono stage).

 

But we are waiting for @gonefishing999 to do an REW sweep of the room, to see if he can identify a room mode which is exciting the Unitrac ... so he can remove this, with the miniDSP software.

 

The same cart in the same arm in my room ... doesn't display this 'echoey' effect - so it would seem to be room-related?

 

Andy