Bottlehead Forum

Bottlehead Kits => Stereomour II => Topic started by: amritdesai on April 09, 2016, 06:19:35 AM

Title: Triad C7-X in Stereomour II
Post by: amritdesai on April 09, 2016, 06:19:35 AM
Can I replace the 270ohm resistors in the PS with c7x chokes? Is this as simple as this sounds?

I was playing around last night, removed the 270 resistors 44L/45L and 41L/42L and attached the leads of the each choke to these terminals - one of the leads from choke A to 44L the other to 45L. For choke B 41L/42L respectively. Because I have a tall base i was able to mount them perpendicular to and below the OT's.

I turned on the amp, it lit up for a second and blew a fuse.

I'm going to buy some fuses at radioshack and have spare 270 ohm resistors to revert to stock but i'd like to the try to make this work.

Any suggestions?

Thank you!
Title: Re: Triad C7-X in Stereomour II
Post by: Paul Joppa on April 09, 2016, 07:17:31 AM
There are no 270 ohm resistors in Stereomour II. I think you have replaced the 270K ohm resistors, which serve to bleed charge from the PSU electrolytic caps when the amp is turned off. This means a nearly short circuit across the power supply - no wonder the fuse blew.

The old Stereomour used 270 ohm resistors (in the form of 360 ohms in parallel with 1200 ohms) in a CRC filter. Stereomour II uses four 130 ohm resistors in a CRCRC filter, they are potential locations to replace with chokes.

You said "...perpendicular to and below the OT's." You didn't explicitly say the coil axis was perpendicular, so I mention it just in case there was some confusion.
Title: Re: Triad C7-X in Stereomour II
Post by: amritdesai on April 09, 2016, 07:27:52 AM
Wow :-[

I completely mis interpreted this condition - yikes. I will revert to stock and stop messing with this thing.

Thank you for your help!
Title: Re: Triad C7-X in Stereomour II
Post by: Paul Joppa on April 09, 2016, 08:45:46 AM
Definitely the first thing to do is revert to stock, in order to be sure there are no problems remaining. (I don't expect any, but better safe than sorry!)

I will correct my previous post to clarify that the original Stereomour used 360 ohms in parallel with 1200 ohms, to make approximately 270 ohms.
Title: Re: Triad C7-X in Stereomour II
Post by: amritdesai on April 09, 2016, 09:32:05 AM
I have soldered back in place new 270K ohm resistors. New 1.6a fast fuse continues to blow when I turn on the amp  :(

Resistance measurements are good. Perhaps the UF4007 rectifier diodes were affected?

Thanks for you help.
Title: Re: Triad C7-X in Stereomour II
Post by: amritdesai on April 09, 2016, 12:37:54 PM
Installed new UF4007 rectifier diodes and tested all of the 130 ohm resistors - no issues here. Also new 270k resistors between terminals L 41 and 42, L 44 and 45. new 1.6amp 250v fast blow. Connections are solid.

Don't know where to go from here - 4 fuses later.

Any assistance is greatly appreciated.
Title: Re: Triad C7-X in Stereomour II
Post by: Bonzo on April 09, 2016, 09:27:58 PM
Just a doubt: the fuse shoul be slow blow...shouldn't it?
Title: Re: Triad C7-X in Stereomour II
Post by: amritdesai on April 10, 2016, 05:00:54 AM
Good question. The unit came with a fast
blow but other users have been okay using also slow blow.
Title: Re: Triad C7-X in Stereomour II
Post by: Lee Hankins on April 10, 2016, 01:59:53 PM
What does the parts list in your manual say the fuse should be?  I have never built a BH kit that doesn't use a slo-blo fuse.
Title: Re: Triad C7-X in Stereomour II
Post by: Natural Sound on April 10, 2016, 02:53:12 PM
What does the parts list in your manual say the fuse should be?  I have never built a BH kit that doesn't use a slo-blo fuse.

The Stereomour II manual I have only specifies a 1.5 A fuse. No mention of fast or slow blow. It looks like some users are having an issue with a spike in inrush current when charging the caps on startup, others are not. Maybe it has to do with variation in mains voltage and component tolerance stack up. But I'm just guessing.
Title: Re: Triad C7-X in Stereomour II
Post by: amritdesai on April 10, 2016, 03:04:10 PM
I was about to say the same thing about the manual. I could have sworn the original fuse was fast blow but my memory, judgment and decision making is questionable based on recent events  :o

Thanks for the feedback guys!

I'll try a slow blow and go from there
Title: Re: Triad C7-X in Stereomour II
Post by: amritdesai on April 11, 2016, 09:43:17 AM
The slow blow fuse fixed the issue! Really appreciate the help!

Now what to do with these extra chokes...

Thanks again.
Title: Re: Triad C7-X in Stereomour II
Post by: Lee Hankins on April 11, 2016, 01:12:38 PM
If the 130 ohm resisters are installed in series (= 260 ohms) then the chokes can be installed in the CRCRC filter.  I do not have a manual for the Stereomour II and I can not tell from the picture in the products page, so this may not be correct.
Title: Re: Triad C7-X in Stereomour II
Post by: Paul Joppa on April 11, 2016, 04:13:25 PM
If the 130 ohm resisters are installed in series (= 260 ohms) then the chokes can be installed in the CRCRC filter.  I do not have a manual for the Stereomour II and I can not tell from the picture in the products page, so this may not be correct.
They are in series, but there's a capacitor from the CT to ground.
Title: Re: Triad C7-X in Stereomour II
Post by: chard on April 12, 2016, 03:16:05 PM
c/choke/c/10 ohm resistor/c      total 280 ohms instead of designed 260 ohms. Hardly any difference. 
Title: Re: Triad C7-X in Stereomour II
Post by: Paul Joppa on April 12, 2016, 06:01:47 PM
The 10 ohms will pretty much eliminate any effect of that stage. Look up PSUD on the Duncan Amps site; it's an excellent learning tool, practically a video game for this community!
Title: Re: Triad C7-X in Stereomour II
Post by: chard on April 12, 2016, 11:14:57 PM
Thanks Paul, for the information.
Title: Re: Triad C7-X in Stereomour II
Post by: Jamier on April 15, 2016, 08:17:28 AM
Would a Hammond 156L (135 ohm / 5H / 400V /  75ma) be a good
choice for replacement of the last 130 ohm resistor? Or the first
130?
Title: Re: Triad C7-X in Stereomour II
Post by: Paul Joppa on April 15, 2016, 12:11:39 PM
Looks good to me.

Try this: install the choke(s) without connecting them to anything at first. Read the AC voltage between the two choke wires - this will be the induced hum from the power transformer magnetic field. If it's very small then you can put the choke in place of the last 130 ohm resistor. If it's large then you'll want it in place of the first 130 ohm resistor. I would guess that 10mVrms is "small". Of course it's not terribly difficult to try it both ways, instead of taking a guess from some dude on the internet (me, in this case).   :^)
Title: Re: Triad C7-X in Stereomour II
Post by: mcandmar on April 15, 2016, 03:27:44 PM
I love how you come out with these brilliant ideas, yet they sound so obvious when you say them :)
Title: Re: Triad C7-X in Stereomour II
Post by: amritdesai on April 25, 2016, 05:27:11 AM
I started this thread so I figured I'd give the Hammonds a shot.

I mounted the Hammond 156L inductors to the amp base with their coil axis perpendicular to the power transformers. I measure the AC voltage between the choke wires without connecting anything with a reading of around 6mVrms for both inductors. I tried moving them around and changing orientation but the reading was pretty consistent. I soldered the chokes in place of the last 130ohm resistors.

All resistance checks were within range - some of the voltage readings were higher. I performed these checks with the stock tubes.

Terminals

1. 370 VDC
2. 407 VDC
19.407 VDC
20. 370 VDC

I tested the amp on a spare set of speakers and everything sounded fine. I'm not sure if there is any audible difference or benefit with the inductors. Previous to making this change the amp was sounding wonderful - very open, sweet and textural.

After a day of listening I'm finding much of the brightness and sparkle has been replaced with a more neutral tone - overall a little less dynamic. The image though has tightened up quite a bit. Likely, things will open up more over time.


Title: Re: Triad C7-X in Stereomour II
Post by: Jamier on April 26, 2016, 10:18:26 AM
Are you still using the spare speakers or have you gone back to the
Zu's? If you did go back to the Zu's and you feel that the tonal
quality is less desireable with the 156Ls could it be that the 5H of
this particular choke is not enough (?). Maybe Paul knows.
Title: Re: Triad C7-X in Stereomour II
Post by: amritdesai on April 26, 2016, 02:37:34 PM
I've got everything hooked up on the main system and it sounds fantastic - I don't think the amplifier has ever sounded so balanced - the imaging is insane!  I would use the term neutral but not in a bad way. The tonal quality isn't less desirable, just different. I was expecting more sparkle and to be honest this change has had the opposite effect - perhaps in a good way.

Replacing the resistors with the the Hammond inductors has not changed the sound as dramatically as tube rolling or capacitors but it seems like it has removed the harshness.  I can listen at higher volumes with less fatigue. There is a richness to the sound and added depth/improved soundstage - these are my initial impressions.

Also, the amp is dead quiet now - previously there was a slight hum.


Title: Re: Triad C7-X in Stereomour II
Post by: Jamier on April 26, 2016, 03:10:46 PM
That's great! When I researched possible PS chokes the Hammond
156Ls were the only ones I could find that met all the criteria.
I was thinking that the inductance might be a little low though.
Glad to hear they seem to be an improvement.
Title: Re: Triad C7-X in Stereomour II
Post by: amritdesai on May 09, 2016, 06:58:01 AM
Jamier,

Let me know if you install the chokes - I'm still undecided about the sound.

A
Title: Re: Triad C7-X in Stereomour II
Post by: Jamier on May 10, 2016, 04:27:31 PM
I just received the chokes today.I don't know when I will get them in
as I just completed the amp and I haven't even voltage tested yet.
I will follow up though and let you know what I think.Others will probably
be adding 156Ls also, so I'm sure their thoughts will also be posted.
I don't know if chokes are like Caps with respect to "burn in", but give
them some time(?).
Title: Re: Triad C7-X in Stereomour II
Post by: Jamier on May 10, 2016, 05:51:53 PM
Look at the site aikenamps.com. This is where I got the idea that
5H might be on the low side for inductance. I was hoping PJ might
weigh in on this subject. There is a section on that site that explains
the function of chokes in power supplies, both choke regulated and
capacitor regulated. In Cap regulated 5H appears to be on the low
side but I do not have enough experience to know myself.I think it
is important to remember that while the CX7 has a dramatic effect in
the Crack circuit, it is different than the Stereomour II (OTL vs OT
etc). Also the CX7 has 10H inductance which might be a factor in it's
effect. Tweeking these circuits is a complicated endeavor especially
for those of us with limited experience.
Title: Re: Triad C7-X in Stereomour II
Post by: Paul Joppa on May 10, 2016, 06:05:48 PM
... I was hoping PJ might
weigh in on this subject. ...
I did. Twice, on this page (didn't check the first page). As you said, it can be complex; that's why I recommended the PSUD software. Be sure to look at the start-up transient in addition to the steady-state performance.
Title: Re: Triad C7-X in Stereomour II
Post by: amritdesai on May 12, 2016, 08:10:32 AM
Thanks Paul. Trying to get PSUD running on bootcamp has been more difficult than it should be. I've been having issues with the installation asking for a second disc - i'll try on my PC at the office.

I've also noticed an excess amount of heat coming from the amp - certainly more with the chokes installed. I think I am going to revert to stock to compare again sonically the differences/see if the heat is an actual issue.

A
Title: Re: Triad C7-X in Stereomour II
Post by: Paul Joppa on May 12, 2016, 10:46:47 AM
There should be no difference at all in heat generated. Something is wrong. Might be time to check the voltages?
Title: Re: Triad C7-X in Stereomour II
Post by: amritdesai on May 12, 2016, 11:35:52 AM
With the chokes some of the voltage readings were higher. I performed these checks with the stock tubes.

Terminals

1. 370 VDC
2. 407 VDC
19.407 VDC
20. 370 VDC

I'm going to revert to stock and test.
Title: Re: Triad C7-X in Stereomour II
Post by: amritdesai on May 16, 2016, 06:02:38 AM
I reverted to stock primarily because of how hot the amp was getting. The voltages at the terminals in question are now back within range.

After going back and forth I actually prefer the sound without the chokes - much brighter and detailed in my setup.

Looking forward to read the impressions of others.
Title: Re: Triad C7-X in Stereomour II
Post by: Tom-s on December 04, 2019, 09:28:11 PM
Digging up this old thread as it covers my question somewhat.

When using PSUDII to see how my PSU will end up. What current should i use for the driver stage with the shunt regulator and CCS upgrade's in place?
Title: Re: Triad C7-X in Stereomour II
Post by: Paul Joppa on December 05, 2019, 04:19:12 AM
If you look in the manual at the circuit diagram, you will see that the shunt reg plus driver is fed from a current source of 13mA, and the bias for that current source is an additional 1.65mA. Total 14.65mA.
Title: Re: Triad C7-X in Stereomour II
Post by: Tom-s on December 05, 2019, 05:21:10 AM
I have to say, i feel very smart for not reading the f.... manual. Thanks PJ :-X