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Voice of Music model 1450 mono tube amp

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I have 2 of these mono tube amps that I would like to recap and incorporate into a 2 channel system. 

My question is: these amps only have a phono input. Do I need to alter the wiring to make them play thru a CD player?

thanks.

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Well, in front of V1 ( first 1./2) is the Volume Control, and prior to V1 ( second half ), we have the unit's Bass and Treble controls, and some sort of EQ I suppose  to comply with the RIAA, as I casually see it. 

 

I would gently PM Maynard, or let him post here.  He is a wonderful whiz at this kinda' stuff.

 

Does your CD player  have a volume control?  If not, and if you use no Preamp or Passive System Attenuator, you will need to control the Volume feed into the VoM amp.

 

These are cute SE units, simple.   I would be VERY careful, conservative about recapping, because you can easily ruin the unit's musicality, unless you are a gifted expert in how parts sound.  

 

If these were my units,  I might modify ONE as follows, putting in GREATLY improved resistors in key spots, and compare amps . ( Save the old resistors , if you don't like the new ones !! )   

 

As follows, all parts from Michael Percy:

 

1) Both 220K plate resistors .... Parallel two Roderstein Resista MK3s at 443K, for each 220K  ( its within 2% value-wise, and stock Rs were likely 5% ).  LISTEN to that first change alone !!

2) The 3,300 Ohm Rk, ..........Parallel two Roderstein Resista MK3s at 6.65K .  LISTEN.

3) The 150 Ohm Rk on 6BQ5, .........Parallel two PRP 301 Ohm 1/2 Watt resistors from Percy.  LISTEN.

4) The 1,000 Ohm Grid stopper on 6BQ5, ..............get RID of it ASAP.  Use a 965 Ohm Roderstein Resista MK3.  LISTEN.  .............. LEARN !!!

 

Assuming you can resolve your circuit changes for the Line Stage function, before making ANY R changes, listen to both units, FIRST, test their tubes, and be sure they play approximately similar.  Have fun.  PM me sometimes later and we can discuss caps

 

The two 220K Ra or Plate Resistors are in DIRE need    !!!!!!!!!!!!!!!!!! - to be buffered........ from interacting with each other.   ALL this, IMHO.

.

Jeff Medwin

 

 

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Mr. Medwin, 

Your suggestions are appreciated. I am by no means an expert at this kind of thing but my soldering skills are ok.

These 2 amps are in very good condition so your recommendation is understood. My CD player does not have a volume control. I was planning on procuring a tube preamp with no tone controls so I would ultimately get stereo sound instead of mono and use the amps tone controls.

i may reach out to you in the future regarding this project. I assume Mr. Percy is a member of this forum?

Thanks.

 

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Wait a minute.  You can get stereo sound with two mono integrated amplifiers ( V o Ms) !!  Plug the Left channel output of your CD player into one VoM, and the Right channel CD player's output into the other VoM.

 

Yes, you do NOT need tone controls, if you have a GOOD hi fi system !!!    You do not necessarily need to buy a Line level Preamp, if you are only using a CD player as a source.  It has a couple of Volts AC, output, all you need to do is turn it DOWN, no gain usually needed. 

 

You can build a Passive System Attenuator, for several hundred dollars, using QUALITY parts, that can sonically out perform MANY  and maybe most of the tube preamps out there.

 

First, you still need to resolve HOW to use these VoMs with a LINE ( CD player ) input !!  If Maynard doesn't see this thread, or if Alex Kittic doesn't, reach out to either of them via a FORUM P.M.

 

Michael Percy is Michael Percy Audio, a class act, for decades, a GREAT source for some of the best sounding parts in AUDIO. Lovely person too.  Download his catalog. from 2-2018.

 

Yes, I will try to assist...... any time you ask. 

 

 

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As I look at this schematic some more,.....................

 

I THINK you could remove the 0.005 uF series input cap's connectionfrom the wiper of the 1 Meg Input / Volume POT, and JUMPER a wire from the 1 MEG POT's wiper to PIN 8 , the second half of the Input tube.  Carefully REMOVE the wire connected to PIN 8, before soldering in the jumper.   This KEEPS the Volume control functional,

 

but eliminates the first 1/2 of the 6EU6, with all the PHONO EQ /Bass/TREBLE control circuitry !!!   How wonderful THAT would be !!

 

You get to TOTALLY ELIMINATE many cheap and degrading stock VoM  parts from the signal path. 

 

Superbly, you stop sending the incoming audio signal through TWO series coupling caps, ( before and after the first triode section ).  Ugh.  A film cap is one of the most degrading parts in audio, to a music signal.  You get to eliminate an entirely UN-needed tube stage.  Additionally, you get to eliminate ALL the parts associated with the Bass and Treble control potentiometers.  Do you think you can willy-nilly thoughtlessly send a music signal through ANY stock cheap VoM potentiomer, one, or in this case, two, and not have it degraded ??  Of course not !!   

 

In my first post, the use of 25 cents each German MK3 resistors, will be a huge improvement over the stock murky, narrow-band carbon composition resistors.  Do it AS I suggested please, listening yourself to each resistor change individually, and be sure you LIKE it, before modding the second unit.  In its day, Audio Research

Corporation used to use these same resistor types in their upscale gear.  They are no longer made, but Percy has some.

 

You must also eliminate the connection of the 6,800 Ohm resistor at PIN 9 of the second half of the triode, while retaining the 3,300 Rk resistor's connection / use there.   

 

The JUMPER wire ( from the wiper of the 1Meg POT, to PIN 8 )  MUST be high quality

 

I would suggest Wonder Wire, at only $1.75 a foot, from Percy.  Order the wire, resistors, and POSSIBLY, some caps, all at ONE time from Percy.   TALK to me, using Forum P.M., about possible cap choices !!  Always with your budget in mind, .....best bang for the dollar. 

 

While you are at it, ELIMINATE that very poor unsoldered /  pressure - contact - only connection between the "HOT" phono input wire and the Microphone switch.  Run a short piece of Wonder Wire from the HOT center of what was the " Phono " INPUT RCA jack ( now a LINE input RCA jack ) to the TOP of the 1 MEG Volume control.  Nice neat soldered connections please, unlike the stock input path, a low-fi / high-loss Microphone Jack connection !!  A new  Neutrik / REAN RCA jack, direct gold plating over brass, at under $3.00 is a very effective sonic upgrade here.

 

Please someone, CONFIRM or critique my ideas. 

 

Yes, will some other tube-savvy readers please review and  critique these suggestions please. 

 

We will upgrade the 0.047 coupling cap, EZ to make a couple great film cap suggestions in 0.047 uF !!!!! 

 

This could be VERY nice sounding, IF I am suggesting the best way to do it !!   I need help here.   Alex, Maynard, somebody???

 

Ohh, and do NOT butcher and remove stock parts !!!   Just please do tell us if this eventually TROMPS all over your Latino tube amp !!  

 

Jeff                                                   Mr. Medwin , Louis, ......................was my Father. 

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You can connect the CD player directly to the phono input.  The amps should be fully recapped (in particular, all the electrolytic and coupling caps).  All resistors should be checked for tolerance and replaced as needed.  The power cord should be replaced with a 3 wire type and the primary of the power transformer needs to be fused.  Otherwise, I don’t agree with Jeffrey’s recommendations.  These are fine amps in their stock form and, while far from being the ultimate, can provide a pleasing experience.  I say this as someone who is not particularly fond of the EL84 tube.

 

 

Maynard

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2 hours ago, tube fanatic said:

You can connect the CD player directly to the phono input.  The amps should be fully recapped (in particular, all the electrolytic and coupling caps).  All resistors should be checked for tolerance and replaced as needed.  The power cord should be replaced with a 3 wire type and the primary of the power transformer needs to be fused.  Otherwise, I don’t agree with Jeffrey’s recommendations.  These are fine amps in their stock form and, while far from being the ultimate, can provide a pleasing experience.  I say this as someone who is not particularly fond of the EL84 tube.

 

 

Maynard

 

 

Hi Maynard, 

 

I liked the power cord and fuse suggestion a lot.  But how do you justify running a CD signal ( needing a flat LINE stage circuit )  through an EQed VoM  Phono Input?  Please tell me, what am I missing, not understanding here??

 

Jeff Medwin

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Jeffrey,  I like tone control circuitry as it allows the user to tailor the sound to their personal taste. And, the 1 meg input load will make the CD player very happy.  Your second thread,  in which you advocate a significant circuit change, was not there earlier.  It could work.  However, eliminating the nfb loop will likely make the amp sound like crap unless running at a fraction of its output power capability.   There really is nothing wrong with this amp as originally designed.  If anything, a different output transformer would probably yield the greatest improvement, but I don’t advocate doing that either.  
 

One last point, it wouldn’t hurt to put a bleeder resistor of around 240k across the power supply filter network as a safety feature.  
 

 

Maynard

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Maynard,

thanks for the input. If I left the tonal controls could I create a tonal circuit with new caps & resistors following a schematic of the tonal pack like the in the attached photo?

F6677621-DC0A-4E1B-8C8B-5145DF4A3D6E.jpeg

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1 hour ago, tube fanatic said:

Jeffrey,  I like tone control circuitry as it allows the user to tailor the sound to their personal taste. And, the 1 meg input load will make the CD player very happy.  Your second thread,  in which you advocate a significant circuit change, was not there earlier.  It could work.  However, eliminating the nfb loop will likely make the amp sound like crap unless running at a fraction of its output power capability.   There really is nothing wrong with this amp as originally designed.  If anything, a different output transformer would probably yield the greatest improvement, but I don’t advocate doing that either.  
 

One last point, it wouldn’t hurt to put a bleeder resistor of around 240k across the power supply filter network as a safety feature.  
 

 

Maynard

 

 Hi Maynard, 

 

Two more questions please :  

 

Would the NFB loop consist of the R= 560 Ohm, R = 6,800 Ohm, C = 0.001 uf, attached to PIN 9, the cathode??

 

Could I eliminate the first tube section and its associated parts, and simply keep the circuitry mentioned  above.???

 

Thanks, have a lovely day .

 

Jeff

 

 

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Are you saying that the VOM tone control circuit components are contained in a couplate which looks like one in the photo above?  My memory is hazy on what VOM used.  
 

 

Maynard

 

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 Upgrading VOM 1450 for use with Owner's Cornwall IIs.

 

1853945275_AMP4.thumb.jpg.9df40e47d52c022408221766d3bb2f79.jpg

 

Note: 

 

The 10 Ohm Choke ( Stancor C-2708 or Triad C-40X ) is just a passing idea. 

 

It reduces the DCR to the Finals stage dramatically, which is wonderful, BUT, such lowered resistance increases the operating VDC to the Finals stage an unacceptable amount.  To properly employ such a low DCR choke, would require PSUD simulating the supply, to see what the VDCs to Finals stage would become, if the FIRST THING the 6X4 rectifier " saw" was this non critical low DCR / 10 Ohm choke - and not a 40 uF cap.. 

 

I would use a C-2708, not a C-40X.  Hammond's 159ZB choke, at only 8 Ohms, is the third possible inductor candidate here.  

 

It takes additional information, a few simple voltage measurements, to simulate this unit's supply in PSUD,.  There is also the question of " room on the chassis ". 

 

The basic goal is to minimize the 1,000 Ohms of series resistance to the Output stage, circled in red.  The original design used a 5 Watt Power resistor, 1,000 Ohms, on a " cost and room " basis.  The EE was likely unaware of the DCR's penalty.   WOW, 1,000 Ohms to 10 Ohms is a 100-fold decrease !!   Reducing series DCR to the Output stage is THE best audio design thing to do.  ( See Dr. Charles A. Halijak,  prior Dean of E.E., University of Alabama, , " Figure of Merit of the Power Supply ".  )  Here :


                                              http://db.audioasylum.com/cgi/m.mpl...figure+of+merit+of+a+power+supply&r=&session=

 

Jeff Medwin

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Hello, 

 

 I have been thinking about the Voice of Music 1450, some more.   

 

I was curious about HOW a 10 Ohm Input choke would work, so I guesstimated the stock circuit into PSUD 2 today, and compared stock VS a low DCR 10 Ohm choke amp..  Yes, with the choke I can get similar VDCs, to run the circuit.  There is a deal-breaker, however, with using the ten Ohm Choke.  It takes two such chokes,, and there is no room.   I normally use two of them, L1/C1/l2/C2 in amps.  With just one choke, the B+ wave form is not sinusoidal.  So.... its a no go.  

 

There is a second concern I have been thinking about, too much gain with the second half of the 6EU7 ( mu or gain of 100 times ) driving the 6BQ5 in a pure Pentode mode.  I deduce this from my 2019 KT88 SE Pentode amp build.   It is  using half a 12BZ7 ( similar mu - of 100  )  driving a Pentode Output tube, and it is NOT long term livable, gain-wise..  The volume pot is only operated in the bottom 5%-20% of its range, and there are other less than optimal things happening.  I'm converting to a mu of 20, 6FQ7 driver tube, later this year.

 

The first half of the 6EU7 ( a dual triode) is similar to them second, in gain.  When the first half is used for all that added circuitry, Phono EQ, bass and treble controls, perhaps it cuts gain down to less than the input signal !!   Whatever !! .....In any case, using the second 6EU7 triode section only will pass a signal fine, but be unlivable, long term.

 

Two solutions :

 

1) Add some series resistance to the music signal, with only the highest quality resistor one can source ( Texas Instruments TF-020  as an example ).  This is the EASY way to solve it, but even the best resistor, is a degrade of SOME sort !!  I will NOT do that in my 2019 KT88 amp.  Why here, other than ease??

 

2) Find another 9 pin miniature vacuum tube, that will fit in the tube socket, and have the right characteristics.  It must be linear, maybe a mu of 30 to 70, draw about 1 mA. of plate current and have a similar filament consumption as the existing 6EU7..  Pin out similarity is not a factor.    

 

Anyone have any driver tube ideas to suggest?  If so, please do !!  Rome was not built in a day .  Thanks.

 

Jeff

 

 

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On 5/31/2020 at 2:50 PM, Could sound better said:

I have 2 of these mono tube amps that I would like to recap and incorporate into a 2 channel system. 

My question is: these amps only have a phono input. Do I need to alter the wiring to make them play thru a CD player?

thanks.

 

It looks like it just has standard, rather basic, bass and treble controls; it doesn't look as if it has RIAA compensation (which is good, because you don't need or want that, when driving from a CD player).  So the best thing would be just to try it as is, after following Maynard's suggestions about recapping and adding a 3-wire mains cable. One amp takes its input from the left-channel output of the CD player, and the other takes the right-channel output. 

 

Tone controls are like a red rag to a bull in some "audiophile" circles, but they have their uses and plenty of people like to have them.  These amps are never going to be super hi fi, so the best thing is just to try them out, after the basic safety replacements a la Maynard, and see what you think of them.

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Jeffrey, you are far too concerned with the gain of the input stage.  Amps like this were typically used with ceramic or crystal phono cartridges having an output of as much as a few volts.  The feedback network employed reduces the gain to a specified degree.  Also, the 1meg input load was usually sufficient to allow the cartridges to function with their own “RIAA equalization.”   Why are you trying to redesign this entire amp?  Given that the EL84 DC plate current draw won’t vary by more than a couple of milliamps or so between idle and full output, having a 1K filter resistor is of no consequence.   While this amp may not meet your standards, it certainly can provide a very enjoyable listening experience  for most  when using Klipsch speakers.

 

 

Maynard

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Backfire, 

I have tried them out thru a CD player and a turntable. The sound isn’t too bad, rather nice but veiled. Almost like a a curtain in front of the speakers. Gonna recap, iec, & fuse for now.

thanks!!

 

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Hello All,

 

I want to thank Backfire and Maynard, for their contributions today to this thread.  That was very nice, and apropos. 

 

I PMed the original poster, the first day of this thread, and I told him

 

" I have large gaps in my E.E. understanding, of Negative Feedback, and of Bass and Treble controls", because in 40+ years of DIY amp building, I have never used either.  There was no need for me to learn it.  

 

We DID agree, and I told him,

 

" Within two days, we will hopefully have contributions to this thread, that will resolve the areas wherein I am deficient in my understanding."   Backfire and Maynard, rather nicely, resolved those deficiencies of mine with their posts today. 

 

Thanks .......for so kindly contributing.

 

Maynard, you realize, my lack of NFB knowledge led me to compare my ZERO NFB 2019 KT88 build, with this VoM1450, having feedback in it, which reduces gain. I did NOT get that.  LOL. Its OK.  And Backfire clarified the Tone Controls and RIAA EQ, questions I had, as did you Maynard today, very nicely.

 

I do know how to eliminate the veiling, and get the unit to play substantially above stock.  Its not particularly expensive to do.  Several things, however, have to be done, not just one change.  Why?   More than one thing needs " help ", and together, all these "needing help" areas contribute to the veiling and can easily be addressed. 

 

Thanks guys, ......it is up the the O.P. now.

 

Jeff 

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Thanks to all for contributing to this endeavor.

i’ll consider all before I decide on a course to follow. 
thanks Jeff!!

Cheers!!

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When replacing the QUAD CAN with a new one, I would suggest making the FIRST section only 20 uF  ( as seen by the rectifier tube ) , and not 40 uF. as shown stock. 

 

Wire it as  :  6X4 /  20 uF  / 1000 Ohms /  40 uf   - to FINALS   /  etc.  etc, ..................and not vice versa uF amount wise.

 

I don't think filtering will be substantially effected, either way, .......  but it should be somewhat easier, more conservative, on the 6X4 rectifier tube.

 

Maynard, or Backfire, what do you gentlemen think??

 

Jeff 

 

 

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10 hours ago, Jeffrey D. Medwin said:

When replacing the QUAD CAN with a new one, I would suggest making the FIRST section only 20 uF  ( as seen by the rectifier tube ) , and not 40 uF. as shown stock. 

 

Wire it as  :  6X4 /  20 uF  / 1000 Ohms /  40 uf   - to FINALS   /  etc.  etc, ..................and not vice versa uF amount wise.

 

I don't think filtering will be substantially effected, either way, .......  but it should be somewhat easier, more conservative, on the 6X4 rectifier tube.

 

Maynard, or Backfire, what do you gentlemen think??

 

Jeff 

 

 


What you propose is reasonable!  
 

 

Maynard

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