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Tube Rolling 12au7, 12ax7 (Read 70551 times)
surfers5
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Re: Tube Rolling 12au7, 12ax7
Reply #100 - 05/07/22 at 00:44:49
 
I wholeheartedly agree with you that adding extra input voltage adds weight to the music.

My current SUT has step up ratios of 5x, 10x, and 20x. When I purchased my 0.5mv cartridge all of my research and calculations pointed to a 10x step up ratio to be optimal - giving 5mv of output, but surprisingly it wasn't.

The 20x step up ratio combined with my low DCR 0.5 mv cartridge took my listening experience to an entirely different level than what I was accustomed to with previous upgrades. The music took on a life of it's own and there is no going back for me.

This is the main reason I have decided to purchase the ZP3 because I think it will be a perfect compliment to my current set up.

I am just a little worried about the extra 2db in gain over my existing phono stage (+40db)....but maybe the magic of tubes will compensate for the extra 2db in gain?

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Archie
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Re: Tube Rolling 12au7, 12ax7
Reply #101 - 05/07/22 at 01:03:06
 
What do you think the downside of the extra gain is?  My experience is that more gain will result in more volume for the same knob position.  With 1 volt input, most of the Decware amps won't be able to reach full power/volume.  And of course, if input exceeds the amp spec for full volume, the input is attenuated by the amp volume knob.

But I may not understand your issue.  I've always thought the ZP3 would benefit from more gain but after reading Steve's White Paper on the development, I think he was happy to get what he got without noise.
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ZLC
Technics 1200G TT w/ Ortofon Jubilee MC cart
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ZP3 (25th A Mods)
ZR2 (25th A Mods)
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ZMA (25th A mods)
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surfers5
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Re: Tube Rolling 12au7, 12ax7
Reply #102 - 05/07/22 at 12:38:30
 
If I had all tubes in the signal chain I do not think I would be having any issues with the extra gain.

The problem is that I do not think my solid state integrated amp can properly handle the extra gain.

When I increase the gain of my current phono preamp above +40 db, the sound definitely worsens because there is too much gain.

From what I have read on this forum and others is that if one uses 5751 tubes in place of 12ax7 tubes, the total output should drop by around 3 db, but I do not know if this same db drop can be applied in the case of the ZP3?

And I do not know if this 3db is being calculated or if it is just a rule of thumb measurement derived by knowing each incremental adjustment of most volume knobs is around 3db?
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Edsonic
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Re: Tube Rolling 12au7, 12ax7
Reply #103 - 05/07/22 at 14:31:38
 
Two questions to ask in these situations are: what is worst case? Which is not informative by itself, so we ask: for what duration?

Through much reading of data provided by Sure Bros. and others, at 1,000Hz the absolute limit in vinyl cutting is 35 cm/s. Reading further, the max found through measuring of many records was ~ 28-30 cm/s, at some place on two records (of many samples). Aside those two, the highest were ~ 12 and 15 cm/s. For a cart output measuring.0005 V (.5 mV) @ 5 cm/s-1,000 Hz, 30 cm/s is 6x and 15 cm/s is 3x above test spec. From an article I dug out from Stereo Review printed in 1968, the writer said that few records have anything much above 15 cm/s. So I have taken for myself that 4x the test record spec is the R/L actual worst case that we should have any concern about.

With a cart of .5mV going into a 20x SUT and a 125x (42 dB) phono pre, that comes to 5V. Worst case.

The second question is duration of the event. Look at the data on this page: https://www.dpamicrophones.com/mic-university/acoustical-characteristics-of-musi...

The attack duration of snare drum measured 5-8ms, bass drum:8-12 ms, tympani (all sizes): 10-18 ms, trumpet: 20-40 ms. These are the loudest instruments in the orchestra. 20 ms is 1/50 of a second. That would be nigh impossible to attract perceptual notice, for one, and I don't think it would trouble even a SS preamp input stage overly much. I don't know for certain, but I don't think even 50 ms (1/20th second) would cause too much trouble, but who knows.

So then with your cart and SUT, we have "an extraordinary vinyl event" resulting in 5 volts output of a 42dB phomo preamp for 5-40 milliseconds.

After all that, your own experience is the final determinant. If you notice distortion when you set the phono preamp higher than 40 dB, then there it lies. But that might or might not occur with another phono pre, SS or tube.

I don't think you need to stress much over it because it might be fine with the ZP3 as is, and if not you have the option of replacing the 12AX7 tubes with the 5751 set.


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Edsonic
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Re: Tube Rolling 12au7, 12ax7
Reply #104 - 05/07/22 at 15:11:36
 
To this-

Quote:
From what I have read on this forum and others is that if one uses 5751 tubes in place of 12ax7 tubes, the total output should drop by around 3 db, but I do not know if this same db drop can be applied in the case of the ZP3?


The discussion of 5751 tubes earlier in this thread was specifically in reference to the ZP3. So, yes.

Quote:
And I do not know if this 3db is being calculated or if it is just a rule of thumb measurement derived by knowing each incremental adjustment of most volume knobs is around 3db?


It was calculated. Amplification factor and gain are two different things, but indirectly related and close enough for this discussion. The 12AX7 has mu of 100, the 5751 has 70.  Log(70/100) x 20 = -3dB. Theoretically, this would change gain of the ZP3 from 42dB to 39dB, or from ~ 125x to ~ 90x.
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Archie
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Re: Tube Rolling 12au7, 12ax7
Reply #105 - 05/07/22 at 17:21:27
 
Edsonic is lightyears ahead of me in his understanding of all of this but this quote stands out:

Quote:
After all that, your own experience is the final determinant. If you notice distortion when you set the phono preamp higher than 40 dB, then there it lies.


All of the analysis aside, you say you get distortion above your 40dB.  Is it in your existing phono pre?  My NAD pre has both MM and MC inputs but the MC is crap.  (I don't use this anymore though.)
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ZLC
Technics 1200G TT w/ Ortofon Jubilee MC cart
ZMC1
ZP3 (25th A Mods)
ZR2 (25th A Mods)
CSP3 (25th A mods)
ZMA (25th A mods)
Homemade Big Betsy Speakers (F15s)
Silver Cabling
DIY Isolation platforms under amps & TT.
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Edsonic
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Re: Tube Rolling 12au7, 12ax7
Reply #106 - 05/07/22 at 17:57:53
 
What he said was:

Quote:
The problem is that I do not think my solid state integrated amp can properly handle the extra gain.

When I increase the gain of my current phono preamp above +40 db, the sound definitely worsens because there is too much gain.


So it looks like his phono preamp, when set above 40dB, is sending out more than his SS integrated amp can deal with.

His calculations are correct that a .5 mV cart through his 20x SUT and the ZP3 should produce 1.25 V output.

Louder portions of a record (not the few extremes) might result in 2x or 3x that. The Decware CPS3 starts overloading at ~ 3.32 V (if I remember correctly) with the input attenuator full open. If his integrated does not have adjustment for input level (likely not), then 3.75 V or even 2.5 V might be a problem.

Addendum: Thinking over that last item, I don't know what phono preamp he has currently, but it is indeed possible that it sounds worse at a 42 or 44dB setting than at 40dB.
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Archie
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Re: Tube Rolling 12au7, 12ax7
Reply #107 - 05/07/22 at 18:08:34
 
More things I am ignorant about.  I assumed that anything with a "volume" knob would attenuate the input signal down to zero.  There must be a knob on his amp otherwise it'd play at full volume always.  What am I missing?
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ZLC
Technics 1200G TT w/ Ortofon Jubilee MC cart
ZMC1
ZP3 (25th A Mods)
ZR2 (25th A Mods)
CSP3 (25th A mods)
ZMA (25th A mods)
Homemade Big Betsy Speakers (F15s)
Silver Cabling
DIY Isolation platforms under amps & TT.
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Edsonic
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Re: Tube Rolling 12au7, 12ax7
Reply #108 - 05/07/22 at 18:23:51
 

First of all, I added to my previous post, so have a look.

To your question above- keep in mind that the CSP3 has three different level controls; input, volume, and output. Many preamps and I'd bet all integrateds do not have an input attenuator. The preamp volume knob controls the amount of gain.
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surfers5
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Re: Tube Rolling 12au7, 12ax7
Reply #109 - 05/07/22 at 18:24:47
 
Hi guys, I appreciate all of the helpful information and feedback.

I now believe the main culprit of the issue I am hearing is what Edsonic mentioned - "extraordinary vinyl events"

My integrated amp and/or phono preamp is not properly handling the "extraordinary vinyl events" that my 20x SUT and 0.5mv cartridge and phono preamp are producing. Events lasting only in milliseconds with output ranging from 2 to 5 volts.

I have two technical follow up questions I hope you don't mind answering-

1. Do you think the maximum input capacity of the ZP3 increases when using the lower mu 5751 tubes? Edsonic - I read one of your other posts where you thought the ZP3 should have at least a maximum input capacity greater than 100mv. Will the use of 5751 tubes increase this maximum capacity number?

2. Edsonic - your calculated db decrease of the 5751 compared to using the 12ax7 was Log(70/100) x 20 = -3dB. Does your calculation encompass the use of 5751 in both v1 and v2 slots? Or is using 5751 tubes in both v1 and v2 slots additive to the drop in db? [Log(70/100) x 20 + Log(70/100) x 20] = -6.19 db for an overall output of around +36db?

thanks for your help
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Archie
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Re: Tube Rolling 12au7, 12ax7
Reply #110 - 05/07/22 at 19:02:15
 
Quote:
The preamp volume knob controls the amount of gain.


Sorry if I'm taking this thread off topic but this is very interesting to me as I've never heard an explanation of what happens when a signal is inputted to an amp.  Also, I've never understood what really goes on with the 3 adjustments of the CSP3 and how they are different.  I thought the input and output settings were a sort of maximum with the Master Volume attenuating from zero to that maximum.

My assumption in my above post was that the amp (Decware anyway) attenuates the input signal from zero to it's actual value -- if the amp doesn't distort before reaching it.  If this doesn't happen then what does?
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ZLC
Technics 1200G TT w/ Ortofon Jubilee MC cart
ZMC1
ZP3 (25th A Mods)
ZR2 (25th A Mods)
CSP3 (25th A mods)
ZMA (25th A mods)
Homemade Big Betsy Speakers (F15s)
Silver Cabling
DIY Isolation platforms under amps & TT.
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Edsonic
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Re: Tube Rolling 12au7, 12ax7
Reply #111 - 05/07/22 at 19:13:49
 
Surfer-

Refresh page and make sure you read the last few items Archie and I talked about. We all might have been typing at the same time.

To your first question above- I can't say for certain. I just know the basics about tubes so I don't think I'm qualified to answer that definitively. I know that 12AX7 tubes overload easier than tubes with less gain, generally speaking. In any case I don't think any cutting levels are above ~ 52-55 cm/s, that occurring at 8kHz-9 kHz. I don't know how to mathematically translate cartridge output from 5cm/s @ 1,000 Hz to other frequencies.

Have a look at this:http://pspatialaudio.com/max_velo.htm Scroll to the chart halfway down the page, past the graph.

My guess about the ZP3 input limit was based on a 'search survey' which brought up several SS phono preamps with 70-120 mV limits and an AR and Manley Chinook w/ 240 mV limits. My estimation of at least 100mV for the ZP3 is probably a low ball figure. That said, there are a number of phono preamps with 40-60 mV limits.

To your question about 2 tubes / 2x the dB calculation, I'm not sure about that either. Standalone, it makes sense, but the circuit might have it otherwise.
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Edsonic
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Re: Tube Rolling 12au7, 12ax7
Reply #112 - 05/07/22 at 19:59:31
 
Archie-

I only know the bare basics of electronics- Ohm's Law, how to express watts in those terms (VČ/R), RMS/peak/p-p, how to calculate gain, etc. I just know how to run the numbers -  the inner workings of circuits, not so much.

I was told by the instructor in my Studio Recording class and by a sound company owner I worked for sometimes (eons ago, both cases) that the 'pad' (input attenuator) determines the level of input, and the fader controls the amount of gain. Input levels are set with the fader at unity gain.
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surfers5
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Re: Tube Rolling 12au7, 12ax7
Reply #113 - 05/07/22 at 20:55:30
 
Edsonic and Archie,

I appreciate the knowledge you have shared with me. I definitely have a better understanding of how much voltage my phono preamp and integrated amp are experiencing even if for a few milliseconds.

When my ZP3 arrives later this year I will be sure to add my experience of how well a ZP3 with various tube compliments works with a 0.5mv cartridge and 20x SUT.

and fyi - my integrated amp does not have an input attenuator, only a volume knob

And in the meantime, if anyone knows if swapping the two 12ax7 tubes for 5751 tubes theoretically reduces the gain by 3db or 6db, please do not hesitate to respond:)

Thanks again

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Archie
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Re: Tube Rolling 12au7, 12ax7
Reply #114 - 05/08/22 at 00:56:49
 
Quote:
and fyi - my integrated amp does not have an input attenuator, only a volume knob


My problem is that I thought these were the same thing.
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ZLC
Technics 1200G TT w/ Ortofon Jubilee MC cart
ZMC1
ZP3 (25th A Mods)
ZR2 (25th A Mods)
CSP3 (25th A mods)
ZMA (25th A mods)
Homemade Big Betsy Speakers (F15s)
Silver Cabling
DIY Isolation platforms under amps & TT.
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Edsonic
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Re: Tube Rolling 12au7, 12ax7
Reply #115 - 05/12/22 at 13:20:58
 

A few things I overlooked in prior discussion.

Surf, I think the reason your SUT sounds better @ 20x setting is because the cart DCR is so low. (Generally speaking, lower cart DCR is a good thing). The SUT steps down the input impedance of the phono preamp by the square of the  turns ratio. So from the 47kΩ input of the phono pre  a 10x ratio would present 470Ω to the cartridge, 20x ratio would make it 117Ω (47k/400). With a cart DCR of 1.4 the second number is a much better fit.

Regarding the gain situation, I think it might be best to have the ZP3 operating as intended to the extent possible. To that end using an in-line attenuator between the phono pre  and the integrated might be just the ticket. (I knew there was something kicking me in the back of the head before, that was it). Here are some from Parts Express -

https://www.parts-express.com/home-a-v/audio-video-accessories/line-level-attenu...

They are cheap enough that you could get both the 3dB and 6dB pairs. I searched around a few years ago and these seem to be well regarded. They should be plugged into the 'line in' / 'aux' of the integrated to keep the signal strong till the end, for better signal vs. EMI/RFI on the cables. That last item is another reason the attenuator pair  might be a better solution than lowering the signal output of the ZP3 by use of lower gain tubes.

If you still want to try the 5751 somewhere I think it should only be after the RIAA section. (Another thing I forgot about). The front tube of the ZP3 is where the signal comes in first. Using the 5751 there would  provide less gain to a weak signal then going through the however slight noise of the resistors and capacitors of the RIAA filter. So then worse signal-to-noise ratio at the worst place.

I think using the 5751 tube in the second slot, after the RIAA, should be okay, in the process obviating the need for our question about dB using two 5751s. If you eventually get into tube rolling you might pay the extra money (for the front tube) to get 12AX7s that are tested for low noise. Vintage Tube Services and Brent Jessee Recording & Supply do that, there might be others.  

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surfers5
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Re: Tube Rolling 12au7, 12ax7
Reply #116 - 05/12/22 at 16:56:41
 
Edsonic -

Your advice and suggestions are much appreciated!

The 3db or 6db in-line attenuators sound like the most cost effective approach to addressing my excess gain problem.

Although, now considering I can add the 12ax7 and 3db or 6db attenuators to the mix of different tubes I now have in my possession, and if my calculations are correct - the number of possible tube/attenuator combinations has jumped from 56x [5!(8-5)!] to 462x [6!(11-6)!]......I guess this is a good problem to have....:)
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