As we discussed earlier, I agree with everything you said. I am just curious as the credibility of the statement that most or many preamp circuits utilize auto or cathode biasing of their signal tubes.
Aesthetix Io Users Group
- Thread starter audioquest4life
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Well that would be difficult to figure out.
And then there is preamp vs phono stage to consider.
My impression is that auto-bias is more critical for output power tubes.
I can't think of a preamp circuit with 12AX7s that uses fixed bias.
I had use of a Amplitrex here for and extended period. I felt that its representation of small tubes especially the 12AX7 types was not really insightful. I use the VTV small tube characterizer and maxi preamp II - even a hickok was good. At the end of the day testers don't tell you nearly enough to be certain on how tubes will perform in circuit. I use several types especially for noise. Comparing results for testers is generally like a UN meeting- no consensus.
I had use of a Amplitrex here for and extended period. I felt that its representation of small tubes especially the 12AX7 types was not really insightful. I use the VTV small tube characterizer and maxi preamp II - even a hickok was good. At the end of the day testers don't tell you nearly enough to be certain on how tubes will perform in circuit. I use several types especially for noise. Comparing results for testers is generally like a UN meeting- no consensus.
@jim94025 I don’t understand why you’re so focused on the biasing of the Amplitrex. I’ve used both fixed bias and auto bias modes while testing various tubes to evaluate their performance.
In your case, and for anyone trying to match tubes, sticking to fixed bias is the best approach. The only factor you should consider when pairing tubes is matching plate currents. If you have a large enough stock of tubes, taking an additional step to match Gm as well is ideal.
How the amplifier circuit operates is irrelevant as long as you have tube pairs that match in both Ip and Gm.
In your case, and for anyone trying to match tubes, sticking to fixed bias is the best approach. The only factor you should consider when pairing tubes is matching plate currents. If you have a large enough stock of tubes, taking an additional step to match Gm as well is ideal.
How the amplifier circuit operates is irrelevant as long as you have tube pairs that match in both Ip and Gm.
Thanks for your response mtemur. My original question wasn't so much about matching tubes, but determining how well a tube is functioning in conditions that as close as possible, mimic how they are driven in a circuit.
For example, in regards to the Amplitrex and different testing modes, Fixed vs Auto Bias, I tested a 12X7 in the first gain stage that had seen use for close to 6 years. In the fixed bias mode ( the grid voltage is fixed to a specified value ) the results were as follows:
DC Plate current- Spec. 1.2, result 1 (0.4), result 2 (0.4)
Mutual Conductance- Spec 1600, result 1 (1100), result 2 (1200)
Bias volts- spec 2.0, result 1 (2.0), result (2.0)
In the Auto bias mode ( the grid voltage is automatically adjusted downward until the specification plate current is achieved ) the results were as follows:
DC plate current- Spec. 1.2, result 1 (1.1), result 2 (1.1)
Mutual Conductance- Spec 1600, Result 1 (1800), result 2 (1900)
Bias volts- spec. 2.0, result 1 (1.5), result 2 (1.5)
So my question was which results shows how this tube is actually functioning in the IO. Unless the IO's circuit also self adjusts the bias of this tube, which I believe it doesn't, the results from the fixed mode are likely more accurate, demonstrating that this tube is functioning significantly lower that spec. In regards to matching, I agree that the fixed mode is best.
That's right in my opinion cause auto bias term used for small signal tubes like ECC83, ECC82, ECC81 etc doesn't actually adjust bias IOT match standard (%100) plate current. One way or another it means fixed bias. On the other hand most amplifiers offer bias potentiometers for output tubes which allows you set bias up to standard %100 even if the tube is worn out. In my opinion fixed bias testing is the way to go for small signal tubes.
Io owners:
What is your experience, please, operating an Io with volume controls with the volume controls all the way open (minimum attenuation) or with fixed step attenuation set at minimum attenuation of 86dB?
What are the sonic pros and cons of running the Io wide open?
Thank you.
What is your experience, please, operating an Io with volume controls with the volume controls all the way open (minimum attenuation) or with fixed step attenuation set at minimum attenuation of 86dB?
What are the sonic pros and cons of running the Io wide open?
Thank you.
Hi Ron,
Have you tried this yourself? What do YOU hear? What is your own experience?
Back in the day, I was always told to use the fixed output on CD players and cassette decks, unless you used the CD or the cassette deck as a preamp connected directly into a amplifier. Maybe different approach with the IO ?
/ Jk
There are no fixed outputs on the Io with volume control Johan. Into my preamp with a VDH Grand Crue cartridge it sounds best around 1-3 o'clock volume with the right amount of drive and dynamic's. Higher volume settings on the Io give potentially more noise, i don't like it wide open. I have plenty of gain from my SS preamp, and better bass with it in the chain.
There are no fixed outputs on the Io with volume control Johan. Into my preamp with a VDH Grand Crue cartridge it sounds best around 1-3 o'clock volume with the right amount of drive and dynamic's. Higher volume settings on the Io give potentially more noise, i don't like it wide open. I have plenty of gain from my SS preamp, and better bass with it in the chain.
What is the output of your Grand Cru, 1mv or so ? With my EMT’s 1mv output, I set the Io’s volume to around 2 o’clock, which then goes into the Callisto (29 db gain max), with vol set to 17-19 out of 45.
Thank you for explaining. Didn’t know that was the case.There are no fixed outputs on the Io with volume control Johan. Into my preamp with a VDH Grand Crue cartridge it sounds best around 1-3 o'clock volume with the right amount of drive and dynamic's. Higher volume settings on the Io give potentially more noise, i don't like it wide open. I have plenty of gain from my SS preamp, and better bass with it in the chain.
A friend reported this yesterday, after brief experimentation. I have not tried it myself.
I have always simply assumed (without experimenting) that wide open the Io would manifest too much tube roar.
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The box says 0,75 mv, i doubt it has more than 0,45 -0,5 mv though, when i compare my other cartridges. Just a little more than my Benz LPS, works well with the Io.
The box says 0,75 mv, i doubt it has more than 0,45 -0,5 mv though, when i compare my other cartridges. Just a little more than my Benz LPS, works well with the Io.
Unfortunately two different cutting speeds are used by cartridge manufacturers - with the help of ChatGPT, it types faster than me:
Cartridge manufacturers typically measure the output voltage of phono cartridges at a standardized cutting speed of 5 cm/s (centimeters per second), often at a frequency of 1 kHz. This speed corresponds to the velocity of the groove modulations on the record and provides a benchmark for comparing cartridge performance.
The cutting speed of 5 cm/s is standardized by most industry organizations, including the RIAA (Recording Industry Association of America), and represents the amplitude of a moderate signal level in the grooves. However:
- Some manufacturers may also specify output at different speeds, such as 3.54 cm/s, which is commonly used in European standards.
- These cutting speeds are always RMS (root mean square) values and represent lateral groove modulation.
Your Results will vary, with cartridge output, overall sensitivity of the system - tube noise will be a factor at maximum gain especially if you don't engage in testing and assigning the best tubes to the most sensitive positions.
I have abandoned current production tubes for the Io almost immediately as they just can't let the Io reach its potential YMMV. If you test your tubes for noise and you hand select you can get outstanding results in quietness for the Io. I have found current production tubes to be of lower sound quality and more prone to regular failure than hand selected NOS. The only good news is they're "cheap" and plentiful.
Another element that I like to mention is something like compression/ distortion once you elevate the gain over "x" position your system. There is a certain point where things don't flow and you get a collapse of front to back depth and compression - the system is over-driven.
With very insensitive cartridges like the Koetsu Jade Platinum and Etsuro gold I can easily be at 3 or 4 o'clock with the Slagle TVC- if you have a line stage ahead of the Io your relative gain position will be much less. The right balance of gain vs noise demands some experimentation here.
I imagine I am running about 65db of gain or more in my config with no noise.
The 45 step control for the Io is, I imagine, a shunt type with just a couple of resistors in each position- this will affect input impedance variably- but I don't think it has much impact in the Io configuration.
I have abandoned current production tubes for the Io almost immediately as they just can't let the Io reach its potential YMMV. If you test your tubes for noise and you hand select you can get outstanding results in quietness for the Io. I have found current production tubes to be of lower sound quality and more prone to regular failure than hand selected NOS. The only good news is they're "cheap" and plentiful.
Another element that I like to mention is something like compression/ distortion once you elevate the gain over "x" position your system. There is a certain point where things don't flow and you get a collapse of front to back depth and compression - the system is over-driven.
With very insensitive cartridges like the Koetsu Jade Platinum and Etsuro gold I can easily be at 3 or 4 o'clock with the Slagle TVC- if you have a line stage ahead of the Io your relative gain position will be much less. The right balance of gain vs noise demands some experimentation here.
I imagine I am running about 65db of gain or more in my config with no noise.
The 45 step control for the Io is, I imagine, a shunt type with just a couple of resistors in each position- this will affect input impedance variably- but I don't think it has much impact in the Io configuration.
I run my IO into a Cary SLP-05 and for my system the sweet spot is pacing the IO's vol controls at 12 noon and adjusting the gain with the Cary. Significantly more IO gain gave me a bit more tube rush noise and wasn't quite as musical. That said, as you all know, this is totally system dependent.......
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