Good to know. I've been looking at it with the idea of a possible build, with a CCS on the 6SN7.
In the time when I designed these things a tail in the CCS was relatively impractical due a lack of good high voltage semiconductors. I used transistors in a differential input stage for one of my long ago line stages it worked well enough. This was in the days before depletion mode high voltage mosfets were common, and I was never crazy about LM317 and LM334(?) used as CCS in long tailed pairs.
Kevin,
I'm curious as to why you didn't find the LM334 to be a good current sink in a long-tailed pair (or differential amplifier) circuit. Walt Jung wrote a thorough two-part article for audioXpress magazine (link below) comparing various kinds of current sources and found the LM334 to have generally good characteristics, noting in particular that it had "exceptional" dynamic impedance, in the 10 Megohm range. Of course, there were current source configurations that boasted better specifications, but for audio applications it could be argued that the LM334 performs well enough.
https://audioxpress.com/article/Sou...lator-Tests-for-High-Performance-Full-Article
I too came up with a differential amplifier driver for the Dynaco ST-70 and Mark III, which uses LM334 current sinks in both the input and driver stages. Because the LM334 has a temperature dependence, I did use the temperature compensated configuration as shown in Figure 15 of the LM334 datasheet (link below).
https://www.ti.com/lit/gpn/LM334
In any case, people who have used this driver have been pleased with it.
I'm curious as to why you didn't find the LM334 to be a good current sink in a long-tailed pair (or differential amplifier) circuit. Walt Jung wrote a thorough two-part article for audioXpress magazine (link below) comparing various kinds of current sources and found the LM334 to have generally good characteristics, noting in particular that it had "exceptional" dynamic impedance, in the 10 Megohm range. Of course, there were current source configurations that boasted better specifications, but for audio applications it could be argued that the LM334 performs well enough.
https://audioxpress.com/article/Sou...lator-Tests-for-High-Performance-Full-Article
I too came up with a differential amplifier driver for the Dynaco ST-70 and Mark III, which uses LM334 current sinks in both the input and driver stages. Because the LM334 has a temperature dependence, I did use the temperature compensated configuration as shown in Figure 15 of the LM334 datasheet (link below).
https://www.ti.com/lit/gpn/LM334
In any case, people who have used this driver have been pleased with it.
I'm responding late to this thread however, I didn't see mention of the Dyna-70 Ultimate Upgrade as a possible ST-70 upgrade option. Originally offered by Erhard Audio, we purchased the rights in late 2022 and have made several upgrades since its release. It is available in both an Auto Bias and Manual Bias configurations, and unlike most ST-70 audio driver updates, we feature a complete Power Supply upgrade which the ST-70 really needs, however, this upgrade gets expensive fast- but we think its produces the best sounding ST-70 upgrade on the market. Visit milleraudiollc.com for more info.
The PS upgrade gets rid of the GZ34/5AR4 Rectifier Tube, the 4 section cap can, uses parallel "stacked" caps, doubling the operating voltage (800-900V) over what most cap cans safely operate as well as increasing capacitance to 90/110/50/50 mF as compared to the cap can offerings, and uses the more powerful PA-060 from Dynakit Parts. It also features a temperature compensated LM334 and like mentioned above, we have had good luck and great performance when using the temp. compensated mode as recommended by TI / National Semiconductor.
We've introduced some new terminal blocks that are a perfect fit for an ST-70 - no hole drilling and looks as if these were designed just for the ST-70; they also fit the Mk II, Mk III & Mk IV mono block amps as well.
Lastly, we'll be at the Lone Star Audio Fest in Dallas, TX June 2, 3 & 4th 2023 at the Embassy Suites-Galleria and welcome all visitors to stop by the Miller Audio demo room to hear our Dyna-70 Upgrade amplifiers paired with GR Research NX series of speakers- also some of the best sleeper speakers you have heard.
Visit milleraudiollc.com for more info.
The PS upgrade gets rid of the GZ34/5AR4 Rectifier Tube, the 4 section cap can, uses parallel "stacked" caps, doubling the operating voltage (800-900V) over what most cap cans safely operate as well as increasing capacitance to 90/110/50/50 mF as compared to the cap can offerings, and uses the more powerful PA-060 from Dynakit Parts. It also features a temperature compensated LM334 and like mentioned above, we have had good luck and great performance when using the temp. compensated mode as recommended by TI / National Semiconductor.
We've introduced some new terminal blocks that are a perfect fit for an ST-70 - no hole drilling and looks as if these were designed just for the ST-70; they also fit the Mk II, Mk III & Mk IV mono block amps as well.
Lastly, we'll be at the Lone Star Audio Fest in Dallas, TX June 2, 3 & 4th 2023 at the Embassy Suites-Galleria and welcome all visitors to stop by the Miller Audio demo room to hear our Dyna-70 Upgrade amplifiers paired with GR Research NX series of speakers- also some of the best sleeper speakers you have heard.
Visit milleraudiollc.com for more info.
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Nearly 3 years ago I made an effort to design some boards in DesignSpark that would fit a Dynaco ST70 that contained, for the most part, the DCPP amp circuit by Pete Millett. It seemed successful as I got it to work with 38HE7 output tubes and 6GU5 tubes in the driver pcb.
Those are Toroidy cathode feedback OPTs.
I designed the board to work with an available auto-bias board. I've since disassembled the amp but I still have the assembled driver board and a few extra prototype pcbs if anyone is interested in them PM me.
Those are Toroidy cathode feedback OPTs.
I designed the board to work with an available auto-bias board. I've since disassembled the amp but I still have the assembled driver board and a few extra prototype pcbs if anyone is interested in them PM me.
