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Toolshed Amps?


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If I’m not mistaken a Toolshed tube amp with volume control and a Primare solid state integrated were used at a Klipsch Pilgrimage three or four year ago ? Each was A - B’d in the demo room by a Klipsch employee. I doubt this would happen today as Klipsch has teamed with Cary for the Cary Heritage line to match with Klipsch Heritage. Yes, they are lookers with great build quality.

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Howdy all, tipped to this thread by a Klipsch customer in Des Moines................. Been busy. :) A new review dropped either late Saturday or early Sunday over at Part-time Audiophile............ here is the link in case you have interest in reading.




Although the reviewer used a single, wide-band speaker, you all know I'm more of a Klipsch/Altec guy. Different strokes for different folks. ;) It's all good.


No hard feelings with Klipsch management about the Cary thing either........... Billy is a great guy and Cary has some decent product. Business is business.





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4 hours ago, captainbeefheart said:

After some quick calculations my guess is the amp is 1% THD at 1 watt output. There is absolutely no way an open loop 300b amp will produce 7-8 watts with only 1% THD.

For SE amps, I aim for less than 0.5% THD @ 1Watt, 1kHz.

It’s easy to do but you have to carefully choose the primary transformer impedance, driver & output tube load lines to compliment each other. Distortion isn’t the only parameter that matters, but it helps to keep it low to begin. 

If you have enough gain, of course you can add some feedback to improve damping and reduce distortion a bit. 

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2 minutes ago, captainbeefheart said:


I am hoping for a confirmation but after some reading I am lead to believe these amps do not have any feedback. You just built a no feedback 300b amp for a member correct? Where were you getting your 1% THD at? And from memory you were around 5% THD with 6.5 watts or so correct?


In your experience have you been able to get 1% THD at 8 watts from a single 300b and zero feedback? Maybe I am doing something completely wrong but before feedback I was never close to getting that low distortion at that power and obviously I try and linearize an amp as much as possible even knowing I will use feedback.

I’ll have to go back and see where 1% is power wise. Unless you drive the 300B into Class A2, you are not going to get 8 Watts @ 1%. And this would be biasing the 300B in an unconventional manner closer to 0V. 

This is just a guess messing around with SE Tubecad.

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10 hours ago, captainbeefheart said:

I had some time to read through the build thread and a couple reviews which leaves me with more questions.


I appear to be wrong as these are open loop or zero feedback amps? Which makes sense that you are triode wiring the E180F and D3a, there isn't enough gain for any feedback. E180F triode wired is probably around 32x gain and the 300b is roughly 3.8x. This jives exactly with the 14db gain of your amps and the need for 2.23v for full output. Nice trick to keep noise low is to have a low gain amplifier for high efficient speakers, downside you may need a preamp to reach full power.


I guess my question is now what is the output power of the 300b amp measured at 1% THD?  After some quick calculations my guess is the amp is 1% THD at 1 watt output. There is absolutely no way an open loop 300b amp will produce 7-8 watts with only 1% THD.

Yes, 0.93% @ 1W w/1KHz sine-wave. No "global" NFB. However, still less than 5% THD at full power. And, yes, carefully selected operating points are key. The C3g driver stage is even slightly more linear, w/distortion slightly lower. However, distortion isn't everything, the design goal was musicality, everything else seems to fall into place within that context given sound engineering practices, a little luck, and mentors such as Gordon, Herb, JC, Joe Roberts... and countless unnamed contributors to MJ Audio magazine over the years.


IMHO, it really is about that 1st watt (or 700mW if you've got K-horns or LaScala's)....... or really anything above 93db efficient. Although headroom is nice. 99% of my customers, family, friends, etc. critically listen with peaks at maybe 88db. Maybe we are all just getting old, who knows.


FWIW, the final amplifier design didn't happen in a vacuum, Gordon and I designed the Iron-Coupled DHT Line-Preamplifier to compliment the amplifier w/approximately 5db of total gain, the 01a and 71a's operate right in their own "sweet-spot" allowing the entire volume control to be used, and just enough gain to drive the amplifier to full output with the "industry-standard" 2v input.


A phono gain amplifier is in the works for this calendar year. This piece will complete the "Trifecta" for customers (and myself) that just want to stop buying gear and just "enjoy the music". Again, the design goal is ultimate musicality, not just vanishingly-low distortion figures. Gordon has, separately, finished his penultimate DAC, the Pelham, which also uses the 71a DHT in it's gain stage for customers digitally inclined.


Lastly, final voicing is being done to the "50" version of the Transcendence amplifier. It uses a choke-loaded driver stage with the EXCELLENT Silk Audio grid choke on the 50. Jury is still out on the input transformer......... it may or may not use it.


Cheers all.



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