Tag: 01 preamp

01a Low Gain DHT preamp

How many times I’ve been asked “how do I lower the gain of the DHT preamp?” many builders love the DHT sound and yet don’t really need that gain. Of course when you use a transformer load, step down is the obvious choice. And it works really well when you invest in a very good quality OPT.

However, when you use DHT with high rp, generally most of the low current ones, you face a tough challenge with regard to frequency response.

With the hybrid mu-follower topology (aka gyrator) we have the problem that the gain is fixed to nearly mu.

I’m in love with the DHT sound and in a preamp a 01a and the 801a/VT-25 DHT Preamp Update preamp cannot be beaten in my view. They all deliver a gain of 8 with a hybrid mu-follower topology.

This can be overcome in the following way: Continue reading “01a Low Gain DHT preamp”

Tony’s 01a Preamp

IMG_3291I went to see my friend Tony today and helped him to fix his 01a preamp implementation. Time ago Tony used a prototype version of my gyrator PCB to build the Gen2 preamp with the addition of an output follower to address the slew rate limitations he had on his system due to the larger capacitive load.

Luckily we found the fault easily and it was a bad solder in one of the smoothing HT chokes. Once fault was rectified, we proceeded to take some measurements of this preamp.

Continue reading “Tony’s 01a Preamp”

Gyrator PCB boards arrived!

Great pleasure this morning to receive the first batch of the gyrator PCB. After extensive testing we refined the layout and options for the PCB and now we have the final product ready for shipping! Unfortunately I will not be able to do some testing and shipping before end of February and I received a large number of requests already. I’m sure this batch will fly very quickly so please confirm your requests.

Bartola Gyrator PCB

I will post soon the specifications and some circuit examples for this flexible gyrator board which can be used for DHT preamps (e.g. 4P1L, 01a, 26), amplifier drivers, A2 drivers, LTP drivers, parafeed output stages and more!

So check the For Sale section soon for more information.

Some days ago we discussed in DIYAudio using this board for a 2J27L preamp like this one:

2J27L Preamp using Gyrator PCB
2J27L Preamp using Gyrator PCB

The output FET follower is needed to for valves which have low current and high anode resistance which will struggle to drive large capacitances. The FET follower of your choice can be used instead.

A minimal circuit which sounds fantastic is the basic configuration of this PCB. With few changes this circuit can be used on many DHTs like 26, 4P1L, 10Y, 30, 30sp, 12, 71a, 45, 46, etc:

01a Preamp Gen2 with Gyrator PCB board

 

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