Warning! Caution! Servicing this preamplifier involves work with high voltages that can kill you. Do not attempt to adjust or modify any circuits or equipment described below without the required training, experience and safety skills when working with dangerously high voltages. It is your responsibility ( I assume none) to ensure that work on this equipment, or DIY build based on information on this web site, is safely done and will not cause life or property threat or damage!
***Shiny Eyes 4P1L Preamplifier***
I’ve started to experiment with the Russian DHT 4P1L years ago. This design is the result as many hours of breadboarding, testing and listening. I’ve concluded that the best sound, lowest microphonic effect and highest driving capability, was offered by a 4P1L in triode mode, filament biased and line output transformer loaded.
- This is a single stage 4P1L in triode mode using Lundahl LL1671/30mA line output transformer.
- The maximum gain is about x2.2 or 6.8 dB.
- Typical THD is less than 0.1% at 1kHz and 2.2Vrms output. Usually, earlier production ( 60s and early 70s) are better sounding tubes and lower THD.
- The frequency response is better than +/- 0.5dB @ 20Hz-30kHz.
The preamplifier is built with 2 PCBs of 2mm, 2oz Cu, one has the power supply and the other one the 4P1L preamplifier stage.
There are 3 options to buy:
- Two PCBs…………………………….. $100 ( shipping not included)……..10 in stock
This comes with a guide on how to build and test the preamplifier, including a BOM for easy parts procuring ( most of the parts are from Mouser Electronics). FYI for DIYers : the cost of the parts is about $510 ( $150 Mouser, $245 pair of LL1671/30mA, $35 pair of Coleman regulators, $80 tubes, sockets, mechanical).
- Assembled and tested PCBs…………………….$850 ( shipping not included)….backordered, allow 2-4 weeks before ready to ship( depending on the parts availability)
In this case I will procure the parts, assembly the Coleman regulators, assembly and test the boards. I will also have the boards wired and ready to install in your proffered enclosure ( recommended enclosure is Modushop Pesante 03PB 3U 4mm BLACK). It is your job to connect the 115/230V jumps, the signal inputs and outputs.
- Ready to use preamplifier………..$1,300 ( shipping not included)… back-ordered allow 3-6 weeks before ready to ship ( depending on the parts availability)
In this case you will receive a finished product. It will come in a Pesante 3U 435x300x120 mm enclosure, American cherry sides, lighted power switch, 1 output and 3 inputs switchable and Alps stereo volume control. It is possible to be wired for 120 or 230V.
There are limited options to upgrade this preamplifier. One of them is to install a different volume control of your choice ( only if there is enough room inside the enclosure). Any modifications will come with their associated extra cost.
For questions please email to firstname.lastname@example.org.
Dave posted here: http://hifiwigwam.com/forum/topic/121649-4p1l-dht-preamplifier-project/?page=5&_fromLogin=1, a review of this preamp built from scratch using my boards.
Upgrade volume control to TKD CP-2511 improves the resolution. Here is a try for a new front plate look:
Maxed out version of the 4P1L preamp
Another 4P1L preamp using the same excellent Lundahl LL1671/30mA line output transformers, an excellent fit to the 4P1L. This preamp was built to order. I’ve been asked to squeeze all possible sound”juice” out of the 4P1L. The power supply was upgraded to all Lundahl transformers and chokes, except the filament transformers which are custom built Heyboer 16V 2A. Both HV and LV supplies are choke input and using 4 poles Mundorf high quality caps. All connections are made with Neotech OFC copper wire.
A nice touch are the Yamamoto loctal sockets. The only thing I don’t like about these loctals is that they lock in too hard.
Volume control is remote controlled by Khozmo. I am very pleased with the sound of this preamp. It is definetely a step up from the standard option. However, the improvement comes with a much higher cost.
It was built in a taller Modushop case to accommodate a bigger and heavier power supply. The finished preamp weights about 50lbs ( double the weight compared to the standard option). The preamp could be a good fit in a system that uses lower than 92 speaker sensitivity and not too high gain amps. For more sensitive systems ( for example low power tube amps and high sensitivity speakers) I definitely recommend separate power supply to increase the signal/noise ratio.