Bottlehead Forum

Bottlehead Kits => Legacy Kit Products => Topic started by: mpdd on April 04, 2015, 05:07:43 PM

Title: Foreplay gain
Post by: mpdd on April 04, 2015, 05:07:43 PM

I built one of the last Foreplay kits sold. The pre amp performs very well, however, the gain is extremely low compared to other pre amps. My question is can I change resistors to boost the gain?

Title: Re: Foreplay gain
Post by: Paul Birkeland on April 04, 2015, 05:12:05 PM

The Foreplay has an insane amount of gain compared to most line preamps (unpadded, it will be around 25dB).

Which Foreplay do you have?  The original Foreplay premaps are on 6"x10" chassis plates, and the Foreplay III is on an 8"x10" plate.

The Foreplay III has padding resistors on each set of inputs to deal with the excess gain in the preamplifier, and these can be changed out to alter the gain.  Based on your assertion that there isn't enough gain, this is most likely the case.  If you have the manual, it gives some values for pads on the inputs and describes their installation.  You would need to measure what you have now to know what alternate values you might want.

-PB

Title: Re: Foreplay gain
Post by: mpdd on April 04, 2015, 07:17:56 PM

It is a Foreplay III, I purchased the kit about two years ago, I think it was one of two or three final kits being packaged and delivered.
Thanks for the input, I'll look at those tomorrow. I would like to have this in my system full time.

Title: Re: Foreplay gain
Post by: mpdd on April 05, 2015, 04:15:32 AM

Attached is a photo of the chassis, I believe this is the Foreplay III

Title: Re: Foreplay gain
Post by: mpdd on April 05, 2015, 05:13:20 AM

I see what you mean. I checked the resistors. I for some reason have 620k resistors installed. I'll put in some 33's and see how that sounds.
Thank you for your help.

Title: Re: Foreplay gain
Post by: Paul Joppa on April 05, 2015, 07:36:54 AM

Yes, that' the problem - 620K is about 22dB attenuation more attenuation than stock, or 32dB total.

Title: Re: Foreplay gain
Post by: mpdd on April 12, 2015, 03:52:20 AM

I put the 33k resistors in and PB was right "the Foreplay has an insane amount of gain". I thought I blew my speakers. At minimum volume it was louder than I've ever played my system. I've taken the Foreplay out of the system, I need to go thru the schematic / build instructions and check everything, I've obviously got a mistake elsewhere. Thank you for your help.

Title: Re: Foreplay gain
Post by: Paul Birkeland on April 12, 2015, 06:27:56 AM

Well, you went from 620K to 33K.  Why not try 100K.

-PB

Title: Re: Foreplay gain
Post by: mpdd on April 12, 2015, 07:22:38 AM

I'll pick some up and give it a try. I just built some Frugalhorns and I'd really like to hear them with the Foreplay. I'll post after the switch.
Thanks again for the help.

Title: Re: Foreplay gain
Post by: Natural Sound on April 12, 2015, 09:23:05 AM

According to the manual 33K is the stock value to achieve an overall gain of 10dB. To pad down from the stock 10dB gain use the following guide.

-6dB (80.6K ohms)
-12dB (182K ohms)
-18dB (360K ohms)

I hope this helps.