Fender Frontman 10G amp comes together with the Fender guitar as a kit. It sounded quite flat. I have to admit that I did not like the sound. So, I opened the amp to look around 🙂 only four screws needed to be unscrewed.
The power stage of Frontman 10G
The amp’s power stage is built on TDA2030 chip. After finding the datasheet for it, it appeared that the chip should deliver 14W with 4 Ohms load. The distortions at max power might reach 0.5%. I would say it’s a bit high. Well, that’s what we got.
Let’s move on to the pre-amp stages
The 4558 opamps are used in pre-amp stages. What caught my attention was that pretty cheap capacitors were used around those opamps, both electrolytic and bi-polar. I got curious about the circuit of the amp and started to search for it and … found it here 🙂
The extract of the pre-amp stages is shown here:
The volume of the amp increases very rapidly. After looking into the datasheet, it appeared that the gain of the power amp was set by R23 and R24 (very high). The datasheet does not even give the distortions at such (original) gain. To change the gain (to 30) and fix such volume, the resistors R23 and R24 should be changed to 4.7kOm and 150kOm. There is a cap C19 nearby, which is responsible for setting the low pass filter. According to the datasheet, it’s value of 22uF should decrease low frequency cutoff.
Warning, the PBC of the amp is not the highest quality and it is pretty easy to destroy by desoldering. So, you should be careful by doing the upgrades.
You should put aside desoldered parts, as you might decide to restore the upgrades if you don’t like the results.
After looking at circuit and analyzing, it appeared that the first three stages (U1A,U1B and U2A) act as filters. A simple solution – get rid of them altogether.
Let’s change C1 and C8 to 0.1 uF values capacitors. Typically, I prefer to use higher quality caps something like Wima (on eBay). They have pretty low ESR value and many diy’ers prefer them 🙂 Let’s change C7 to Wima 1 uF (from eBay). Ok, let’s assemble everything back and let’s plug the guitar and let’s play a bit 🙂
Do we like new sound? If yes, let’s do another upgrade
Just desolder electrolytic caps C3, C11 and shorter their place. Next, there are two caps C33 and C34 with the values of 0.1uF. Just replace them with Wima (on eBay) 0.1 uF too.
We can either assemble everything or do a bit more…
We could replace also electrolytic caps C9,C14, C16 and C17 to better caps, let’s say Panasonic FC 10uF (on eBay).
Assemble everything back and enjoy the final sound!
I was quite amazed how the amp (clean channel) started to perform after all those upgrades, hope you will be too 🙂
You still have that bag with desoldered parts, if you consider going back…
but I don’t think that you will do so 😉
Is there anything more that could be done/upgraded?
Yes. One option is to change the opamps to something like 4560 or even OPA2134 (on eBay).